Brainstem cavernous malformations: anatomical, clinical, and surgical considerations

Axial Sections of Brainstem Safe Entry Zones and Clinical Importance of Intrinsic Structures: A Review

Brainstem surgery is more difficult and riskier than surgeries in other parts of the brain due to the high density of critical tracts and cranial nerves nuclei in this region. For this reason, some safe entry zones into the brainstem have been described. The main purpose of this article is to bring on the agenda the significance of the intrinsic structures of the safe entry zones to the brainstem. Having detailed information about anatomic localization of these sensitive structures is important to predict and avoid possible surgical complications. In order to better understand this complex anatomy, we schematically drew the axial sections of the brainstem showing the intrinsic structures at the level of 9 safe entry zones that we used, taking into account basic neuroanatomy books and atlases. Some illustrations are also supported with intraoperative pictures to provide better surgical orientation. The second purpose is to remind surgeons of clinical syndromes that may occur in case of surgical injury to these delicate structures. Advanced techniques such as tractography, neuronavigation, and neuromonitorization should be used in brainstem surgery, but detailed neuroanatomic knowledge about safe entry zones and a meticulous surgery are more important. The axial brainstem sections we have drawn can help young neurosurgeons better understand this complex anatomy.

Clinical Features and Treatment of Pediatric Cerebral Cavernous Malformations

Cerebral cavernous malformation (CCM) is a vascular anomaly commonly found in children and young adults. Common clinical presentations of pediatric patients with CCMs include headache, focal neurological deficits, and seizures. Approximately 40% of pediatric patients are asymptomatic. Understanding the natural history of CCM is crucial and hemorrhagic rates are higher in patients with an initial hemorrhagic presentation, whereas it is low in asymptomatic patients. There is a phenomenon known as temporal clustering in which a higher frequency of symptomatic hemorrhages occurs within a few years following the initial hemorrhagic event. Surgical resection remains the mainstay of treatment for pediatric CCMs. Excision of a hemosiderin-laden rim is controversial regarding its impact on epilepsy outcomes. Stereotactic radiosurgery is an alternative treatment, especially for deepseated CCMs, but its true efficacy needs to be verified in a clinical trial.

Role of Genetics and Surgical Interventions for the Management of Cerebral Cavernous Malformations (CMM)

Cerebral cavernous malformations (CCMs) are comprised of tissue matter within the brain possessing anomalous vascular architecture. In totality, the dilated appearance of the cavernomatakes on a mulberry-like shape contributed by the shape and relation to vascular and capillary elements. Analyzing its pathophysiology along with its molecular and genetic pathways plays a vital role in whether or not a patient receives GKRS, medical management, or Surgery, the most invasive of procedures. To avoid neurological trauma, microsurgical resection of cavernomas canbe guided by the novel clinical application of a 3D Slicer with Sina/MosoCam. When cavernomas present in deep lesions with poor accessibility, gamma knife stereotactic radiosurgery (GKSR) is recommended. For asymptomatic and non-multilobal lesions, medical and symptom management is deemed standard, such as antiepileptic therapy. The two-hit hypothesis serves to explain the mutations in three key genes that are most pertinent to the progression of cavernomas: CCM1/KRIT1, CCM2/Malcavernin, and CCM3/PDCD10. Various exon deletions and frameshift mutations can cause dysfunction in vascular structure through loss and gain of function mutations. MEKK3 and KLF2/4 are involved in a protein kinase signaling cycle that promotes abnormal angiogenesis and cavernoma formation. In terms of potential treatments, RhoKinase inhibitors have shown to decrease endothelial to mesenchymal transition and CCM lesion development in mice models. All in all, understanding the research behind the molecular genetics in CCMs can foster personalized medicine and potentially create new neurosurgical and medicative treatments.

A taxonomy for brainstem cavernous malformations: subtypes of medullary lesions

OBJECTIVE

Medullary cavernous malformations are the least common of the brainstem cavernous malformations (BSCMs), accounting for only 14% of lesions in the authors' surgical experience. In this article, a novel taxonomy for these lesions is proposed based on clinical presentation and anatomical location.

METHODS

The taxonomy system was applied to a large 2-surgeon experience over a 30-year period (1990-2019). Of 601 patients who underwent microsurgical resection of BSCMs, 551 were identified who had the clinical and radiological information needed for inclusion. These 551 patients were classified by lesion location: midbrain (151 [27%]), pons (323 [59%]), and medulla (77 [14%]). Medullary lesions were subtyped on the basis of their predominant surface presentation. Neurological outcomes were assessed according to the modified Rankin Scale (mRS), with an mRS score ≤ 2 defined as favorable.

RESULTS

Five distinct subtypes were defined for the 77 medullary BSCMs: pyramidal (3 [3.9%]), olivary (35 [46%]), cuneate (24 [31%]), gracile (5 [6.5%]), and trigonal (10 [13%]). Pyramidal lesions are located in the anterior medulla and were associated with hemiparesis and hypoglossal nerve palsy. Olivary lesions are found in the anterolateral medulla and were associated with ataxia. Cuneate lesions are located in the posterolateral medulla and were associated with ipsilateral upper-extremity sensory deficits. Gracile lesions are located outside the fourth ventricle in the posteroinferior medulla and were associated with ipsilateral lower-extremity sensory deficits. Trigonal lesions in the ventricular floor were associated with nausea, vomiting, and diplopia. A single surgical approach was preferred (> 90% of cases) for each medullary subtype: the far lateral approach for pyramidal and olivary lesions, the suboccipital-telovelar approach for cuneate lesions, the suboccipital-transcisterna magna approach for gracile lesions, and the suboccipital-transventricular approach for trigonal lesions. Of these 77 patients for whom follow-up data were available (n = 73), 63 (86%) had favorable outcomes and 67 (92%) had unchanged or improved functional status.

CONCLUSIONS

This study confirms that the constellation of neurological signs and symptoms associated with a hemorrhagic medullary BSCM subtype is useful for defining the BSCM clinically according to a neurologically recognizable syndrome at the bedside. The proposed taxonomical classifications may be used to guide the selection of surgical approaches, which may enhance the consistency of clinical communications and help improve patient outcomes.

Safety of brainstem safe entry zones: comparison of microsurgical outcomes associated with superficial, exophytic, and deep brainstem cavernous malformations

OBJECTIVE

Safe entry zones (SEZs) enable safe tissue transgression to lesions beneath the brainstem surface. However, evidence for the safety of SEZs is scarce and is based on anatomical studies, case reports, and small series.

METHODS

A cohort of 154 patients who underwent microsurgical brainstem cavernous malformation (BSCM) treatment during a 23-year period and who had preoperative MR images and intraoperative photographs or videos was retrospectively examined. This study assessed the safety of SEZs for access to deep BSCMs, preoperative MRI to predict BSCM surface proximity, and the relationships between BSCM subtype, surgical approach, and SEZs. Lesions were characterized as exophytic, superficial, or deep on the basis of preoperative MRI and intraoperative inspection. Outcomes were scored as good (modified Rankin Scale [mRS] score ≤ 2) or poor (mRS score > 2) and relative outcomes as stable/improved or worse relative to baseline (± 1 point).

RESULTS

Resections included 34 (22%) in the midbrain, 102 (66%) in the pons, and 18 (12%) in the medulla. Of those, 23 (15%) were exophytic, 57 (37%) were superficial, and 74 (48%) were deep. Established SEZs were used for 97% (n = 72) of deep lesions; the preferred SEZ associated with its subtype was used for 91% (n = 67). MR images accurately depicted exophytic BSCMs that did not require SEZ approaches (sensitivity, 96%) but overestimated the proximity of lesions superficial to brainstem surfaces (specificity, 67%), resulting in unanticipated SEZ use. Final neurological outcomes were good in 80% of patients with follow-up data (119/149), and relative outcomes were stable/improved in 93% (139/149). Outcomes for patients with brainstem transgression through an SEZ did not differ from outcomes for patients with superficial or exophytic lesions that did not require SEZ use (final mRS score ≤ 2 in 72% of all patients with deep lesions vs 82% of all patients with superficial or exophytic lesions [p = 0.10]). Among patients with follow-up, the rates of permanent new cranial nerve deficits in patients with deep BSCMs and superficial or exophytic BSCMs were 21% and 20%, respectively (p = 0.81), with no significant change in overall cranial nerve deficit (0 and -1, p = 0.65).

CONCLUSIONS

Neurological outcomes for patients with deep BSCMs were equivalent to those for superficial or exophytic BSCMs, validating the safety of SEZs for deep BSCMs. Preoperative T1-weighted MR images overestimated the lesion's surface proximity, necessitating detailed knowledge of SEZs and readiness to use them in cases of radiological-microsurgical discordance. Most patients achieved favorable outcomes despite the transgression of eloquent brainstem tissue in and around SEZs.

A taxonomy for brainstem cavernous malformations: subtypes of pontine lesions. Part 1: basilar, peritrigeminal, and middle peduncular

OBJECTIVE

Brainstem cavernous malformations (BSCMs) are complex, difficult to access, and highly variable in size, shape, and position. The authors have proposed a novel taxonomy for pontine cavernous malformations (CMs) based upon clinical presentation (syndromes) and anatomical location (findings on MRI).

METHODS

The proposed taxonomy was applied to a 30-year (1990-2019), 2-surgeon experience. Of 601 patients who underwent microsurgical resection of BSCMs, 551 with appropriate data were classified on the basis of BSCM location: midbrain (151 [27%]), pons (323 [59%]), and medulla (77 [14%]). Pontine lesions were then subtyped on the basis of their predominant surface presentation identified on preoperative MRI. Neurological outcomes were assessed according to the modified Rankin Scale, with a score ≤ 2 defined as favorable.

RESULTS

The 323 pontine BSCMs were classified into 6 distinct subtypes: basilar (6 [1.9%]), peritrigeminal (53 [16.4%]), middle peduncular (MP) (100 [31.0%]), inferior peduncular (47 [14.6%]), rhomboid (80 [24.8%]), and supraolivary (37 [11.5%]). Part 1 of this 2-part series describes the taxonomic basis for the first 3 of these 6 subtypes of pontine CM. Basilar lesions are located in the anteromedial pons and associated with contralateral hemiparesis. Peritrigeminal lesions are located in the anterolateral pons and are associated with hemiparesis and sensory changes. Patients with MP lesions presented with mild anterior inferior cerebellar artery syndrome with contralateral hemisensory loss, ipsilateral ataxia, and ipsilateral facial numbness without cranial neuropathies. A single surgical approach and strategy were preferred for each subtype: for basilar lesions, the pterional craniotomy and anterior transpetrous approach was preferred; for peritrigeminal lesions, extended retrosigmoid craniotomy and transcerebellopontine angle approach; and for MP lesions, extended retrosigmoid craniotomy and trans-middle cerebellar peduncle approach. Favorable outcomes were observed in 123 of 143 (86%) patients with follow-up data. There were no significant differences in outcomes between the 3 subtypes or any other subtypes.

CONCLUSIONS

The neurological symptoms and key localizing signs associated with a hemorrhagic pontine subtype can help to define that subtype clinically. The proposed taxonomy for pontine CMs meaningfully guides surgical strategy and may improve patient outcomes.

Overview of the microanatomy of the human brainstem in relation to the safe entry zones

OBJECTIVE

The primary objective of this anatomical study was to apply innovative imaging techniques to increase understanding of the microanatomical structures of the brainstem related to safe entry zones. The authors hypothesized that such a high-detail overview would enhance neurosurgeons' abilities to approach and define anatomical safe entry zones for use with microsurgical resection techniques for intrinsic brainstem lesions.

METHODS

The brainstems of 13 cadavers were studied with polarized light imaging (PLI) and 11.7-T MRI. The brainstem was divided into 3 compartments-mesencephalon, pons, and medulla-for evaluation with MRI. Tissue was further sectioned to 100 μm with a microtome. MATLAB was used for further data processing. Segmentation of the internal structures of the brainstem was performed with the BigBrain database.

RESULTS

Thirteen entry zones were reported and assessed for their safety, including the anterior mesencephalic zone, lateral mesencephalic sulcus, interpeduncular zone, intercollicular region, supratrigeminal zone, peritrigeminal zone, lateral pontine zone, median sulcus, infracollicular zone, supracollicular zone, olivary zone, lateral medullary zone, and anterolateral sulcus. The microanatomy, safety, and approaches are discussed.

CONCLUSIONS

PLI and 11.7-T MRI data show that a neurosurgeon possibly does not need to consider the microanatomical structures that would not be visible on conventional MRI and tractography when entering the mentioned safe entry zones. However, the detailed anatomical images may help neurosurgeons increase their understanding of the internal architecture of the human brainstem, which in turn could lead to safer neurosurgical intervention.

A taxonomy for brainstem cavernous malformations: subtypes of pontine lesions. Part 2: inferior peduncular, rhomboid, and supraolivary

OBJECTIVE

Part 2 of this 2-part series on pontine cavernomas presents the taxonomy for subtypes 4-6: inferior peduncular (IP) (subtype 4), rhomboid (5), and supraolivary (6). (Subtypes 1-3 are presented in Part 1.) The authors have proposed a novel taxonomy for pontine cavernous malformations based on clinical presentation (syndromes) and anatomical location (MRI findings).

METHODS

The details of taxonomy development are described fully in Part 1 of this series. In brief, pontine lesions (323 of 601 [53.7%] total lesions) were subtyped on the basis of predominant surface presentation identified on preoperative MRI. Neurological outcomes were assessed according to the modified Rankin Scale, with score ≤ 2 defined as favorable.

RESULTS

The 323 pontine brainstem cavernous malformations were classified into 6 distinct subtypes: basilar (6 [1.9%]), peritrigeminal (53 [16.4%]), middle peduncular (100 [31.0%]), IP (47 [14.6%]), rhomboid (80 [24.8%]), and supraolivary (37 [11.5%]). Subtypes 4-6 are the subject of the current report. IP lesions are located in the inferolateral pons and are associated with acute vestibular syndrome. Rhomboid lesions present to the fourth ventricle floor and are associated with disconjugate eye movements. Larger lesions may cause ipsilateral facial weakness. Supraolivary lesions present to the surface at the ventral pontine underbelly. Ipsilateral abducens palsy is a strong localizing sign for this subtype. A single surgical approach and strategy were preferred for subtypes 4-6: for IP cavernomas, the suboccipital craniotomy and telovelar approach predominated; for rhomboid lesions, the suboccipital craniotomy and transventricular approach were preferred; and for supraolivary malformations, the far lateral craniotomy and transpontomedullary sulcus approach were preferred. Favorable outcomes were observed in 132 of 150 (88%) patients with follow-up. There were no significant differences in outcomes between subtypes.

CONCLUSIONS

The neurological symptoms and signs associated with a hemorrhagic pontine subtype can help define that subtype clinically with key localizing signs. The proposed taxonomy for pontine cavernous malformation subtypes 4-6 meaningfully guides surgical strategy and may improve patient outcomes.

Anatomy of the greater occipital nerve: implications in posterior fossa approaches

PURPOSE

Because of its superficial location in the dorsal regions of the scalp, the greater occipital nerve (GON) can be injured during neurosurgical procedures, resulting in post-operative pain and postural disturbances. The aim of this work is to specify the course of the GON and how its injuries can be avoided while performing posterior fossa approaches.

METHODS

This study was carried out at the department of anatomy at Bordeaux University. 4 specimens were dissected to study the GON course. Posterior fossa approaches (midline suboccipital, paramedian suboccipital, retrosigmoid and petrosal) were performed on 4 other specimens to assess potential risks of GON injuries.

RESULTS

The GON runs around the obliquus capitis inferior (100%), crosses the semispinalis capitis (100%) and the trapezius (75%) or its aponeurosis (25%). Direct GON injuries can be seen in paramedian suboccipital approaches. Stretching of the GON can occur in midline suboccipital and paramedian suboccipital approaches. We found no evidence of direct or indirect GON injury in retrosigmoid or petrosal approaches.

CONCLUSION

Our study provides interesting data regarding the risk GON injury in posterior fossa approaches. Direct GON injuries in paramedian suboccipital approaches can be avoided with careful dissection. Placing retractors in contact with the periosteum and performing a minimal retraction may help to avoid excessive GON stretching in midline suboccipital and paramedian suboccipital approaches. Furthermore, the incision for retrosigmoid approaches should be as lateral as possible and not too caudal. Finally, avoiding extreme patient positioning reduces the risk of GON stretching in all approaches.

A taxonomy for brainstem cavernous malformations: subtypes of midbrain lesions

OBJECTIVE

Anatomical taxonomy is a practical tool that has successfully guided clinical decision-making for patients with brain arteriovenous malformations. Brainstem cavernous malformations (BSCMs) are similarly complex lesions that are difficult to access and highly variable in size, shape, and position. The authors propose a novel taxonomy for midbrain cavernous malformations based on clinical presentation (syndromes) and anatomical location (identified with MRI).

METHODS

The taxonomy system was developed and applied to an extensive 2-surgeon experience over a 30-year period (1990-2019). Of 551 patients with appropriate data who underwent microsurgical resection of BSCMs, 151 (27.4%) had midbrain lesions. These lesions were further subtyped on the basis of predominant surface presentation identified on preoperative MRI. Five distinct subtypes of midbrain BSCMs were defined: interpeduncular (7 lesions [4.6%]), peduncular (37 [24.5%]), tegmental (73 [48.3%]), quadrigeminal (27 [17.9%]), and periaqueductal (7 [4.6%]). Neurological outcomes were assessed using modified Rankin Scale (mRS) scores. A postoperative score ≤ 2 was defined as a favorable outcome; a score > 2 was defined as a poor outcome. Clinical and surgical characteristics and neurological outcomes were compared among subtypes.

RESULTS

Each midbrain BSCM subtype was associated with a recognizable constellation of neurological symptoms. Patients with interpeduncular lesions commonly presented with ipsilateral oculomotor nerve palsy and contralateral cerebellar ataxia or dyscoordination. Peduncular lesions were associated with contralateral hemiparesis and ipsilateral oculomotor nerve palsy. Patients with tegmental lesions were the most likely to present with contralateral sensory deficits, whereas those with quadrigeminal lesions commonly presented with the features of Parinaud syndrome. Periaqueductal lesions were the most likely to cause obstructive hydrocephalus. A single surgical approach was preferred (> 90% of cases) for each midbrain subtype: interpeduncular (transsylvian-interpeduncular approach [7/7 lesions]), peduncular (transsylvian-transpeduncular [24/37]), tegmental (lateral supracerebellar-infratentorial [73/73]), quadrigeminal (midline or paramedian supracerebellar-infratentorial [27/27]), and periaqueductal (transcallosal-transchoroidal fissure [6/7]). Favorable outcomes (mRS score ≤ 2) were observed in most patients (110/136 [80.9%]) with follow-up data. No significant differences in outcomes were observed between subtypes (p = 0.92).

CONCLUSIONS

The study confirmed the authors' hypothesis that taxonomy for midbrain BSCMs can meaningfully guide the selection of surgical approach and resection strategy. The proposed taxonomy can increase diagnostic acumen at the patient bedside, help identify optimal surgical approaches, enhance the consistency of clinical communications and publications, and improve patient outcomes.

The BSCM score: a guideline for surgical decision-making for brainstem cavernous malformations

Microsurgical resection of brainstem cavernous malformations (BSCMs) can be performed today with acceptable morbidity and mortality. However, in this highly eloquent location, the indication for surgery remains challenging. We aimed to elaborate a score system that may help clinicians with their choice of treatment in patients with BSCMs in this study. A single-center series of 88 consecutive BSCMs patients with 272 follow-up visits were included in this study. Univariable and multivariable generalized estimating equations (GEE) were constructed to identify the association of variables with treatment decisions. A score scale assigned points for variables that significantly contributed to surgical decision-making. Surgical treatment was recommended in 37 instances, while conservative treatment was proposed in 235 instances. The mean follow-up duration was 50.4 months, and the mean age at decision-making was 45.9 years. The mean BSCMs size was 14.3 ml. In the multivariable GEE model, patient age, lesion size, hemorrhagic event(s), mRS, and axial location were identified as significant factors for determining treatment options. With this proposed score scale (grades 0–XII), non-surgery was the first option at grades 0–III. The crossover point between surgery and non-surgery recommendations lay between grades V and VI while surgical treatment was found in favor at grades VII–X. In conclusion, the proposed BSCM operating score is a clinician-friendly tool, which may help neurosurgeons decide on the treatment for patients with BSCMs.

Three-Dimensional Quantitative Analysis of the Brainstem Safe Entry Zones Based on Internal Structures

OBJECTIVE

Brainstem safe entry zones (EZs) are gates to access the intrinsic pathology of the brainstem. We performed a quantitative analysis of the intrinsic surgical corridor limits of the most commonly used EZs and illustrated these through an inside perspective using 2-dimensional photographs, 3-dimensional photographs, and interactive 3-dimensional model reconstructions.

METHODS

A total of 26 human brainstems (52 sides) with the cerebellum attached were prepared using the Klingler method and dissected. The safe working areas and distances for each EZ were defined according to the eloquent fiber tracts and nuclei.

RESULTS

The largest safe distance corresponded to the depth for the lateral mesencephalic sulcus (4.8 mm), supratrigeminal (10 mm), epitrigeminal (13.2 mm), peritrigeminal (13.3 mm), lateral transpeduncular (22.3 mm), and infracollicular (4.6 mm); the rostrocaudal axis for the perioculomotor (11.7 mm), suprafacial (12.6 mm), and transolivary (12.8 mm); and the mediolateral axis for the supracollicular (9.1 mm) and infracollicular (7 mm) EZs. The safe working areas were 46.7 mm² for the perioculomotor, 21.3 mm² for the supracollicular, 14.8 mm² for the infracollicular, 33.1 mm² for the supratrigeminal, 34.3 mm² for the suprafacial, 21.9 mm² for the infrafacial, and 51.7 mm² for the transolivary EZs.

CONCLUSIONS

The largest safe distance in most EZs corresponded to the depth, followed by the rostrocaudal axis and, finally, the mediolateral axis. The transolivary had the largest safe working area of all EZs. The supracollicular EZ had the largest safe area to access the midbrain tectum and the suprafacial EZ for the floor of the fourth ventricle.

The benefit and outcome prediction of acute surgery for hemorrhagic brainstem cavernous malformation with impending respiratory failure

OBJECTIVES

Impending respiratory failure is catastrophic neurological deterioration caused by repeated c of a brainstem cavernous malformation (BSCM). The benefit and outcome prediction of acute surgery for this fatal condition is rarely reported. In this study, the authors reported a case series of acute surgical treatment (≤3 weeks after the last hemorrhagic episode) for the BSCM with impending respiratory failure and reviewed literature over the past 20 years.

MATERIALS AND METHODS

Clinical and outcome data from 6 consecutive acute surgically-treated BSCM patients were analyzed. Intracerebral hemorrhage (ICH) scores, primary pontine hemorrhage (PPH) scores, and Lawton's BSCM grading were applied for surgical outcome prediction. Ten related articles were included for the literature review.

RESULTS

There were three men and three women, with a mean age of 32.2 ± 9.3 years (range 15-45 years). The BSCMs were located at the pons in 5 cases and the medulla in 1 case. The ICH score was 1-2 in all cases, while the PPH score was 0 in all pontine BSCMs. For Lawton's BSCM grading, 3 cases were grade 2, 2 cases were grade 3, and 1 case was grade 1. All patients achieved spontaneous respiratory dysfunction relief postoperatively and significantly improved at follow-up (mean 4.47 ± 0.24 years;range4.0-5.6 years).

CONCLUSIONS

Repeated hemorrhagic BSCM with impending respiratory failure can benefit from acute surgical treatment. The ICH score, PPH score, and Lawton's BSCM grading are promisingly useful tools for fast and efficient surgical outcome prediction.

Microsurgical management of midbrain cavernous malformations: does lesion depth influence the outcome?

Background

The purpose of this study was to clarify whether the intrinsic depth of midbrain cavernous malformations (MCMs) influenced the surgical outcome.

Methods

The authors conducted a retrospective study of 76 consecutive patients who underwent microsurgical resection of a MCM. The vascular lesions were categorized into 4 distinct groups based on how these lesions had altered the brainstem surface. Additionally, it was verified whether the actual aspect of the brainstem surface could be predicted only by evaluating the pertinent preoperative MRI slices. Clinical outcome was assessed by determining the modified Rankin Scale Score (mRS) before and after surgery.

Results

Twenty-three MCMs (30.3%) were located deeply within the midbrain. The overlying midbrain surface appeared to be normal (group nl). In 33 patients (43.4%), the midbrain surface showed only a yellowish discoloration (group yw). In another 14 individuals (18.4%), the midbrain surface was distorted by the underlying MCM and bulging out while the vascular lesion still remained covered by a thin parenchymal layer (group bg). In the smallest group comprising 6 patients (7.9%), the exophytic MCM had disrupted the midbrain surface and was clearly visible at microsurgical exposure (group ex). The mean mRS decreased in the group nl from 1.43 preoperatively to 0.61 at follow-up.

Conclusion

This study demonstrates in a large patient population that a deep intrinsic MCM location is not necessarily associated with an unfavorable clinical outcome after microsurgical lesionectomy. Predicting the aspect of the midbrain surface by evaluating preoperative MR images alone was not sufficiently reliable.

Predictive Value of Intraoperative Neuromonitoring in Brainstem Cavernous Malformation Surgery

OBJECTIVE

To evaluate the predictive value of intraoperative neuromonitoring (IONM) in brainstem cavernous malformation (BSCM) surgery.

METHODS

Surgically treated patients with BSCM were included. All patients received IONM consisting of motor-evoked potentials (MEPs) and somatosensory-evoked potentials (SSEPs). Neurologic examination was conducted preoperatively and at discharge and follow-up >3 months after BSCM removal. Demographic, radiographic, and clinical features were assessed. Study end points were new motor or somatosensory deficits and functional disability.

RESULTS

A total of 62 patients were included. MEP decrease was associated with new motor deficits at discharge (P = 0.022), and SSEP decrease was associated with new somatosensory deficits at discharge (P < 0.001) and follow-up (P < 0.001). Sensitivity and specificity values for MEPs (discharge: 31% and 93%; follow-up: 33% and 91%) and SSEPs (discharge: 82% and 80%; follow-up: 85% and 79%) were calculated, respectively. Receiver operating characteristic analyses with area under the curve (AUC) metrics revealed acceptable performance of MEPs (AUC, 0.75; P = 0.022) and SSEPs (AUC, 0.72; P = 0.004) in predicting early deficits. Intraoperative decrease of MEPs (P = 0.047) and SSEPs (P = 0.017) was associated with early functional disability. Surgery-related subdural air accumulation impaired IONM reliability in predicting early (P = 0.048) and long-term (P = 0.013) deficits.

CONCLUSIONS

Established IONM warning criteria may be valid for BSCM removal. However, surgical approaches in the sitting position significantly limit the predictive value of IONM, to some extent because of intraoperative pneumocephalus.

Assessment and validation of proposed classification tools for brainstem cavernous malformations

OBJECTIVE

Treatment indications for patients with brainstem cavernous malformations (BSCMs) remain difficult and controversial. Some authors have tried to establish classification tools to identify eligible candidates for surgery. Authors of this study aimed to validate the performance and replicability of two proposed BSCM grading systems, the Lawton-Garcia (LG) and the Dammann-Sure (DS) systems.

METHODS

For this cross-sectional study, a database was screened for patients with BSCM treated surgically between 2003 and 2019 in the authors' department. Complete clinical records, preoperative contrast-enhanced MRI, and a postoperative follow-up ≥ 6 months were mandatory for study inclusion. The modified Rankin Scale (mRS) score was determined to quantify neurological function and outcome. Three observers independently determined the LG and the DS score for each patient.

RESULTS

A total of 67 patients met selection criteria. Univariate and multivariate analyses identified multiple bleedings (p = 0.02, OR 5.59), lesion diameter (> 20 mm, p = 0.007, OR 5.43), and patient age (> 50 years, p = 0.019, OR 4.26) as predictors of an unfavorable postoperative functional outcome. Both the LG (AUC = 0.72, p = 0.01) and the DS (AUC = 0.78, p < 0.01) scores were robust tools to estimate patient outcome. Subgroup analyses confirmed this observation for both grading systems (LG: p = 0.005, OR 6; DS: p = 0.026, OR 4.5), but the combined use of the two scales enhanced the test performance significantly (p = 0.001, OR 22.5).

CONCLUSIONS

Currently available classification systems are appropriate tools to estimate the neurological outcome after BSCM surgery. Future studies are needed to design an advanced scoring system, incorporating items from the LG and the DS score systems.

Follow the Venous Path to the Hidden Lesion: A Technical Trick in Brainstem Cavernous Malformation Surgery

OBJECTIVE

Deep-seated brainstem cavernous malformations (BSCMs) pose a particular challenge for brainstem entry intraoperatively and their treatment can require comprehensive application of neuronavigation, electrophysiological brainstem mapping and monitoring, and full knowledge of safe brainstem entry zones. In the present report, we have introduced a supplementary technical trick for localizing a hidden tiny lesion inside the brainstem when a developmental venous anomaly (DVA) is present on the brainstem surface.

METHODS

A retrospective analysis of a 74-case cohort treated surgically from January 2011 to December 2019 was conducted. We identified 11 patients (14.9%) whose deep-seated BSCMs were exposed and removed following a brainstem surface DVA path as a supplementary technical trick. We have presented 2 typical cases to illustrate the operative nuances.

RESULTS

Of the 11 patients, 5 were male and 6 were female. Their average age was 38.0 ± 14.0 years (range, 15-62 years). Most BSCMs were located in the pons (n = 5; 45.5%), followed by the pontomesencephalic area (n = 3; 27.3%), midbrain (n = 2; 18.2%), and medulla oblongata (n = 1; 9.1%). All BSCMs were successfully located and completely removed. In 5 cases, the DVA was impaired after lesion removal (45.5%). However, no aggravated postoperative brainstem edema occurred in any of the 11 patients. After 3.6 ± 2.0 years of follow-up (2 patients were lost to follow-up; follow-up rate, 81.8%), no rebleeding was found, and the modified Rankin scale score of the patients had improved from 2.7 ± 1.1 preoperatively to 1.7 ± 0.9 at follow-up (P = 0.031).

CONCLUSIONS

The presented method could help surgeons trace deep-seated BSCMs with minimal brainstem parenchyma impairment, avoiding unnecessary aggressive exploration.

Anterior transpetrosal resection of the lower ventral pontine cavernous malformation: A technical case report with operative video

Background

Surgical treatment of pontine cavernous malformations (CMs) is challenging due to the anatomical difficulties and potential risks involved. We successfully applied an anterior transpetrosal approach (ATPA) to remove a lower ventral pontine CM, and herein we discuss the outline of our procedure accompanied by a surgical video.

Case Description

A 50-year-old woman presenting with progressively worsening diplopia was urgently admitted to our hospital. Preoperative images showed a lower ventral pontine CM compressing the corticospinal tract posteriorly. Considering the location of the CM, we determined that an ATPA was the appropriate approach to achieve a more anterolateral trajectory. We performed extradural anteromedial petrosectomy and penetrated the brainstem from the point just below the anterior inferior cerebellar artery and above the root exit zone of the abducens nerve, which might be located in the somewhat lowest border of actual maneuverability in the ATPA. Maneuverability through this corridor was sufficient without hindering and darkening the high magnification microscopic view, as demonstrated in our surgical video.

Conclusion

This report demonstrates surgical treatment of a lower ventral pontine CM using the ATPA. The surgical video we present provides information that is useful for understanding this technique's maneuverability and working window.

Retrosigmoid transhorizontal fissure approach to lateral pontine cavernous malformation: comparison to transpetrosal presigmoid retrolabyrinthine approach

OBJECTIVE

The retrosigmoid (RS) approach is a classic route used to access deep-seated brainstem cavernous malformation (CM). The angle of access is limited, so alternatives such as the transpetrosal presigmoid retrolabyrinthine (TPPR) approach have been used to overcome this limitation. Here, the authors evaluated a modification to the RS approach, horizontal fissure dissection by using the RS transhorizontal (RSTH) approach.

METHODS

Relevant clinical parameters were evaluated in 9 patients who underwent resection of lateral pontine CM. Cadaveric dissection was performed to compare the TPPR approach and the RSTH approach.

RESULTS

Five patients underwent the TPPR approach, and 4 underwent the RSTH approach. Dissection of the horizontal fissure allowed for access to the infratrigeminal safe entry zone, with a direct trajectory to the middle cerebellar peduncle similar to that used in TPPR exposure. Operative time was longer in the TPPR group. All patients had a modified Rankin Scale score ≤ 2 at the last follow-up. Cadaveric dissection confirmed increased anteroposterior working angle and middle cerebellar peduncle exposure with the addition of horizontal fissure dissection.

CONCLUSIONS

The RSTH approach leads to a direct lateral path to lateral pontine CM, with similar efficacy and shorter operative time compared with more extensive skull base exposure. The RSTH approach could be considered a valid alternative for resection of selected pontine CM.

Sub-telo-velo-tonsillar approach to resect dorsal pons cavernoma through fourth ventricular floor opening: how I do it

BACKGROUND

Dorsal pons cavernoma can be approached through telo-velar approach instead of transvermian approach, with lower risk of neurological deficits since it uses natural clefts to reach the floor of the fourth ventricle.

MATERIALS AND METHODS

We present our surgical technique for telo-velar approach to address pathologies of the dorsal pons, assisted by neuronavigation and neuromonitoring. This surgical technique is illustrated by a surgical video of a dorsal pons cavernoma.

CONCLUSION

Dorsal pons cavernomas can be reached through telo-velar approach after suboccipital midline craniotomy. The accurate patient positioning, cisternal dissection, and neuromonitoring use are mandatory to avoid neural injuries and identify the safe entry points into the brainstem.

The lateral cerebral peduncle approach to ventrally placed intra-axial midbrain tumors: A technical note

We describe the anatomical landmarks and surgical feasibility of a novel 'safe' brainstem entry zone to approach ventrally placed intra-axial midbrain tumors. The anatomy of the brainstem was specifically studied to evaluate safe surgical entry zone in the midbrain on two formalin fixed silicon injected cadaver head specimens. A novel entry point through the lateral one - fifth of the cerebral peduncle was identified to be 'safe' to approach lesions of the ventral midbrain. Three patients, having oculomotor schwannoma, peduncular glioma and a peduncular cavernoma were operated using this safe entry zone. To approach the midbrain, retrosigmoid lateral supracerebellar route was used in two patients and a basal subtemporal avenue was deployed in one patient. On the basis of fine microanatomical dissection on cadavers, a novel entry point through the lateral one-fifth of the cerebral peduncle, 5 mm anterior to the lateral mesencephalic sulcus and approximately 5 mm superior to the fourth nerve was identified. The proposed brainstem entry point traverses the parieto-temporo-occipital pontine fibers and the trajectory is between the corticospinal tracts ventrally and the substantia nigra dorsally. Three patients were operated successfully using the approach. There were no post-operative motor, sensory or extra-pyramidal deficits. The corridor through the lateral one-fifth of the cerebral peduncle presents a safe and relative 'easy' surgical route to approach ventrally placed intra-axial midbrain tumors.

Endoscopic Endonasal Transclival Approach to Ventral Pontine Cavernous Malformation: Case Report

Ventral medial pontine cavernous malformations are challenging due to the location in eloquent tissue, surrounding critical anatomy, and potential symptomatic bleeding. Conventional approaches, such as anterolateral, lateral and dorsal approach, are associated with high risk of deleterious consequences due to excessive traction and damage to the surrounding tissues. The authors present an endoscopic endonasal approach for the resection of midline ventral pontine cavernous malformations, which follows principles of optimal access to brainstem cavernous malformations as the “two-point method.” No CSF leak or any other complications are obtained. The successful outcomes indicate that an individualized approach should be chosen before the surgery for brainstem cavernous malformations. With the advance of techniques, endoscopic endonasal approach could provide the most direct route to ventral pontine lesions with safety and efficiency.

The brainstem and its neurosurgical history

Brainstem is one of the most complex structures of the human body, and has the most complex intracranial anatomy, which makes surgery at this level the most difficult. Due to its hidden position, the brainstem became known later by anatomists, and moreover, brainstem surgery cannot be understood without knowing the evolution of ideas in neuroanatomy, neuropathology, and neuroscience. Starting from the first attempts at identifying brainstem anatomy in prehistory and antiquity, the history of brainstem discoveries and approach may be divided into four periods: macroscopic anatomy, microscopic anatomy and neurophysiology, posterior fossa surgery, and brainstem surgery. From the first trepanning of the posterior fossa and later finger surgery, to the occurrence of safe entry zones, this paper aims to review how neuroanatomy and brainstem surgery were understood historically, and how the surgical technique evolved from Galen of Pergamon up to the twenty-first century.

Cerebral Cavernous Malformation: What a Practicing Clinician Should Know

Cavernous malformations (CMs) are angiographically occult, low-flow vascular malformations of the central nervous system. They are acquired lesions, with approximately 80% of patients having the sporadic form and 20% the familial form of the disease. The lesions may also develop years after radiotherapy. At the microscopic level, they consist of endothelium-lined cavities (or "caverns") containing blood of different ages. The endothelium proliferates abnormally, and tight junctions are absent or dysfunctional, resulting in leakiness of the endothelium and clinical manifestations in some patients. Cavernous malformations can be an incidental finding or can present with focal neurologic deficits, seizures, or headache, with or without associated hemorrhage. Management of the CM lesion requires knowledge of the natural history of the disease compared with the risk of surgical intervention. Surgery is often considered for symptomatic patients with lesions in a noneloquent location. Medical management is warranted for symptoms related to the CM. Research aimed at understanding the genes and signaling pathways related to CMs have provided potential drug targets, and clinical trials are underway to determine whether medications reduce the risk of future bleeding without surgery or modify the disease course. In addition, recent epidemiologic data have aided practitioners in determining how to treat comorbid conditions in patients with a potentially hemorrhagic lesion. This review provides an overview of the epidemiology, presentation, and clinical management of CMs.

Microsurgical anatomy of the facial nerve

The facial nerve connections and pathways from the cortex to the brainstem are intricate and complicated. The extra-axial part of the facial nerve leaves the lateral part of the pontomedullary sulcus and enters the temporal bone through the internal acoustic meatus. In the temporal bone, the facial nerve branches into fibers innervating the glands and tongue. After it emerges from the temporal bone it supplies various facial muscles. It contains a motor, general sensory, special sensory, and autonomic components. The physician needs comprehensive knowledge of the anatomy and courses of the facial nerve to diagnose and treat lesions and diseases of it so that surgical complications due to facial nerve injury can be avoided. This review describes the microsurgical anatomy of the facial nerve and illustrates its anatomy in relation to the surrounding bone, connective, and neurovascular structures.

Microsurgical Resection of a Middle Cerebellar Peduncle Cavernous Malformation: 3-Dimensional Operative Video

Brainstem cavernous malformations are frequently surrounded by vital structures, which often makes surgical treatment a challenging task even to the most skilled surgeon. Accordingly, microsurgical excision is preferably offered to symptomatic patients and superficial lesions.1-3 We present the case of a 41-yr-old male presenting with progressive dizziness and diplopia. Neurological examination showed horizontal nystagmus, dysmetria, and unbalance. Preoperative magnetic resonance imaging (MRI) suggested a cavernous malformation in the right middle cerebellar peduncle. A telovelar approach was employed with the guidance of intraoperative neurophysiological monitoring. An exophytic lesion was identified in the right middle cerebellar peduncle and a clear cleavage plane was obtained allowing circumferential dissection around the capsule. The lesion was removed en bloc. Postoperative MRI confirmed a complete excision of the malformation. The patient presented an improvement in his initial symptoms, with no new neurological deficit. Cavernous malformations related with the fourth ventricle can be successfully resected through a telovelar approach in select cases, especially when exophytic, where the surgeon might take advantage of the path created by the lesion. Informed consent was obtained from the patient for the procedure and publication of this operative video. Anatomic images were a courtesy of the Rhoton Collection, American Association of Neurological Surgeons (AANS)/Neurosurgical Research and Education Foundation (NREF).

Virtual Exploration of Safe Entry Zones in the Brainstem: Comprehensive Definition and Analysis of the Operative Approach

BACKGROUND

A detailed and accurate understanding of the intrinsic brainstem anatomy and the interrelationship between its internal tracts and nuclei and external landmarks is of paramount importance for safe and effective brainstem surgery. Using anatomical models can be an important step in increasing such understanding. In the present study, we have shown the applicability of our developed virtual 3-dimensional (3D) model in depicting the safe entry zones (SEZs) to the brainstem.

METHODS

Accurate 3D virtual models of brainstem elements were created using high-resolution magnetic resonance imaging and computed tomography to depict the brainstem SEZs.

RESULTS

All the described SEZs to different parts of the brainstem were successfully depicted using our 3D virtual models.

CONCLUSIONS

The virtual models provide an immersive experience of brainstem anatomy, allowing users to understand the intricacies of the microdissection that is necessary to appropriately work through the brainstem nuclei and tracts toward a particular target. The models provide an unparalleled learning environment to understand the SEZs into the brainstem that can be used for training and research.

Transmastoid presigmoid retrolabyrinthine approach for removal of pontine cavernous malformation: how I do it

BACKGROUND

Bleeding of brainstem cavernous malformations (BSCM) cause high morbidity and should be treated surgically whenever possible.

METHOD

We present a 56-year-old man, who was diagnosed with a BSCM at right pons, which caused functional impairments of dorsal column, spinothalamic tract, cochlear nucleus, and middle cerebellar peduncle. A transmastoid presigmoid retorlabyrinthine approach via the lateral pontine zone (LPZ), with an assistance of imaging guidance and intraoperative neurophysiological monitoring, was performed to completely resect the BSCM. The patient recovered despite a transient worsening of cerebellar sign and hemiparesthesia for 1 week, without surgical complications.

CONCLUSIONS

A transmastoid presigmoid retrolabyrinthine approach through LPZ is safe and effective for lateral pontine BSCM resection.

Primary Brainstem Angiosarcoma Mimicking Cavernous Malformation

BACKGROUND

Cerebral angiosarcoma is an extremely rare malignant tumor that originates from vascular endothelial cells of the brain or meninges. Especially, primary brainstem angiosarcoma has not been reported.

CASE DESCRIPTION

A 64-year-old man presented with left subjective weakness, hypesthesia, and dizziness. Brain imaging showed a multistage hemorrhagic mass in the right dorsal pons, which was initially misdiagnosed as a cavernous malformation. The patient's neurologic status suddenly deteriorated over a few months, and the mass grew rapidly. Surgical resection was performed, and the final pathology showed brainstem angiosarcoma.

CONCLUSIONS

To our knowledge, this is the first case of brainstem angiosarcoma confirmed by pathology after surgical resection. This report highlights that clinicians need to consider angiosarcoma as part of the differential diagnosis for rare hemorrhagic lesions in the brainstem when both imaging findings and neurologic deterioration indicate rapid progression.

An Eyebrow, Supracarotid Triangle Approach for Lesions at the Ventral Thalamopeduncular Junction: A Technical Report

BACKGROUND

Lesions arising at the ventral thalamopeduncular junction are difficult to resect. In addition to being relatively inaccessible, these lesions are located in one of the most sensitive areas of the brain. A critical question is whether new approaches could be developed to allow surgeons to adequately resect these lesions with reasonable outcomes. In the present report, we describe our approach to resect lesions in this region of the brain using an eyebrow craniotomy approach with a trajectory through the supracarotid triangle.

METHODS

Through retrospective data collection, we present a small series of patients who had undergone an eyebrow, supracarotid triangle approach to resect lesions located at the thalamopeduncular junction. We describe our surgical technique and report patient outcomes using this approach.

RESULTS

Three patients had undergone an eyebrow, supracarotid approach for resection of a lesion arising at the ventral thalamopeduncular junction. Two patients had presented with a cavernoma and one with a pilocytic astrocytoma. Complete resection of all 3 lesions was achieved during surgery without any intraoperative complications. No patient developed permanent contralateral weakness despite entering the peduncle during surgery. One patient developed permanent paresthesia in his left hand.

CONCLUSIONS

Lesions arising at the ventral thalamopeduncular junction can be adequately resected with reasonable outcomes using an eyebrow, supracarotid triangle approach. This operative technique establishes another potential operative corridor by which neurosurgeons can resect lesions arising within this relatively inaccessible part of the brain.

Interpeduncular Sulcus Approach to the Posterolateral Pons

OBJECTIVE

In this article, we describe a new safe entry point for the posterolateral pons.

METHODS

To show the adjacent anatomy and measure the part of the interpeduncular sulcus that can be safely accessed, we first performed a review of the literature regarding the pons anatomy and its surgical approaches. Thereafter, 1 human cadaveric head and 15 (30 sides) human brainstems with attached cerebellums were bilaterally dissected with the fiber microdissection technique. A clinical correlation was made with an illustrative case of a dorsolateral pontine World Health Organization grade I astrocytoma.

RESULTS

The safe distance for accessing the interpeduncular sulcus was found to extend from the caudal end of the lateral mesencephalic sulcus to the point at which the intrapontine segment of the trigeminal nerve crosses the interpeduncular sulcus. The mean distance was 8.2 mm (range, 7.15-8.85 mm). Our interpeduncular sulcus safe entry zone can be exposed through a paramedian infratentorial supracerebellar approach. When additional exposure is required, the superior portion of the quadrangular lobule of the cerebellar hemispheric tentorial surface can be removed. In the presented case, surgical resection of the tumor was performed achieving a gross total resection, and the patient was discharged without neurologic deficit.

CONCLUSIONS

The interpeduncular sulcus safe entry zone provides an alternative direct route for treating intrinsic pathologic entities situated in the posterolateral tegmen of the pons between the superior and middle cerebellar peduncles. The surgical corridor provided by this entry point avoids most eloquent neural structures, thereby preventing surgical complications.

Brainstem cavernous malformations - no longer a forbidden territory? A systemic review of recent literature

BACKGROUND

Due to its eloquent location and potentially devastating neurological consequences, the management of brainstem cavernous malformations (CCMs) attracts considerable debate. There is currently a paucity of Level 1 evidence for their management. The aim of this literature review is to explore the current evidence on the risk-benefit profile of different management options.

METHODS

A systemic literature search, following the PRISMA algorithm was performed on publications between 2010 and 2018 using the Pubmed database, with the relevant keywords. Only English articles were included. Articles focusing on spinal CCMs and studies with less than 30 participants were excluded.

RESULTS

A total of 222 search results were reviewed and after removal of duplicates and screening of abstracts, 28 clinical papers comprising 30 or more brainstem CCM cases were included in the study. The heterogeneity of the publications precluded a formal meta-analysis of results. The general consensus is that for CCMs presenting with severe symptoms and/or multiple haemorrhages that reach an accessible pial surface, surgery is considered to be the gold-standard treatment, with some authors suggesting the optimal timing to be within two to six weeks of ictus. For those patients with multiple, deep-seated CCM related haemorrhages that do not reach the pial surface, stereotactic radiosurgery (SRS) can be considered. Conservative treatment is generally considered in incidental cases. Management of brainstem cavernomas of other categories still remains controversial.

CONCLUSIONS

Due to their highly eloquent location, brainstem CCMs are challenging lesions to manage. Management must be balanced by the risk-benefit profile and tailored to the individual patients and their treating clinicians. This review provides a comprehensive reference considering all treatment options and provides a basis for evidence-based patient counselling.

Surgical managements and patient outcomes after severe hemorrhagic events from brainstem cavernous malformations

To evaluate the surgical outcomes and predictors and the impact of surgical timing of patients who suffered a severe hemorrhagic event from brainstem cavernous malformations (CMs). The clinical data of all patients who underwent surgical treatment after a severe bleeding ictus from brainstem CMs between 2011 and 2017 were retrospectively reviewed. The study population consisted of 61 surgical patients (40, 65.6% female). Surgical times of < 3 weeks, ≥ 3-8 weeks, and > 8 weeks since the last bleeding ictus were observed in 23 (37.7%), 24 (39.3%), and 14 (23.0%) patients, respectively. The mean modified Rankin scale (mRS) score evaluated on admission was 4.2. With a mean follow-up of 39.8 months, 39 patients (63.9%) had a favorable outcome (mRS ≤ 2), and the mean mRS score was 2.3. The logistic regression analysis identified age, having disrupted consciousness and/or respiration, and time to surgery from last hemorrhage as significant predictors of long-term outcome. In particular, patients with surgery performed during the acute period (< 3 weeks, P = 0.06) or chronic period (> 8 weeks, P = 0.01) tended to have poor outcomes when compared with those with surgery during the subacute period (≥ 3-8 weeks). Favorable neurological outcomes can be achieved in patients who were surgically treated after a severe hemorrhagic ictus from brainstem CMs, and operation during subacute hemorrhage (≥ 3-8 weeks) could benefit these patients.

Trans-labyrinthine Infra-trigeminal Approach for Recurrent Pontomedullary Cavernoma: A Step-wise Technical Note

Recurrent brainstem cavernoma is a challenging lesion due to the neurological risks associated with different surgical approaches. In this technical report, we present a 35-year-old female with a history of multiple brain cavernomas. She underwent midline suboccipital craniotomy and trans-fourth ventricle approach for resection of the brain stem cavernoma following two major bleeding episodes, one year prior to the presentation. Following the trans-labyrinthine infra-trigeminal approach, the patient recovered well postoperatively with a baseline neuro exam and was discharged to acute rehab on postoperative day 5 (POD5). The translabyrinthine approach is a safe and effective corridor for pontine or pontomedullary lesions in carefully selected patients. Appropriate selection of surgical approach (based on location), meticulous surgical technique, and intraoperative neuromonitoring help in maximizing surgical resection while minimizing neurological deficits.

Posterior petrosectomy for resection of pontine cavernous malformation

Cavernous malformations (CMs) are low-pressure, focal, vascular lesions that may occur within the brainstem and require treatment, which can be a substantial challenge. Herein, we demonstrate the surgical resection of a hemorrhaged brainstem CM through a posterior petrosectomy approach. After dissection of the overlying vascular and meningeal structures, a safe entry zone into the brainstem is identified based on local anatomy and intraoperative neuronavigation. Small ultrasound probes can also be useful for obtaining real-time intraoperative feedback. The CM is internally debulked and resected in a piecemeal fashion through an opening smaller than the CM itself. As brainstem CMs are challenging lesions, knowledge of several surgical nuances and adoption of careful microsurgical techniques are requisite for success. The video can be found here: https://youtu.be/szB6YpzkuCo.

Surgical treatment of pontine cavernous malformations via subtemporal transtentorial and intradural anterior transpetrosal approaches

The aim of this study was to report our surgical experience on resection of the pontine cavernous malformations (CMs) via subtemporal transtentorial approach (STTA) and intradural anterior transpetrosal approach (ATPA). Clinical data were retrospectively reviewed in 61 patients with pontine CMs that were surgically treated by the STTA and the intradural ATPA. The surgical procedures, complications, and outcomes were analyzed. The study consists of 61 patients with a total of 61 pontine CMs. Other than 4 lesions located medially in the pons, all CMs were in the lateral pons with a left or right lateral epicenter (the left/right ratio was 22/35). Totally, 11 patients (18.0%) with lesions located in the upper pons were treated by the STTA, and 50 patients (82.0%) with lesions involving the lower pons were treated by the intradural ATPA. Postoperatively, the complete resection was achieved in 58 patients (95.1%) and incomplete resection in 3 patients (4.9%). Twenty-seven patients (44.3%) suffered from a new or worsened neurological deficit in the immediate postoperative period, and 8 patients (13.1%) encountered a non-neural complication, including rebleeding, cerebrospinal fluid leak, intracranial infection, and pulmonary infection, and 3 patients had contusion of temporal lobe. With a mean follow-up of 54.2 months, the patients' neurological condition had improved in 43 cases (71.6%), not changed in 10 cases (16.7%), and worsened in 7 cases (11.7%), respectively. The Karnofsky Performance Scale (KPS) score evaluated at the last time for per patient was significantly better than their baseline status (t = 6.677, p < 0.001). However, 21 patients (35.0%) suffered from a new or worsened persistent postoperative deficit. The lateral and anterolateral pons can be exposed well by the subtemporal transtentorial and intradural anterior transpetrosal approaches. Lesions of CMs located in the lateral pons, including ventrolateral and dorsolateral pons, could be totally removed by these two lateral approaches with an acceptable surgical morbidity.

Posterolateral route for a midbrain cavernous malformation reaching the anterior surface of the brainstem

Cavernous malformations in the midbrain can be accessed via several safe entry zones. The accepted rule of thumb is to enter at the point where the lesion is visible at the surface of the brainstem to pass through as little normal brain tissue as possible. However, in some cases, in order to avoid critical neural structures, this rule may not apply. A different safe entry zone can be chosen. Our video presents a case of a ruptured cavernous malformation in the midbrain reaching its anterior surface which was successfully resected via a posterolateral route using the supracerebellar infratentorial approach. The video can be found here: https://youtu.be/7kt-OQuBmz0.

Subtemporal approach for the resection of a midbrain cavernous malformation: evaluation of safe surgical corridors

Brainstem cavernous malformation management is complex due to its critical location and deleterious effect when bleeding. Therefore, every case should be thoroughly analyzed preoperatively. We present the case of a female patient with a midbrain cavernous malformation. A comprehensive anatomical and clinical analysis of the surgical corridors is done to decide the safest route. A subtemporal approach was done and the lateral mesencephalic sulcus and vein were important anatomical landmarks to guide the safe entry zone. Nuances of technique and surgical pearls related to the safe entry zones of the midbrain are discussed and illustrated in this operative video.

The video can be found here: https://youtu.be/vYA-IgiT2lU.

Microsurgical resection of a medullary cavernous malformation through a far lateral approach

The decision to resect a cavernous malformation of the brainstem is based on patient- and lesion-specific factors. The patient’s age, comorbidities, neurologic condition, and number and severity of symptomatic hemorrhages are crucial to consider.^1,3,5 The proximity to the brainstem surface, amount of hematoma, and true lesion size help dictate the surgical corridor.^2,4 We present a patient with a medullary cavernous malformation who had three hemorrhages and neurologic worsening. The surgical approach was based on detailed preoperative imaging. We performed a far lateral posterior fossa exposure to resect the lesion. The details of surgical planning and the microsurgery are presented.

The video can be found here: https://youtu.be/2y-OJ22Zjw8.

Supracerebellar transtentorial resection of a ruptured thalamomesencephalic cavernous malformation

Thalamomesencephalic cavernous malformations are located high in the brainstem and may be difficult to reach. We present a case of such a lesion which was successfully approached via the supracerebellar transtentorial route. Our enclosed video provides elements to justify this posterior approach and illustrates the steps required for the cavernoma’s safe removal, which include opening of the tentorium and gentle retraction of the exposed temporal lobe.

The video can be found here: https://youtu.be/Ex5OfLyBzPY.

Fully endoscopic access and resection of hemorrhaged cavernous malformation of the posterior midbrain

Cavernous malformations in the midbrain can be accessed via several safe entry zones. The accepted rule of thumb is to enter at the point where the lesion is visible at the surface of the brainstem to pass through as little normal brain tissue as possible. However, in some cases, in order to avoid critical neural structures, this rule may not apply. A different safe entry zone can be chosen. Our video presents a case of a ruptured cavernous malformation in the midbrain reaching its anterior surface which was successfully resected via a posterolateral route using the supracerebellar infratentorial approach.

The video can be found here: https://youtu.be/j7VTqRO7qd4.

Microsurgical resection of an inferior cerebellar peduncle cavernous malformation: 3-Dimensional operative video

Brainstem cavernous malformations are especially difficult to treat because of their deep location and intimate relation with eloquent structures. This is the case of a 26-year-old female presenting with dizziness, dysmetria, nystagmus and unbalance. Imaging depicted a lesion highly suggestive of a cavernous malformation in the left inferior cerebellar peduncle. Following a suboccipital midline craniotomy, the cerebellomedullary fissure was dissected and the lesion was identified bulging the surface. The malformation was completely removed with constant intraoperative neurophysiological monitoring. The patient presented improvement of initial symptoms with no new deficits. Surgical resection of brainstem cavernous malformations can be successfully performed, especially when superficial, using the inferior cerebellar peduncle as an entry zone. The video can be found here: https://youtu.be/-GGZe_CaZnQ.

Analysis of safe entry zones into the brainstem

Intra-axial brainstem surgeries are challenging. Many experience-based "safe entry zones (SEZs)" into brainstem lesions have been proposed in the existing literature. The evidence for each one seems limited. English-language publications were retrieved using PubMed/MEDLINE. Studies that focused only on cadaveric anatomy were also included, but the clinical case number was treated as zero. The clinical evidence level was defined as "case report" when the surgical case number was ≤ 5, "limited evidence" when there were more than 5 but less than 25 cases, and "credible evidence" when a publication presented more than 25 cases. Twenty-five out of 32 publications were included, and 21 different SEZs were found for the brainstem: six SEZs were located in the midbrain, 9 SEZs in the pons, and 6 SEZs in the medulla. Case report evidence was found for 10 SEZs, and limited evidence for 7 SEZs. Four SEZs were determined to be backed by credible evidence. The proposed SEZs came from initial cadaveric anatomy studies, followed by some published clinical experience. Only a few SEZs have elevated clinical evidence. The choice of the right approach into the brainstem remains a challenge in each case.

Extended exposure of the petroclival junction: The combined anterior transpetrosal and subtemporal/transcavernous approach

Background:

The combined anterior transpetrosal and subtemporal/transcavernous (atsta) approach to the petroclival junction provides a wide exposure facilitating resection of large tumor lesions such as petroclival mengiomas, chondrosarcomas, or chordomas. In this article we provide technical instructions on the approach with anatomical consideration and a literature review of previous applications of this approach.

Methods:

The combined approach was performed in two cadaveric specimen and relevant anatomical aspects were studied. Additionally, the authors performed a review of the literature focusing on indications, neurologic outcome, and complications associated with the technique.

Results:

A combined atsta approach offers a wide exposure of the crus cerebrum, pons, basal temporal lobe, cranial nerves III to VII/VIII, posterior cerebral artery (PCA), superior cerebellar artery (SCA), basilar artery (BA), anterior inferior cerebellar artery (AICA), and posterior communicating artery (Pcom). It has been successfully applied with acceptable morbidity and mortality rates, mainly for (spheno-) petroclival meningiomas.

Conclusion:

The combined approach studied here is a useful skull base approach to the petroclival junction and can be applied to treat large or complex pathologies of the region. Detailed anatomical knowledge is essential.

Timing of Surgery and Surgical Strategies in Symptomatic Brainstem Cavernomas: Review of the Literature

Brainstem cavernomas (BSCs) are angiographically occult, benign low flow vascular malformations that pose a significant surgical challenge due to their eloquent location. The present study includes an extensive review of the literature and three illustrative cases of BSC with emphasis on the timing of surgery: surgical approaches, usage of intraoperative monitoring, and complication avoidance. A systematic search was performed using the PubMed database was from January 1, 1999, to June 2018. The relevant articles were reviewed with particular attention to hemorrhage rates, timing of surgery, indications for surgery, surgical approaches, and outcome. Along with this, a retrospective analysis of three cases of symptomatic BSC, who were operated for the same, during the year 2018 in our institute was conducted. All the three patients presented with at least 1 episode of hemorrhage before surgery. Of these, one patient was operated immediately due to altered sensorium whereas the other two were operated after at least 4 weeks of the hemorrhagic episode. The patients who were operated in the subacute phase of bleed were seen to have liquefaction of hematoma, thus providing a good surgical demarcation and thereby reduced surgery-related trauma to the surrounding eloquent structures. Two patients improved neurologically during the immediate postoperative period, whereas one had transient worsening of neurological deficits during the immediate postoperative period in the form of additional cranial nerve palsies which completely improved on follow-up after 2 months. Radical resection is recommended in all patients with symptomatic BSCs. Surgery should be considered after the first or the second episode of hemorrhage as multiple rebleeds can cause exacerbation of deficits and sometimes mortality as well. Considering surgical timing, anywhere between 4 and 6 weeks or the subacute phase of the hemorrhage is considered appropriate. The aims of surgical intervention must be to improve preoperative function, minimize surgical morbidity and to reduce hemorrhagic rates. In spite of the significant surgical morbidity associated with BSCs, appropriate patient selection, meticulous surgical planning with adjuncts such as intraoperative monitoring and neuronavigation will go a long way in avoidance of major postoperative complications.

3D microsurgical anatomy of the cortico-spinal tract and lemniscal pathway based on fiber microdissection and demonstration with tractography

OBJECTIVE

To demonstrate tridimensionally the anatomy of the cortico-spinal tract and the medial lemniscus, based on fiber microdissection and diffusion tensor tractography (DTT).

MATERIAL AND METHODS

Ten brain hemispheres and brain-stem human specimens were dissected and studied under the operating microscope with microsurgical instruments by applying the fiber microdissection technique. Brain magnetic resonance imaging was obtained from 15 healthy subjects using diffusion-weighted images, in order to reproduce the cortico-spinal tract and the lemniscal pathway on DTT images.

RESULTS

The main bundles of the cortico-spinal tract and medial lemniscus were demonstrated and delineated throughout most of their trajectories, noticing their gross anatomical relation to one another and with other white matter tracts and gray matter nuclei the surround them, specially in the brain-stem; together with their corresponding representation on DTT images.

CONCLUSIONS

Using the fiber microdissection technique we were able to distinguish the disposition, architecture and general topography of the cortico-spinal tract and medial lemniscus. This knowledge has provided a unique and profound anatomical perspective, supporting the correct representation and interpretation of DTT images. This information should be incorporated in the clinical scenario in order to assist surgeons in the detailed and critic analysis of lesions located inside the brain-stem, and therefore, improve the surgical indications and planning, including the preoperative selection of optimal surgical strategies and possible corridors to enter the brainstem, to achieve safer and more precise microsurgical technique.

Surgical Management and Functional Outcomes of Cavernous Malformations Involving the Medulla Oblongata

OBJECTIVE

The aim of this study was to evaluate the clinical features, surgical complications, and functional outcomes of the surgical treatment of patients with cavernous malformations (CMs) involving the medulla oblongata.

METHODS

The charts of 69 patients undergoing surgical treatment of CMs in the medulla oblongata, pontomedullary, and cervicomedullary junctions between 2011 and 2017 were retrospectively reviewed. Patient demographics, lesion characteristics, operative documents, and patient outcomes were examined.

RESULTS

Of the 69 patients, the male-to-female ratio was 1.3. The mean patient age was 32.6 years, and the mean mRS score was 2.7 on admission. Postoperatively, 21 patients (30.4%) had deficits of cough reflexes, and 6 patients (8.7%) experienced respiratory rhythm disorder and dyspnea. The mean follow-up duration was 35.3 months. At the last follow-up evaluation, the mean mRS score was 1.8, and 53 patients (80.3%) had favorable outcomes, with mRS scores ≤2. The conditions of the patients improved in 45 cases (68.2%), remained unchanged in 11 cases (16.7%), and worsened in 10 cases (15.1%) relative to their preoperative baseline. The independent adverse factors for long-term functional outcome were increased age, multiple hemorrhages, presence of developmental venous anomalies, and lack of perilesional edema.

CONCLUSIONS

Respiratory dysfunction and deficits of cough reflexes can commonly occur during the early postoperative period for surgical resection of CMs involving the medulla oblongata. Favorable functional outcomes can be achieved by surgery, especially for younger patients who experience fewer hemorrhages and have lesions with perilesional edema and the absence of developmental venous anomalies.