How I do it: horizontal fissure approach to the middle cerebellar peduncle

BACKGROUND

The horizontal fissure approach is a workhorse for brainstem lesions in the central and dorsolateral pons and middle cerebellar peduncle (MCP). The cerebellopontine fissure is a V-shaped fissure with a superior and inferior limb between the cerebellum, pons, and MCP. The horizontal or petrosal fissure is at the apex of the cerebellopontine fissure and extends laterally to divide the petrosal surface of the cerebellum into superior and inferior parts. Splitting this fissure exposes the posterolateral aspect of the MCP without excessive retraction or transgression of the cerebellum.

METHOD

We demonstrate and describe the horizontal fissure operative approach to the middle cerebellar peduncle for resection of a pontine cavernoma with illustrative figures and operative video.

CONCLUSION

Splitting the horizontal (petrosal) fissure of the cerebellum brings the middle cerebellar peduncle into view behind the root entry zone of the trigeminal nerve, providing an expanded, safe corridor to the central and dorsolateral pons.

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.

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.

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.

Surgical Treatment of Brainstem Cavernous Malformation with Concomitant Developmental Venous Anomaly

Surgical resection of brainstem cavernous malformations (BCMs) is a high-risk procedure and can be challenging to the neurosurgeon. Lateral surgical routes are becoming increasingly used to approach ventrolaterally brainstem cavernoma. Surgical approach decision depends on the location of the cavernoma in the brainstem and a possible association with brainstem developmental venous anomalies (DVAs). DVA can affect the formation and clinical course of cavernous malformation (CM). CMs related to DVAs tend to have more aggressive behavior than isolated CM. In cases of DVAs associated with hemorrhage, CMs are most often the site of bleeding rather than DVAs themselves. In this case report, we present a 24-year-old woman with a pontomedullary CM and associated dorsally located DVA. BCM was operated through a far lateral suboccipital craniotomy. Brainstem entry point was at inferior olive with extension to the pontomedullary sulcus. This approach should be preferred as a safe surgical exposure to the central and paramedian pontomedullary cavernoma, especially in the cases with associated intraparenchymal brainstem DVA. Such surgical exposure allows preservation of the concomitant brainstem DVA.

Low Retrosigmoid Infratonsillar Approach to Lateral Medullary Lesions

OBJECTIVE

In our study, we comprehensively detail the technique of the low retrosigmoid approach to the lateral medullary area, including the inferior cerebellar peduncle, postolivary sulcus, pontomedullary sulcus, and inferior olivary nucleus, as well as the lateral recess of the fourth ventricle.

METHODS

Four formalin-fixed, silicone-injected, cadaveric human heads were examined under the operating microscope to demonstrate pertinent descriptive anatomy using the low retrosigmoid approach in a stepwise manner. Clinical parameters of a patient with a lateral medullary lesion were reviewed retrospectively to describe preoperative and postoperative examination and surgical details of the approach to the lateral medulla.

RESULTS

The clinical case report describes a low retrosigmoid craniotomy performed to access the exiting points of cranial nerves IX (glossopharyngeal) and X (vagus), foramen of Luschka, inferior cerebellar peduncle (lateral medullary zone), postolivary sulcus, and olivary nucleus. The lesion was exposed using the inferior cerebellar peduncle and removed using standard microsurgical technique.

CONCLUSIONS

The lower retrosigmoid infratonsillar approach provides excellent exposure to medullary safe entry zones, including the transolivary, postolivary sulcus, pontomedullary sulcus, and lateral medullary (inferior cerebellar peduncle) zones, for removal of lesions in this area.

Brainstem and cerebellar cavernous malformations

Cavernous malformations are vascular lesions that occur throughout the central nervous system, most commonly in the supratentorial location, with brainstem and cerebellar cavernous malformations occurring more rarely. Cavernous malformations are associated with developmental venous anomalies that occur sporadically or in familial form. Patients with a cavernous malformation can present with headaches, seizures, sensorimotor disturbances, or focal neurologic deficits based on the anatomic location of the lesion. Patients with infratentorial lesions present more commonly with a focal neurologic deficit. Cavernous malformations are increasingly discovered incidentally due to the increasing use of magnetic resonance imaging. Understanding the natural history of these lesions is essential to their management. Observation and surgical resection are both reasonable options in the treatment of patients with these lesions. The clinical presentation of the patient, the location of the lesion, and the surgical risk assessment all play critical roles in management decision-making.

Endoscopic endonasal approach to the ventral brainstem: anatomical feasibility and surgical limitations

OBJECTIVE Sporadic cases of endonasal intraaxial brainstem surgery have been reported in the recent literature. The authors endeavored to assess the feasibility and limitations of endonasal endoscopic surgery for approaching lesions in the ventral portion of the brainstem. METHODS Five human cadaveric heads were used to assess the anatomy and to record various measurements. Extended transsphenoidal and transclival approaches were performed. After exposing the brainstem, white matter dissection was attempted through this endoscopic window, and additional key measurements were taken. RESULTS The rostral exposure of the brainstem was limited by the sella. The lateral limits of the exposure were the intracavernous carotid arteries at the level of the sellar floor, the intrapetrous carotid arteries at the level of the petrous apex, and the inferior petrosal sinuses toward the basion. Caudal extension necessitated partial resection of the anterior C-1 arch and the odontoid process. The midline pons and medulla were exposed in all specimens. Trigeminal nerves were barely visible without the use of angled endoscopes. Access to the peritrigeminal safe zone for gaining entry into the brainstem is medially limited by the pyramidal tract, with a mean lateral pyramidal distance (LPD) of 4.8 ± 0.8 mm. The mean interpyramidal distance was 3.6 ± 0.5 mm, and it progressively decreased toward the pontomedullary junction. The corticospinal tracts (CSTs) coursed from deep to superficial in a craniocaudal direction. The small caliber of the medulla with very superficial CSTs left no room for a safe ventral dissection. The mean pontobasilar midline index averaged at 0.44 ± 0.1. CONCLUSIONS Endoscopic endonasal approaches are best suited for pontine intraaxial tumors when they are close to the midline and strictly anterior to the CST, or for exophytic lesions. Approaching the medulla is anatomically feasible, but the superficiality of the eloquent tracts and interposed nerves limit the safe entry zones. Pituitary transposition after sellar opening is necessary to access the mesencephalon.

Anatomy and approaches along the cerebellar-brainstem fissures

OBJECT Fissure dissection is routinely used in the supratentorial region to access deeply situated pathology while minimizing division of neural tissue. Use of fissure dissection is also practical in the posterior fossa. In this study, the microsurgical anatomy of the 3 cerebellar-brainstem fissures (cerebellomesencephalic, cerebellopontine, and cerebellomedullary) and the various procedures exposing these fissures in brainstem surgery were examined. METHODS Seven cadaveric heads were examined with a microsurgical technique and 3 with fiber dissection to clarify the anatomy of the cerebellar-brainstem and adjacent cerebellar fissures, in which the major vessels and neural structures are located. Several approaches directed along the cerebellar surfaces and fissures, including the supracerebellar infratentorial, occipital transtentorial, retrosigmoid, and midline suboccipital approaches, were examined. The 3 heads examined using fiber dissection defined the anatomy of the cerebellar peduncles coursing in the depths of these fissures. RESULTS Dissections directed along the cerebellar-brainstem and cerebellar fissures provided access to the posterior and posterolateral midbrain and upper pons, lateral pons, floor and lateral wall of the fourth ventricle, and dorsal and lateral medulla. CONCLUSIONS Opening the cerebellar-brainstem and adjacent cerebellar fissures provided access to the brainstem surface hidden by the cerebellum, while minimizing division of neural tissue. Most of the major cerebellar arteries, veins, and vital neural structures are located in or near these fissures and can be accessed through them.