Anatomy and Microsurgical Relevance of the Outer Arachnoid Envelope around the Olfactory Bulb Based on Endoscopic Cadaveric Observations

BACKGROUND

 There is high risk of injury to the olfactory tract and olfactory bulb during surgery of the anterior cranial fossa. The goal of this study was to describe the outer arachnoid envelope around the olfactory bulb, which plays a significant role in approach-related injury of the nerve.

METHODS

 A total of 20 fresh human cadaveric heads were examined. Five cadaveric heads were used to describe a gross overview of the topographic anatomy of the outer arachnoid cover of the olfactory bulb. In 15 cadaveric heads, endoscopic surgical approaches were performed to examine the in situ undisrupted anatomy of the outer arachnoid around the olfactory bulb. Four cadaveric heads were used for the lateral subfrontal approach, 5 heads for the medial subfrontal approach, 3 heads for the median subfrontal approach, and 3 heads for the anterior interhemispheric approach.

RESULTS

 The outer arachnoid membrane of the frontal lobe attaches the olfactory bulb strongly to the above lying olfactory sulcus. Only the most rostral portion of the olfactory bulb became slightly detached from the frontal lobe. The outer arachnoid forms a decent protrusion around the tip of the olfactory bulbs. The fila olfactoria have their own outer arachnoid cover as a continuation of the same layer of the olfactory bulb. The effect of brain retraction and manipulation forces on the olfactory bulb and the role of the arachnoid membranes located here were visually analyzed and described in detail through the four different neurosurgical approaches we performed.

CONCLUSION

 The results of our observations provide important anatomical details for preserving the sense of smell during neurosurgical procedures.

Microsurgical anatomy and pathoanatomy of the outer arachnoid membranes in the cerebellopontine angle: cadaveric and intraoperative observations

PURPOSE

The cerebellopontine angle (CPA) is a frequent region of skull base pathologies and therefore a target for neurosurgical operations. The outer arachnoid is the key structure to approach the here located lesions. The goal of our study was to describe the microsurgical anatomy of the outer arachnoid of the CPA and its pathoanatomy in case of space-occupying lesions.

METHODS

Our examinations were performed on 35 fresh human cadaveric specimens. Macroscopic dissections and microsurgical and endoscopic examinations were performed. Retrospective analysis of the video documentations of 35 CPA operations was performed to describe the pathoanatomical behavior of the outer arachnoid.

RESULTS

The outer arachnoid cover is loosely attached to the inner surface of the dura of the CPA. At the petrosal surface of the cerebellum the pia mater is strongly adhered to the outer arachnoid. At the level of the dural penetration of the cranial nerves, the outer arachnoid forms sheath-like structures around the nerves. In the midline, the outer arachnoid became detached from the pial surface and forms the base of the posterior fossa cisterns. In pathological cases, the outer arachnoid became displaced. The way of displacement depends on the origin of the lesion. The most characteristic patterns of changes of the outer arachnoid were described in case of meningiomas, vestibular schwannomas, and epidermoid cysts of the CPA.

CONCLUSION

The knowledge of the anatomy of the outer arachnoid of the cerebellopontine region is essential to safely perform microsurgical approaches as well as of dissections during resection of pathological lesions.

A procedure in mice to obtain intact pituitary-infundibulum-hypothalamus preparations: a method to evaluate the reconstruction of hypothalamohypophyseal system

PURPOSE

The histopathological study of brain tissue is a common method in neuroscience. However, efficient procedures to preserve the intact hypothalamic-pituitary brain specimens are not available in mice for histopathological study.

METHOD

We describe a detailed procedure for obtaining mouse brain with pituitary-hypothalamus continuity. Unlike the traditional methods, we collect the brain via a ventral approach. We cut the intraoccipital synchondrosis, transection the endocranium of pituitary, broke the spheno-occipital synchondrosis, expose the posterior edge of pituitary, separate the trigeminal nerve, then the intact pituitary gland was preserved.

RESULT

We report an more effective and practical method to obtain continuous hypothalamus -pituitary preparations based on the preserve of leptomeninges.

COMPARED WITH THE EXISTING METHODS

Our procedure effectively protects the integrity of the fragile infundibulum preventing the pituitary from separating from the hypothalamus. This procedure is more convenient and efficient.

CONCLUSION

We present a convenient and practical procedure to obtain intact hypothalamic-pituitary brain specimens for subsequent histopathological evaluation in mice.

Anatomical Study of Arachnoid Granulation in Superior Sagittal Sinus Correlated to Growth Patterns of Meningiomas

Meningiomas in the parasagittal region were formed by arachnoidal cells disseminated among arachnoid granulations. The purpose of this study was to characterize the morphology of chordae willisii, and AGs found in the superior sagittal sinus. This study used 20 anatomical specimens. Rigid endoscopes were introduced via torcula herophili into the sinus lumen. The morphological features of arachnoid granulation and chordae willisii were analyzed, and then arachnoid granulations and chordae willisii were assessed by elastic fiber stains, Masson’s stains, and imaging analysis. Three types of arachnoid granulations were present in the examined sinuses. There were 365 counts of arachnoid granulations in examined sinuses by imaging analysis, averaging 1.36 ± 2.58 per sinus. Types I, II, and III made up 20.27, 45.20, and 34.52% of 268 patients, respectively. Microscopy of chordae willisii transverse sections indicated the existence of a single layer and a multiple-layered dura sinus wall. The dural sinus wall was the thickest one in the superior sagittal sinus. The thickness of longitudinal lamellae was significantly greater than trabeculae. This study reveals the anatomical differences between arachnoid granulations in the superior sagittal sinus. The arachnoid granulations classification enables surgeons to predict preoperatively growth patterns, followed by safely achieving the optimal range of parasagittal meningioma resection.

Delineation of Subarachnoid Cisterns Using CT Cisternography, CT Brain Positive and Negative Contrast, and a Three Dimensional MRI Sequence: A Pictorial Review

The basic anatomy and morphology of subarachnoid cisterns of the brain are interesting and challenging topics with high clinical significance. These enlarged CSF-filled expansions are important as they transmit various neurovascular structures. The cisterns can be classified based on their location as supratentorial, at the level of the tentorium, and infratentorial. They are also classified as paired and unpaired cisterns. The anatomical and radiological information about the cisterns is clinically and surgically relevant in diagnosing and managing many neurological disorders. It is also essential in medical teaching. This pictorial essay reviews the radiological images where the subarachnoid cisterns are delineated in four unique circumstances.

Arachnoid Membranes: Crawling Back into Radiologic Consciousness

The arachnoid membranes are projections of connective tissue in the subarachnoid space that connect the arachnoid mater to the pia mater. These are underappreciated and largely unrecognized by most neuroradiologists despite being found to be increasingly important in the pathogenesis, imaging, and treatment of communicating hydrocephalus. This review aims to provide neuroradiologists with an overview of the history, embryology, histology, anatomy, and normal imaging appearance of these membranes, as well as some examples of their clinical importance.

Arachnoid and dural reflections

The dura mater is the major gateway for accessing most extra-axial lesions and all intra-axial lesions of the central nervous system. It provides a protective barrier against external trauma, infections, and the spread of malignant cells. Knowledge of the anatomical details of dural reflections around various corners of the skull bases provides the neurosurgeon with confidence during transdural approaches. Such knowledge is indispensable for protection of neurovascular structures in the vicinity of these dural reflections. The same concept is applicable to arachnoid folds and reflections during intradural excursions to expose intra- and extra-axial lesions of the brain. Without a detailed understanding of arachnoid membranes and cisterns, the neurosurgeon cannot confidently navigate the deep corridors of the skull base while safely protecting neurovascular structures. This chapter covers the surgical anatomy of dural and arachnoid reflections applicable to microneurosurgical approaches to various regions of the skull base.

The membrane of Liliequist-a safe haven in the middle of the brain. A narrative review

BACKGROUND

The membrane of Liliequist is one of the best-known inner arachnoid membranes and an essential intraoperative landmark when approaching the interpeduncular cistern but also an obstacle in the growth of lesions in the sellar and parasellar regions. The limits and exact anatomical description of this membrane are still unclear, as it blends into surrounding structures and joins other arachnoid membranes.

METHODS

We performed a systematic narrative review by searching for articles describing the anatomy and the relationship of the membrane of Liliequist with surrounding structures in MEDLINE, Embase and Google Scholar. Included articles were cross-checked for missing references. Both preclinical and clinical studies were included, if they detailed the clinical relevance of the membrane of Liliequist.

RESULTS

Despite a common definition of the localisation of the membrane of Liliequist, important differences exist with respect to its anatomical borders. The membrane appears to be continuous with the pontomesencephalic and pontomedullary membranes, leading to an arachnoid membrane complex around the brainstem. Furthermore, Liliequist's membrane most likely continues along the oculomotor nerve sheath in the cavernous sinus, blending into and giving rise to the carotid-oculomotor membrane.

CONCLUSION

Further standardized anatomical studies are needed to clarify the relation of the membrane of Liliequist with surrounding structures but also the anatomy of the arachnoid membranes in general. Our study supports this endeavour by identifying the knowledge hiatuses and reviewing the current knowledge base.

A retaining sphenoid and dura procedure in the rat to obtain intact pituitary-infundibulum-hypothalamus preparations

BACKGROUND

The histopathological study of brain tissue is a conventional method in neuroscience. However, procedures specifically developed to recover intact hypothalamic-pituitary brain specimens, are not available.

NEW METHOD

We describe a detailed protocol for obtaining intact rat brain with pituitary-hypothalamus continuity through an intact infundibulum. The brain is collected via a ventral approach through removing the skull base. Membranous structures surrounding the hypothalamus-pituitary system can be preserved, including vasculature.

RESULTS

We report a retaining sphenoid and dura technique to obtain intact hypothalamic-pituitary brain preparations, and we confirm the practicability of this method. By combination of this technique with histological analysis or 3D brain tissue clearing and imaging methods, the functional morphology structure of the hypothalamus-pituitary can be further explored.

COMPARISON WITH EXISTING METHOD

The current procedure is limited in showing the connection between the hypothalamus and the pituitary. Our procedure effectively protects the integrity of the fragile infundibulum and thus prevents the pituitary from separating from the hypothalamus.

CONCLUSIONS

We present a convenient and practical approach to obtain intact hypothalamus-pituitary brain specimens for subsequent histopathological evaluation.

The Basal Subarachnoid Cisterns: Surgical and Anatomical Considerations

The basal subarachnoid cisterns are expansions of the subarachnoid space and transmit cranial nerves and intracranial vessels. Providing neurosurgeons with key concepts, anatomical landmarks, and techniques can result in safer procedures and better patient outcomes. In this review, we discuss the major basal subarachnoid cisterns including their embryology, history, anatomical descriptions, and use during surgical approaches.

The Superior Hypophyseal Arteries: Anatomical Study with an Endoscopic Endonasal Perspective

BACKGROUND

The use of high-definition endoscopes in extended transsphenoidal approaches to the suprasellar area has significantly improved visualization of its vascularization.

OBJECTIVE

To systematically examine the superior hypophyseal arteries (SHAs) anatomy from an endonasal endoscopic perspective.

METHODS

The endoscopic endonasal transsphenoidal trans-tuberculum approach was performed in 19 adult, fresh and latex injected specimens. Dissections recordings were reviewed to analyze SHAs type, number, and branches, as well as internal carotid arteries (ICA) branches that vascularized optic nerves and chiasm.

RESULTS

Identification of SHAs was possible in all specimens (37/38 sides). The number of SHAs varied from 1 to 3 per side (mean: 1.7). The anterior superior hypophyseal artery was visible in almost all cases (35/37 sides) and originated at the level of the carotid cave in 18/35 specimens; number of branches ranged from 1 to 6 (mean: 3.5), directed to the optic nerve (86%), chiasm (57%), infundibulum (86%), and/or parallel to the pituitary stalk (74%). The 4 main branches and patterns, originally described by McConnell in 1953, were confirmed. The posterior superior hypophyseal artery was evident in 28/37 sides with number of branches ranging from 0 to 4 (mean: 2.1), directed to the optic chiasm (50%), optic tract (32%), infundibulum (79%), and/or pituitary stalk (36%). The surgical implications of this study, together with anatomical and clinical videos, are also briefly discussed.

CONCLUSION

SHAs constitute a complex of anterior and posterior branches that stem from the medial ICA with different patterns, vascularizing the optic apparatus and pituitary stalk.

Outcome of Radical Surgical Resection for Craniopharyngioma with Hypothalamic Preservation: A Single-Center Retrospective Study of 1054 Patients

OBJECTIVE

A retrospective review of the surgical outcome for patients with craniopharyngioma (CP) treated in a single neurosurgical center with surgical resection using visualization to ensure hypothalamic preservation.

METHODS

The study included 1054 patients. Before 2003, a pterional cranial approach was preferred for 78% of patients; after 2004, the unifrontal basal interhemispheric approach was performed in 79.1% of patients.

RESULTS

Complete tumor resection was achieved in 89.6% of patients; vision improved in 47.1% of patients who had preoperative vision impairment. However, diabetes insipidus worsened in 70.4% of patients and new-onset diabetes insipidus occurred in 29.7% of the remaining patients. Pituitary stalk preservation occurred in 48.9% of cases. There were 89.6% of patients with total tumor removal; 13.3% of patients showed tumor recurrence within an average of 2.8 years. Of 69 follow-up patients with a subtotal or partial resection, 94.2% showed tumor recurrence within an average of 4.3 months. Of the total patients, 82.3% fully recovered.

CONCLUSIONS

This study has shown that radical surgical resection of CP using microsurgical excision can be effective with a good patient outcome without more limitations on each individual tumor of distinct features despite the impact of recent endoscopic techniques on CP surgery. The surgical approach depends on a direct and wider visualization of CP located in the midline with preserving hypothalamic structures by identifying some hypothalamic landmark structures. After surgery, most patients can resume their normal activities even after aggressive tumor removal, although patients require postoperative hormonal replacement.

Growth patterns of craniopharyngiomas: clinical analysis of 226 patients

OBJECT Craniopharyngiomas (CPs) are rare epithelial tumors that are often associated with an enigmatic and unpredictable growth pattern. Understanding the growth patterns of these tumors has a direct impact on surgical planning and may enhance the safety of radical tumor removal. The aim of this study was to analyze the growth patterns and surgical treatment of CPs with a focus on the involvement of the hypothalamopituitary axis and the relationship of the tumor to the arachnoid membrane and surrounding structures. METHODS Clinical data from 226 consecutive patients with primary CP were retrospectively reviewed. Tumor location and the relationship of the tumor to the third ventricle floor and the pituitary stalk were evaluated using preoperative MRI and intraoperative findings. A topographic classification scheme was proposed based on the site of tumor origin and tumor development. The clinical relevance of this classification on patient presentation and outcomes was also analyzed. RESULTS The growth of CPs can be broadly divided into 3 groups based on the site of tumor origin and on tumor-meningeal relationships: Group I, infrasellar/infradiaphragmatic CPs (Id-CPs), which mainly occurred in children; Group II, suprasellar subarachnoid extraventricular CPs (Sa-CPs), which were mainly observed in adults and rarely occurred in children; and Group III, suprasellar subpial ventricular CPs (Sp-CPs), which commonly occurred in both adults and children. Tumors in each group may develop complex growth patterns during vertical expansion along the pituitary stalk. Tumor growth patterns were closely related to both clinical presentation and outcomes. Patients with Sp-CPs had more prevalent weight gain than patients with Id-CPs or Sa-CPs; the rates of significant weight gain were 41.7% for children and 16.7% for adults with Sp-CPs, 2.2% and 7.1% for those with Id-CPs, and 12.5% and 2.6% for those with Sa-CPs (p < 0.001). Moreover, patients with Sp-CPs had increased hypothalamic dysfunction after radical removal; 39% of patients with Sp-CPs, 14.5% with Id-CPs, and 17.4% with Sa-CPs had high-grade hypothalamic dysfunction in the first 2 postoperative years (p < 0.001). CONCLUSIONS The classification of CPs based on growth pattern may elucidate the best course of treatment for this formidable tumor. More tailored, individualized surgical strategies based on tumor growth patterns are mandatory to provide long-term tumor control and to minimize damage to hypothalamic structures. Differences in the distribution of growth patterns between children and adults imply that hierarchical comparison is necessary when investigating outcomes and survival across treatment paradigms in patients with CP.

A membranous structure separating the adenohypophysis and neurohypophysis: an anatomical study and its clinical application for craniopharyngioma

OBJECT This study aimed to identify the membranous septation between the adeno- and neurohypophysis. The clinical impact of this septation in the surgical removal of infradiaphragmatic craniopharyngioma (Id-CP) is also clarified. METHODS The sellar regions from 8 fetal and 6 adult cadavers were dissected. After staining first with H & E and then with picro-Sirius red, the membranous structures were observed and measured under normal light and polarization microscopy. The pre- and postsurgical images and intraoperative procedures in 28 cases of childhood Id-CP were reviewed and analyzed. RESULTS There is a significant membranous septation (termed the adenoneurohypophysis septation [ANHS]) lying behind the intermediate lobe to separate the adeno- and neurohypophysis. The average thicknesses are 21.9 ± 16.9 μm and 79.1 ± 43.2 μm in fetal and adult heads, respectively. The median segment of the septation is significantly thicker than the upper and lower segments. The ANHS extends from the suprasellar pars tuberalis to the sellar floor, where it is fused with the pituitary capsule. During Id-CP surgery performed via a transcranial approach, the ANHS can be identified to reserve the neurohypophysis. Moreover, by understanding the anatomy of this membrane, the pituitary stalk was preserved in 3 patients (10.7%). CONCLUSIONS There is a significant membrane separating the anterior and posterior lobes of the pituitary gland, which lies behind the intermediate lobe. Understanding the anatomy of this septation is important for identifying and preserving the neurohypophysis and pituitary stalk during Id-CP surgery.

Extended endoscopic transsphenoidal approach infrachiasmatic corridor

An extended endoscopic transsphenoidal approach is required for skull base lesions extending to the suprasellar area. Inferior approach using the infrachiasmatic corridor allows access to the lesions through the tumor growth that is favorable for the extended transsphenoidal approaches. Infrachiasmatic corridor is a safer route for the inferior approaches that is made up by basal arachnoid membrane and Liliequist's membrane with its leaves (diencephalic and mesencephalic leaf). This area extends from the optic canal and tuberculum sella to the corpus mamillare. We performed extended endoscopic approach using the infrachiasmatic corridor in 52 cases, including tuberculum sella meningiomas (n:23), craniopharyngiomas (n:16), suprasellar Rathke's cleft cyst (n:6), pituitary adenoma (n:2), fibrous dysplasia (n:1), infundibular granulosa cell tumor (n:2), and epidermoid tumor (n:2). Total resection was achieved in 17 of 23 (74%) with tuberculum sellae meningioma using infrachiasmatic approach. Twenty patients presented with visual disorders and 14 of them improved. There were two postoperative cerebrospinal fluid (CSF) leakages and one transient diabetes insipidus and one permanent diabetes insipidus. Sixteen patients were operated on by the infrachiasmatic approach for craniopharyngiomas. Improvement was reached in seven of eight patients presented with visual disorders. Complete tumor resection was performed in 10 of 16 cases and cyst aspiration in 4 cases, and there were remnants in two cases. Postoperative CSF leakage was seen in two patients. Infrachiasmatic corridor provides an easier and safer inferior route for the removal of middle midline skull base lesions in selected cases.

The subdiaphragmatic cistern: historic and radioanatomic findings

BACKGROUND

In the past, sporadic demonstrations of the existence of a subarachnoid subdiaphragmatic cistern have been published. The aim of this study was to evaluate the anatomical characteristics of the subdiaphragmatic cistern of the pituitary gland.

METHODS

After a complete review of the literature published on the topic, we report anatomical observations of the subdiaphragmatic cistern and its relationship to the pituitary gland and to the chiasmatic cistern. Ten cadaveric heads were studied using different techniques and surgical methods (plastination, plastic casts of the subarachnoid spaces, microscopic and transsphenoidal endoscopic approaches). Moreover, 3-T magnetic resonance images of ten healthy volunteers were analyzed to investigate the presence and anatomical variability of the subdiaphragmatic cistern.

RESULTS

By means of our qualitative radioanatomic study, we found that the roof of the subdiaphragmatic cistern is formed by the diaphragma sellae, the floor by the superior face of the pituitary gland, the lateral walls by the arachnoidea extending laterally through the medial walls of the cavernous sinus, and the medial walls by the infundibular stem. The subdiaphragmatic cistern communicates by means of the ostium of the diaphragm with the chiasmatic cistern.

CONCLUSION

We confirmed the existence of the subdiaphragmatic cistern. The overused term "suprasellar cistern" refers more to a complex of cisterns, formed by the subdiaphragmatic cistern, below the diaphragma sella, and by the chiasmatic cistern, above it, in direct communication with the lamina terminalis and carotid cisterns.

Endonasal management of sellar arachnoid cysts: simple cyst obliteration technique

Object

Symptomatic sellar arachnoid cysts (ACs) have typically been treated via the transsphenoidal route. After sellar cyst wall fenestration, some authors have advocated cyst wall resection and increasing communication between the AC and suprasellar subarachnoid space (SAS). This study is a report of the authors' experience using a simplified approach to reinforce a defective diaphragma sellae or unseen arachnoid diverticulum by deliberately not enlarging the AC-SAS communication and obliterating the cyst cavity with adipose tissue followed by skull base reconstruction.

Methods

A retrospective analysis was conducted of patients who underwent an endonasal transsphenoidal obliteration of symptomatic ACs with a fat graft and skull base repair.

Results

Between July 1998 and September 2010, 8 patients with a sellar AC were identified (6 women and 2 men, mean age 57 years). Clinical presentation included headache, pituitary dysfunction, and visual dysfunction (4 patients each group). Maximal cyst diameter averaged 22 mm (range 15–32 mm). In all cases the sellar communication to the SAS was deliberately not enlarged. The endoscope was used for visualization in 8 of 9 procedures. Postoperatively, headache improved in all 4 patients, vision in all 4 patients, and partial resolution of endocrine dysfunction (hyperprolactinemia and/or recurrent hyponatremia) occurred in 3 (75%) of 4 patients. No new endocrinopathy, CSF leak, meningitis, or neurological deficits occurred. Two patients experienced cyst reaccumulation: 1 symptomatic recurrence was treated with reoperation at 43 months postsurgery, and 1 asymptomatic partial recurrence continued to be monitored at 29 months postsurgery.

Conclusions

Sellar ACs can be effectively treated using endonasal fenestration and obliteration with fat with resultant reversal of presenting symptoms in the majority of patients. This simplified technique of AC cavity obliteration without enlarging communication to the SAS has a low risk of CSF leakage, and in most cases appears to effectively disrupt cyst progression, although longer follow-up is required to monitor for cyst recurrence.

Microsurgical and endoscopic anatomy of Liliequist's membrane and the prepontine membranes: cadaveric study and clinical implications

BACKGROUND

Liliequist's membrane is mostly described as having a diencephalic leaf, mesencephalic leaf, and diencephalic-mesencephalic leaves in the literature. Also different descriptions of the prepontine membranes were reported. In this study, we visualized the regular structural forms of membranes without disturbing any attachments and defined infrachiasmatic and prepontine safety zones. We discussed the clinical significance of these structures.

MATERIALS AND METHODS

The study was carried out on 24 adult human cadavers at the Morgue Specialization Department of the Forensic Medicine Institution following the initial autopsy examination. Liliequist's membrane and the prepontine membranes were explored after retraction of the frontal lobes. Dissections were performed under the operative microscope. A 0- and 30-degree, 2.7-mm angled rigid endoscope (Aesculap, Tuttlingen, Germany) was advanced through the prepontine cistern from the natural holes of membranes, or small holes were opened without damaging the surrounding structures.

RESULTS

The basal arachnoid membrane (BAM) continued as Liliequist's membrane (LM) without any distinct separation in all specimens. The LM coursed over the posterior clinoids and split into two leaves as the diencephalic leaf (DL) and mesencephalic leaf (ML) in 18 specimens; the medial pontomesencephalic membrane (MPMM) coursed anterolaterally as a continuation of the ML and attached to the medial surfaces of the fifth and sixth nerves, joining with the lateral pontomesencephalic membrane (LPMM), which was also a posterolateral continuation of the ML in all specimens. The medial pontomedullar membrane (MPMdM) and lateral pontomedullar membrane (LPMdM) were observed in 21 specimens. The MPMdM membrane was a continuation of the MPMM, and the LPMdM was a continuation of the LPMM in all 21 specimens.

CONCLUSION

We observed that the LM is a borderless continuation of the BAM. The MPMM and LPMM split from the ML without any interruptions. The MPMdM and LPMdM were a single membrane continuing from the MPMM and LPMM. We determined infrachiasmatic and prepontine areas that can be important for inferior surgical approaches.

Diaphragma sellae: a surgical reference for transsphenoidal resection of pituitary macroadenomas

OBJECTIVE

To classify patterns of descent of the diaphragma sellae (DS) to the sella turcica after transsphenoidal resection of pituitary macroadenomas and to determine whether there is any correlation between type of descent and volume or growth pattern of the tumor, as well as the presence of any postoperative hormone alteration, cerebrospinal fluid leak, and/or residual tumor.

METHODS

One hundred patients with pituitary macroadenomas in which microsurgical transsphenoidal approach was indicated were prospectively included. We classified patterns of descent of the DS into four types: type A: symmetrical descent with a central fold corresponding to the pituitary stalk; type B: asymmetrical with a lateralized fold; type C: symmetrical and uniform descent without any fold; and type D: minimal or no descent in absence of visible residual tumor. A correlation was made between these types of descent and clinical and radiological findings.

RESULTS

The largest tumors were types A and B; endocrine deficit was more frequent in types A and C, whereas the possibility of residual tumor was more elevated in types B and D. No statistically significant differences were found regarding tumor morphology and cerebrospinal fluid leakage.

CONCLUSIONS

Our results suggest that pattern of descent of the DS may serve as a reference to determine the risk of leaving residual tumor as well as the possibility of developing postoperative endocrine deficit. It is apparent that tumor volume, more than morphology, is the main factor determining type of descent of the DS.

Anatomical study of the arachnoid envelope over the pineal region

BACKGROUND

The distribution of the arachnoid membrane and its relationship with the neurovascular structures in the pineal region are still not fully understood.

OBJECTIVE

Because the arachnoid membrane has an intimate relationship with the neurovascular structures in the pineal region and it will always be encountered surgically, we attempted to clarify the formation and distribution of the arachnoid envelope over the pineal region (AEPG).

METHODS

The formation and distribution of the AEPG and its relationship with the neurovascular structures in the pineal region were examined by anatomic dissection in 20 adult cadaveric formalin-fixed heads.

RESULTS

The supratentorial and infratentorial outer arachnoid membranes converged at the tentorial apex and then embraced and ran forward along the vein of Galen to form the AEPG. The AEPG could be divided into 2 parts. Typically, the posterior part of the AEPG enveloped the vein of Galen and the terminal segments of its tributaries, and the anterior part of the AEPG enveloped the suprapineal recess, the pineal gland, and the distal segment of the internal cerebral veins. The compartment demarcated by the AEPG did not communicate with the adjacent subarachnoid cisterns or space.

CONCLUSION

Previous knowledge about the AEPG, as well as the superior boundary and the contents of the quadrigeminal cistern, needs to be revised. The arrangement and individual variation of AEPG are important for a better understanding of the various growth patterns of the pineal tumors and the relationship between the tumor and the neurovascular structures in the pineal region.

Anatomic relations of the arachnoidea around the pituitary stalk: relevance for surgical removal of craniopharyngiomas

Purpose

The growth pattern of craniopharyngiomas (CP) is yet to be understood due to challenges arising from the diversity of morphological features that exist. This in turn has had implications on the development of safe surgical strategies for management of these lesions. The aim of this study is to propose a morphological classification of CP based on their tumor–membrane relationship. It is hoped that this will contribute to better understanding of CP morphology and prediction of the intraoperative classification.

Methods

Histological techniques were used to study eight fetuses. Following Masson staining, the membranes around the pituitary stalk were observed under microscope. Pre-operative MRI and intraoperative images of 195 patients with CP were also analyzed.

Findings

The arachnoidal sleeve around the pituitary stalk (ASPS) was noted to be comprised of a compact fibrous component and a related loose trabecular component. The pituitary stalk was divided into four segments in accordance with the folds of the ASPS. Correspondingly, the growth of CPs was divided into four basic patterns—infra-diaphragmatic (ID), extra-arachnoidal (EA), intra-arachnoidal (IA) and sub-arachnoidal (SA) growth. The IA growth pattern can be further subdivided into two subtypes—namely, IA1 (with tumor growing within the fibrous component of the ASPS) and IA2 (with tumor growing within the trabecular component). This method of topographical division can be used to understand the growth of CP—infra-diaphragmatic CP show growth pattern ID or ID together with EA. Suprasellar CP can show an extra-ventricular growth pattern (EA or IA2), an extra- and intra-ventricular (IA2 + SA) growth pattern, a trans-infundibular growth pattern (ID + IA1 + SA) and an infundibulo-tuberal growth pattern (SA or SA + IA1). There is a statistically significant difference between CP growth patterns in children and adults. A predominance of ID growth is noted in children while adults tend to show a pattern of predominantly Extra-ventricular (EV) growth.

Conclusion

Our proposed classification details the relationship of the surrounding structures to CPs and purports to predict and identify the intraoperative anatomical stratification. It also attempts to help predict the growth patterns of these tumors. A knowledge of the intimate relations of the tumor and its key surrounding structures allows for safe surgical removal.