Surgical approaches to the brain stem

Direct drainage of the basal vein of Rosenthal into the superior petrosal sinus: a literature review

An adult male was found to have a variation of the left basal vein of Rosenthal after presenting with complaints of headache and balance issues. In this case, the vein drained directly into the left superior petrosal sinus (SPS) instead of the great vein of Galen. Anatomical variation of the basal vein is likely due to embryonic development of the deep cerebral venous system as primitive structures either differentiate regress or further with age. These changes may result in the uncommon presentation seen in this case. To our knowledge, this is the first case that shows the basal vein drains into the SPS. The normal and variant anatomy of this vessel are discussed.

Microsurgical anatomy and internal architecture of the brainstem in 3D images: surgical considerations

OBJECT Brainstem surgery remains a challenge for the neurosurgeon despite recent improvements in neuroimaging, microsurgical techniques, and electrophysiological monitoring. A detailed knowledge of the microsurgical anatomy of the brainstem surface and its internal architecture is mandatory to plan appropriate approaches to the brainstem, to choose the safest point of entry, and to avoid potential surgical complications. METHODS An extensive review of the literature was performed regarding the brainstem surgical approaches, and their correlations with the pertinent anatomy were studied and illustrated through dissection of human brainstems properly fixed with 10% formalin. The specimens were dissected using the fiber dissection technique, under ×6 to ×40 magnification. 3D stereoscopic photographs were obtained (anaglyphic 3D) for better illustration of this study. RESULTS The main surgical landmarks and their relationship with the cerebellum and vascular structures were identified on the surface of the brainstem. The arrangements of the white matter (ascending and descending pathways as well as the cerebellar peduncles) were demonstrated on each part of the brainstem (midbrain, pons, and medulla oblongata), with emphasis on their relationships with the surface. The gray matter, constituted mainly by nuclei of the cranial nerves, was also studied and illustrated. CONCLUSIONS The objective of this article is to review the microsurgical anatomy and the surgical approaches pertinent to the brainstem, providing a framework of its external and internal architecture to guide the neurosurgeon during its related surgical procedures.

Three-dimensional microsurgical anatomy and the safe entry zones of the brainstem

BACKGROUND

There have been no studies of the structure and safe surgical entry zones of the brainstem based on fiber dissection studies combined with 3-dimensional (3-D) photography.

OBJECTIVE

To examine the 3-D internal architecture and relationships of the proposed safe entry zones into the midbrain, pons, and medulla.

METHODS

Fifteen formalin and alcohol-fixed human brainstems were dissected by using fiber dissection techniques, ×6 to ×40 magnification, and 3-D photography to define the anatomy and the safe entry zones. The entry zones evaluated were the perioculomotor, lateral mesencephalic sulcus, and supra- and infracollicular areas in the midbrain; the peritrigeminal zone, supra- and infrafacial approaches, acoustic area, and median sulcus above the facial colliculus in the pons; and the anterolateral, postolivary, and dorsal medullary sulci in the medulla.

RESULTS

The safest approach for lesions located below the surface is usually the shortest and most direct route. Previous studies have often focused on surface structures. In this study, the deeper structures that may be at risk in each of the proposed safe entry zones plus the borders of each entry zone were defined. This study includes an examination of the relationships of the cerebellar peduncles, long tracts, intra-axial segments of the cranial nerves, and important nuclei of the brainstem to the proposed safe entry zones.

CONCLUSION

Fiber dissection technique in combination with the 3-D photography is a useful addition to the goal of making entry into the brainstem more accurate and safe.

Surgical resection of cavernous malformations of the brainstem: evolution of a minimally invasive technique

OBJECTIVE

The purpose of this study is to provide an institutional retrospective review of surgically treated brainstem cavernous malformations.

METHODS

Between 2005 and 2010, 22 consecutive patients with brainstem cavernous malformations (15 female and 7 male) with a mean age of 43 years underwent surgical treatment. Mean volume of the resected cavernous malformations was 0.65 cm(3). A minimally invasive resection technique was used for these cases, in conjunction with skull base approaches.

RESULTS

The mean follow-up period was 26.6 months (range, 4-68 months). Of the 22 patients, 9% did not have clear evidence of hemorrhage at the time of presentation. Of the remainder, 22% had two or more instances of hemorrhage documented by magnetic resonance imaging. After resection and during follow-up, 54% of patients had an improvement in their modified Rankin scale, whereas 14% were worse compared with their preoperative presentation; 32% were unchanged and 9% of patients were found to have residual cavernoma post-surgery.

CONCLUSION

Our longitudinal experience has guided us to emphasize minimally invasive approaches during resection of the brainstem cavernous malformations, occasionally at the expense of achieving a complete resection, to improve patient outcomes.

Brainstem cavernous malformations: anatomical, clinical, and surgical considerations

Symptomatic brainstem cavernous malformations carry a high risk of permanent neurological deficit related to recurrent hemorrhage, which justifies aggressive management. Detailed knowledge of the microscopic and surface anatomy is important for understanding the clinical presentation, predicting possible surgical complications, and formulating an adequate surgical plan. In this article the authors review and illustrate the surgical and microscopic anatomy of the brainstem, provide anatomoclinical correlations, and illustrate a few clinical cases of cavernous malformations in the most common brainstem areas.

Lateral Transpeduncular Approach to Intrinsic Lesions of the Rostral Pons

Objective:

We describe the lateral transpeduncular approach to access lesions in the rostral pons. The surgical indications and technique are discussed in the context of an illustrative case and pertinent anatomic considerations.

Methods:

A 38-year-old man with acute right hemiparesis and bulbar symptoms had a left pontine hemorrhage with an associated cavernous malformation and venous anomaly. There was no pial or ependymal representation of the lesion. To avoid disruption of eloquent structures, the pia was entered in the posterolateral aspect of the middle cerebellar peduncle. Subsequent dissection was guided by stereotactic neuronavigation in a ventromedial trajectory along the course of the pontocerebellar fibers.

Results:

The cavernous malformation was resected completely without procedure-related morbidity. The patient’s preoperative deficits slowly improved to a functionally independent state.

Conclusion:

The lateral transpeduncular approach may be used to access intrinsic lesions of the rostral pons with relatively low morbidity. Stereotactic neuronavigation and intra-operative electrophysiological monitoring are important surgical adjuncts to guide dissection and lesion extirpation. Candidate selection, microsurgical technique, and pragmatic treatment goals remain fundamental to optimal patient outcomes.

Surgical Management Of Posterior Fossa Arteriovenous Malformations

Objective:

Arteriovenous malformations (AVMs) involving the cerebellum and brainstem are relatively rare lesions that most often present clinically as a result of a hemorrhagic episode. Although these AVMs were once thought to have a more aggressive clinical course in comparison with supratentorial AVMs, recent autopsy data suggests that there may be little difference in hemorrhage rates between the two locations. Although current management of these lesions often involves preoperative embolization and stereotactic radiosurgery, surgical resection remains the treatment of choice, conferring immediate protection to the patient from the risk of future hemorrhage.

Methods:

Most symptomatic AVMs that involve the cerebellum and the pial or ependymal surfaces of the brainstem are candidates for surgical resection. Preoperative angiography and magnetic resonance imaging studies are critical to determine suitability for resection and choice of operative exposure. In addition to considering the location of the nidus, arterial supply, and predominant venous drainage, the surgical approach must also be selected with consideration of the small confines of the posterior fossa and eloquence of the brainstem, cranial nerves, and deep cerebellar nuclei.

Results:

Since the 1980s, progressive advances in preoperative embolization, frameless stereotaxy, and intraoperative electrophysiologic monitoring have significantly improved the number of posterior fossa AVMs amenable to microsurgical resection with minimal morbidity and mortality.

Conclusion:

Future improvements in endovascular technology and stereotactic radiosurgery will likely continue to increase the number of posterior fossa AVMs that can safely be removed and further improve the clinical outcomes associated with microsurgical resection.