44 Anatomy of the Posterior Incisural Space: Endoscopic Perspective
Roberta Rehder and Alan R. Cohen
Abstract
Direct approaches to the posterior and posterolateral incisural space remain surgical challenges. Endoscope-assisted microsurgery techniques provide improved operative view of the target lesion and the surrounding anatomy. Therefore, these techniques have the potential to reduce parenchymal trauma and neurovascular injuries. Minimally invasive operative approach is feasible surgical method to treat pathologies in the ambient cistern and posterior incisural space in selected cases. In this chapter, we demonstrate the benefits of endoscope-assisted microsurgical maneuvers to approach the posterior incisural space.
Keywords: minimally invasive neurosurgery, endoscope-assisted microsurgery, posterior incisural space, neuroendoscopy, pineal tumors
44.1 Introduction
Endoscope-assisted microsurgery for the management of brain tumors has evolved over the decades. Recent advances in optics, miniaturization, and imaging technology have enabled surgeons to approach neurosurgical lesions with reduced brain exposure and retraction.1 , 2 , 3 , 4 Most importantly, endoscope-assisted maneuvers can reduce recovery time, maximize surgical resection, and optimize patient outcome.
Approaches to the posterior and posterolateral incisural space are considered challenging despite innovations in surgical instruments and techniques. Lesions in the posterior and posterolateral region of the brainstem are in a deep location and near critical neurovascular structures.
Currently the basic surgical approaches to the posterior incisural space include the interhemispheric transcallosal, occipital transtentorial, and infratentorial supracerebellar routes.5 , 6 Modifications to these approaches are the paramedian supracerebellar, supracerebellar transtentorial, and combined supra-/infratentorial-trans-sinus approaches. Operative routes to the posterolateral incisura include the infratentorial supracerebellar approach, its variations, and transpetrosal routes.5
A comprehensive knowledge of the patient’s anatomy, location, and extent of the target lesion is essential to choose the best surgical route and carry out safe resections. Preoperative three-plane MRI scans and angiographic review of the arterial and venous anatomic features are essential for surgical planning and treatment, thus assisting neurosurgeons in choosing a particular approach.7
Endoscope-assisted microsurgery enhances illumination of the operative field and its surroundings, improving the magnified view and different perspectives of the surgical target. The current chapter describes the benefits of endoscope-assisted microsurgery to approach lesions in the posterior and posterolateral incisural spaces.
44.2 History
Surgical approaches to the posterior incisura include the infratentorial supracerebellar, occipital transtentorial, and transcallosal interhemispheric. The first attempt to remove a tumor in the pineal region was described by Victor Horsley in 1910; however, it was an unsuccessful operation.8 The next attempt was performed by Brunner on two patients, reported by Rorschach in 1913, which was also ineffective.9
In 1913, Hermann Oppenheim and Fedor Krause reported the first successful removal of a pineal region tumor on a 10-year-old boy.10 The patient was in a sitting position and Krause approached the lesion through a supracerebellar route. The encapsulated tumor, described as “fibrosarcoma,” was completely removed.
In 1915, Walter Dandy developed his first approaches to the pineal gland in dogs.11 In 1921, Dandy described the parieto-occipital transcallosal approach to the pineal region in three patients with poor results.12 Years later, in 1936, he reported the successful removal of 20 pineal tumors with a mortality of 20%.13
In 1926, Krause revised the operative technique and performed the infratentorial supracerebellar approach on three patients.14 In the first case, a 24-year-old student presented with a typical quadrigeminal tumor syndrome. On that occasion Krause performed only a surgical decompression as the patient deteriorated during the operation. Although he performed the supracerebellar route on three patients, only one case presented with good outcome.
In 1931, Van Wagenen described a successful resection of a pineal tumor in a 34-year-old woman through a transcortical transventricular approach.15 A year later, Cushing set a note advising conservative treatment of these tumors: “Personally, I have never succeeded in exposing a pineal tumor sufficiently well to justify an attempt to remove it.”16
In 1971, Bennett Stein popularized Krause’s infratentorial supracerebellar approach, showing its benefits as a feasible route to approach lesions in the pineal region, dorsal midbrain, and superior vermis.17 In 1976, Voigt and Yaşargil described a variation of the infratentorial supracerebellar route, known as the suboccipital-supracerebellar approach, for the removal of cavernous malformations in the posterior hippocampal region.18 The paramedian variant route enhanced visualization of lesions located more laterally, thus avoiding injury to the optic radiation. The technique improved operative view of pathologies in the superior and inferior colliculi, superior and middle cerebellar peduncles, and quadrangular lobules.
The combined supra-/infratentorial-trans-sinus approach is an alternative route for the removal of large tumors in the pineal region.19 The technique is performed with nondominant transverse sinus section to provide the maximal surgical exposure for the resection of large lesions. Indications for choosing the combined route include tumors larger than 4.5 cm that extend above and below the tentorium and those that encase the great venous complex in the posterior incisural space.20 The supracerebellar route described here is a modification of the early works proposed by surgeons to approach midline lesions.
44.3 Anatomy
The tentorial incisural space refers to the region between the upper brainstem and tentorial edges, which separates the supratentorial and infratentorial compartments.6 The incisural region includes the anterior, middle, and posterior incisural spaces. The anterior incisura, anterior to the midbrain and pons, extends forward above the diaphragma sellae. The middle incisural space includes the paired lateral regions by the brainstem, related to the hippocampal formation. The posterior incisura refers to the quadrigeminal cistern and to the area posterior to the midbrain, corresponding to the pineal region.
Several lesions have been reported in the posterior and posterolateral incisural regions, such as aneurysms, cavernomas, meningiomas of the free edge of the tentorium, neuromas of the trigeminal and trochlear nerve, gliomas of the thalamus, and pineal tumors.6 , 21 , 22
These lesions can be restricted to one region or extend to different directions, making surgical resection challenging. The most appropriate operative approach depends on the location and extent of the pathology, surgical experience, and clinical judgment.
