Supracerebellar Infratentorial Approach: Endoscopic Perspective

47 Supracerebellar Infratentorial Approach: Endoscopic Perspective

Robert T. Wicks, Xiaochun Zhao, and Peter Nakaji

Abstract

The supracerebellar infratentorial approach can provide direct access to potential pathologies of the pineal region, quadrigeminal plate, and superior cerebellar artery. The medial pulvinar, bilateral atria of the lateral ventricles, and mesial temporal region can also be approached through a transtentorial extension. Complications are minimized through a minimally invasive, off-midline craniotomy and integration of the high-definition endoscope from the beginning of the case. Three representative cases showing the dynamic options available through this surgical approach are presented.

Keywords: endoscope, extreme lateral, lateral ventricle, pineal, pulvinar, splenium, superior colliculus, supracerebellar infratentorial, third ventricle

47.1 Introduction

The supracerebellar infratentorial (SCIT) approach provides direct access to an array of potential pathologies in the region of the pineal gland, vein of Galen complex, and quadrigeminal plate. This approach also offers the option of transtentorial extension to expose the posterior third ventricle, the bilateral atria of the lateral ventricles, and the mesial temporal region.1 ^, ² ^, ³ ^, ⁴ ^, ⁵ ^, ⁶ ^, ⁷ The evolution of the SCIT approach has been gradual, transitioning from a large midline craniotomy centered at the inion to a more tailored, lateral craniotomy that allows for transtentorial extension when necessary and avoids the sacrifice of midline venous drainage. The integration of high-definition, angled endoscopes to this approach improves surgeon ergonomics during lengthy cases and offers more detailed visualization that renders the operative microscope unnecessary in most instances.

47.2 Evolution of a Surgical Approach

47.2.1 Supracerebellar Infratentorial Approach

Reaching the pineal region and the posterior midbrain has historically been a great challenge to neurosurgeons. In his review of 2,000 brain tumors, Harvey Cushing referenced 14 cases of pineal region tumors that resulted in 100% mortality.⁸ He therefore pursued surgical management that was limited to cranial decompression followed by radiation treatment to tumors located in this region. The German surgeon Fedor Krause in 1926 was the first to describe the SCIT approach to the pineal region and tectum.⁹ Bennett Stein of the Neurological Institute of New York further refined this surgical technique in his description of six cases and recommended this approach for all tumors of the pineal region.¹⁰

At our institution, the senior author (Peter Nakaji) has transitioned from use of the traditional midline craniotomy to a more lateral craniotomy when approaching the supracerebellar space and posterior incisura. The paramedian supracerebellar approach was first described by Yasargil when approaching peripheral aneurysms of the superior cerebellar artery.¹¹ Laborde et al¹² in 1992 and Ogata and Yonekawa¹³ in 1997 went on to describe their experiences using predominantly paramedian craniotomies with the patient in the sitting position to approach lesions in the upper brainstem or cerebellum via the supracerebellar trajectory. They found that this approach and positioning optimized gravity retraction and venous drainage, prevented the need for retractor placement, and allowed for direct visualization of the upper culmen cerebelli and region of the quadrigeminal plate.

47.3 Optimization of Gravity Retraction: Sitting Position

The sitting position was first described in the literature in 1913 by the French surgeon De Martel, who reported its use during awake craniotomies in which patients received local anesthesia for brain tumor resections.¹⁴ The early American pioneer in neurosurgery, Dr. Charles Frazier, witnessed the use of the procedure during a visit to Paris and, along with his trainee W. James Gardner, popularized the position in the United States for many posterior fossa lesions.¹⁵ Gardner went on to develop a specialized neurosurgical operating chair for the procedure during his time at the Cleveland Clinic. Advantages of the sitting position include lower venous pressure that results in decreased blood loss as well as utilization of gravity retraction with any pooling of blood or cerebrospinal fluid (CSF) naturally draining away from the surgical field. Although the sitting position reached its peak popularity during the 1960s and 1970s,¹⁴ it has recently undergone a resurgence in popularity due to rediscovery of its many advantages, with practitioners establishing standardized steps to minimize its associated risks.

Complications of the sitting position, although rare, have been widely reported. Such complications include venous air embolism (VAE), postoperative quadriplegia, tension pneumocephalus, and subdural hematoma. In a modern series of 1,792 cranial cases performed in the sitting position, the risk of VAE was 4.7% and the rate of VAE requiring clinical intervention was 1.06%.¹⁶ No deaths were reported; however, two cases were aborted intraoperatively due to complications. Spektor et al,¹⁷ in their series of 93 sitting and 150 lateral-position craniotomies for comparable lesions, found no increase in intraoperative complications when using the sitting position compared with the lateral position. Craniotomies performed in the sitting position have historically required the surgical microscope for intraoperative microdissection. This requirement led to additional complications for the operating surgeon, namely, increased fatigue during prolonged cases and potential exaggerated tremor due to prolonged arm extension when operating on deep-seated lesions (Fig. 47.1). The integration of the neurosurgical endoscope has mitigated many of these later concerns, as it allows the surgeon to stand during the procedure and to hold the arms in a more natural position.

Fig. 47.1Intraoperative photograph of a surgeon performing the supracerebellar infratentorial approach using the operative microscope. Although some improvements in arm support could be made, the photograph exemplifies the uncomfortable surgeon ergonomics that can result when operating on deep lesions via the SCIT approach, due to the steep trajectory of the tentorium. (Used with permission from Barrow Neurological Institute, Phoenix, Arizona.)

47.4 Use of the Endoscope in Neurosurgery

The incorporation of the high-definition endoscope into minimally invasive posterior fossa approaches has revolutionized microsurgical techniques in this arena. The endoscope was first popularized in the field of neurosurgery by Walter Dandy.18 However, he limited its use to the resection or coagulation of the choroid plexus in infants and young children with a diagnosis of hydrocephalus. In 1977, Apuzzo et al¹⁹ reported on the introduction of the Hopkins side-viewing telescope for endoscopic procedures. As high-definition cameras of ever-decreasing size developed, endoscopes gradually revolutionized minimally invasive skull base approaches, beginning with the endonasal transsphenoidal approach. The integration of the high-definition endoscope is not limited to transnasal or transoral approaches, however. It can also be used in a wide variety of keyhole neurosurgical approaches to optimize visualization and surgeon ergonomics.²⁰

47.5 Nuances of the Surgical Technique

Over the past decade, the senior author has standardized a supracerebellar approach for lesions located within the superior posterior fossa and posterior incisura regions. Critical to this approach are the following components: effective use of gravity retraction via the sitting position, strategic placement of a paramedian or lateral minimally invasive craniotomy, and use of dynamic endoscopic visualization. Similar to the radical advancements made in the arena of extended endonasal approaches to the anterior skull base, the endoscopic SCIT approach can be utilized for pathology of the posterior fossa, midbrain, and mesial supratentorial regions via transtentorial extension and application, where appropriate, of contralateral trajectories.

47.6 Sitting Position

Capitalizing on gravity retraction and minimizing venous congestion are key ways to optimize operative conditions during supracerebellar approaches. In most instances, this is best achieved via the sitting position. Adequate preoperative planning is necessary to safely proceed with a craniotomy in this position. One of the greatest risks of the sitting position is that a VAE may transition directly from the right atrium to the left atrium and, therefore, directly to the brain, resulting in a paradoxical air embolism and cerebral infarction.²¹ This risk can be mitigated by ruling out any direct communication between the venous and arterial circulations. This communication can be identified by a transthoracic echocardiogram with bubble contrast study to evaluate for a patent foramen ovale.²² If a patent foramen ovale is identified, the sitting-position craniotomy should be avoided and a viable alternative, such as the lateral “park-bench” position, should be used.

When no patent foramen ovale is present, the sitting position can safely be pursued. Fig. 47.2a and Fig. 47.2b show key elements of a safe, appropriate sitting position. Note that the patient is positioned with the back of the bed ending at the level of the mid scapula. This prevents the back of the bed from obstructing the surgeon’s hands. When the back of the bed is too high—at shoulder level or at the lower neck, for example—it can place the surgeon at a farther distance from the patient and can obstruct both the surgeon’s range of motion and the positioning of the endoscope, especially after draping. Another critical positioning point is that the crossbar adapter for the Mayfield skull clamp should be attached to the back segment of the operating table, not the seat segment (i.e., the crossbar adapter should not be separated by a joint in the bed from the patient’s Mayfield skull clamp) ( Fig. 47.2b). Positioning in this manner allows for safe intraoperative bed movement if necessary. If the Mayfield crossbar attachment for the skull clamp is attached to the seat of the bed, the bed must be locked throughout the surgery without the possibility of movement of the back of the bed ( Fig. 47.2a). Movement of the back of the bed in the latter situation would not allow the Mayfield skull clamp to move in tandem with the bed crossbar attachment and would result in severe scalp lacerations in the best-case scenario and internal decapitation of the patient in the worst case.