10 Keyhole Approaches to Parasellar Masses and the Interpeduncular Space

10.1055/b-0035-104222

10 Keyhole Approaches to Parasellar Masses and the Interpeduncular Space

Michael E. Sughrue and Charles Teo

10.1 Introduction

There are a great number of acceptable ways to surgically access various portions of the parasellar region. In our opinion, the eyebrow approach is the best of this long list, and as such it is the approach of choice whenever possible. We are enthusiastic about this approach for many reasons, most notably because it takes one of the best possible trajectories to this region. This approach competes with first the direct anterior-to-posterior trajectory provided by the bifrontal approach, which gives an excellent view of the optic chiasm, but poorer access to the opticocarotid space and is inherently more invasive than a unilateral approach. The other competitor approach, the pterional, the pterional-transsylvian approach is more lateral to medial and allows access to the opticocarotid triangle, but requires more temporalis elevation and also manipulation of the sylvian fissure and temporal lobe, which are initially in the way. The eyebrow approach, however, achieves the best of both worlds, providing a good angle on the optic apparatus and opticocarotid space without the need for very much manipulation of the temporalis, or any manipulation of the temporal lobe, and without requiring a large bilateral approach (see Fig. 10.1). It is simple and the cosmetic results are generally excellent when this approach is performed correctly.

**Fig. 10.1** Illustration demonstrating the trajectory provided by the eyebrow approach (diagonally hatched area).

The interpeduncular fossa is a more difficult area to reach, and there are no simple solutions for safely removing tumors from this area. The subtemporal approach is simple, but requires a good deal of temporal lobe retraction, and is limited in its rostral extent. The temporopolar approach provides a lot of working space, but generally requires removal of the zygoma, extensive sylvian dissection, and retraction of the temporal pole. Endonasal approaches provide an excellent view and the correct angle, but reaching the interpeduncular fossa is challenging without mobilizing the pituitary, which is technically demanding and carries a risk to gland function. The eyebrow approach, in contrast, is simple with low morbidity, and provides an ideal trajectory to the interpeduncular fossa. Excellent visualization of this area can be achieved using arachnoidal dissection and the use of endoscopic assistance to look through the opticocarotid space (see Fig. 10.2).

**Fig. 10.2** **a, b** Illustrations demonstrating the use of the endoscope to access lesions in the interpeduncular fossa. A1, A1 segment of the anterior cerebral artery; A2, A2 segment of the anterior cerebral artery; MCA, middle cerebral artery.

In this chapter on parasellar tumors we discuss the eyebrow approach in detail (as this region is where the eyebrow approach truly comes into its own), and provide guidelines for determining when it is inappropriate. We also describe our method for continuing this approach deep into the cisternal regions, including the interpeduncular fossa.

10.2 The Eyebrow Approach for Parasellar Pathology

As we have indicated above, entering through the eyebrow provides a great angle of attack for this region, allowing one to approach on an anterolateral-to-posteromedial direction, along a paramedian angle just medial to the temporal lobe. A similar angle of attack can be obtained by removing the orbital rim. However, in addition to the associated increase in morbidity, the standard curvilinear scalp incisions (behind the hairline) that are used to perform this approach causes some folded scalp flap to obstruct the line of sight and working angles along the sphenoid wing.

These advantages aside, the keyhole principle suggests that from the vantage point of the eyebrow approach, a wide variety of deeper structures are potentially accessible once the frontal lobe has moved out of view. With the use of the endoscope, the only truly limiting structures are the sphenoid wing, the dorsum sellae, and structures which are so far behind the orbit that they are most ergonomically reached via a more direct approach (we will discuss these limits in more detail later). Thus, the first task is to get the frontal lobe out of the way, and this is achieved by placing the head in extension with the malar uppermost. After opening the dura, we gently retract the frontal lobe to obtain aggressive cerebrospinal fluid (CSF) drainage by opening the cisterns (see Video 10.1). We usually find that relaxation of the brain and access to the cisterns is easily achieved, without injuring the frontal lobe or abrading the inferior frontal cortex, by (1) positioning the head somewhat extended so the frontal lobe falls away; (2) aggressively flattening the orbital roof with a drill; (3) good anesthesia conditions, including mannitol if necessary; (4) padding the brain with a long thin strip of Telfa™ wound dressing (a nonstick material), which is advanced along the cortical surface as we gradually approach the cisterns; and (5) patience, allowing CSF to slowly leak out, and cutting as much of the arachnoid as we can. Once the frontal lobe is relaxed, the proximal portion of the sylvian fissure can be partially split to provide even more room, especially at the tentorial incisura if necessary.

Following these maneuvers, the operation proceeds as it would through any other approach, and usually no more than minimal frontal lobe retraction is necessary (Fig. 10.3). Multiple examples are provided in this chapter (Fig. 10.3, Fig. 10.4, Fig. 10.5, Fig. 10.6, Fig. 10.7, Fig. 10.8, Fig. 10.9, see Videos 10.1, 10.3, and 10.4). In specific cases, the endoscope will need to be brought in at some point during the procedure, especially if there is significant extension underneath the clinoid process (see Video 10.2) or the sphenoid wing (Fig. 10.7), as these can be challenging to work around with the microscope. In many cases, tumor invasion into the optic canals or sella can be removed using the endoscope, avoiding the need to drill the optic canals, clinoid process, or planum sphenoidale, and the risk associated with these procedures (see Video 10.3). The endoscopic portions are typically saved until the end of the resection, after most of the tumor has been removed and hemostasis is obtained. It is essential in this region that one is aware of the position of the endoscope relative to the optic nerve and carotid artery. It is, therefore, essential that the endoscope is held and manipulated in safe corridors, and thus some of these applications are not ideal situations to use the endoscope for the first time; experience counts here.

**Fig. 10.3** **a–h** Eyebrow approach to a clinoid meningioma. **(a)** Preoperative imaging demonstrating a meningioma of the anterior clinoid process with invasion of the optic canal. **(b)** Postoperative imaging. **(c)** Preoperative and **(d)** postoperative visual fields.

**Fig. 10.3 continued (e)** View of the meningioma following brain relaxation. **(f)** Image following resection. **(g)** Image after resection demonstrating the carotid-oculomotor triangle with the third nerve visible. **(h)** View of the interoptic triangle.

**Fig. 10.4** **a–d** Eyebrow approach to a meningioma of the tuberculum sellae. **(a)** Preoperative imaging demonstrating a meningioma of the tuberculum sellae. **(b)** Postoperative imaging. **(c)** Arachnoidal dissection to expose the optic apparatus and tumor. **(d)** View of the tuberculum sellae during tumor removal.

**Fig. 10.5** **a–h** Eyebrow approach to a hypothalamic glioma. **(a)** Preoperative imaging demonstrating a hypothalamic glioma. **(b)** This tumor was approached through the eyebrow. **(c)** Following exposure, the lamina terminalis is opened, and **(d)** tumor is removed through this corridor. **(e)** Schematic demonstrating the use of the endoscope to work inside the third ventricle through this approach. **(f)** The endoscope is introduced through the lamina terminalis and tumor is removed using the suction. **(g)** endoscopic view of working within the third ventricle, **(h)** Final view of the optic apparatus after the endoscopic work.

**Fig. 10.6** **a–c** Eyebrow approach to a posterior clinoid meningioma. **(a)** Preoperative imaging demonstrating a meningioma of the posterior clinoid process. Although deep, it lies perfectly along the trajectory of the eyebrow approach. **(b)** This tumor was successfully removed using an eyebrow approach. The endoscope was helpful in ensuring complete removal. **(c)** Postoperative imaging.

**Fig. 10.7** **a–g** Eyebrow approach to a sphenoid wing mass. **(a)** Preoperative imaging demonstrating a low-lying mass of the medial sphenoid wing in a patient who presented with a visual field defect. The mass is slightly below the wing, and at the limit of what can be achieved in this region with endoscopic assistance. **(b)** The positioning for the eyebrow approach, with the head extended to encourage the frontal lobe to fall away from the orbit. **(c)** The eyebrow incision. **(d)** The bony opening. **(e)** Microscopic image following exposure. Note that a small section of the medial sphenoid wing has been removed, exposing the top of the mass. **(f)** Schematic demonstrating the use of the endoscope to view below the level of the wing in the eyebrow approach. **(g)** The endoscopic view of this mass, at a late stage in the resection. We are looking at the lateral wall of the cavernous sinus. The medial cut edge of the sphenoid wing bone is seen in the upper left. The mass is seen under the suction, being separated from the nerves entering at the superior orbital fissure.

**Fig. 10.8** **a–h** Eyebrow approach to a middle fossa epidermoid. **(a)** Preoperative imaging demonstrating an epidermoid of the middle fossa in a patient with intractable facial pain. The mass lies just medial to the uncus and along the anterior tentorial incisura, which is along the trajectory of the eyebrow approach. **(b)** Postoperative images. **(c)** After dissecting the cisterns and splitting the medial sylvian fissure, we obtain an excellent view of the mass tucked behind the middle cerebral vein. **(d)** Tumor removal proceeds under microscopic guidance. **(e)** View after the microscopic portion of the case. **(f)** The endoscope is then used to inspect the deep portions of the cavity, to ensure we are not leaving behind any fragments. In this view, the optic and olfactory nerves are visible. **(g)** Further inward, we observe the junction between the anterior clinoid process and tentorium and can see the entry point of the third nerve through the oculomotor triangle. **(h)** The endoscopic view at the depths of this resection cavity. The view of the uncus is far superior to what is achievable with the microscope.

**Fig. 10.9** **a–h** Eyebrow approach to a large meningioma of the tuberculum sellae. **(a, b)** Preoperative imaging demonstrating a very large meningioma of the tuberculum sellae involving both supraclinoid carotid arteries. Even very large parasellar tumors can be addressed with the eyebrow approach.

**Fig. 10.9 continued (c)** This image demonstrates all the superficial exposure necessary to completely remove this tumor. **(d)** After arachnoidal dissection, the tumor is visible, protruding through the interoptic space. **(e)** Further lateral angulation demonstrates the carotid vasculature, which is dissected free of the tumor. **(f)** After freeing the tumor from the vessels, the tumor is dissected from underneath the frontal lobe. The endoscope can be helpful in some patients with gaining access to the interhemispheric fissure, but was not needed in this case. **(g)** The tumor bulk, detached from the important structures, is being removed through an opening smaller than the tumor. **(h)** View of the optic nerve and carotid artery after tumor removal. The endoscope is useful at this point for removing tumor from the medial optic canals and the sella, eliminating the need for intracranial drilling in some patients. This is highlighted in a different case in Video 10.3.

10.2.1 The Interpeduncular Fossa via the Eyebrow Approach

Tumor in the interpeduncular fossa is usually accessed via the eyebrow approach using the endoscope (see Video 10.5). In patients with isolated interpeduncular fossa masses or retrodorsal masses, this implies that the endoscopic portion of the case begins as soon as the arachnoidal dissection of the basal cisterns is complete and the operative corridor is defined (Fig. 10.10 ). In more extensive masses involving the interpeduncular fossa secondarily, this portion is saved for the end of the operation, after the rest of the tumor is out (or at least as much of it as will be resected in that operation) (Fig. 10.11 , see Video 10.6).

**Fig. 10.10** **a–e** Eyebrow approach to an interpeduncular fossa teratoma. **(a)** Preoperative image demonstrating a mass in the interpeduncular fossa. **(b–c)** Postoperative images. **(d)** Endoscopic view of the mass in the interpeduncular fossa, being removed using an endoscope and angled suctions. The endoscope is placed through the opticocarotid triangle as indicated in Fig. 10.2 .

**Fig. 10.11** **a–h** Keyhole interhemispheric approach to a giant midbrain glioma. **(a–c)** Preoperative images demonstrating a giant pilocytic astrocytoma of the midbrain and thalamus, spilling into the interpeduncular fossa. Even tumors of this size can be completely removed through a keyhole (2 × 1.5 cm) craniotomy, with endoscopic assistance. **(d, e)** Postoperative images. **(f)** The arachnoid of the interpeduncular fossa is identified, and the tumor is dissected free of the third nerve seen here. **(g)** The microscope is used for rapid debulking of the middle of this large tumor, and it is dissected away from the anterior surface of the midbrain as seen here. **(h)** The endoscope is placed through the newly created tumor bed and is used to inspect the cavity and resect tumor at the margins under direct visualization, allowing for a complete resection of this tumor. The eventual outcome of the patient was excellent after a stormy postoperative course, and she remains in remission several years after this operation.

The best corridor for reaching the interpeduncular fossa/retrodorsal space is through the optic carotid triangle, as it is the most direct when working in the eyebrow trajectory. It is sometimes necessary to perform extensive arachnoidal dissection to mobilize this space, but ultimately this is worth the time taken (see Videos 10.6, and 10.7). Given the proximity of the endoscope to the optic nerve and several perforators, it is very important that the scope be held still, manipulated delicately, and not used in a slashing motion (see Video 10.8). In some patients, this requires the surgeon to become one-handed, if they do not have an assistant who is experienced enough to hold the endoscope. Such limitations can be overcome by the use of combination instruments, such as the suction bipolar.

Introduction of the endoscope requires some finesse, and if necessary should be performed under direct vision with the microscope (see Video 10.8 to grasp the logistics of performing this). This is especially true when steering an angled endoscope into position. As always, but especially in this situation, instruments should be visualized externally then followed into place under direct endoscopic guidance. As the examples demonstrate, these techniques allow one to work effectively and safely throughout the interpeduncular fossa, the anterior midbrain, the cerebral peduncles, and the posterior dorsum sellae down to the mid clivus (see Video 10.9).

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