14 Tackling the Petrous Apex through a Keyhole

10.1055/b-0035-104226

14 Tackling the Petrous Apex through a Keyhole

Michael E. Sughrue and Charles Teo

14.1 Introduction

Operating at the petrous apex is generally agreed to be one of modern neurosurgery’s greatest challenges. It is deep in the head. The angles of attack are unfavorable in nearly every direction. The working areas are surrounded by cranial nerves and major vascular structures on almost all sides. The surgeon frequently needs to peel tumor off the brainstem, often underneath or around a cranial nerve.

Approaches to address this problem area are numerous, but none are ideal. Complex “skull base type” approaches can provide access to the entire tumor, but are time consuming and inherently morbid. They have longer incisions, more bone is removed, and more soft tissue is manipulated, and all of these have the potential to cause problems. Simpler approaches are less morbid, but they often do not allow access to the entire tumor in a single surgery.

Despite these challenges (or we would suggest because of these challenges) we provide in this chapter a description of a “less is more” philosophy for this area, which stresses workhorse approaches, staged procedures, and a hypermodern philosophy, based on the idea that tumor biology should dictate ideology.

14.2 The “Less Is More” Philosophy

It is certainly unfortunate to have a tumor of the petrous apex. In anyone’s hands, these tumors can be difficult to eradicate definitively. It should be noted, however, that many of the diseases commonly encountered here are not life threatening cancers, but rather are benign or at least slow growing tumors with good adjuvant therapy options, such as radiosurgery, for controlling remnant disease. Given that these tumors do not usually present as rapidly progressive or imminently fatal, it is critical to precisely define the goals of treatment, as this will dictate the best approach or combination of approaches.

Whenever possible we attempt cure in these patients in a single procedure; however, with more extensive and complex tumors, we prepare the patient for the potential need for multiple operations. We then begin with the procedure that best achieves the initial goals, usually the one that is able to remove the largest bulk of the tumor, or that decompresses the symptomatic portion of the tumor, or both. Frequently, a minimal modification of a common workhorse approach, such as cutting the tentorium or altering the patient’s position slightly, can allow one to achieve much more than with a simple approach. A lot can often be accomplished through a single keyhole approach if the endoscope is used to obtain viewing and working angles typically not available in the traditional variations of these familiar workhorse approaches.

Our philosophy is that, when necessary, two small approaches are better than one extensive one. If nothing else, a keyhole craniotomy is simple and fast, enabling the surgeon to start working on the tumor after far less initial preparation, compared to a complex skull base approach designed to address everything in a single procedure. We think it is advantageous to perform the key steps of the tumor resection as early in the day as possible, and would argue that the critical part of these cases is not the temporal bone drilling but rather the tumor surgery. Furthermore, in our experience, complex approaches designed to address two parts of the tumor at the same time seldom provide easy angles for either part. In most patients, using a single approach leads to the surgeon working off the long axis, through a small corridor, and/or at an unfamiliar angle. We think there is a major argument to be made for selecting simple approaches that provide comfortable, familiar working angles. By reducing operative time and tissue destruction, we feel these patients recover faster, while still receiving an anatomically excellent resection.

14.3 Approach Selection at the Petrous Apex

14.3.1 Endonasal Endoscopic Approaches

While, on the whole, most pathology of the petroclival region is best addressed via a craniotomy, it is worth mentioning a few instances when one should consider endonasal surgery as a first, and possibly the only, procedure.

14.3.2 Petrous Apex Granulomas/Abscesses

See Video 14.1

In our opinion, this is the most clear-cut indication for endonasal surgery in this region. Given that the goal is to enter the fluid-filled space and drain it into the sinus, it is hard to find a more direct and less morbid route to achieving this goal than through the sphenoid sinus. It is important to identify the relationship between the tumor and the paraclival carotid artery, in order to locate a window to the lesion through the sinus on the preoperative imaging, prior to selecting an endonasal endoscopic approach. Most lesions of the petrous apex can be accessed through a window posterior to the paraclival carotid artery and superior to the entry of the sixth cranial nerve into Dorello canal. For larger tumors that extend laterally, entering the petrous apex lateral to the paraclival carotid artery runs the risk of injury to the intra-cavernous portion of the sixth cranial nerve. We do not necessarily place stents in all of these cases and have yet to have recurrences using this algorithm.

14.3.3 Chordomas, Other Midline Midclival Pathology

See videos in Chapter 7.

Few areas of skull base surgery have benefitted more from the introduction of endonasal endoscopic approaches to the skull base than the management of midline clival tumors such as chordomas. These tumors typically are medial to all of the cranial nerves, and the endonasal approach is excellent for providing direct access to these tumors between the nervous structures. In some patients, severe lateral extension mandates an additional approach, but this is uncommon. It should be noted that, although there are always exceptions to the rule, in the majority of patients clival chordomas are incurable with surgery alone, and the aim of surgery is, therefore, to palliate with as complete and radical a resection as possible, at minimal neurological cost to the patient. The endonasal approach is extremely well tolerated, and patients with purely extradural lesions are often discharged within hours of surgery with little pain and minimal discomfort. This is a big improvement over transpalatal and transfacial approaches in our opinion.

14.3.4 Meningiomas with Limited Goals

Fig. 14.1

Experience has taught us that a gross total tumor resection is not always necessary to achieve a good outcome in these patients, especially in the era of radiosurgery. In some cases, especially in older patients, patients with significant comorbidities, etc., the goal is simply decompressive cytoreduction, to relieve symptoms, establish a histological diagnosis, and make the tumor a good radiosurgery target, if necessary. In some of these patients, the easiest route to the brainstem is though the sphenoid sinus, and a good subtotal resection and brainstem decompression can be obtained without the need to retract the cerebellum or to manipulate the cranial nerves.

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