OBJECTIVE

The objective of neurotologic skull base surgery is exposure of the skull base through precise management of the temporal bone. In subsequent chapters, procedures are presented that accomplish ample surgical exposure and minimize brain retraction in posterior, medial, and lateral skull base lesions.

The modern era of neurotologic transtemporal skull base surgery began in 1961, when House introduced the operating microscope and multidisciplinary surgery for removal of acoustic neuromas. The conceptual advantage of this transtemporal technique was a wide exposure of the lesion with substantially less cerebellar retraction than the techniques available at that time, in addition to direct facial nerve preservation. With its low mortality rate and enhanced facial nerve preservation rate, House established the translabyrinthine procedure as a technique with which all other microsurgical approaches to the cerebellopontine angle are compared.¹ The emphasis on functional preservation has increased over the years from the initial enthusiasm with ablative skull base approaches.^2,3 As surgeons and patients are demanding better outcomes, such strategies as the fallopian bridge technique⁴ to avoid facial nerve mobilization, partial labyrinthine occlusion to preserve hearing,^5–7 and endoscopic strategies⁸ to minimize incisions have decreased the morbidity of surgery.

Neurotologic skull base surgery includes various techniques that permit the surgeon to tailor the procedure to a particular patient’s pathology and physiologic status. An array of neurotologic procedures provide safe exposure of the midbrain, clivus, cerebellopontine angle, vertebrobasilar junction, petrous apex, and infratemporal fossa. The modern skull base surgeon has an expanding armamentarium of treatments, including surgery, stereotactic radiosurgery, and advanced imaging. New strategies combining observation, surgery, and stereotactic radiation are part of modern patient management. This chapter presents an anatomic framework for organizing and planning transtemporal neurotologic skull base approaches. In addition, the difficulties of terminology and classification of approaches are discussed. The emphasis is on anatomic descriptions rather than eponyms.

Figure 43-1 presents an organizational framework for transtemporal surgery based on management of the otic capsule. The otic capsule is selected as the organizational center based on its function and location. Functionally, anatomic preservation of the otic capsule is the requirement for preservation of audiovestibular function (although exceptions to this principle are developing). Anatomically, the paired petrous pyramids encompass the center of lateral skull base exposure. The approaches presented in Figure 43-1 can be used individually; however, in certain cases, combinations of these approaches offer the ideal exposure.

FIGURE 43-1 Transtemporal neurologic skull base approaches, based on management of the otic capsule. Transcapsular: translabyrinthine (TL), transotic (TO), transcochlear (TC), and transpetrous (TP). Retrocapsular: retrolabyrinthine (RL), retrosigmoid (RS), and extended retrosigmoid (ERS). Supracapsular: middle fossa (MF) and middle fossa transpetrous (MFT). Infracapsular: infralabyrinthine (IL) and infracochlear (IC). Precapsular: infratemporal fossa (ITF).

Approaches that traverse the otic capsule (transcapsular) permit wide exposure by sacrificing hearing: translabyrinthine (see Chapter 49), transcochlear (see Chapter 52), and transotic (see Chapter 51). The posterior approaches that spare the otic capsule (retrocapsular) provide varying degrees of cerebellopontine angle exposure with an opportunity for hearing preservation: retrolabyrinthine (see Chapter 36) and retrosigmoid (see Chapter 50). Superior approaches (supracapsular) permit unroofing the internal auditory canal with varying degrees of petrous apex exposure and an opportunity for hearing preservation: middle fossa (see Chapter 48) and middle fossa transpetrous (see Chapter 53).

Combined approaches permit the widest transtemporal exposure with varying opportunities for preservation of neurologic function: retrolabyrinthine petrosal (see Chapter 56), translabyrinthine petrosal (see Chapter 56), and transcochlear petrosal (see Chapter 56). The inferior approaches (infracapsular) permit minimally invasive access for drainage of cystic lesions of the petrous apex: infracochlear and infralabyrinthine (see Chapter 45). The anterior approaches (precapsular), such as the infratemporal fossa (see Chapter 54) techniques, permit exposure to the middle skull base, including the region of the foramen ovale, foramen spinosum, foramen lacerum, pterygoid space, and avenues to the nasopharynx and paranasal sinuses. These lateral approaches can be combined with facial disassembly and endoscopic sinus approaches in selected cases.

Neurotologic skull base surgery is not a hodgepodge of unrelated techniques. Instead, when considered in the context of the management of the otic capsule, these approaches are a spectrum of techniques for three-dimensional surgical exposure of the cranial base.

NOMENCLATURE

There has been a rapid expansion of terminology describing skull base surgical approaches. The techniques and their applications have evolved extensively. In the context of this rapid expansion of application and techniques, there has been a conflicting development of terminology for these approaches. Not only are various eponyms attached to the approaches, but also the same terms are used for different surgical techniques. Because of the potential conflict and debate over attribution, eponyms for the description of surgical approaches generally should be avoided. Instead, anatomic terminology should be selected. Considering transtemporal surgical approaches to the skull base, even this concept becomes confusing. Conceptually, most of these transtemporal approaches involve management of the petrous bone. These approaches have all rightfully been described as petrosal approaches in various modifications at different times. The terminology in Figure 43-1 is anatomically descriptive based on the structures of the otic capsule itself. Generally, we use the term petrosal approaches for combined posterior fossa and subtemporal surgical techniques that include division of the superior petrosal sinus (see Chapter 56).

The following chapters summarize the current state of the art in neurotologic skull base surgery. Although the terminology is the same, many of these approaches have been modified from their original description. The standard translabyrinthine approach includes removal of bone posterior to the sigmoid sinus and along the tegmen mastoideum. As these techniques have evolved, it is unnecessary to refer to this as an extended translabyrinthine technique. Similarly, with the transcochlear approach, House originally described an anterior extension of the translabyrinthine approach without transection of the ear canal and removal of the middle ear contents. In the current context, the transcochlear approach usually includes transection of the ear canal, removal of the skin of the ear canal, removal of the tympanic membrane and ossicular chain, and cochlear removal.

COLLABORATION IN TRANSTEMPORAL SURGERY

Multidisciplinary transtemporal approaches for posterior fossa skull base neoplasms are an adjunct and not a substitute for standard neurosurgical techniques in managing these lesions. The neuro-otologist and neurosurgeon are truly cosurgeons in the management of these lesions, each having intimate familiarity with the other’s role.⁹ Many of the following chapters are coauthored by otolaryngologists and neurosurgeons reflecting the true collaborative nature of modern skull base surgery. Precise temporal bone management offers the operative team flexibility to tailor the management to a patient’s specific anatomic and functional needs.

As a team considers an individual patient’s management, it is useful to consider each of the basic categories of surgical approaches systematically in terms of otic capsule management. A lesion can be managed in many different ways; however, systematic consideration of these approaches and their respective merits ensures that all surgical options are being considered.

SUMMARY

The fundamental prerequisite for success in transtemporal skull base surgery is complete, three-dimensional understanding of temporal bone anatomy and its surgical and functional applications. The following chapters present the indications, contraindications, and technical details of neurotologic skull base surgery.