Overview of Transtemporal Skull Base Surgery

Objective

The objective of neurotologic skull base surgery is the 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 fossa, middle fossa, and lateral skull base lesions. An important consideration is the possibility of full three-dimensional approaches for certain lesions, including anterior endoscopic visualization and access. Creatively combining these different corridors of access offers the modern skull base surgeon strategies of management that can optimize functional outcomes for patients.

The modern era of neurotologic transtemporal skull base surgery began in 1961, when House introduced the operating microscope and multidisciplinary surgery for the removal of acoustic neuromas. The conceptual advantage of this transtemporal technique was the wide exposure of the lesion with substantially less cerebellar retraction than that in the techniques available at that time. 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. The emphasis on functional preservation has increased over the years from the initial enthusiasm with ablative skull base approaches. ^, As surgeons and patients are demanding better outcomes, such strategies as the fallopian bridge technique to avoid facial nerve mobilization, partial labyrinthine occlusion to preserve hearing, and endoscopic strategies 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 pathological and physiological status. An array of neurotologic procedures provides 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. Moreover, the emphasis is on anatomical descriptions rather than eponyms.

Fig. 38.1 presents an organizational framework for transtemporal surgery based on the 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 required for the preservation of audiovestibular function (although exceptions to this principle are a reality, with consistent hearing preservation with careful anatomic occlusion and excision of semicircular canals being achieved). Anatomically, the paired petrous pyramids encompass the center of the lateral skull base exposure. The approaches presented in Fig. 38.1 can be used individually; however, in certain cases, combinations of these approaches offer the ideal exposure.

The approaches that traverse the otic capsule (transcapsular) permit wide exposure by sacrificing hearing; these are the translabyrinthine (see Chapter 44 ), transcochlear, and transotic (see Chapter 46 ) approaches. The posterior approaches that spare the otic capsule (retrocapsular) provide varying degrees of cerebellopontine angle exposure with an opportunity for hearing preservation; these are the retrolabyrinthine (see Chapter 33 ) and retrosigmoid (see Chapter 45 ) approaches. The superior approaches (supracapsular) permit unroofing the internal auditory canal with varying degrees of petrous apex exposure and an opportunity for hearing preservation; these are the middle fossa (see Chapter 43 ) and middle fossa transpetrous (see Chapter 48 ) approaches.

The combined approaches permit the widest transtemporal exposure with varying opportunities for the preservation of neurological function; these are the retrolabyrinthine petrosal (see Chapter 51 ), translabyrinthine petrosal (see Chapter 51 ), and transcochlear petrosal (see Chapter 51 ) approaches. The inferior approaches (infracapsular) permit minimally invasive access for drainage of cystic lesions of the petrous apex; these are the infracochlear and infralabyrinthine (see Chapter 40 ) approaches. The anterior approaches (precapsular), such as the infratemporal fossa (see Chapter 49 ) 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. Chapter 50 outlines an array of endoscopic endonasal approaches that offer an anterior perspective on the structures of the central cranial base.

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.