Chapter 66. Neurotologic Skull Base Surgery

Although in widespread use, the term “skull base surgery” is somewhat of a misnomer. Only a minority of such procedures are undertaken to expose lesions actually located primarily within the skull base. Most procedures are conducted to expose deep-seated intracranial lesions situated either adjacent to the brainstem (eg, midbrain, pons, or medulla) or beneath the cerebral cortex. Previously, many such tumors were approached via simple openings in the calvaria, which require vigorous and often injurious degrees of brain retraction.

The fundamental principle in transbasal craniotomy is removal of the skull base bone to minimize the need for brain retraction. Although current techniques represent a major enhancement in our ability to control inaccessible tumors while minimizing morbidity, they are not panaceas. For example, experience has shown that these procedures are far more suitable for benign lesions (eg, meningiomas, schwannomas, and paragangliomas) and even for low-grade malignant growths (eg, chordomas and chondrosarcomas) than for high-grade malignant lesions (eg, squamous cell carcinoma, adenocystic carcinoma, and soft tissue sarcomas). Currently, more emphasis is placed on the preservation of function, especially cranial nerves, than on the necessity for radical resection in every case. The value of neurophysiologic nerve monitoring for motor nerves within the surgical field has become well established. In the developmental years of skull-base surgery, two-stage procedures were common. More recently, single-stage procedures have become preferred in most centers, even for tumors with sizable intra- and extracranial components, as well as those involving multiple cranial fossae. Computerized imaging modalities provide localizing information that guides the surgeon around vital structures and helps to enable thorough tumor removal.

Temporal Bone

Temporal bone resection is a fairly radical operation conducted for malignant disease, particularly squamous cell carcinoma originating in the external auditory canal. Some other indications include adenomatous tumors, such as the aggressive papillary adenocarcinoma of the endolymphatic sac and those arising in salivary tissue (eg, adenocystic carcinoma). In most cases, the lateral portion of the temporal bone housing the ear canal is removed en bloc (Figure 66–1). The posterior margin consists of the dural lining of the petrous pyramid, which is exposed via mastoidectomy. The anterior margin often includes some or all of the parotid gland and, at times, the mandibular condyle and the temporomandibular joint (Figure 66–2).