The skull base consists of 3 fossae (anterior, middle, and posterior) (Figure 68–1). Although in widespread use, the term skull base surgery is somewhat of a misnomer. Only a minority of these procedures are undertaken to expose lesions actually located primarily within the skull base. A substantial portion of the 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. We prefer to use the term transbasal surgery for intracranial tumors.
Oblique view of skull base 3 fossae. Anterior in green, middle in blue, and posterior in purple. (Reprinted with permission of Jackler RK.)
Previously, many such tumors were approached via simple openings in the calvaria, which require vigorous and often injurious degrees of brain retraction. Nowadays, the anterior skull base is mostly approached by a team of rhinologists and neurosurgeons via endoscopic-assisted endonasal or transoral approach. The middle and posterior skull base are approached laterally, using a microscope, by a team of neurotologists (who have the expertise in drilling the bone around vital structures) and neurosurgeons.
The fundamental principle in transbasal craniotomies is the removal of the skull base bone to minimize the need for brain retraction. Although current techniques represent a major advancement in our ability to control what in the past were considered 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). When a new patient is being diagnosed, the treatment options are watchful waiting, radiation treatment, surgical intervention, or different combinations of these options. Currently, the treatment decision analysis leans toward more emphasis on the preservation of function, especially when related to 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, 2-stage procedures were common. More recently, single-stage procedures have become preferred in most centers, even for tumors with sizable intracranial and extracranial components, as well as those involving multiple cranial fossae. Navigation systems that incorporate various imaging modalities provide localizing information that guides the surgeon around vital structures and helps to enable thorough tumor removal.
RK. Atlas of Skull Base Surgery and Neurotology. Theime; 2009.
APPROACHES TO SKULL BASE LESIONS
The temporal bone, which consists of 4 parts (squama, tympanic, mastoid, and petrous), encases the sound-conduction mechanism and the hearing and balance organs.
Temporal bone resection ...