Chapter 62: Lesions of the Anterior Skull Base

GENERAL CONSIDERATIONS

Neoplasms of the anterior skull base (ASB) continue to challenge skull base surgeons, despite tremendous advances in multidisciplinary management. These lesions represent a diverse group of tumor types located within a surgically treacherous region. Historically, these tumors were considered unresectable. If surgery was attempted, it generally consisted of a lateral rhinotomy, which inevitably resulted in incomplete tumor resection and dismal survival outcomes. The first combined neurosurgical and transfacial resections were reported in the mid-1950s, and the craniofacial resection was popularized by Ketcham and colleagues in 1963. Since this time, advances in diagnostic technology, interventional radiology, endoscopic endonasal surgery, and minimally invasive neurosurgery have facilitated the emergence of the young subspecialty of skull base surgery. Contemporary ASB surgical techniques have significantly expanded the limits of technical resectability while consolidating the gains that have been made in reducing morbidity and mortality.

The ASB is located at the interface of the central nervous system and the upper aerodigestive tract. ASB lesions may therefore arise from the bones of the skull base, “from above” (intracranially), or “from below” (the sinonasal cavity and orbits).

ANATOMY

Anatomy of the skull base is covered in detail in Chapter 1 and will only be briefly addressed in this section. The ASB is separated from the central or middle skull base by a line running through the chiasmatic sulcus, the anterior clinoid processes, along the posterior margin of the lesser sphenoid wings, and the superior rims of the greater sphenoid wings. The ASB borders the posterior wall of the frontal sinus anteriorly, the frontal bones laterally, and the planum sphenoidale, or roof of the sphenoid sinus, posteriorly. The major components of the ASB are the orbital plates of the frontal bone, the fovea ethmoidalis, and the cribriform plate. The cribriform plate, situated more inferiorly than the ethmoid roof, is composed of thin bone that is traversed by olfactory nerve fibers, and is easily invaded by tumors. The dura mater attaches anteriorly at the frontal crest and crista galli to form the falx cerebri. The anterior cranial fossa contains the frontal lobes, the olfactory bulb, and the olfactory tract.

It is important to clarify that the ASB is distinct from neighboring structures that are often surgically approached with similar techniques. The sella turcica and pituitary gland are constituents of the middle or central skull base, and the clivus is a component of the posterior skull base, not the ASB. The ASB overlaps partially with the anterolateral skull base, which is the region between the midorbit and the petrous internal carotid artery, and includes the lateral orbit, infratemporal fossa, and portions of the frontal, sphenoid and temporal bones. This chapter will focus on lesions of the ASB.