Surgical Anatomy
The complex anatomy of the nose, the paranasal sinuses, and the adjacent nasopharynx and intracranial and intraorbital structures has been explored in considerable detail from the seminal works of Johannes Lang and Heinz Stammberger in several recent publications1–8 and it seems inappropriate to reinvent the wheel. However, an intimate knowledge of the anatomy (and physiology) of the area is a prerequisite to understanding the natural history of tumor pathology and its treatment.
Intrinsic areas of weakness exist throughout the area (Fig. 3.1). The lamina papyracea is well named and may be dehiscent in the young and old, though the orbital periosteum is fortunately resistant (Figs. 3.2 and 3.3). Unfortunately, even when the orbital periosteum resists tumor spread, disease can run extraperiosteally to the apex and thence into the middle cranial fossa. The superior and inferior orbital fissures also offer routes of tumor exit and entry. The inferior fissure communicates with the pterygopalatine fossa medially and the infratemporal fossa laterally while the superior fissure leads to the cavernous sinus.
Similarly, the dura is relatively robust even when tumor infiltrates the bone of the skull base. Areas of vulnerability are found, however, in the cribriform plate with the many fenestrations for the olfactory fibrils connecting to the bulbs and tracts, together with dural prolongations and emissary veins to the sagittal sinus. The length and depth of the cribriform niche varies considerably (length 15.5 to 25.8 mm; depth 0 to 15.5 mm). The roof of the ethmoids is largely composed of hard frontal bone (Fig. 3.4) but the lateral lamina of the cribriform plate is effectively an extension of the vertical attachment of the middle turbinate, the depth of which has been divided into three using the Keros-Kainz classification. As this bone is very thin, it represents an easy route into the anterior cranial fossa. This situation is further compounded by the route and foramina of the anterior and posterior ethmoidal neurovascular bundles offering access to the orbit. The anterior ethmoidal artery is most vulnerable, usually running across the anterior skull base posterior to a suprabullar cell, often in a mesentery of mucosa or in a dehiscent bony canal. The posterior ethmoidal artery is generally more protected, running within the bone of the roof.
The sphenoid has important relationships with the optic nerve, carotid artery, and pituitary (Fig. 3.5). These structures vary in their prominence in the sinus walls and in the thickness of bony covering, which is dependent on the shape of the sinus cavity and its degree of pneumatization. The cavernous sinus also lies laterally and the foramen rotundum (V2) and pterygoid canal may impinge on the sinus cavity, especially if well pneumatized. The intersinus septum is often asymmetric and can attach to the lateral wall in the region of the carotid. Posterior to the jugum of the sphenoid, lies the optic chiasm (mean distance 21 mm).2 In 5 to 12% of the population, the posterior ethmoids may extend superiorly and laterally to the sphenoid, forming a sphenoethmoidal cell. The optic nerve and carotid artery are usually found in the lateral wall of these cells when present, rendering these structures at risk from disease and surgery.
The maxillary sinus also has areas of potential weakness, notably the medial wall through the maxillary hiatus, which in life is closed by the inferior turbinate, uncinate process, and bulla of the ethmoid, lacrimal, and perpendicular plate of the palatine (Figs. 3.6, 3.7, 3.8, 3.9, 3.10, 3.11). However, areas without bone such as the natural ostium, anterior and posterior fontanelles, and accessory ostia are easily breached by disease. In the sinus roof, in the infraorbital canal and foramen, and in the floor the dental roots provide access to the orbit, cheek, and oral cavity.
Attached to the posterior wall of the maxilla are the pterygoid plates, which are part of the sphenoid. The space between the plates and the sinus is the pterygomaxillary fissure, through which the maxillary artery runs. This in turn connects with the pterygopalatine fossa and the infratemporal fossa. This is an area in which angiofibromas typically arise. The pterygopalatine fossa is divided into a neural component composed of pterygopalatine ganglion and maxillary nerve and a vascular component containing the terminal part of the maxillary artery and its branches. The infratemporal fossa lies beneath the skull base between the side wall of the pharynx and ascending ramus of the mandible. It contains the pterygoid muscles, branches of the mandibular nerve, the maxillary artery, and the pterygoid venous plexus in the lateral pterygoid muscle. While the bone of the posterior wall of the maxillary sinus is strong, once it invaded by a malignant tumor such as a squamous cell carcinoma, the excellent blood supply of these areas rapidly facilitates tumor spread and therefore has a significant detrimental effect on prognosis.
The frontal sinus is unique in size and shape to each individual once developed and may be absent in ~1% of a white population. As it arises embryologically from the anterior ethmoids, (Fig. 3.12) it has a complex anatomy with asymmetric septations and a range of cellular pneumatization that has been the subject of many classifications (Kuhn). The drainage into the middle meatus is also variable, more like an hourglass than a “duct” and is referred to as the frontonasal recess. However, this is influenced by the configuration of the agger nasi and suprabullar cells. Given the complexity of these clefts and the capacity for retrograde mucociliary flow back into the sinus, it is perhaps surprising that the frontal sinus is so rarely a primary site of neoplasia.
Nasal Septum
The nasal septum is composed of a small membranous area, the quadrilateral and vomeronasal cartilages with a contributions from the upper and lower lateral cartilages and bone, including the perpendicular plate of the ethmoid, vomer, and crests of the maxilla and palatine (Figs. 3.3, 3.6, 3.9, 3.13). Primary tumors of the septum are rare, but it is one of the commoner sites of origin for chondrosarcoma, which can spread covertly into the skull base and/or palate. Anteroinferiorly the upper lip and gingivobuccal sulcus can also be affected.
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