Chapter 39: Nasal Cavity, Nose & Paranasal Sinuses

Nasal Cavity, Nose & Paranasal Sinuses details the anatomy and clinical importance of the nose, nasal cavity, and the surrounding paranasal sinuses, defining these structures as the initial segment of the upper respiratory tract responsible for air conditioning, filtering inspired air, and olfaction. The external nose is a complex pyramidal structure supported by bone and fibroelastic cartilages, including the paired lateral and major alar cartilages. The size, shape, and attachments of these cartilages define the major and minor tip support mechanisms, which are critical surgical considerations in procedures like rhinoplasty to prevent loss of projection. Nasal mobility and facial expression are governed by several muscles, notably nasalis, procerus, and depressor septi, which assist in widening or compressing the nasal aperture during inspiration. Internally, the nasal cavity is sagittally divided by the osseocartilaginous nasal septum and features a lateral wall characterized by three curved projections: the inferior, middle, and superior conchae (turbinates in surgical terminology). These conchae create underlying grooves, or meatuses, which serve as drainage pathways for the paranasal sinuses. The narrowest point regulating airflow is the internal nasal valve, typically ranging from 10 to 15 degrees. The olfactory mucosa is located in the superior olfactory cleft/groove, where bipolar olfactory receptor neurones transmit information through the cribriform plate to the olfactory bulb. The four air-filled paranasal sinuses—frontal, ethmoidal, sphenoidal, and maxillary—are lined by a respiratory mucosa that utilizes a mucociliary escalator for drainage into the nasal cavity. The functionally unified drainage region for the maxillary and anterior ethmoidal sinuses is the ostiomeatal complex, which includes the ethmoidal infundibulum and hiatus semilunaris. The ethmoidal sinuses are split into anterior and posterior groups by the basal lamella of the middle turbinate. Clinically significant anatomical variants within the ethmoid include the pneumatized middle concha (concha bullosa), infraorbital (Haller) cells, and the sphenoethmoidal (Onodi) cell, which is closely related to the optic nerve and internal carotid artery. Vascular supply involves branches of the ophthalmic, maxillary, and facial arteries. A major clinical concern is epistaxis, or nosebleeds, which frequently originates from the anastomotic plexus in Little’s area (Kiesselbach’s plexus) on the anterior nasal septum. Infections can spread rapidly from the sinuses, facilitated by thin bony barriers like the lamina papyracea, which may lead to serious sequelae like orbital cellulitis or cavernous sinus thrombosis.