ANATOMY, HISTOLOGY, 1 AND EMBRYOLOGY An understanding of the anatomic divisions composed of the vomer. This bone extends from of the head and neck, as well as their associ- the region of the sphenoid sinus posteriorly and ated normal histologic features, is of consider- superiorly, to the anterior edge of the hard pal- able importance when approaching head and ate. Superior to the vomer, the septum is formed neck pathology. The large number of disease by the perpendicular plate of the ethmoid processes that involve the head and neck area bone. The most anterior portion of the septum is a reflection of the many specialized tissues is septal cartilage, which articulates with both that are present and at risk for specific diseases. the vomer and the ethmoidal plate. Many neoplasms show a sharp predilection for The supporting structure of the lateral border this specific anatomic location, almost never of the nasal cavity is complex. Portions of the occurring elsewhere. An understanding of the nasal, ethmoid, and sphenoid bones contrib- location of normal olfactory mucosa allows ute to its formation. The lateral nasal wall is visualization of the sites of olfactory neuro- distinguished from the smooth surface of the blastoma; the boundaries of the nasopharynx nasal septum by its “scroll-shaped” superior, and its distinction from the nasal cavity mark middle, and inferior turbinates. The small su- the interface of endodermally and ectodermally perior turbinate and larger middle turbinate are derived tissues, a critical watershed in neoplasm distribution. Angiofibromas and so-called lym- phoepitheliomas, for example, almost exclu- sively arise on the nasopharyngeal side of this line, whereas schneiderian papillomas, lobular capillary hemangiomas, and sinonasal intesti- nal-type adenocarcinomas almost entirely arise anterior to the line, in the nasal cavity. NASAL CAVITY Anatomy Although usually referred to as a single struc- ture, the nasal cavity consists of paired midfacial nares divided into two more or less mirror images by the nasal septum and at its extreme anterior, the columella (figs. -, -2). Midline asymmetry of the nasal septum is common, however, result- ing in considerable variation in the contours and volumes of the left and right chambers. Each cav- ity is bounded anteriorly by the external naris, marking its junction with the external world; posteriorly by the nasal choana, forming its junction with the nasopharynx; and medially by the smooth-surfaced nasal septum. Figure 1-1 Beneath the mucosa, the septum is formed SAGITTAL VIEW OF UPPER RESPIRATORY TRACT by one cartilaginous and two osseous support- A midline sagittal section shows the major structures of ing structures. Posteriorly and inferiorly, it is the nasal cavity, pharynx, and larynx. Tumors of the Upper Aerodigestive Tract and Ear Figure 1-2 CORONAL VIEW OF UPPER RESPIRATORY TRACT A coronal section through the head at the level of the molar teeth displays the anatomy of the nasal cavity, as well as the pharynx, larynx, and some of the paranasal sinuses. formed from the ethmoid bone (9). The lower Histology turbinate is a separate bone (9). There are multiple openings along the lateral The most anterior portion of the nasal cav- wall of the nasal cavity, primarily to the adjacent ity, or nasal vestibule, is an inward extension paranasal sinuses. The frontal sinus ostium is of the skin of the external nose. It is lined by located in the frontal recess at the anterior of the keratinized squamous epithelium with associ- middle turbinate. The sphenoid sinus opening ated dermal adnexa, including hair follicles, is in the sphenoethmoid recess located behind sebaceous glands, and sweat glands. This in- the superior turbinate. The opening to the ward cutaneous extension averages to 2 cm posterior ethmoid air cells is located under the in depth, at which point there is a gradual loss superior turbinate, with openings to the middle of adnexal structures and replacement of the and anterior cells located in the ethmoid bulla keratinized squamous epithelium by schneide- and hiatus semilunaris of the middle turbinate rian epithelium (9), denoted with this eponym (9). The primary maxillary antrum ostium is primarily to emphasize its ectodermal origin, also located in the hiatus semilunaris, and there as distinct from the endodermal origin of the may be an accessory ostium located posterior mucosa lining the pharynx and larynx. The to the primary maxillary ostium. schneiderian epithelium lines the nasal cav- The most superior portion of the nasal cavity ity and paranasal sinuses. With the exception consists of the cribriform plate with its special- of olfactory mucosa, schneiderian epithelium ized olfactory mucosa (fig. -3). This merges lacks any histologic distinction from the lin- with the remainder of the cavity roof, which ings of the pharynx and larynx. It is primarily slopes downward posteriorly to form the su- composed of a mixture of nonkeratinizing squa- perior portion of the choana. The floor of the mous cells, ciliated respiratory cells, scattered nasal cavity is formed by a combination of the mucus-containing goblet cells, and “intermedi- hard and soft palates. ate” cells. The mucosa varies in thickness from 2 Anatomy, Histology, and Embryology Figure 1-3 NASAL CAVITY The olfactory mucosa is confined to the most superior portion of the nasal cavity (blue shading). It involves the superior portion of the superior turbinate, the cribriform plate, and the superior approximate- ly one third of the nasal sep- tum. In adults, the distribution becomes patchy, due to multi- focal replacement by non- olfactory mucosa. The olfactory cells send processes through the cribriform plate to connect with the olfactory bulb. Figure 1-4 NASAL STROMA Prominent blood vessels below the nasal seromucinous glands resemble erectile tissue and should not be confused with a vascular neoplasm. (Fig. -5 from Stelow EB, Mills SE. Biopsy interpretation of the upper aerodigestive tract and ear. Lippincott, Williams & Wil- kins, Philadelphia, 2008:4.) more prominent pseudostratified columnar lamina with underling loose stroma containing cells overlying the portions of the middle and variably prominent seromucinous glands. Deep inferior turbinates in direct contact with airflow, to the glands is a prominent erectile type of vas- to thinner layers of cuboidal cells lining the cular tissue which should not be confused with recesses of the nasal cavity and the paranasal a vascular neoplasm (fig. -4). sinuses (9). Areas of squamous metaplasia are The olfactory mucosa is normally confined occasionally found, primarily on the anterior to the cribriform plate, medial surface of the surfaces of the middle and lower turbinates superior turbinate, and superior one third of the and the anterior portion of the nasal septum nasal septum. The total surface area in adults (36). Beneath the mucosal surface is thin basal is approximately .5 cm2. Over time, areas of 3 Tumors of the Upper Aerodigestive Tract and Ear Figure 1-5 OLFACTORY MUCOSA Left: Specialized olfactory mucosa is composed of a mixture of olfactory cells (OC) with neuronal processes that penetrate the cribriform plate, sustentacular epithelial cells (SC), and regenerative basal cells (BC). The olfactory cells extend to the surface where they form olfactory vesicles (OV). Above: The stratified, specialized olfactory epithelium has underlying Bowman glands, nerve fibers, and bone of the cribriform plate. (Fig. 5-5 from Balogh K, Pantanowitz L. Mouth, nose, and paranasal sinuses. In: Mills SE, ed. Histology for pathologists, 3rd ed. Philadelphia: Lippincott, Williams & Wilkins; 2007:428.) olfactory mucosa may be partially replaced by in a protective mucus blanket. Proximally, the schneiderian epithelium, resulting in a patchy neuronal cells form thin cytoplasmic processes distribution that presumably accounts for the containing unmyelinated nerve fibers which generally diminishing sense of smell with advanc- penetrate the cribriform plate to synapse in ing age. Whether olfactory neurons can regenerate the olfactory bulb. Small basal cells just above in humans is unclear, but has been demonstrated the basement membrane differentiate to form in other mammals (2). Rarely, ectopic foci of replacement sustentacular cells and may also olfactory mucosa lower in the nasal cavity have form replacement neuronal cells. Just beneath been described. Several studies using an olfactory the olfactory mucosa is a group of simple serous marker protein have allowed for easy mapping glands, referred to as the glands of Bowman (fig. of the mucosal distribution (6,22,23). -5). The distinctive appearance of these glands The specialized olfactory mucosa is composed and, particularly, their lack of mucin, aid in of three cell types (fig. -5). Most common are distinguishing olfactory mucosa from normal epithelial sustentacular cells, tall columnar schneiderian epithelium. eosinophilic cells anchored to the basement Embryology membrane but extending upward to the surface where they form microvilli. Interdigitated be- The nasal cavity is of ectodermal origin. Dur- tween the sustentacular cells are the elongated ing the fourth week of embryologic develop- neuronal olfactory cells. At the surface, these ment, a proliferation of ectoderm beneath the cells form widened peripheral processes con- forebrain forms a hollow invagination known taining olfactory vesicles. These are embedded as the olfactory pit. Cells within this pit acquire 4 Anatomy, Histology, and Embryology