NASAL CAVITY AND 1 PARANASAL SINUSES By Dr. Bruce M. Wenig EMBRYOLOGY, ANATOMY, AND the horizontal part and separates the nasal cav- HISTOLOGY OF THE NASAL CAVITY ity from the anterior cranial fossa (medial part of foor). This area represents the deepest part Embryology of the cavity. The body of the sphenoid bone The facial prominences (frontonasal, max- forms the posterior sloping part; 2) the inferior illary, and mandibular) appear around the 4th aspect (foor) is formed by the palatine processes week of gestation and give rise to the boundaries of the maxillary bone, which represents the and structures of the face (1). The nasal placodes, majority (75 percent) of the foor and, thereby, bilateral thickenings of the surface ectoderm intervenes between the oral and nasal cavities; along the frontonasal prominence, form the the remainder of the foor is formed by the hori- nasal pits, which, by growth of the surrounding zontal process of the palatine bone; 3) the lateral mesenchyme, become progressively depressed aspect is formed mostly by the nasal surface of along their length, giving rise to the primitive the maxilla below and in front, posteriorly by nasal sacs, the forerunners of the nasal cavities. the perpendicular plate of the palatine bone, The anterior portion of the nasal cavity is the ves- and above by the nasal surface of the ethmoidal tibule, the epithelium of which is ectodermally labyrinth separating the nasal cavity from the derived and represents the internal extension orbit. Along the lateral wall of each nasal cavity of the integument of the external nose (1). are three horizontal bony projections: the su- The epithelium lining the nasal cavities proper perior, middle, and inferior conchae; occasion- (Schneiderian membrane) is also ectodermally ally a small fourth concha is identifed above derived (1). The nasal septum develops from the the superior concha and is called the supreme merged medial nasal prominences. concha (3). The air spaces or meatuses (superior, The regions of continuity between the nasal middle, and inferior) lie beneath and lateral to and oral cavities following rupture of the oro- the conchae and are named according to the nasal membrane develop into the choanae. The concha immediately above it; and 4) the medial conchae (turbinates) develop as elevations along aspect is the bony nasal septum entirely formed the lateral wall of each nasal cavity. The olfactory by the vomer and the perpendicular plate of epithelia develop in the superiposterior portion the ethmoid; the anterior portion of the nasal of each nasal cavity and differentiate from cells in septum represents the septal cartilage (2). the ectodermally derived nasal cavity epithelium. Histology Anatomic Borders The nasal vestibule is a cutaneous structure The nasal cavity is divided into right and left composed of keratinizing squamous epitheli- halves by the septum; each half opens onto the um and underlying subcutaneous tissue, with face via the nares, or nostrils, and communi- cutaneous adnexal structures (hair follicles, cates behind with the nasopharynx through the sebaceous glands, and sweat glands) (4). The posterior nasal apertures, or the choanae (2,3). mucocutaneous junction (limen nasi) is ap- Each half of the nasal cavity has the following proximately 1 to 2 cm posterior to the nares borders (walls) (fgs. 1-1, 1-2): 1) the superior as- and represents the point at which the epithelial pect, or the roof, slopes downward in front and surface changes from keratinizing squamous back and is horizontal in its middle; the frontal epithelium to ciliated pseudostratifed columnar and nasal bones form the anterior sloping part; (respiratory) epithelium, the latter lining the the cribriform plate of the ethmoid bone forms entire nasal cavity (fg. 1-3) and, as previously 1 Non-Neoplastic Diseases of the Head and Neck Figure 1-1 ANATOMY OF THE SINONASAL 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. detailed, ectodermally derived. The submucosa underlying the epithelium is thin, has seromu- cous (minor salivary) glands arranged in distinct lobules (fg. 1-3), normally contains a mixed infammatory cell infltrate including mature lymphocytes and scattered plasma cells but no lymphoid follicles/aggregates, and has a distinct vascular component consisting of large thick- walled blood vessels. The vascular structures are particularly prominent along the inferior and middle turbinates, resemble erectile tissue ow- ing to the prominent smooth muscle wall, and may be mistaken for a hemangioma (fg. 1-4) (4). The nasal septum separates the nasal cavities and contains elastic cartilage and lamellar bone. The nasal mucosa is closely apposed to the un- derlying structures of the nasal septum, with the periosteum and perichondrium attached so closely as to constitute a single membrane, referred to as mucoperiosteum (fg. 1-5). Along Figure 1-2 the anterior part of the nasal septum the sub- SAGITTAL VIEW OF THE UPPER RESPIRATORY TRACT mucosa is rich in thin-walled blood vessels. This location is referred to as Little, or Kiesselbach, A midline sagittal section shows the major structures of the nasal cavity, pharynx, and larynx. area and represents a frequent site of nose 2 Nasal Cavity and Paranasal Sinuses Figure 1-3 HISTOLOGY OF THE SINONASAL TRACT A: Ciliated respiratory epithelium lines the entire sinonasal tract, including the nasal cavity and paranasal sinuses. It overlies submucosal seromucous glands arranged in lobules with subjacent thick-walled blood vessels (arrows). B: At higher magnifcation, the serous and mucous cells are evident. C: The submucosa contains an admixture of infam- matory cells, including mature lymphocytes and scattered plasma cells. bleeds (fg. 1-6) (4). The nasal cartilage is of VNO between day 37 and 43 (1). The VNO ends the hyaline type and has a bluish, translucent, blindly posteriorly and reaches its greatest devel- homogeneous appearance. opment between 12 and 14 weeks (1). The VNO Melanocytes migrating from their origin in is consistently present in the form of a bilateral the neural crest are present in the normal muco- duct-like structure on the nasal septum, superior sa of the entire upper aerodigestive tract. In the to the paraseptal cartilage, at all ages (1). Grad- sinonasal tract, melanocytes are present in the ual replacement of the receptor cell population respiratory epithelium as well as in submucosal with patchy ciliated cells occurs. The human seromucous glands (5). VNO is a true homolog of the VNO in other The vomeronasal organ of Jacobson (VNO) is animals (e.g., mammals, reptiles, amphibians) a chemosensory structure that develops from and is lined by chemosensory epithelium similar the vomeronasal primordia, bilateral epithelial to the olfactory epithelium except that the VNO thickenings on the nasal septum (1). Invagina- chemoreceptors lack cilia, accounting for their tion of the primordia gives rise to the tubular highly developed sense of smell (1,4). 3 Non-Neoplastic Diseases of the Head and Neck Figure 1-4 HISTOLOGY OF THE SINONASAL TRACT Left: The nasal turbinates, particularly the inferior and middle turbinates, are normally characterized by the presence of thick-walled vascular structures. Right: The vascular structures resemble erectile tissue owing to a prominent smooth muscle wall and may be mistaken for a vascular neoplasm. Figure 1-5 HISTOLOGY OF THE SINONASAL TRACT The nasal mucosa is closely apposed to the underlying structures of the nasal septum, with the periosteum and peri- chon drium attached so closely as to constitute a single mem- brane, referred to as the muco- periosteum. 4 Nasal Cavity and Paranasal Sinuses The olfactory mucosa is located in the most Anatomic Borders superior portion of the nasal cavity, involving the superior portion of the superior turbinate Maxillary Sinus. The maxillary sinus rep- (cribriform plate) and approximately a third of resents the largest of the paranasal sinuses and the superior nasal septum (fg. 1-7). The olfacto- is located in the body of the maxilla (2,3). From ry epithelium consists of bipolar, spindle-shaped above, the maxillary sinus has a triangular olfactory neural (receptor) cells composed of myelinated axons that penetrate the basal lam- ina to protrude from the mucosal surface and nonmyelinated proximal processes that traverse the cribriform plate, columnar sustentacular or supporting cells, rounded basal cells that lie on basal lamina, and olfactory or Bowman glands in the lamina propria that represent purely se- rous type glands (fg. 1-8) (3,4). The olfactory epithelial cells are reactive for neuron-specifc enolase (NSE) (fg. 1-8). EMBRYOLOGY, ANATOMY, AND HISTOLOGY OF THE PARANASAL SINUSES Embryology The paranasal sinuses (maxillary, ethmoid, sphenoid, and frontal) develop as outgrowths of the walls of the nasal cavities and become air-flled extensions of the nasal cavities (fg. Figure 1-6 1-9). Some of the nasal sinuses (the maxillary and portions of the ethmoidal sinuses) develop HISTOLOGY OF THE SINONASAL TRACT during late fetal life and others (frontal and Along the anterior part of the nasal septum the submucosa is rich in thin-walled blood vessels. This location sphenoid sinuses) are not present at birth but is referred to as Little or Kiesselbach area and represents a develop during the early years of life. frequent site of nose bleeds. Figure 1-7 NASAL CAVITY The olfactory mucosa is confned 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 approximately one third of the nasal septum. In adults, the distribution becomes patchy, due to multifocal replacement by nonolfactory mucosa. The ol- factory cells send processes through the cribriform plate to connect with the olfactory bulb. 5 Non-Neoplastic Diseases of the Head and Neck Figure 1-8 NASAL CAVITY A: Specialized olfactory mucosa is composed of a mixture of olfactory cells (OC) with neuronal processes penetrating the cribriform plate, susten- tacular epithelial cells (SC), and regenerative basal cells (BC).