Basic Otorhinolaryngology (eBook)

1 Anatomy, Physiology, and Immunology of the Nose, Paranasal Sinuses, and Face

1.1 Basic Anatomy of the Nose, Paranasal Sinuses, and Face

The shape and appearance of the external nose affect not only the overall appearance of the face, but also the functional processes that take place inside the nose. The structural anatomy of the nose is important for both aesthetic and functional reasons, since the nose, as the gateway to the respiratory tract, performs a variety of physiologic functions.

Facial Skin and Soft Tissues

For the effective surgical treatment of soft-tissue defects in the face, whether of a traumatic or neoplastic nature, it is important to consider some distinctive features of the morphology and topographic anatomy of the face, since this is a highly conspicuous region in which the faulty or inadequate treatment of tissue changes will have obvious consequences. One such feature involves the tension lines of the skin (Fig. 1.1a), known also as the relaxed skin tension lines. Scars can be made less conspicuous by taking these tension lines into account when suturing facial skin injuries. The aesthetic units of the face are an important consideration in the treatment of larger soft-tissue defects (Fig. 1.1b). Failure to take these units into account will produce a poor cosmetic result.

The Facial Skeleton

Knowing the various components of the bony facial skeleton (Fig. 1.2) and their relationship to one another is important in trauma management and also in the diagnosis and treatment of inflammatory diseases of the facial skeleton and their complications. The upper jaw bone, or maxilla, houses the maxillary sinus and articulates laterally with the zygomatic bone (zygoma) via the zygomatic process (Fig. 1.2). The upper part of the maxilla borders the nasal bone, and its frontal process projects upward to the frontal bone. The zygoma also has a frontal process that connects superiorly with the frontal bone lateral to the orbit. The zygoma communicates posteriorly with the zygomatic arch.

External Nose

The shape of the external nose is defined by the nasal bones, a pair of rectangular bones in the upper nasal dorsum, and by the paired lateral cartilages (upper nasal cartilages) and alar cartilages (major alar cartilages) in the central and lower portions of the nose (Fig. 1.3). The lateral portions of the nasal alae also contain several small accessory cartilages, called the minor alar cartilages, which are embedded in the lateral soft tissues of the nose.

The shape and stability of the alar cartilages, each of which consists of a medial and lateral crus, chiefly determine the appearance of the nasal tip and the shape of the nares. As a result, they are also important in maintaining an effective nasal airway. Besides the medial crura, the inferior septal margin and the connective-tissue septum (columella) are also responsible for stabilizing the base of the nose (Fig. 1.4a). Subluxation of the inferior septal margin can also hamper nasal breathing by partially obstructing the nasal airway (Fig. 1.4b).

Nasal Cavities

The nasal cavities begin anteriorly at the nasal vestibule, which is bordered posteriorly by the internal nasal valve (limen nasi) located between the posterior border of the alar cartilage and the anterior border of the lateral cartilage. This valve area is the narrowest portion of the upper respiratory tract and, as such, has a major bearing on the aerodynamics of nasal airflow (see also 1.3). The anterior bony opening of the nasal cavity, called the piriform aperture, is bounded laterally and inferiorly by the maxilla and superiorly by the nasal bone (see Fig. 1.2). The interior of the nose behind the nasal valve is divided by the nasal septum into two main cavities. The nasal septum is composed of an anterior cartilaginous part and two posterior bony parts. Abnormalities in the shape of the nasal septum (see also 3.2, Septal Deviation), which may consist of a deviated septum, tension septum, spurs, or ridges, are a frequent cause of nasal airway obstruction. The choanae are the paired posterior openings through which the nasal cavities communicate with the nasopharynx.

The nasal cavity is bounded laterally by the lateral nasal walls, which are formed by the ethmoid bone and maxilla, and posteriorly by the palatine bone and the pterygoid process of the sphenoid bone. Several functionally important structures are located on the lateral nasal wall: the nasal turbinates and their associated passages (meati), sinus ostia, and the orifice of the nasolacrimal duct (Fig. 1.5).

The inferior turbinate consists of a separate bone that is attached to the medial wall of the maxillary sinus. The opening of the nasolacrimal duct is located in the corresponding inferior meatus ( 1.1). The middle and superior turbinates are part of the ethmoid bone. In rare cases, a rudimentary “supreme turbinate” is also present above the superior turbinate.

The middle turbinate has by far the greatest functional importance, because most of the drainage tracts from the surrounding paranasal sinuses open into the middle meatus (see also 1.3, Anatomy of the Ostiomeatal Unit).

The nasal cavity is bounded superiorly by the cribriform plate of the ethmoid bone. This thin bony plate has numerous openings for the passage of the fila olfactoria and also forms the boundary of the anterior cranial fossa. The floor of the nasal cavity is formed mostly by the hard palate, which is formed in turn by the two palatine processes of the maxilla and the horizontal laminae of the palatine bone.

Paranasal Sinuses

The paranasal sinuses are air-filled cavities that communicate with the nasal cavities (Fig. 1.6). All but the sphenoid sinus are already present as outpouchings of the mucosa during embryonic life, but except for the ethmoid air cells, they do not develop into bony cavities until after birth. The frontal sinus and sphenoid sinus reach their definitive size in the first decade of life. The maxillary sinus is present at birth but remains very small until the second dentition, because the presence of tooth germs in the maxilla limits the extent of the sinuses. The maxillary sinus, frontal sinus, and anterior ethmoid cells drain into the nasal cavity through the middle meatus—i.e., below the middle turbinate (Fig. 1.5). The posterior ethmoid cells drain into the nasal cavity through the superior meatus. The ostium of the sphenoid sinus is located in the anterior wall directly above the choanae. The anatomic connections between the nasal cavity and paranasal sinuses are functionally important and play a key role in the pathogenesis of many rhinologic diseases that involve the paranasal sinuses (see also 1.3, Anatomy of the Ostiomeatal Unit).