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Anatomy and Embryology of the Nose

Development of the nasal airway begins during the fourth week of gestation. Collections of neural crest cells undergo proliferation and form the nasal pla-codes.5,19 On the fetal face, adjacent cells proliferate and give rise to the medial and lateral nasal processes. The frontal and maxillary processes fuse to give origin to the lateral two thirds of the upper lip, the superior alveolar ridges, and the palatal shelves. The medial nasal processes join the maxillary processes to form the philtrum and columella; they also fuse with the frontal prominence to form the frontonasal process, which eventually encompasses the nasal bones, the frontal bones, the cartilaginous nose, the ethmoid bones, the central incisors, and the hard palate. With the growth of the medial and lateral nasal processes, two nasal pits form that invaginate until only the nasobuccal membrane remains. This membrane eventually ruptures by the tenth week, thereby allowing communication between the nose and the nasopharynx.5,59

The nasal septum develops as a downgrowth from the merged medial nasal processes and the nasofrontal process, thus defining the right and left nasal cavities. The nasal septum and the palatine processes begin to fuse anteriorly during the ninth week, and fusion is completed posteriorly by the twelfth week.5,59

During the late embryonic period, the epithelium invaginates on each side of the nasal septum, thereby forming diverticula that are known as the vomeronasal organs. A vomeronasal cartilage develops ventral to each diverticulum. Shortly before birth, the vomeronasal organs begin to regress and usually disappear completely; the vomeronasal cartilages are usually the only adult remnants. These narrow strips of cartilage are located between the inferior edge of the cartilage of the nasal septum and the vomer.59 They are often found in conjunction with a septal spur, and they can be used as cartilage grafting material when other sources are absent or exhausted (Figure 44-1).

The cartilaginous framework of the nose develops from three paired mesenchymal condensations in both the medial and lateral nasal swellings. Part of this cartilage begins to ossify, thereby forming the membranous bone encasing the vomer and perpendicular cartilaginous plates. The perpendicular plate of the ethmoid and the nasal bones do not completely ossify until puberty.5 Injury to the nose in the young child or teenager may not elicit a true fracture, but it may instead create growth changes in this transitioning tissue, which may ultimately result in a deviated posterior bony septum or even the formation of a spur.

Figure 44-1. Intraoperative photo showing a septal spur with cartilage and bone overlap beginning at the bony-cartilaginous junction of the septum and going posteriorly. This cartilage strip can be utilized for grafting material if no other source of autologous cartilage is available. To view this image in color, please go to www.ototext.com or the Electronic Image Collection CD, bound into your copy of Cummings Otolaryngology—Head and Neck Surgery, 4th edition.

he nasal septum has functional and aesthetic significance. The septum is the main support structure of the external nose.82 It divides the nose into two cavities, regulates airflow through the nose, and supports the mucosal lining of the nasal cavities.82 Where once the lining was afforded greater significance, now both the mucosa and the cartilage are recognized as codependent and necessary.

The bony components of the septum include the nasal crest of the palatine bone, the nasal crest of the maxilla and premaxilla, the vomer, the perpendicular plate of the ethmoid, the nasal crest of the frontal bone, and the spine of the paired nasal bones. The anterior septum is composed of the quadrilateral cartilage, with its caudal-most projection extending beyond the nasal spine. Because of the complicated embryologic development of the septum, any one of a number of arrangements of the bone and cartilage contributions may be encountered during surgery (Figure 44-2).

Figure 44-2. This lateral schematic depicts one of many configurations of the bony and cartilaginous posterior of the septum that vary substantially from patient to patient. What is fairly consistent however is the posterior triangular segment of cartilaginous septum which often overlaps the bony septum.

Turbinates

The lateral nasal wall is composed of the laminae papyracea of the lacrimal bone, portions of the ethmoid bone, and the inferior and middle nasal conchae or turbinates. The turbinate bones develop from a cartilage ossification center during the fifth intrauterine month. The inferior, middle, and superior turbinates are composed of a thin bone for structural support and covered by an adherent mucoperiosteum. Stratified squamous epithelium is found on the anterior tip of the inferior turbinate, whereas pseudostratified ciliated columnar respiratory epithelium covers all other surfaces. The continually beating ciliated mucosa provides constant motion to the mucous blanket within the nose; this blanket acts as a cleaning and filtering system for the upper respiratory tract and also helps to maintain the moisture content within the nose. The turbinates maximize the effective intranasal surface area and rapidly humidify and warm the inspired air.89

Blood Supply and Innervation

Blood supply and innervation of the nasal septum are delivered within the mucoperiosteal and mucoperichondrial linings. The arterial blood supply originates from the ophthalmic branch of the internal carotid artery and the maxillary and facial branches of the external carotid artery. Blood to the upper nasal septum is supplied by anastomoses of the anterior and posterior ethmoid arteries, which originate from the ophthalmic branch. The external carotid artery contributes via a major branch of the sphenopalatine artery that perfuses the posterior and inferior septum. The columella and caudal septum receive blood supply from the septal branch of the superior labial artery. The septal mucosa itself contains complex arteriovenous anastomoses and venous sinusoids that can become engorged or constricted via neural or extrinsic pathways.

A variably located incisive artery and its associated neural fibers are found at the superior border of the vomer. This neurovascular bundle may be encountered when trimming a badly deviated maxillary crest or when elevating periosteum when a nasal floor approach is needed. Control of bleeding from this site may be obtained by infiltrating the incisive foramen from below, “plugging” the site from above, or carefully using suction Bovie cautery. After resection or trimming of the maxillary crest or work on the nasal spine, patients may complain of numbness or pain of the central incisors or of the mucosa of the hard palate just posterior to the incisors. This lack of sensation or complaint of pain is generally a short-lived phenomenon (Figure 44-3).

Figure 44-3. Depiction of the blood and neural supply to the nasal septum.

Innervation of the nasal mucosa includes both autonomic and sensory components. The autonomic nervous system regulates the degree of vascular tone, turbinate congestion, and nasal secretions present in the nose at any given time. Presynaptic parasympathetic fibers travel along the facial nerve and continue as the greater superficial petrosal nerve at the geniculate ganglion. These fibers then join the deep petrosal nerve to form the vidian nerve. Within the vidian nerve, the fibers travel to the sphenopalatine ganglion and synapse with the postganglionic neurons before innervating the nasal mucosa. Postsynaptic sympathetic fibers pass through the sphenopalatine ganglion and terminate in the nasal mucosa. The first and sec- Chapter 44 The Nasal Septum 3 ond divisions of the trigeminal nerve supply sensory innervation to the nasal mucosa. Trigeminal nerve fibers also pass through the sphenopalatine ganglion and transmit sensations of pain, temperature, and touch.

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