Nasal anatomy

A comprehensive review of nasal anatomy is beyond the scope of this subject. In this section, the pertinent anatomy relevant to patterns of nasal trauma is discussed. In particular, the structural anatomy of the nasal bones and nasal septum has bearing on the patterns of injury following trauma. This section reviews this general anatomy. The following section outlines variations of anatomy based on variable ethnic features.

The skeletal framework of the nose is often divided into 3 sections: the upper third consists of the osseous vault; the middle third consists of the upper cartilaginous vault; and the lower third consists of the lower cartilaginous vault. The nasal septum provides support in all 3 sections and divides the nasal cavity in half. The septum has 2 distinct portions, a cartilaginous portion anteriorly and a bony portion posteriorly.

The nasal septum is a sagittal midline structure that divides the nose into 2 cavities, and provides structural support to the osseous and cartilaginous vaults. The septum is divided into 2 components. The cephalic-posterior osseous septum consists of the perpendicular plate of the ethmoid and the vomer. The caudal-anterior cartilaginous septum consists of the quadrangular cartilage. The dorsal aspect of the osseous septum is formed by the perpendicular plate of the ethmoid. The thickness of the perpendicular plate of the ethmoid varies considerably. This plate attaches superiorly to the frontal bone, anteriorly the nasal spine, and posteriorly the cribriform plate. The septum articulates with the inward projection of the nasal bones in the midline anterosuperiorly, and it borders the quadrangular cartilage anteroinferiorly. Posteroinferiorly it borders the vomer. The vomer is shaped like the keel of a boat. The vomer articulates with the perpendicular plate of the ethmoid superiorly. Along its inferior aspect, the vomer attaches to the midline nasal crest of the palatine bone posteriorly and the maxilla anteriorly. Anterior to its articulation with the vomer, the maxillary crest forms a groove into which the quadrangular cartilage sits.

The cartilaginous septum comprises the quadrangular cartilage. The inferior aspect of the septum rests within a groove in the nasal spine and maxillary crest. The ventral surface of the quadrangular cartilage is typically thickened in comparison to the remainder of the structure. The dorsal aspect of the quadrangular cartilage forms the external contour of the nasal bridge. The dorsum of the central third of the nose is formed by the upper lateral cartilages’ articulation with the cephalic aspect of the quadrangular cartilage. The least rigid portion of the cartilage is the most caudal, which extends anterior to the nasal spine. The membranous septum is the soft tissue continuation of the cartilaginous septum. The membranous septum consists of a central layer of subcutaneous areolar tissue between the vestibular skin on each side, thereby bridging the caudal edge of the cartilaginous septum to the medial crura of the lower lateral cartilages and columella. Within the membranous septum are the ligamentous attachments of the medial crura to the caudal septum. The membranous septum is mobile, and displaces easily with manipulation of the columella due to the lack of cartilage.

The inner layer of the septum consists of either perichondrium or periostium, covered by an outer layer of mucosa. The vascular and nervous supply to the septum is contained within the 2 septal lining layers. In a traumatic septal hematoma, separation of the mucoperichondrium from the underlying cartilage may occur, which in turn may lead to ischemic necrosis of the affected septum and result in a perforation or a saddle nose deformity. This situation arises due to the fact that the perichondrial and periostial layers bear the majority of the biomechanical strength of the septal lining and bone.

Septal deviations off the mid-sagittal plane often have both functional and cosmetic implications, especially in the setting of nasal trauma. Deviations along the floor of the nasal airway may cause considerable airway obstruction. Combinations of cartilaginous and osseous deformities often contribute to the obstruction. Portions of the septum may be jagged and angulated in the setting of nasal trauma. Surgical treatment may require removing or repositioning these deviated skeletal elements. If deviations of the perpendicular plate of the ethmoid and vomer are not adequately corrected, persistent posterior airway obstruction after septal surgery may result.

Deviations of the caudal and dorsal edge of the septum also have cosmetic and functional implications. Along the rhinion to the anterior nasal spine, septal deviations may manifest as visible external deformities. A crooked nose deformity at the upper cartilaginous vault, the nasal tip, the columella, or the columellar base may be due to a deviation of the mid-dorsal septum, anterior septal angle, mid-caudal septum, or posterior septal angle, respectively. These irregularities may originate from a traumatic event, and thus correction of a severely crooked nose may require surgical intervention.

Together with the bony septum, the osseous vault is a pyramidal structure that provides the principal structural support for the nose. The distance from nasion to rhinion defines the cephalic-caudal length of the osseous vault. This vault consists of the frontal process of the maxilla and the paired nasal bones. The osseous vault articulates cephalically with the frontal bone at the nasofrontal suture line. The nasal bones superiorly derive midline support from the perpendicular plate of the ethmoid. At the keystone area, the caudal edge of the nasal septum is joined by a connective tissue to the upper cartilaginous vault. Each nasal bone can be described as an elongated quadrangle, with its lateral long edge articulating with the frontal process of the maxilla and its medial long edge articulating in the midline with the contralateral nasal bone. The bones cephalically are narrow and thin at the nasofrontal suture line, and wider and thinner along its free caudal edge. Most traumatic nasal fractures occur in the caudal, more projecting portion of the nasal bones where they are the thinnest.

In brief, the upper cartilaginous vault consists of the paired, shieldlike upper lateral cartilages that are fused in the midline to the dorsal edge of the cartilaginous septum. The nasal bones provide the majority of reinforcement to the upper lateral cartilages at their cephalic margin, the keystone area. The key elements in the lower cartilaginous vault are the paired lower lateral (or alar) cartilages. With the septum, the lower lateral cartilages provide support to the nasal tip.