Applied nasal anatomy — The layers, the framework, the ligaments and the valves

The layers and the dissection plane

The nasal covering is organised in four layers over the skeleton: skin, subcutaneous fat, musculoaponeurotic layer — the nasal SMASThe nasal continuation of the superficial musculoaponeurotic system of the face, in which the nasal muscles and the vascular plexus lie — and a deep areolar layer that is virtually avascular. The vascular plexus supplying the skin runs above the SMAS, whence the rule that governs the whole dissection: work is carried out beneath the SMAS, subperichondrially over cartilage and subperiosteally over bone. That plane offers three advantages apparent postoperatively: it is avascular, so bleeding is minimal; it preserves cutaneous vascularity, which is decisive in secondary surgery; and it leaves a layer of tissue interposed between skin and skeleton that attenuates irregularities. The layered organisation of the facial covering is developed in The layers of the face.

Identifying that plane is not always immediate. The practical reference is to begin in the midline at the level of the upper septum and scrape until the instrument glides without resistance; from there the dissection extends laterally. Over bone, the change in resistance on passing from the upper lateral cartilage to the nasal bone is unmistakable and serves as confirmation.

The osteocartilaginous framework

The nose rests on three interlocking vaults. The bony vault is formed by the nasal bones and the ascending processes of the maxilla. The middle cartilaginous vault is formed by the upper lateral cartilages joined to the dorsal septum in a T arrangement. And the lower vault is formed by the alar cartilages. Where the first two meet is the keystone areaT-shaped zone where the nasal bones overlap the upper lateral cartilages and the septum, some 10 mm centrally and 5 mm laterally. It constitutes the structural support of the dorsum, whose surface point is the rhinion. That overlap explains two technical decisions: why, when detaching the upper laterals, support must be taken on them rather than on bone, and why preservation techniques avoid dividing that junction.

Below, the septum is a rhomboid cartilage articulating with the maxillary and premaxillary crest inferiorly and with the vomer and the perpendicular plate of the ethmoid posteriorly. Two points have direct surgical consequence. First: the junction of the cartilage with the premaxilla and the anterior nasal spine is a perichondrium-periosteum transition of different embryological origin, considerably firmer and harder to dissect than the junction with the rest of the crest. Second: the perpendicular plate of the ethmoid is not removed by traction, since the cribriform plate lies above it and transmitted force may produce a cerebrospinal fluid leak.

The ligamentous system

Between the vaults lies a ligamentous system that supports the tip and which contemporary rhinoplasty has ceased to regard as a mere obstacle to exposure. Pitanguy’s ligamentFibrous band descending from the dorsum, between the medial crura, to the anterior nasal spine. It is the suspensory ligament of the nasal tip has a cephalic or superficial portion and a caudal or deep one; dividing it eases access to the septum, but its preservation or reconstruction is what maintains the supratip and prevents late descent of the tip. The scroll ligamentsJunction between the caudal border of the upper lateral cartilage and the cephalic border of the alar cartilage, at the level of the sesamoid cartilages sustain the relation between the middle and lower vaults. And the interdomal ligament joins the two domes.

The two valves

Respiratory function depends on two specific points, and both may be altered during a rhinoplasty performed for aesthetic reasons. The internal nasal valve is the angle between the caudal border of the upper lateral cartilage and the dorsal septum; in Caucasian populations it measures between 10 and 15 degrees and constitutes the point of greatest resistance in the whole airway. Lowering the dorsum detaches the upper laterals from the septum and that angle disappears: without reconstruction the result is obstruction and, in time, the inverted-V deformityV-shaped shadow appearing in the middle dorsum when the upper lateral cartilages collapse and the caudal border of the nasal bones becomes visible under the skin. The external nasal valve corresponds to the vestibule, supported by the lateral crus and the ala; its collapse appears as a nostril that indraws on forced inspiration, and arises from a weak alar cartilage, excessive cephalic resection or a malpositioned lateral crus.

The skin, which is not operated on

Rhinoplasty operates on the skeleton, but what the patient perceives is the covering over it. Thin skin reveals every detail of the structural work: it permits sharply marked definition and exposes any irregularity. Thick skin damps the relief, prolongs oedema and limits the definition attainable at the tip irrespective of the quality of the underlying work. It constitutes not a complication but a starting condition, to be assessed in consultation and explained together with the real timetable: the splint is removed around the seventh day, the appearance becomes socially comfortable at one month, and the definitive result is not assessed before 12 months, or 18 to 24 in thick skin and in secondary surgery.

With the anatomy established, assessment of the patient is ordered through facial analysis — lines, angles and proportions in each view — developed in Facial analysis: lines, angles and proportions.