Cervical anatomy — The layers and the five elements that define the contour

Why the neck deserves its own study

The neck is treated surgically together with the face and shares with it the layered organisation, the dissection planes and much of the structures at risk. Its anatomy, however, introduces elements with no facial equivalent: a superficial muscle of variable midline arrangement, a fat compartment lying beneath that muscle, two salivary glands that may protrude and a mobile bone whose position sets the limit of the result. The consequence is that a cervical assessment transposed from the facial one proves insufficient, and explains why a neck may remain uncorrected after a technically sound facelift.

The cervical layers

The structure of the neck reproduces that of the face, so nomenclature and planes are continuous between the two regions. From surface to depth: the skin, thinner and more mobile than facial skin and with fewer adnexa; the subcutaneous fat, arranged in a continuous plane without the strict compartmentalisation of the cheek; the platysma, the cervical continuation of the superficial muscular layer, prolonged upwards into the SMAS without interruption; the middle cervical fascia, within whose thickness the marginal mandibular branch runs; and beneath it the submuscular plane, occupied by deep fat, the anterior digastric bellies and the submandibular glands. This correspondence with the face is why the safety principle established for the facial nerve — remaining superficial to the deep fascia — applies unmodified in the neck.

The platysma and its variants

The platysma is a thin, broad cutaneous muscle arising from the fascia over pectoralis major and deltoid, ascending across the anterolateral neck and inserting on the lower border of the mandible and into the SMAS, its upper fibres interdigitating with depressor anguli oris and risorius. Its innervation comes from the cervical branch of the facial nerve. Its surgical relevance lies not in its function, which is slight, but in two facts: it constitutes the plane separating the two fat compartments of the neck and its midline arrangement conditions the appearance of the ageing neck.

De Castro’s classical description distinguishes three patterns of midline decussation, and recognising them bears directly on technique. In type I, the most frequent, the bellies interdigitate only for the first few centimetres below the chin; below that point they remain separate, and the resulting diastasis allows the medial borders to become visible as bands on contraction. In type II the decussation extends to the thyroid cartilage, giving the midline broader support. In type III there is no interdigitation at all and the bellies run parallel to the mandible. The clinical reading is that midline bands express not an excess of muscle but the absence of midline support, and that correction consists in restoring that continuity rather than resecting tissue.

The two fat compartments

The platysma divides cervical fat into two compartments that behave independently and demand different manoeuvres. Supraplatysmal fat lies between skin and muscle, is diffusely distributed and responds well to liposuction because the working plane is directly accessible from a submental incision. Subplatysmal fat occupies the space bounded by the deep surface of the muscle, the anterior digastric bellies and the floor of the mouth; reaching it requires opening the platysma in the midline, and its excision must be carried out under direct vision. The cadaveric studies of Larson and colleagues confirmed that both compartments are separate entities, with their own boundaries and a volume that varies between individuals.

The submuscular plane

Beneath the platysma and the deep fat lie two structures that may condition the contour independently of the soft tissue covering them. The anterior digastric bellies delimit the submental triangle and, when hypertrophic, produce a paramedian fullness that persists after adequate lipectomy. The submandibular gland occupies the triangle of the same name and, with laxity of its investing fascia, may descend and become visible as a prominence below the mandibular border. Mendelson and Tutino described its management in aesthetic neck surgery and established that partial resection of the superficial lobe is preferable to suspension, which tends to recur.

The hyoid and the limit of the result

The hyoid bone supports the floor of the mouth and determines the depth of the cervicomental angle. Ellenbogen and Karlin established the visual criteria of the youthful neck and placed the ideal angle between 105 and 120 degrees, with the hyoid high and posterior. When the hyoid is low or anterior, the angle is obtuse for skeletal reasons, and no manoeuvre on the soft tissue alters it. It is the only cervical variable that admits no correction, and must therefore be examined before planning technique: it indicates the achievable result and avoids proposing an operation that cannot meet the patient’s expectation.

The five elements of the cervical contour

The combined reading of the table is what orders the indication: each element is corrected by its own manoeuvre and none compensates for the deficiency of another. A neck may require one or all five, and preoperative examination consists precisely in deciding which are involved in that patient. The technical development of each manoeuvre, and the choice between lateral and anterior approach, is addressed in the note on platysmaplasty and cervical contour.