CHAPTER 20 Deep plane procedures in the neck

Introduction

The cervicomental angle and the contours of the neck are very important determinants of facial aesthetics and are readily modified in facial rejuvenative surgery. Deep plane procedures in the neck are often required to reach the aesthetic endpoint of a defined, less obtuse cervicomental angle and smooth surface contours. Four structures are altered in deep plane procedures of the neck: the platysma, subplatysmal fat, the anterior belly of the digastric muscle, and the submandibular gland. Deep plane procedures involving these structures are most effective when employed in concert with other rejuvenation efforts in the superficial structures of the neck and the remainder of the face. With that in mind, this chapter focuses on deep plane procedures and how they are integrated into a global approach to cervicofacial rejuvenation.

History

Skoog was one of the first surgeons to advocate deep plane dissection in facial rejuvenation surgery. Mitz and Pyronie characterized the SMAS and identified its continuity with the plastysma, the major investing supportive structure of the neck. Based on this anatomy, Hamra, Owsley, Connell, Aston and others have advocated raising the platysma as a continuous flap with the SMAS of the face, with or without elevation of the overlying skin in a separate plane of dissection.

Aston described the eight most common platysmal deformities and Ellenbogen established visual criteria for the successful rejuvenation of the neck. De Souza Pinto, Souther and later Feldman demonstrated the importance of midline tightening of the plastysma. Connell advocated low myotomy to treat a short platysma, one of the etiologic factors causing an obtuse cervicomental angle, and to treat platysmal bands. Furthermore, Connell popularized medial platysmal elevation for access to the submental and submandibular deep structures and advocated resection, total or subtotal, of the anterior belly of digastric muscle. Guyuron observed that this resection results in retropositioning of the hyoid bone and thus favorable deepening of the cervicomental angle. De Pina and Connell discussed resection of the submandibular gland and Guerrerosantos and Feldman have discussed suspension of the gland.

Physical evaluation

• The first step in evaluation for the neck is a visual inspection. The front view is helpful in identifying platysmal bands and the lateral view permits assessment of the configuration of the cervicomental angle (Fig. 20.1).

• Visual inspection and palpation are performed to assess skin quality and skin excess. Sun-damaged skin, inelastic skin and skin with a crepe-like quality will likely require more excision in the postauricular region to facilitate envelope redraping (Fig. 20.2).

• The patient is instructed to flex her platysma muscle to accentuate the visibility of bands (Fig. 20.3). The submental region is palpated with the thumb in opposition to the fore and long fingers before and after activation of the platysma in order to differentiate subplatysmal bulk (anterior belly of the digastric muscle and fat) from preplatysmal fat (Fig. 20.4).

• With the head in the neutral position (Frankfort horizontal parallel to the ground) the bulk in the region of the anterior belly of the digastric muscle is visualized and palpated.

• Thyroid cartilage position and prominence are noted and are important to consider in female patients in whom a platysmal myotomy is planned. The myotomy is planned sufficiently low (2 cm below the cartilage) so that the thyroid cartilage prominence is not unmasked, thus producing a masculine appearance.

• The submandibular triangle is inspected by palpation for a discrete firm mass that can often be balloted against the medial and/or caudal surface of the body of the mandible. When such a mass is appreciated, the submandibular gland is hypertrophic and/or ptotic and excision may be considered to improve the neck contour.

Fig. 20.1 Lateral view of the cervical region in a patient with an obtuse cervicomental angle.

Fig. 20.2 Physical exam. The upper figure demonstrates a patient at rest to show excess skin.

Fig. 20.3 Physical exam. The middle figure demonstrates cervical animation to identify platysmal bands.

Fig. 20.4 Physical exam. The lower figure demonstrates pinching the soft tissue at rest and with muscle contraction to distinguish the cervical bulk caused by preplatysmal fat from bulk caused by subplastysmal structures. Bulk due to subplastysmal structures “escapes” from the pinch with contraction.

Anatomy

Procedures on the neck are designed to modify the submental/submandibular regions and the cervicomental angle regions by reduction and/or relocation of volume. The excess volume exists in three planes: the superficial plane between the skin and platysma, the intermediate plane comprised of the platysma and interplatysmal fat lying between the bilateral medial platysma edges, and the deep plane beneath the platysma containing the subplatysmal fat, the anterior belly of the digastric muscles, and the submandibular glands.

The platysma muscles are thin bilateral structures that extend from the SMAS in the face to the clavicles. There are three variations of platysmal anatomy in the submental region (Fig. 20.5):

• Type I (75%): Interdigitation of the plastysma muscles to a point 1–2 cm posterior to the mandibular symphysis.

• Type II (15%): Interdigitation of the plastysma muscles from the mandibular symphysis to the thyroid cartilage.

• Type III (10%): No interdigitation.

Fig. 20.5 Three types of platysmal anatomy.

Thus it is apparent that the majority of patients don’t have a significant extent of medial platysmal interdigitation. With age the retaining ligaments that maintain the free medial edges approximated to the deep cervical fascia attenuate. The unrestrained edges shorten and pull away from the underlying structures resulting in the formation of plastysmal bands.

In patients with minimal to no plastysmal interdigitation, interplatysmal fat is found in the submental region between the medial edges of the two platysma muscles. This interplatysmal fat is considered a structure of the intermediate plane, but is contiguous with the subplatysmal fat of the deep plane. In those with complete interdigitation (no platysmal decussation) there is no interplatysmal fat and the fat referred to as “subplatysmal fat” is located deep to the plastysma, superficial to, between, and lateral to the anterior bellies of the digastric muscles.

The anterior bellies of the bilateral digastric muscles may be hypertrophied or more visible in some patients resulting in excess submental bulk. These muscles are paired bilateral structures that extend between the lesser cornu of the hyoid bone and the posterior surface of the mandible on either side of the symphysis (Fig. 20.6). Each anterior belly forms one side of the bilateral submandibular triangles. The other two borders of the submandibular triangles are the posterior belly of the digastric muscle and the inferior edge of the body of the mandible. These triangles contain the submandibular gland, facial artery and vein, lingual nerve and the marginal mandibular branch of the facial nerve. Motor innervation of the anterior belly of the digastric muscle is a branch of the mandibular division of the trigeminal nerve. The muscles function as week depressors of the mandible. Excision proceeds without noticeable alteration in function.

Fig. 20.6 Digastric muscle and submandibular gland anatomy.

The submandibular gland, a salivary gland, may produce a visible bulge in the region of the submandibular triangle, when it is hypertrophied and/or ptotic (Figs 20.7, 20.8). This bulge disrupts the otherwise planar surface that typifies the smooth contour of a youthful appearing neck. The facial artery and vein run obliquely over the posterior portion of the gland and the marginal mandibular can run horizontally across the superior aspect of the gland in a plane just superficial the facial artery and vein. Both the lingual nerve and the hypoglossal nerve lie deep to the gland. These vascular and neural structures are located in an extracapsular location, thus intracapsular resection of the gland is one strategy to reduce the risk of excessive bleeding and nerve injury.