6.7.2Lymphatic Drainage

Lymph nodes of the neck region secondarily receive drainage from most nodes of the face. These eventually empty into the venous circulation via the thoracic duct.

•Reconstruction of the haired areas of the head and neck must proceed with caution to avoid patches of alopecia.

•Donor site selection in full-thickness skin graft reconstruction should be tailored to the hair and sebaceous gland content of the recipient site.

Summary: Special Anatomic Considerations

in Mohs Micrographic Surgery

•Anatomic considerations specifically applicable to tumor extirpation by Mohs micrographic surgery include knowledge of danger zones for motor nerve injury on the face as well as awareness of free margins of the face during reconstruction.

a

6.8Special Anatomic Considerations in Mohs Micrographic Surgery

6.8.1Danger Zones

The relevant danger zones that a Mohs micrographic surgeon must be aware of revolve around several key

b

Lesser occipital N. (C2, C3)

Great auricular N. (C3, C4)

Accessory N.

(CN XI)

Erb’s point

Transverse cervical N.

(C2, C3)

Supraclavicular N.

(C3, C4)

Trapezius muscle

Fig. 6.11 (continued)

Sternocleidomastoid muscle

External jugular vein

Platysma muscle

neural and vascular structures as well as the free margins of the face. The two nerves most susceptible to injury during Mohs surgery are the temporal and marginal mandibular branches of the facial nerve (CN VII). CN VII exits the cranium at the stylomastoid foramen, which is only rarely encountered during the Mohs procedure owing to its deep location. Deeply infiltrating tumors that involve CN VII at its exit point should generally be referred to head and neck surgery since a superficial parotidectomy and cranial nerve dissection are frequently required. The temporal branch of CN VII courses through the parotid gland and emerges approximately 2.5 cm anterior to the tragus (Fig. 6.8) [1]. Subsequently, the temporal nerve travels just superficial to the superficial fascia, a short distance from the lateral canthus, to provide motor innervations to the frontalis muscle. Avoidance of deep undermining during reconstruction is the key to

preventing injury to this nerve. In some instances, however, tumor extension forces a surgeon’s hand in damaging this nerve branch, resulting in ipsilateral brow ptosis and facial asymmetry. Appropriate patient discussion is essential prior to procedures in this area. Subsequent corrective measures may include an elliptical excision above the ipsilateral brow, and botulinum toxin treatment of the contralateral forehead will often restore symmetry to the face.

Similarly, the marginal mandibular nerve is susceptible to injury with deep undermining at the angle of the mandible (Fig. 6.8). Injury to this nerve branch results in an inability to purse the lips and smile on the ipsilateral side of the mouth. Cosmetic asymmetry will also result due to lack of motor innervations to lip depressors on the injured side of the mouth. Therefore, deep undermining and V to Y flap closures should be avoided in this area in order to preserve the integrity of this motor