Surgical Anatomy of the Head and Neck
Danger zones
Candidates must know the anatomic danger zones for Mohs on the face: the temple (frontal branch of the facial nerve), the nasolabial fold and cheek (buccal and zygomatic branches), the periauricular region (great auricular nerve, parotid duct), and the medial canthus (lacrimal apparatus). Understand the course of the facial nerve and the risk of injury during deep dissection.
Vascular and neural anatomy
Know the supratrochlear and supraorbital neurovascular bundles, the angular artery, and the temporal artery. Understand lymphatic drainage patterns relevant to staging and recurrence. Recognize the eyelid anatomy - tarsus, levator aponeurosis, and canaliculi - because injury here causes functional deficits.
Traps
A frequent trap is underestimating the depth of tumor over the temple or medial canthus, where tumor can track along nerves or the lacrimal system. Another is confusing sensory and motor nerve territories. Also know that the parotid duct (Stensen duct) crosses the masseter and is at risk in cheek surgery.
Worked example
A tumor near the lateral canthus with deep extension may involve the zygomatic branch of the facial nerve; preoperative counseling should include risk of brow ptosis or incomplete eye closure. The rule: map the nearest named nerve before deep excision.