BENIGN AND MALIGNANT EPITHELIAL TUMORS: LESIONS OF CUTANEOUS (SKIN) ORIGIN
- Skin cancer is usually not life threatening but can be if more advanced lesions are not evaluated properly before definitive treatment plans are chosen.
- Imaging contributes most in these patients by showing the local extent of tumor, especially with regard to bone invasion, detecting and quantifying perineural spread, and to a lesser extent looking for regional lymph node spread.
The vast majority of all skin carcinoma occurs in the head and neck region. Sun exposure is the major etiologic factor. There is a lower incidence in dark-skinned races compared to those with lighter complexions.1,2 The rate of occurrence and aggressiveness of skin cancer increases in immune-compromised patients. Toxic exposures and hereditary disorders can also predispose patients to this risk.
The critical anatomy in evaluating skin cancer relates the skin to the subcutaneous fat and that deeper fat beneath the superficial musculoaponeurotic system (SMAS) of the face. The SMAS is the facial equivalent of the superficial fascia in the neck. The fat deep to the SMAS and its relationship to the neurovascular bundles of the face is critical knowledge for evaluating imaging studies of patients with advanced skin cancer. The relationships are particularly important with reference to the distal branches of the facial nerve and all three divisions of the trigeminal nerve, as discussed in Chapter 21. The more proximal course of V1, V2, and V3, as well as that of the facial nerve, must also be completely understood to assure the best medical decision making (Figs. 21.9, 21.10, 21.50–21.52, and 24.1–24.9).
The anatomy and physiology of lymphatic spread must also be completely understood to most effectively interpret images in patients with skin cancer (Figs. 24.10–24.14). The most superficial lymphatics in the skin are the valveless capillary channels of the dermis. Deeper dermal lymphatic trunks and subcutaneous trunks have valves. The primary lymph nodes for carcinomas of the scalp and face are levels 1A, 1B, 5, those of the parotid region, and the mastoid, occipital and posterior neck nodes, as discussed in Chapters 149 and 157. The less well known facial nodes are also at significant risk. Subsequent drainage of level 1 nodes to level 2 put levels 2, 3, and 4 at secondary risk.