Cutaneous Melanoma

Nayela Keen, MD

Christine M. Glastonbury, MBBS

Key Facts

Terminology

Cutaneous malignancy arising from melanocytes of neural crest origin
5% of skin cancers but ˜ 65% of skin cancer deaths

Imaging

On whole body: Females most often extremities, males on trunk
25-35% arise in H&N; most often face
CT/MR: Primary site may not be evident; small or previously resected
Radiologist’s role is to search for deep invasion, perineural tumor, nodal and distant metastases
PET: Melanoma has high FDG avidity

Top Differential Diagnoses

Cutaneous SCCa
Merkel cell carcinoma
Cutaneous basal cell carcinoma

Pathology

Associated with ultraviolet radiation
Increased incidence in genetic syndromes
Clinicopathologically > 95% are superficial spreading, nodular, lentigo maligna or acral lentiginous type
Multiple distinct variants, which may behave differently

Clinical Issues

Incidence increasing at faster rate than any other cancer
Wide local excision performed for early-stage disease
Regional lymph nodes most frequent site of metastasis (stage III)
Sentinel lymph node biopsy (SLNB) &/or complete regional lymphadenectomy
Stage III (nodal metastases) 5-year survival = 40-78%
Stage IV (distant metastases) 1-year survival = 40-60%

(Left) Axial CECT in a patient who had vertex scalp melanoma excised 6 months prior shows multiple nodules bilaterally in the scalp

representing metastatic spread along subdermal lymphatics. (Right) Coronal CECT reformation in the same patient shows extensive bilateral lymphadenopathy in the neck with intraparotid adenopathy

and level 2 nodes

. Note that most nodes are not particularly large, and most are less than a centimeter in this case. Some show necrosis.

(Left) Lymphoscintigraphy study in a different patient with no clinical adenopathy is shown. Technetium-99m thiosulfate colloid was injected at 4 points around site of prior resected right scalp melanoma

. (Right) Lymphoscintigraphy obtained shows injection site

with channel that divides into 2

. Multiple sentinel nodes are appreciated

in right posterior triangle, with no activity on left. Surgical resection performed immediately after showed 0.7 cm metastatic focus in 1 node.

TERMINOLOGY

Definitions

Cutaneous malignancy arising from melanocytes
- Originates in neural crest
- Widely distributed in skin

IMAGING

General Features

Best diagnostic clue
- Multiple nodal masses
Location
- In females most often extremities, in males on trunk
- 25-35% arise in H&N, most often face
  - Increased sun exposure
  - 2-3x higher melanocytic content
Size
- Variable, both in superficial and deep extent
  - Tumor thickness (in mm) important for T stage
Morphology
- Infiltrative lesion of skin ± ulceration of overlying epidermis
- Ulceration is predictor of reduced survival

CT Findings

Most widely used modality for staging, surveillance, and assessment of treatment response
Primary site may not be evident: Small or previously resected
- Look for deep extent to bone and soft tissues
Some melanomas have propensity for perineural spread
- Expansion or erosion of skull base foramina
Nodal metastasis round, often necrotic