Metastatic Melanoma

Michael P. Federle, MD, FACR

Amir A. Borhani, MD

Key Facts

Terminology

Spectrum of metastatic lesions originating from known or occult malignant melanoma

Imaging

Multiple “bull’s-eye” lesions of variable size in GI tract of patient with history of skin lesion
Multiple hypervascular hepatic lesions with variable size in patient with history of melanoma
Most common sites of metastases are skin, lymph node (75%), lung (70%), liver (58%), CNS (54%), GI tract (40%)
Most common primary sites associated with abdominal metastases are head and neck, eye
- Ocular melanoma has extremely high occurrence of liver metastases
Lesions are typically multiple and well circumscribed
“Bull’s-eye” or “target” lesion (secondary to central ulceration)

Top Differential Diagnoses

Clinical Issues

(Left) Axial CECT in a middle-aged man with cutaneous melanoma and a distended abdomen shows massive, malignant ascites due to peritoneal metastases

. Also noted are metastases to the perirenal space bilaterally

. (Right) Axial CECT in the same patient shows additional metastases to the peritoneum

, abdominal wall

, lymph nodes, and perirenal space

. “Unusual” sites of metastases are typical in patients with melanoma.

(Left) Axial PET/CT shows FDG-avid metastases in the kidney

and perirenal space

. (Right) Axial PET/CT in the same patient shows an additional lesion in the bowel

. Despite the large size of the metastasis, there was no bowel obstruction.

TERMINOLOGY

Definitions

Spectrum of metastatic lesions originating from known or occult malignant melanoma

IMAGING

General Features

Best diagnostic clue
- Multiple “bull’s-eye” lesions of variable size in GI tract of patient with history of melanoma
Location
- Most common sites of metastases: Skin, lymph nodes (75%), lung (70%), liver (58%), CNS (54%), GI tract (40%)
- Most common involved sites in abdominal cavity include liver and small bowel
Morphology
- Typically multiple, in any site of body
- Well-circumscribed, spherical or oval
- Nodule, plaque, polypoid mass
- “Bull’s-eye” or “target” lesion (central ulceration)

Imaging Recommendations

Best imaging tool
- CECT, PET/CT best for total body screening
  - Sensitivity and specificity are ↑ by simultaneous interpretation of diagnostic quality CT
  - Melanoma may not be FDG avid or may be misinterpreted as normal bowel or kidney on PET
Protocol advice
- Triphasic CECT
  - Hepatic metastases may not be visualized on monophasic CECT
  - 86% of hepatic lesions are detected on portal venous phase as hypodense lesions