Subcutaneous metastases from malignant melanoma: prevalence and findings on CT

We reviewed 197 body CT studies on 53 sequential patients who had a histologic diagnosis of malignant melanoma in order to determine the CT appearance, pattern of spread, and prevalence of subcutaneous melanoma metastases. Seventeen (38%) of 45 patients with CT evidence of metastatic melanoma had subcutaneous nodules shown on CT. Five patients (11%) had subcutaneous nodules as the only indication of metastatic disease on their CT scans. All patients who developed subcutaneous metastases had primary lesions classified as Clark level IV or V. (The Clark classification is based on the depth of tumor invasion and is rated I to V.) Metastases appeared as small, discrete rounded densities in the subcutaneous fat; lesions were occasionally subtle because of their small size and peripheral location. The location of subcutaneous nodules could not be predicted consistently on the basis of the site of the primary malignancy. We conclude that subcutaneous metastases are common with melanoma in patients with Clark level IV or V lesions. These subcutaneous nodules are readily detected on CT scans if the subcutaneous tissues are carefully examined. The detection of these lesions may affect management or prognosis of patients, especially in those cases where subcutaneous nodules are the only CT evidence of metastatic disease.