Amelanotic Subungual Melanoma Mimicking Telangiectatic Granuloma: Clinical, Histologic, and Radiologic Correlations.

Subungual melanoma is uncommon and accounts for just 2% to 3% of all cutaneous melanomas. Less than 10% of subungual melanomas are amelanotic and 90% of these occur on the thumb or great toe. They typically appear in the seventh decade of life and are associated with a delayed diagnosis and a poor prognosis. Amelanotic subungual melanoma generally manifests as a persistent vascular or ulcerated nodule. On ultrasound (US), subungual melanoma appears as a moderately well-defined hypoechoic area with increased thickness and decreased echogenicity of the nail bed, which frequently erodes into the bone margin of the distal phalanx, viewed as a hyperechoic structure pushing up and eroding into the bilaminar hyperechoic structure of the nail plate. Color Doppler US shows marked hypervascularization. Telangiectatic granuloma is the main entity to be considered in the differential diagnosis. This benign acquired vascular tumor is relatively common, and frequently affects the nail, the nail bed, and the periungual tissues. On US, subungual telangiectatic granuloma appears as a focal hypoechoic area with thickening and decreased echogenicity of the nail bed, which pushes up the nail plate but does not erode into the bone margin of the distal phalanx; hypervascularization is also observed. Subungual melanoma requires a high index