Longitudinal ridging is prominent in the affected nail. A tendency toward transverse overcurvature of the affected nail portion which is more pronounced as the yellow colour is more extensive. Nail avulsion exposes a villous tumor emerging from the matrix while the nail appears as a thickened funnel, storing filamentous digitations of matrix fitting into the holes of the proximal nail. The villous projections in the nail plate can be so pronounced that cutting the nail may produce bleeding. This swelling gives the affected nail the texture of a cutaneous horn.
Histologic examination establishes the diagnosis.
In 3 cases, the tumor was associated with an onychomycosis . MR images are typical. The sagittal images highlight the tumor core in the matrix area and the invagination of the lesion into the funnel-shaped nail plate. The centre shows a low signal on all images with a peripheral rim with a signal identical to that of normal epidermis. The distal filamentous extensions present a higher signal on T2-weighted images due to a mucoid stroma with high water content.