Onychomatricoma
Robert Baran
Dermatology Online Journal 7(1): 23B

Onychomatricoma was recently identified as an uncommon tumor specific to the nail apparatus.

Four main clinical signs are striking and suggest the diagnosis.

• 1. A yellow longitudinal band of variable width, leaving a single or double portion of normal pink nail, on either side. Splinter haemorrhages may be seen in the yellow area involving the proximal nail region in a characteristic manner. Longitudinal ridging is prominent in the affected nail.
• 2. A tendency toward transverse overcurvature of the affected nail portion which is more pronounced as the yellow colour is more extensive.
• 3. 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. However, in some cases the clinical presentation may be confusing: longitudinal melanonychia may hide the yellow hue, sometimes the proximal nail fold may be swollen at its junction with the lateral nail fold. 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. Axial slices accurately show the holes in the substance of the nail plate, filled with the filamentous extensions.

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© 2001 Dermatology Online Journal