Onychomatricoma: clinical and histopathologic findings in 12 cases

Onychomatricoma is a nail matrix tumor that has been well characterized clinically but not histologically.

The purpose of this study was to establish histologic criteria for the diagnosis of onychomatricoma to differentiate it from other fibroepithelial tumors of the nail matrix.

We observed 12 cases and were able to examine 4 of these excised specimens, including the attached nail plate. In 8 patients, avulsion of the nail was performed before excision of the tumor so that the nail plate was examined separately from the tumor.

Onychomatricoma is a fibroepithelial tumor consisting of 2 anatomic zones. The proximal zone is located beneath the proximal nail fold with a proximal border starting at the root of the nail and distal border corresponding to the cuticle. It is characterized by deep epithelial invaginations filled with a thick V-shaped keratogenous zone, a thickened nail plate without cavitation but with an undulating inferior border ending in ungual spurs, and a fibrillary stroma clearly demarcated from the undersurface. The distal zone corresponds to the lunula and is characterized by multiple "glove finger" digitations lined with matrix epithelium and oriented around antero-oblique connective tissue axes; perforation of the nail plate by multiple cavities that, generally at the distal edge of the lunula, lose their epithelial digitations and become filled with serous fluid; the connective-tissue stoma of the digitations extends deeply into the dermis and is not demarcated form healthy tissue.

On the basis of the mentioned characteristics, we have been able to define onychomatricoma histologically. In addition, we have identified an unusual clinical form of onychomatricoma that has the appearance of a cutaneous horn and is situated at the junction of the undersurface of the proximal nailfold and the lateral nailfold.