Onychomatricoma: New Clinical and Histological Features. A Review of 19 Tumors

Abstract

To further define the clinicopathological spectrum of onychomatricoma (OM). We report the clinical feature, histological, and immunophenotypic characteristics of 19 cases of OM diagnosed between 2002 and 2007. The characteristic histologic appearance of OM is sometimes difficult to grasp because of 3 main factors: the anatomic particularities of the nail apparatus, the often fragmented aspect of the tissue specimen, and the choice of the section planes, which strongly modified the morphologic appearances observed. To prevent these difficulties, we built a tridimensional model using serial, transverse, and longitudinal sections. This reconstitution gives us a better understanding of the apparent diversity of the morphologic aspects observed in linking them to the anatomic site of the tumor. OM of the matrix is characterized by a thick nail plate with porch roof. OM of the ventral aspect of the proximal nail fold (PNF) is characterized by a nail plate without porch roof, exhibiting either a woodworm-like appearance or multiple cavities. In this second category, the fibrous base becomes elongated in shape, taking the shape of the anatomic contour of the PNF. The stroma gives rise to numerous fibroepithelial digitations. This pattern is different from the classical OM visualized in longitudinal sections, which appears as a single and large fibroepithelial tumor, that is, the multiple distal epithelial digitations arranged along a transversal plane are not seen. In the PNF variant, the characteristic clinical signs of OM fail to appear. We individualize 3 misleading clinical variants: tumor with a verrucous surface that is located in the lateral nail fold, as a band pattern suggesting wart or Bowen disease; a total dystrophy of the nail unit mimicking a squamous cell carcinoma; and pseudofibrokeratoma type. In the OM located on the ventral matrix, 3 new specific histologic variants were noted: pleomorphic OM, OM with a predominantly collagenous stroma, and superficial acral fibromyxoma-;like OM. OM is a benign tumor with a broader morphologic spectrum than previously thought. When the nail plate is not available, the immunohistochemistry can aid diagnosis by highlighting the peculiar immunophenotyping of OM, which expresses CD34 but not CD99, epithelial membrane antigen, S-100 protein, actin, and desmin.

Asymptomatic Longitudinal Pachyxanthonychia of the Fingernail

“…When the tumor primarily involves the short apical matrix and the ventral surface of the proximal nail fold, the tumor is characterized on longitudinal sections by thick V-shaped keratogenous zones arising from deep epithelial invaginations. This epithelial architecture is associated with a thickened nail plate with an inferior border that terminates into ungual spurs [2,6]. Transverse sections may show pseudocanals due to the breaking up of the roof of the OM cavities.…”

“…Based on the tumor's anatomic localization and the evaluated planes of section, OM may have varying histomorphology that may present diagnostic challenges [4,6]. When the tumor primarily involves the short apical matrix and the ventral surface of the proximal nail fold, the tumor is characterized on longitudinal sections by thick V-shaped keratogenous zones arising from deep epithelial invaginations.…”

“…Transverse sections may show pseudocanals due to the breaking up of the roof of the OM cavities. Hence, apical matrix OM may clinically mimic a wart, nail unit squamous cell carcinoma in situ, and fibrokeratoma [6]. …”

Dermoscopic Features of Onychomatricoma: A Study of 34 Cases

“…Onychomatricoma is a benign fibroepithelial tumor specific to the nail apparatus that was first described in 1992 by Baran and Kint [1], with a peculiar expression of CD34 in its connective tissue compartment [2]. …”

Onychomatrichoma

“…Potentially misleading clinical Clinical Image findings, such as verrucous surface, total dystrophy of the nail unit, and a pseudofibrokeratoma appearance, have been reported as well. Thus, differential diagnoses may include verruca or Bowen's disease, squamous cell carcinoma, and fibrokeratoma, respectively [5,6]. Diagnosis is often clinical, however histopathologic examination is required in less obvious cases, such as those mentioned above.…”