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This is an extremely rare tumor arising from the nail matrix. Less than 50 cases have been reported in the literature to date. Clinically, these tumors present with a yellow discoloration of the nail plate with splinter hemorrhages, prominent ridging of the nail plate, transverse overcurvature of the nail plate, and exposure of a filiform tumor arising from the nail matrix after avulsion of the nail plate. It is benign.


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General Two zones identified
Proximal zone

Thickening of the nail plate and acanthotic and papillomatous epithelium with deep projections within the dermis

Suprabasal cells with clear cytoplasm centered upon optically empty cavities

Underlying connective tissue with superficial layer of thin wavy fibroblast nuclei oriented in random array with deep layer of thickened collagen bundles oriented along a horizontal axis

Distal zone
Begins at the proximal border of the lunula with a thickened ventral nail plate and glove-finger dermal projections lined by matrix epithelium

Am J Dermatopathol. 2010 Feb;32(1):1-8.
Onychomatricoma: new clinical and histological features. A review of 19 tumors.

Perrin C, Baran R, Balaguer T, Chignon-Sicard B, Cannata GE, Petrella T, Michiels JF.

Laboratoire Central d'Anatomie Pathologique, Hôpital Pasteur, University of Nice, Nice, France.

Am J Dermatopathol. 2010 Feb;32(1):1-8. Abstract quote

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.

The Onychomatricoma: Additional Histologic Criteria and Immunohistochemical Study

Christophe Perrin, M.D.; Robert Baran, M.D.; Anne Pisani; Jean-Paul Ortonne, M.D.; Jean-Francois Michiels, M.D.

Am J Dermatopathol 2002; 24(3):199-203 Abstract quote

Onychomatricoma (OM) is a tumor of the nail matrix typified histologically by multiple distal fibroepithelial projections and a thick keratogenous zone forming multiple V-shaped invaginations at the level of epithelial ridges, with the formation of a thick nail plate. In its proximal portion, the thickness of the nail looks like a spur originating from the ventral part of the nail plate. In its distal part, beyond the lunula, the nail plate is globally thickened and filled with cavities containing serous fluid. Often, however, the pathologist is not provided with the nail plate. The diagnosis then rests on the presence of a fibroepithelial tumor.

In this article the histologic criteria of OM without nail plate are refined and OM is characterized immunohistochemically using three tumors fixed in liquid nitrogen and examined separately from the nail plate. On longitudinal section OM without nail plate appears as a unique pedunculated fibroepithelial tumor i.e., the multiple distal epithelial digitations arranged along a transversal plane are not seen. The feature is reminiscent of fibrokeratoma.

When OM is visualized in longitudinal section, 3 main criteria differentiate OM from fibrokeratoma: the presence of epithelial-lined invaginations around optical cavities, a stroma organized in 2 layers, and the absence of horny corn. Patterns of expression of cytokeratins and integrins in OM are identical to that observed in the normal nail matrix.

Involucrin finds expression from the basal layer through to the top of the epithelium, where it is more marked and where transglutaminase 1 is restricted. Merkel cells detected by CK 20 are increased in number and sometimes disposed in clusters. The fibrous component of OM is composed of 2 layers: a superficial stroma made of numerous fines fibrils of collagen IV intermingled with collagen I, and deep stroma made principally of collagen I.

Antibody AE13, specific to trichocytic keratins Ha 1-4, represent a good potential marker of OM. Its V-shaped expression in epithelium ridges offers early identification of the keratogenous zone of OM, on tumors separated from their nail plates and limited to their fibroepithelial components.

Unguioblastoma and unguioblastic fibroma - an expanded spectrum of onychomatricoma.

Ko CJ, Shi L, Barr RJ, Molne L, Ternesten-Bratel A, Headington JT.

Dermatopathology Laboratory, University of California, Irvine, USA, Department of Dermatology and Department of Pathology,Sahlgren's Hospital, Gothenburg, Sweden.
J Cutan Pathol. 2004 Apr;31(4):307-11. Abstract quote

Onychomatricoma is a rare tumor that appears to originate from cells of the nail matrix. Three cases of onychomatricoma that met Perrin et al.'s1 histologic criteria of onychomatricoma are described. However, using a single term to classify all three tumors ignores the apparent microscopic differences that exist among them.

To demonstrate better the spectrum of so-called onychomatricoma and properly acknowledge the noticeable disparity among our cases, a series of terms is proposed. This terminology is based on the histologic spectrum of epithelial-stromal ratio of stromal cellularity and of extent nuclear pleomorphism. Use of such criteria has a precedent in the classification of follicular and odontogenic fibroepithelial neoplasms.

This new nomenclature includes 'unguioblastoma' for tumors with a predominant epithelial component and 'unguioblastic fibroma' for tumors where a cellular stroma is more prominent and characteristic. The term 'atypical unguioblastic fibroma' is used to describe a third rare neoplasm, in which the cellular stroma shows nuclear pleomorphism and atypia with an increase of mitotic activity.



Bowen's disease clinically simulating an onychomatricoma.

Baran R, Perrin C.

Nail Disease Center, Cannes, and the Histopathology Department, Hopital Pasteur, Nice.

J Am Acad Dermatol 2002 Dec;47(6):947-9 Abstract quote

Onychomatricoma (OM) is an uncommon benign tumor clinically characterized by a thickened yellowish nail with transverse over curvature. A pigmented variant has recently been described.

Histologically, the diagnosis requires 3 prerequisites: (1) a fibroepithelial tumor consisting of 2 portions: the proximal zone (under the proximal nailfold, characterized by deep epithelial invaginations and a fibrillary and fibrocytic stroma), whereas the distal zone (corresponding to the lunula) presents with multiple digitations along its connective tissue axes; (2) a matricial tumor typified by a thick keratogenous zone; and (3) a thick nail plate, perforated by cavities.

We describe a case that appears clinically identical to a pigmented OM, but with histologic malignant patterns. Because histologic features were consistent with Bowen's disease, we ruled out a malignant OM.

We report a new variant of Bowen's disease presenting as OM, and this observation underlines the necessity for a histologic assessment of all forms of OM, especially those associated with a pigmented band (a sign sometimes observed in Bowen's disease).

FIBROKERATOMA Marked hyperkeratosis lacking multiple digitate fibroepithelial projections
No serous-filled cavitations of the distal nail plate
Lack of deep dermal projections of epithelium around optically clear cavities
Prominent capillaries and focally dense collage
Onycholemmal carcinoma.

Department of Dermatology, Kawasaki Medical School, Kurashiki, Japan.


J Cutan Pathol. 2006 Aug;33(8):577-80 Abstract quote

A 70-year-old Japanese man presented with a 5-year history of refractory indolent onycholysis of the little finger of the right hand. Roentgenograms did not show involvement of the bone.

Histological examination revealed an epithelial tumor consisting of lobular masses varying in size. The tumor was composed of keratinocytes varying in atypicality and showed infiltrative growth into the dermis but not into the phalangeal bone. The tumor had cystic structures composed of eosinophilic amorphous keratin and a surrounding thin layer of keratinocytes. Characteristically, the epithelium in the center of the tumor abruptly changed into amorphous keratin without the formation of intervening keratohyaline granules.

From these findings, the mass was diagnosed as onycholemmal carcinoma. Immunohistochemically, the tumor showed a keratin profile comparable to that of the nail bed epithelium and a smaller number of Ki-67-positive proliferating tumor cells compared with those of a previous case of onycholemmal carcinoma.
Onycholemmal Carcinoma.

Alessi E, Coggi A, Gianotti R, Parafioriti A, Berti E.

*Institute of Dermatological Sciences, University of Milan-IRCCS Ospedale Maggiore of Milan, Milan, Italy; dagger Department of Pathology, Orthopaedic Institute Gaetano Pini, Milan, Italy; and double dagger the Department of Dermatology, University of Milano-Bicocca, Milan, Italy.
Am J Dermatopathol. 2004 Oct;26(5):397-402. Abstract quote

We report on a slowly growing malignant tumor of the nail bed epithelium in a 69-year-old male.

On light microscopic examination, the tumor was composed of: (1) some small cysts filled with eosinophilic, amorphous keratin and lined by an atypical squamous epithelium devoid of a granular layer and (2) solid nests and strands of atypical keratinocytes filling the dermis and penetrating the phalangeal bone. Because the nail bed epithelium is comparable to the outer root sheath, or trichilemma of the hair follicle, and since the reported tumor showed some analogies with trichilemmal carcinoma, we suggest that this entity be designated ‘onycholemmal carcinoma’.

Disarticulation of the involved phalanx was performed and neither local recurrence nor distant metastasis was observed during 4 years of follow up.


Prognostic Factors Benign

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Last Updated February 8, 2010

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