tumors of the nail apparatus often present a challenge to diagnosis as well as treatment due to the specialized nail anatomy . the nail plate may conceal the tumor as well as alter the tumor growth pattern . however , alterations in the color , thickness , curvature of the nail plate may often provide a clue . a 40-year - old male presented with yellowish discoloration , thickening and altered curvature of the right great toe nail for the past 2 years . there was history of mild pain on walking and application of pressure for the past 2 weeks . , there was a markedly thickened nail plate , increased proximal transverse curvature and yellowish band - like discoloration of medial two thirds of the nail ( xanthonychia ) [ figure 1 ] . however , there was no friability of the nail plate . there was swelling and brownish discoloration of medial two thirds of the proximal nail fold . there was minimal pain on applying pressure on medial part of nail and nail fold . markedly thickened nail plate , increased proximal transverse curvature and yellowish band like discoloration ( xanthonychia ) of medial two thirds of the right great toe nail . also , note swelling of medial two thirds of proximal nail fold the patient underwent a total nail avulsion which revealed a well - defined tumor extruding from below the proximal nail fold toward the distal end of the nail bed [ figure 2a ] . the proximal nail fold was everted and the tumor was excised in entirety . the excised tumor ( 3 cm  2 cm  0.5 cm ) was firm in consistency with parallel ridges corresponding to the ridges on the nail plate [ figures 2b  d ] . a differential diagnosis of onychomatricoma , fibrokeratoma of the nail matrix , superficial acral fibromyxoma , fibroma and glomus tumor was considered . histopathology of proximal transverse section [ figure 3 ] revealed a polypoid fibroepithelial tumor with a foliated pattern , acanthosis , papillomatosis and deep epithelial invaginations of multilayered basal and suprabasal cells with elongated nuclei oriented perpendicular to the basement membrane , absent granular layer with clear v - shaped clefts . at places , the stroma had a superficial cellular , fibrillary and vascular layer and a deep , relatively , acellular layer with denser collagen . a distal longitudinal section [ figure 4a and b ] showed a different pattern of the tumor : glove finger - like / monodigitate pattern with marked papillomatosis and multiple thick and deep epithelial ridges . on immunohistochemical analysis , the fibrous stroma showed diffuse staining for cd34 and negative staining for cd99 [ figures 5a and b ] . ( a ) post nail avulsion ; a well - defined tumor extruding from below the proximal nail fold toward the distal end of the nail bed . ( b ) the excised tumor showing parallel ridges ( r ) corresponding to the ridges on the nail plate . ( c ) dorsal view of the avulsed nail plate showing thin proximal portion and thickened yellowish distal portion ( d ) ventral view showing ridges on the nail corresponding to the tumor histopathology : proximal transverse section h and e ( 10 and 40 ) ( a ) a polypoid fibroepithelial tumor with a foliated pattern ; acanthotic , papillo matous epithelium with v - shaped clefts ( v ) corresponding to the avulsed nail . the stroma had a superficial cellular , fibrillary and vascular layer and a deep relatively acellular layer with denser collagen . ( b ) the tumor was lined by mature malpighian epithelium resembling normal matriceal epithelium ; absent stratum granulosum with multilayered basal and suprabasal cells with elongated nuclei oriented perpendicular to the basement membrane . at places , ( c ) numerous mast cells ( m ) in the stroma immunohistochemistry : ( 10 ) fibrous stroma showing diffuse staining for cd34 ( a ) and negative staining for cd99 ( b ) histopathology ( h and e ) a ( 10 ) , b ( 40 ) . a distal longitudinal section showing a glove finger - like / monodigitate pattern with marked papillomatosis and multiple thick and deep epithelial ridges onychomatricoma ( om ) is a rare onychogenic tumor of the nail matrix , described mostly in caucasians . the usual clinical presentation is a thickened nail with xanthonychia , increased transverse curvature and proximal splinter hemorrhages ( due to vascular stroma ) . perrin et al . have defined two types of om based on tumor and nail characteristics : ( 1 ) onychomatricoma of ventral matrix ( om type i ) : characterized by a single large fibroepithelial tumor . the nail plate is thinned out proximally and thick distally giving the appearance of a porch roof . ( 2 ) onychomatricoma of the proximal nail fold ( om type ii ) : characterized by a tumor with multiple fibroepithelial projections . om type ii often presents with unusual clinical features such as pterygium , fibrokeratoma like om , total onychodystrophy and verrucous band - like pattern ( suggesting wart or bowen 's disease ) . histopathologically , om type i shows two different architectural patterns in transverse and longitudinal sections . on proximal transverse sections , a lobulated / foliated pattern is observed while a glove finger monodigitate pattern is observed on longitudinal distal sections . awareness of these different patterns is important when only fragmented specimens are available for histological analysis . a three - dimensional model using proximal and distal transverse and longitudinal sections helps in better understanding and visualization of the morphology of this rare tumor . om is characterized by deep epithelial invaginations with a thick v - shaped keratogenous zone overlying the prekeratogenous zone . on avulsion of the nail plate , this is seen as an optically empty v - shaped zone . the epithelium corresponds to the matriceal epithelium with absent granular layer , basal cells with thin elongated nuclei and multi - layered suprabasal cells with oval nuclei . keratin markers , k5 and 17 , are positive through the epithelium ( indicative of matriceal differentiation ) , while k 85 stains the prekeratogenous zone . the stroma contains several mast cells and is arranged in two layers : a superficial cellular , vascular layer with fibrillary collagen and a deeper relatively less cellular layer with dense collagen bundles . the two - layered stroma is more frequently observed in the proximal portion than in the distal zone of the tumor . based on the proportion of epithelial and mesenchymal components and presence / absence of atypia in the stroma , ko et al . have proposed a different nomenclature with three categories : ( 1 ) unguioblastoma ( predominant epithelial component ) ( 2 ) unguioblastic fibroma ( predominant stromal component ) , and ( 3 ) atypical unguioblastic fibroma ( nuclear pleomorphism , atypia in the stroma ) . differential diagnosis of om includes fibrokeratoma , fibroma , superficial acral fibromyxoma ( saf ) , onycholemmal horn , malignant proliferating onycholemmal cyst , subungual warts , subungual keratoacanthoma , subungual squamous cell carcinoma and bowen 's disease . all of these are easily distinguishable by histopathology except fibrokeratoma , fibroma and saf , which need more careful differentiation . in distal longitudinal sections , the structure of om tends to resemble a fibrokeratoma . however , absence of a horny corn , multiple fibroepithelial digitations and two layered stroma ( on transverse section ) rules out fibrokeratoma . the stroma of om may resemble a fibroma , which can however be excluded by the hyperplastic and onychogenic epithelium of om . saf has a close resemblance to om due to highly vascular collagenous stroma , presence of mast cells and epidermal hyperplasia with papillomatosis . also , a single case of om with myxocollagenous stroma ( superficial acral fibromyxoma like om ) has been reported . saf shows diffuse cd34 , cd99 expression , while om shows diffuse expression of cd34 , but is cd99 negative . treatment of om is complete surgical excision . despite the atypical nature of stroma reported in some cases , no frank malignant variant has been described to date . in conclusion , onychomatricoma is a rare fibroepithelial tumor mostly arising from the nail matrix . it needs to be distinguished from other subungual / periungual tumors ; immunohistochemical markers cd34 and cd99 are useful adjuncts in the diagnosis of om . a three - dimensional spatial reconstitution of om helps in better understanding of its variable morphological characteristics . histopathological patterns of onychomatricoma vary in proximal and distal sections ; foliated pattern on proximal transverse sections and a glove finger - like pattern on the distal longitudinal section.study of onychomatricoma in multiple sections and planes is important for a three - dimensional spatial reconstitution of the tumor and differentiation from other subungual / periungual tumors.patterns of stromal immunohistochemical markers , cd34 and cd99 are especially useful in differentiating onychomatricoma from superficial acral fibromyxoma , a subungual tumor with several similar histological features as onychomatricoma . histopathological patterns of onychomatricoma vary in proximal and distal sections ; foliated pattern on proximal transverse sections and a glove finger - like pattern on the distal longitudinal section . study of onychomatricoma in multiple sections and planes is important for a three - dimensional spatial reconstitution of the tumor and differentiation from other subungual / periungual tumors . patterns of stromal immunohistochemical markers , cd34 and cd99 are especially useful in differentiating onychomatricoma from superficial acral fibromyxoma , a subungual tumor with several similar histological features as onychomatricoma .