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 .
 onychomatricoma is a tumor of the nail matrix which often presents with alterations in the nail plate while the tumor itself is concealed beneath the nail plate . 
 it is a benign , biphasic fibroepithelial tumor which has to be differentiated from other subungual and periungual tumors . 
 we report a rare case of onychomatricoma and describe a three - dimensional histopathological analysis and immunohistochemical patterns of onychomatricoma . 
Introduction
Case Report
Discussion