Dear Editor,
Poroid hidradenoma, a recently recognized variant of adnexal neoplasms of skin was first described by Abenoza and Ackerman in the year 1990.[1] So far, a handful of cases have been reported in world literature.[2] A 45-years-old female presented with 1 cm-sized, solitary, asymptomatic gradually progressive, bluish nodulocystic swelling over scalp since 4 months [Figure 1]. Nodule was excised and sent for histopathological examination. Interestingly, yellow-green fluid exuded from the tumor during biopsy. Histopathological examination revealed a well-circumscribed lesion surrounded by a zone of compressed connective tissue in the dermis. No apparent connection with the overlying epidermis was noted [Figure 2a]. The cells were arranged in sheets, trabeculae and nests with minimal palisading. The lesion was predominantly solid with few duct-like structures containing an amorphous eosinophilic material [Figure 2b]. Two cell types were noted; small, dark-staining monomorphic poroid cells and larger pale cuticular cells with round to oval uniform nuclei and scanty cytoplasm. Hyalinization and thickening of the basement membrane was noted in some areas. The architectural features of the neoplasm simulated a hidradenoma, where the tumor is usually confined to the dermis and is composed of both solid and cystic areas. Accordingly, a diagnosis of poroid hidradenoma was rendered. Poroid hidradenoma is reported to occur in age group of 17 years to 91 years with no sexual predisposition. Trunk, scalp, face and extremities are the usual sites of affliction. Asymptomatic, skin-colored, red or blue (due to Tyndall effect) solitary, intradermal papule or nodule of size 0.5 cm to 4 cm is the cardinal clinical feature.[3] Histopathologically, poroid hidradenoma shows architectural features of hidradenoma as it is confined to dermis and is composed of both solid and cystic areas and has cytological features of a poroid neoplasm with large pale staining cuticular cells with large nucleus with occasional multinucleation and small dark staining poroid cells with scant cytoplasm and round to oval nucleus with inconspicuous nucleoli.[3]
Figure 1.
Bluish nodulocystic swelling over scalp
Figure 2.
a: Well-circumscribed lesion in the dermis without any apparent connection with the overlying epidermis. The cells are arranged in sheets and nests. (H&E 100X). b: predominantly solid lesion with a duct-like structure in the center. Two cell types are noted; small, dark monomorphic poroid cells and larger pale cuticular cells. (H&E 200X)
Hidradenoma simplex, dermal duct tumor and apocrine hidradenoma are the differential diagnosis of poroid hidradenoma. Hidradenoma simplex shows intraepidermal nests of round cells,[4] dermal duct tumor is intradermal with clear monomorphous cuboidal cells arranged around sweat glands,[5] apocrine hidradenoma is composed of clear, mucinous and polygonal cells.[3] Malignant transformation occurs in less than 1% of cases. Treatment is complete surgical excision.
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References
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