A Curious Case of Discharging Sinus over Groin

Sir, Hidradenomas are relatively rare benign tumours of sweat gland origin. This tumour can exhibit a varied morphological spectrum. It commonly presents as a solitary dermal nodule and is usually found over the scalp, face, anterior trunk and proximal extremities.[1,2] Herein we report a case of nodular hidradenoma (NH) presenting as a discharging sinus over the groin. A 27-year-old woman presented with a painless sinus over her right groin for the last one year, discharging serous material intermittently. She had no history of any ulcer over genitalia or any other significant systemic illness in the recent past. On examination, there was a small sinus of 8 mm diameter over the right inguinal fold [Figure 1a]. A firm nodule of approximately 2 cm in diameter was palpable beneath the lesion. The nodule was freely movable over the underlying structure but attached to the overlying skin. No other abnormality was detected on local and systemic examination. A provisional diagnosis of scrofuloderma was considered. Mantoux test and chest radiograph were within normal limits. A fine-needle aspiration cytology (FNAC) was performed, and hidradenoma was provisionally diagnosed. Later on, an excisional biopsy was performed. The nodule was well-defined, and it was attached to the overlying skin surrounding the sinus-like opening [Figure 1a-d]. On histopathological examination, there was a well-circumscribed dermal tumour [Figure 2a] with cystic spaces of various sizes and multiple tubular lumina [Figure 2b]. In the tumour lobule, there were mostly two types of cells: one was polyhedral cell with rounded nucleus and slightly basophilic cytoplasm, and another was round cell containing clear cytoplasm [Figure 2c]. Cells with features of both types were also observed [Figure 2d]. All these findings confirmed the diagnosis of NH. No recurrence was observed during the 6 months follow-up period.Figure 1: (a) Sinus over right inguinal fold; (b-d) appearance of the tumour during and after the excisionFigure 2: (a) Histopathology showing a well-defined tumour with multiple cystic spaces [H and E, 40×]. (b) Histopathology of the solid portion of the tumour showing multiple tubular lumina (arrow) [H and E, 400×]. (c) Two types of cells in the tumour-polygonal cells with basophilic cytoplasm (white arrow) and cells with clear cytoplasm (black arrow), [H and E, 400×]; (d) Photomicrograph of the cells with features of both types with eosinophilic cytoplasm [H and E, 400×]Hidradenomas are benign sweat gland tumours that can exhibit either eccrine or apocrine differentiation. This tumour is commonly seen in 4th to 8th decade of age, and there is a female preponderance. Cases of NH in young adults are also not uncommon.[2] The tumour usually presents as a solitary, slow-growing, asymptomatic firm dermal nodule of 5–30 mm in diameter although larger lesions have also been described.[1,3] The lesions are usually freely movable and may be cystic or pedunculated.[2] The overlying skin can be smooth, thickened, atrophic or ulcerated and the lesion can be attached to it.[1,4] There may be a history of serous or haemorrhagic discharge from the lesion.[4] The scalp and the anterior trunk were reported as the commonest sites of involvement by Nandeesh et al.[2] and Winkelmann et al.[3], respectively. A few cases have also been reported over the groin.[3] Histopathologically, NH usually presents as a well-defined lobulated mass with islands of tumour cells located mainly in the dermis.[2] The overlying epidermis can be attached in some cases.[1,5] Tubular lumina of varied sizes are often observed in the tumour lobule. Cystic spaces which may result from tumour cell degeneration are also seen frequently. The solid portion of the tumour is composed of mainly two types of cells. One type is polyhedral cell with rounded nucleus and slightly basophilic cytoplasm. Another cell type is round cell containing clear cytoplasm with small and dark nucleus. The clear cells contain large amounts of glycogen and may also show PAS-positive, diastase-resistant material along the periphery. There may be cells with features of both varieties, and those show a light eosinophilic cytoplasm.[5] All these characteristic features were present in our case. The relatively unusual location with the sinus-like presentation of NH mimicking scrofuloderma made our case very unique and reportable. The sinus formation could be the result of the rupture of the cystic spaces formed within the tumour. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.