Tubulopapillary hidradenoma: A rare case with cytohistopathological correlation
A 30-year-old male patient was referred from surgical out patient department with complaint of a painless swelling on the scalp overlying the right frontal bone, which had slowly increased in size over the past 6 months. On local examination, a 1 × 1 cm well defined, soft to firm, non-tender, mobile swelling was palpable with no overlying skin changes []. FNAC was performed, which yielded 1.5 mL of brown colored fluid. Smears prepared showed cohesive clusters, papillaroid fragments, monolayered branching sheets and few singly lying epithelial cells []. On closer examination, two types of cell populations were seen. One population of cells were small cuboidal and exhibited scant to moderate amount of basophilic cytoplasm, round to oval nuclei with regular nuclear membrane, fine chromatin and inconspicuous nucleoli. At places, some of these cells showed tubular/acinar formations. The other population consisted of cells that were larger and showed abundant amount of pale bluish to grayish, fragile, granular cytoplasm, round to oval nuclei with regular nuclear membrane, fine chromatin and visible nucleoli. At places, these cells also showed attempted tubule formation []. Few of these cells were singly scattered and exhibited prominent secretory activity in the form of large cytoplasmic vacuoles filled with eosinophilic material []. No pleomorphism, mitoses or necrosis were noted. Background showed numerous foamy macrophages as well as few pigment laden macrophages in abundant amorphous secretions.\nA cytodiagnosis of “benign adnexal tumor (both eccrine and apocrine morphology seen)” was rendered. No attempt was made for specific subtyping of the adnexal tumor at this point.\nExcision biopsy of the lesion was performed. The histological sample consisted of a grey white nodular tumor measuring 0.8 × 0.5 × 0.5 cm. Hematoxylin and eosin stained sections showed a well circumscribed tumor located in the dermis with no connection to the epidermis. The overlying epidermis was unremarkable. The tumor had a nodular growth pattern with the nodules separated by stroma containing loosely arranged spindle cells and areas of hyalinized collagen. These nodules consisted of numerous irregularly shaped, closely packed well-formed tubules lined by two layers of epithelial cells; the peripheral layer consisting of cuboidal to flattened cells, and the luminal layer composed of columnar cells. Many of the tubules showed luminal cells with abundant granular cytoplasm that exhibited decapitation secretions with presence of eosinophilic granular debris in some lumina. Some of the tubules were cystically dilated with short papillary projections extending into the lumina []. These papillary projections were devoid of fibro-vascular cores and were also lined by double layer of epithelial cells consisting of outer cuboidal and inner columnar cells. In a focal area, few tubules showed clear cell change in the epithelial lining cells. No pleomorphism, mitoses or necrosis were seen. The light microscopic diagnosis was consistent with tubulo-papillary hidradenoma.\nPeriodic acid-Schiff (PAS) positive diastase resistant material was seen in some of the tubular lumina as well as in the cells that had abundant granular cytoplasm.\nOn immunohistochemistry, the luminal cells were diffusely positive for Pan cytokeratin (CK), while sharp luminal positivity was seen with epithelial membrane antigen (EMA) and carcinoembryonic antigen (CEA) consistent with differentiation towards the secretory epithelium of sweat glands. The abluminal cells showed diffuse intense positivity for S-100 and smooth muscle actin (SMA), whereas the periadnexal dermis was positive for vimentin and CD10 (focally).\nCytohistological correlation was then attempted considering histological diagnosis as final.