Associate Professor

Senior Specialist

Specialist

Dept. of Pathology

ESI Hospital, Rohini, Delhi

Address for correspondence

Dr Annu Nanda

G-506, Som Vihar, Sector 12, RK Puram, New Delhi - 110 022

E-mail: annunanda@rediffmail.com

Keywords

Nodular hidradenoma, adnexal tumor, eccrine tumor

Nodular hidradenoma (NH) is a rare benign adnexal tumor usually presenting as a solitary, firm, slow growing intradermal nodule. Understanding of the cytologic features of skin adnexal tumors is valuable as distinguishing benign cutaneous neoplasms from malignant primaries or metastatic disease on cytology is often difficult. While the cytomorphology of a variety of primary cutaneous neoplasms has been described knowledge of the cytological features of hidradenomas is limited because only rare case reports have been described in the literature.

We report cytological features of a case of benign adnexal tumor with a subsequent histological diagnosis of NH occurring at gluteal region being a rare site.

CASE REPORT

A 48-year-old male presented with a 2.5 cm firm swelling in left gluteal region for the last 8 months. Fine needle aspiration (FNA) yielded mucoid material. Smears were cellular and showed sheets, cohesive clusters and singly scattered epithelial cells in a myxoid background (Fig. 1). These cells showed round to oval nuclei, evenly distributed nuclear chromatin and moderate amount of eosinophilic cytoplasm (Figs. 2 and 3).

At places cellular clusters showed closely intermingled eosinophilic stromal matrix and a few mutlinucleate giant cells and histiocytes were noted in the background. A diagnosis of benign adnexal tumor was rendered and the mass was excised. On histopathological examination, a diagnosis of NH was made (Fig. 4).

DISCUSSION

Nodular hidradenomas (NH) are regarded as benign adnexal tumors of eccrine origin occurring more commonly in adults with a male to female ratio of 1:1.7. They are freely movable and may have pedunculated or cystic appearance with smooth, thickened, atrophic or ulcerated overlying skin. The average size is 0.5-2 cm but larger ones have been reported and occasionally, multiple lesions can be seen. Although any site may be affected, hidradenomas are found most frequently on the head and neck. Gluteal region is an uncommon site as was seen in the present case.

Fine needle aspiration cytology (FNAC) is a time and cost-effective easily accessible technique for diagnosis of adnexal tumors and helps in differentiating it from other tumors. However, cytology of NH has rarely been reported as there are very few reports in the literature of the cytologic characteristics of malignant NHand NH. The cytology smears from the tumor show cohesive clusters of polygonal cells having a bland nucleus and abundant cytoplasm that may stain eosinophilic, clear or basophilic. Intranuclear cytoplasmic pseudoinclusions may be seen.

Occasional rosettes or duct like structures are noted. Cystic degeneration represented by amorphous background material and foam cells, is a common feature in hidradenoma as was seen in the index case although the exact subtyping could not be performed prospectively.

To the best of our knowledge, no prospective diagnoses of hidradenoma have been made on FNA and published. In all the cases of NH reported by Dubb et al, a diagnosis of a benign skin adnexal tumor was made on FNA. Kumar and Verma indicated that unusual cytomorphologic features and a diversity of cell types such as polygonal cells, clear cells and spindle cells should raise the suspicion of a cutaneous adnexal tumor. If amorphous background material with or without foam cells is seen in a subcutaneous mass aspirate with a biphasic staining pattern with both eosinophilic cytoplasm and cells staining clear to basophilic associated with epithelial duct like cells and tubular structures, the possibility of hidradenoma should be considered. Rekhi et al observed metachromatic stroma, intranuclear grooves and pseudoinclusions that have been uncommonly described by Khurshid et al. Eosinophilic stromal material with attached epithelial cells was noted in the present case also. On finding nuclear pleomorphism and hyperchromatism, macronucleoli, giant cells and mitotic activity in addition to the above-mentioned features an atypical hidradenoma with increased risk of recurrence and possible malignant behavior must be considered. The malignant variants show high cellularity and nuclear pleomorphism on FNA.

Even though NH is regarded as a benign tumor, it may recur after inadequate surgical excision. Thus, they need to be excised with adequate margins.

Although all skin adnexal tumors, even if they appear overtly benign should have histopathologic confirmation, the recognition and attention to the cytologic features described above should allow distinguishing from other lesions. Recognition that the lesion is a skin adnexal tumor and if possible, being able to subtype it will allow appropriate management.

SUGGESTED READING

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