Solitary Nodule on the Thigh

A 65-year-old apparently healthy male presented with an asymptomatic growth over the right thigh, present for the past 1 year. Initially, the lesion was a pea-sized growth which gradually increased in its dimension and morphology to attain the the present size. (2.5 cm × 3 cm). Cutaneous examination showed a solitary moist firm slightly tender nodule over the lateral aspect of the right thigh. The mass had an eroded surface, fixed to the underlying structures, and bled on touch [Figure 1]. Regional lymphadenopathy was notably absent. The mass was excised in toto and histology showed a well-circumscribed epithelial neoplasm, connected to the epidermis at multiple points. The neoplasm was composed of monomorphous cells, with several of them showing abundant pale or clear cytoplasm. Besides, there were features of ductal differentiation, cystic changes, and necrosis [Figures 2 and 3]. The stroma was characterized by thickening and hyalinization of collagen.

Figure 1.

Solitary moist nodule with eroded surface on the lateral aspect of thigh

Figure 2.

Well-circumscribed neoplasm of monomorphous cells showing connections to the epidermis (H and E, ×40)

Figure 3.

Dermal tumor showing both poroid and clear cells along with ductal differentiation (H and E, ×400)

Question

What is your diagnosis?

Answer

Nodular hidradenoma.

Discussion

Clear cell hidradenoma was first described in 1949; since then, it has been reported under various designations such as nodular hidradenoma and eccrine acrospiroma.[1] Clinically, it presents as a slow growing, solitary firm nodule, mostly distributed over the scalp, face, thorax, abdomen, and gluteal region; mainly in adults. Some tumors discharge serous material while others have a tendency to ulcerate.[1,2]

The histopathological findings of nodular hidradenoma are classical. It is seen as a well circumscribed (often encapsulated) tumor containing an admixture of both solid and cystic components. The solid portion is composed of two types of cells, one cell type is polyhedral with a rounded nucleus and slightly basophilic cytoplasm; whereas the other cell type being round and having a clear cytoplasm due to the presence of glycogen. Nuclear grooving is found to be a useful morphological feature to aid in its diagnosis.[1,3] Squamous differentiation may be found, with infundibular type of keratinization being the most common type. Sebaceous differentiation is also common.[4] Immunohistochemistry shows positive staining with antibodies against cytokeratin-CAM 5.2, Ber-EP4, p63, epithelial membrane antigen, S-100 protein, smooth muscle actin, and vimentin.[2,3,4]

The tumor has a high rate of local recurrence (10%) and limited potential for malignant transformation. Malignant sweat gland adnexal tumors are rare with an incidence of 0.001%. Of these, clear cell hidradenocarcinoma accounts for 6% of malignant eccrine sweat gland tumors. Therapeutic options include surgical excision and Mohs micrographic surgery.[5] The case is being reported for its rarity.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.