A 47-year-old female presented with a well-defined skin colored non-tender asymptomatic nodule of 1x1cm over the vulva for almost one year. There was no history of any sexually transmitted disease. General physical examination was within normal limits and there was no inguinal lymphadenopathy. Haemotological and biochemical investigations were within normal limits. Serological tests for syphilis and HIV were non reactive. The clinical possibilities considered were inclusion cyst and skin tag. The nodule was excised and sent for histopathology. (Figure 1)
The sample was processed for routine histopathological examination. The hematoxylin and eosin stained sections were examined under light microscopy. The epidermis was relatively unremarkable. Dermis shows numerous horn cysts lined by multiple layers of eosinophilic cells. There was attempted gland formation at places. Some of the cysts were dilated. Few islands of eosinophilic cells without keratinization are seen. Occasional cysts showed presence of granular layer between the keratin and eosinophilic cells. One of the cysts ruptured eliciting lymphohistiocytic reaction in the surrounding area. (Figure 2) There were no basaloid cells surrounding the eosinophilic cells. There were no hair shafts.
Adnexal tumors of skin are an interesting and complex entity in dermatopathology. It is important to differentiate the adnexal tumors as benign and malignant and also differentiate them from the epidermal and epithelial tumors. Hair follicle and its pilosebaceous unit are adnexal structures with different group of tumors. This group comprises of various tumors with differentiation towards hair structure. Trichoadenoma is one among them which is also know as trichoadenoma of Nikolowski.1, 2, 3, 4
Absence of basaloid cells around the eosinophilic cells differentiates it from the trichoepithelioma and absence of hair shaft differentiates it from trichofolliculoma. Trichoblastoma is another benign adnexal tumor with differentiation towards hair structure composed of islands of basaloid cells without connection with the overlying epidermis. Trichoadenoma, at times may be difficult to differentiate from keratotic basal cell carcinoma in exceptional cases. A careful and thorough microscopic examination of the tissue should help differentiate them.