Nodulo-Ulcerative Plaque Over the Vertex of Scalp.

Abstract

A 45-year-old man presented with a 12-year-old swelling in the vertex region of his scalp that had gradually grown in size for the last few years. Pus discharge and minor pain had been present for the previous 10 days. Patient had received treatment with oral and topical antibiotics. There was no history of preceding trauma, nevoid lesions, or associated comorbidities. Cutaneous examination revealed a hard non-tender fixed plaque of 3 cm × 2 cm size over vertex area of scalp with central ulceration and yellowish white discharge. It was separated from surrounding skin with a sharp demarcation [Figure 1]. There was no regional lymphadenopathy.Figure 1: Single hard, non-tender fixed plaque of 3 cm × 2 cm size over vertex area of scalpSkin biopsy from the lesion revealed an epithelial neoplasm in the dermis reaching up to the base and both lateral margins without any connection with the epidermis [Figure 2]. Upper dermis and mid-dermis showed numerous dilated keratin cysts and orthokeratotic corneocytes [Figure 2]. Mid- and lower dermis showed numerous small rounded and elongated tumor islands made up of basaloid cells without too much atypia with ductal structures or differentiation at their center and surrounded by dense fibroblastic stroma. Some of these ducts were elongated and dilated but were lined by cuboidal basaloid cells without any signs of apocrine differentiation [Figure 3].Figure 2: An epithelial neoplasm in the dermis reaching up to the base and both lateral margins but showing no connection with surface epidermis (H & E 40x)Figure 3: In the mid-dermis and lower dermis, the neoplasm shows numerous keratin cysts, many of which are dilated and show orthokeratotic corneocytes, majority of the tumor islands are small and rounded, while others are small irregular and surrounded by dense fibroblastic stroma, numerous rounded and elongated tumor islands made up of basaloid cells without too much atypia (H&E 100x)What is the diagnosis? Answer Microcystic adnexal carcinoma. Discussion Microcystic adnexal carcinoma (MAC) is a rare, slow-growing but locally aggressive malignant neoplasm with low mortality rate and it rarely metastasizes.[1] It arises from pluripotent keratinocytes and shows characteristic pilar and eccrine differentiation.[1] It was first described in 1982 by Goldstein et al. as a distinct clinicopathologic entity.[2] It is reported mainly in adults between 55 and 60 years of age with a slight female preponderance. Clinically, it presents as a solitary asymptomatic plaque or nodule most commonly on the head and neck areas. Occasionally, patients may present with pain, itching, burning sensation, numbness, and tingling as a result of perineural invasion by the tumor.[2] Immunosuppression, UV radiation exposure, and radiotherapy are the predisposing factors.[2] MAC is commonly misdiagnosed as desmoplastic trichoepithelioma (DT), syringoma, morpheaform basal cell carcinoma (mbcc), and desmoplastic squamous cell carcinoma (SCC) on histopathology.[3] It is often difficult to clinically distinguish MAC from other skin-colored growths on the head and neck including BCC. Histopathologically, the presence of ductal structures helps to differentiate MAC from DT, whereas the presence of calcification, prominent horn cysts, and single-file strand formation differentiates MAC from syringoma. Among all these tumors, perineural and subcutaneous involvement is characteristic feature of MAC on histopathology. MAC is also characterized by presence of normal tissue between epidermis and dermis.[4] Immunohistochemical markers that help to distinguish MAC from morpheaform BCC and SCC include cytokeratin 15 (CK15), carcinoembryonic antigen (CEA), and BerEP4 [Table 1].[5]Table 1: Immunohistochemical markers to distinguish MAC from morpheaform BCC and SCCThe most definitive treatment for MAC is complete surgical excision. Mohs micrographic surgery (MMS) is the preferred option as it is associated with low recurrence rate.[6] MAC has a high recurrence rate that ranges from 15% to 60% depending on the treatment option used. Recurrence may occur many years following the excision; hence, long-term follow-up is mandatory. Other treatment options include wide local excision, adjuvant or definitive radiotherapy, and chemotherapy.[7] Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.