To the Editor:
Microcystic adnexal carcinoma (MAC), described by Goldstein et al1 in 1982, is a relatively uncommon cutaneous neoplasm. This locally aggressive malignant adnexal tumor has high potential for local recurrence. The skin of the head, particularly in the nasolabial and periorbital regions, most often is involved.2 Involvement of the external auditory canal (EAC) is relatively rare. We report a case of MAC of the EAC.
A 52-year-old man presented with 1 palpable nodule on the right EAC of approximately 1 year’s duration. The lesion was asymptomatic, and the patient had no history of radiation exposure. The patient was an airport employee required to wear an earplug in the right ear. Endoscopic examination identified a 1×1 cm2 erythematous nodule on the anterior inferior quadrant of the right external ear canal orifice (Figure 1). Axial and coronal computed tomography demonstrated a soft tissue mass in the right EAC without any bony erosion. No clinical signs of regional lymphadenopathy or distant metastasis were present. Excision was performed under microscopic visualization.
Histopathology of the nodule showed marked proliferation of multiple keratin-containing cysts, irregular ductal structures, and solid epithelial nests in the deep dermis (Figure 2). Irregular ductal structures with 2 cell layer walls and several epithelial strands or small nests of tumor cells within desmoplastic stroma were noted (Figure 3). No perineural infiltration or tumor infiltration existed at the margin. Based on the clinical and histopathologic findings, the final diagnosis was MAC. Complete resolution was noted after the excision. The patient returned for regular follow-up and no signs of recurrence were noted for 7 years postoperatively.
Microcystic adnexal carcinoma, also known as sclerosing sweat duct (syringomatous) carcinoma, malignant syringoma, and syringoid eccrine carcinoma, is characterized by slow and locally aggressive growth with high likelihood of perineural invasion and frequent recurrence.2 Regional lymph node metastasis is uncommon, and systemic metastasis is rare.2-4
Although the head most often is involved, a PubMed search of articles indexed for MEDLINE using the terms microcystic adnexal carcinoma and external auditory canal revealed 4 cases (Table).5-8 Our report adds another case of MAC arising solely in the EAC. Although the etiology of MAC is unknown, prior studies indicated that radiotherapy is a risk factor for MAC. Other possible risk factors include UV light exposure and immunodeficiency.2 Our patient had no history of these factors and experienced chronic friction caused by use of an occupational unilateral earplug, which may be a notable factor. Locations of MAC arising outside the head region include the axilla, vulva, breast, palm, toe, perianal skin, buttock, chest, and an ovarian cystic teratoma.3,9 Friction commonly occurs in many of these areas. Therefore, we propose that friction may be a risk factor for MAC.
Microcystic adnexal carcinoma should be included in the differential diagnosis of any slowly growing cutaneous tumor, even in the EAC. Once diagnosed, the tumor should be surgically excised. Because local recurrence is common and may occur several decades after excision, lifetime follow-up for recurrence signs is essential.