A Rare Case of Cutaneous Leiomyosarcoma Arising From the External Auditory Canal

Leiomyosarcoma (LMS) is a malignant tumor that originates from smooth muscle. Cutaneous LMS is a distinct, superficial sarcoma that arises from dermal smooth muscle. It generally has a more favorable prognosis than subcutaneous or deep soft tissue LMS. Head and neck LMS accounts for a small proportion of all LMS cases, and primary tumors in the external auditory canal are extremely rare. We report a case of cutaneous LMS arising from the external auditory canal. The patient was a 32-year-old woman. She presented with a two-month history of a left external auditory canal mass, hearing loss, and ear pain. Contrast-enhanced CT and MRI revealed a 17-mm tumor confined to the cartilaginous portion of the external auditory canal, with no obvious infiltration into the bony portion. Biopsy results showed features of a smooth muscle tumor, and the level of Ki-67 expression led to a diagnosis of LMS. We resected the tumor via a preauricular incision and a longitudinal incision of the external auditory canal, including the external auditory canal cartilage, the surrounding soft tissue, and part of the temporomandibular joint capsule. Histopathology revealed tumor cells with moderately atypical, spindle-shaped nuclei arranged in fasciculated patterns. Necrosis was observed at a rate of 30%-40%, and mitotic cells were observed at a rate of 5 per 10 high-power fields. This led to a diagnosis of Fédération Nationale des Centres de Lutte Contre le Cancer (FNCLCC) Grade 2 LMS. Tumor cells were noted near the resection margin, and the safety margin appeared inadequate. Postoperative epithelialization of the external auditory canal was favorable, and no recurrence was detected on contrast-enhanced CT at five months. Although there is no established treatment strategy for head and neck soft tissue sarcomas, complete resection with adequate margins is essential. However, achieving adequate surgical margins is challenging due to functional and cosmetic considerations in the head and neck region. As in this case, small, brownish LMS are clinically considered to be cutaneous LMS, which generally have a relatively good prognosis. Close follow-up is required in cases involving resection close to the margin, and adjuvant therapies such as radical resection or radiation should be considered if recurrence occurs. A treatment strategy tailored to the tumor type and resection margin is necessary for primary LMS of the head and neck region.