Cutaneous metaplastic synovial cyst of the first metatarsal head area.

A cutaneous metaplastic synovial cyst (CMSC) is a cyst lined with metaplastic synovial tissue, which includes the formation of an intracystic villous structure resembling hyperplastic synovial villi. Clinically, the lesion is a tender, subcutaneous nodule that usually occurs at the site of previous surgical trauma and is frequently misdiagnosed as a suture granuloma. The actual cause remains unclear; however, trauma is presumed to be a precipitating factor, as most reported cases have demonstrated a history of antecedent cutaneous injury. Here, we present a case of CMSC in a 51-year-old woman who presented with a cystic mass localized in the left sole. She had no history of previous trauma or surgical procedures performed in the area. Although the case explained in this report is a spontaneous case of CMSC that occurred without a history of trauma, it is believed to have been caused by constant and chronic pressure since CMSC occurred in the first metatarsal head area, a part of the sole where heavy pressure is consistently applied.