Cutaneous metaplastic synovial cyst of the first metatarsal head area

Abstract

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.

Keywords: Chronic pressure; Cutaneous metaplastic synovial cyst; Sole.

Fig. 1

Solitary, well-demarcated 3.0×3.0 cm-sized, skin-colored hyperkeratotic mass with cystic consistency.

Fig. 2

Dermal cyst containing numerous villous-like structures that consisted of hyaline fibrous tissue projecting toward the center of cyst cavity (H&E, ×40).

Fig. 3

Magnification of the rectangle in Fig. 2. The villous structures were lined by membrane of varying cellularity, which mimicked synovium. Some were composed of hyalinized connective tissue covered with by fibrin whereas others were highly cellular and were lined by multilayers of epithelioid and fibroblastic cells (H&E, ×200).

Fig. 4

Immunohistochemistry showed that the cells lining the cyst reacted positively for vimentin, but negative for CD34 and CD68 (×100).