cutaneous metaplastic synovial cyst: a case report

cutaneous metaplastic synovial cyst (cmsc), presents as a solitary, tender subcutaneous nodule that usually occurs at the site of previous surgery or trauma. histologically, the lesion is characterized by a cystic structure with villous-like projections that lined by metaplastic synovial tissue. the main cause remains unclear, but trauma is presumed to be a precipitating factor, as most reported cases have a history of antecedent cutaneous injury. here we present a case of cmsc in a 51 yr old man, presented with a painless deep-seated dermal nodule in the medial aspect of left ankle without history of any trauma or surgery in this site. immuno-histochemistry study reveals positive reaction for cd68 in the cystic wall and negative reactions for s-100. cmsc is a unique lesion and worthy to attention, and should be included in the differential diagnosis of deep dermal cutaneous cysts.