Early detection of a deep-seated synovial sarcoma by magnetic resonance imaging

An 18-year-old man who complained of left thigh pain was referred to our institute. No abnormal findings were detected on physical examination and plain roentgenogram or gallium scintigram. On magnetic resonance imaging (MRI), a high-signal of 1-cm diameter was seen in the left vastus medialis muscle on T1- and T2-weighted images. The lesion was initially considered to be: (1) angiolipoma, which is usually associated with fatty tissue, based on the MR findings or (2) a sport-induced inflammation based on the patient's history of baseball playing. Because of the persistent thigh pain and similar findings on the second MRI, an excisional biopsy was performed; the lesion was diagnosed histologically as synovial sarcoma. Additional wide resection was carried out later, without adjuvant therapy. He has been disease-free for 3 years postoperatively. Many soft tissue sarcomas are discovered with extensive tumor formation and are accompanied by obvious abnormal findings on various imaging studies. It is extremely rare that deep-seated sarcomas are discovered without obvious abnormalities. To the best of our knowledge, this is one of the smallest detected deep-seated soft tissue sarcomas. MRI was the most sensitive and useful procedure for detecting the lesion. Physicians should recognize that painful lesions may possibly be synovial sarcoma, even if they are demonstrated as a subtle lesion of 1-cm diameter on MRI.