The diagnosis and arthroscopic treatment of angioleiomyoma presenting loose body in the knee joint: two case reports.

BACKGROUND: Angioleiomyoma is a very rare benign solitary soft tissue neoplasm originating from smooth muscle layer of blood vessels. The tumor is usually located in the subcutis or the superficial fasciae, but less often in the deep fasciae, especially rare in the knee joint cavity. Diagnosis is frequently delayed or misdiagnosed as loose body or anterior knee pain because of its rare occurrence and poor awareness of physicians. Few studies have presented intra-articular angioleiomyoma and such cases become rarer and more difficult to diagnose when it presents as loose body.

CASE PRESENTATION: Two patients, a middle-aged man and an old woman, presented to our outpatient clinic with persistent anterior knee pain and both of them suffered from a solitary mass in the right knee that had slowly enlarged. One of two patients showed negative in the routine radiographic imaging and the other showed a "loose body" beside the lateral femoral condyle in the knee. MRI showed both a well-demarcated intra-articular mass of isointense signal to muscle on T1-weighted images and heterogeneous intensity on T2-weighted images. Their tumors were excised under arthroscopy finally, with the pathological results revealed vascular leiomyomas. They both recovered well with pain free after operation and no signs of recurrence were seen at the 7-year follow-up.

CONCLUSIONS: This case report illustrates the atypical locations of angioleiomyoma in the knee joint should arouse our attention and be included in the differential diagnosis of nodular lesions mimicking loose bodies.