Aim: Extraskeletal chondromas in the region of the knee joint are very rare tumors which may cause diagnostic problems and have concomitant therapeutic consequences.
Method: In a case report we present the clinical, radiological and histological features of an a extraskeletal chondroma.
Results: A 47-year-old female patient presented with an infrapatellar, painless tumor of the knee joint. The clinical features were unspecific. On plain X-ray images, calcifications were visabled within Hoffa's fat pad. An important preoperative imaging procedure was MRI, which showed a well defined mass of 2.5 cm in diameter with a hyperintense signal on fat suppressed images. Subsequent operative therapy involved marginal resection of the tumor.
Conclusion: The differentiation of this entity especially from myxoid chondrosacroma and synovial chondroamatosis was crucial with respect to an adequate therapy. Further differential diagnoses included heterotopic ossifications, synovial sarcoma, mesenchymoma and soft-tissue osteosarcoma.