Unusual osteolitic intraosseous ganglion cyst of the medial tibial condyle in a patient affected by mild osteoarthritis of the knee

Bone lesions of the proximal tibia are common findings; depending on the site, age of the patient and symptoms at the time of presentation a carefull differential diagnosis must be carried out. Benign and malignant lesion must be taken into account to perform the correct therapeutic procedure; histological findings are of fundamental importance to complete and clarify radiological findings. We present the case of a 60 years old active patient complaining of atraumatic medial knee pain. X-Rays performed at the time of the first visit to the outpatient clinic revealed an osteolityc lesion of the medial tibial condyle. We performed an MRI that highlighted a lobulated cystic lesion of the medial tibial condyle eroding the cortical bone and expanding to the surrounding soft tissue.The cavity appeared populated of a mixed and various tissue with a low signal intensity on T1 weighted images and a high signal intensity on T2 images. Differential diagnosis can be considered with epiphyseal bone lesions such as giant cell tumor, chondroblastoma or fibrous dysplasia, and also rheumatoid related lesions or ganglion cyst of bone. The tissue obtained from the incisional biopsy macroscopically revealed a clear, yellowish gelatinous and mucinous material. The microscopical histological exam confirmed a cystic area of the lesion; the lumen contained some dense, fibrous material with focal mucoid degeneration. The patient’s clinical history, the imaging appearance, the locally aggressive aspect of the lesion and its slow growing together with the pathological confirmation allowed us to diagnose an intraosseous ganglion cyst. According to the age of the patient, his working and recreational habits and the moderate grade of osteoarthritis, we decided to perform an extra articular-sparing procedure: curettage and grafting with bone bank allograft (bone chips). Post operative X-Rays showed a good filing appearance of the lesion without reabsorption or any out flow of the graft. With limitations concerning the short follow up, the patient showed a very high level of satisfaction, especially in terms of pain relief and time to regain his working and recreative activities about two weeks after surgery. An accurate and long follow up must be carried out to verify the integration of the allograft and any articular degenerative progression (www.actabiomedica.it).