45 year-old woman with knee pain. Plain radiographs demonstrate distal femur mass. Radiologist recommends bone scan for further evaluation.
Patient with non-specific knee pain. Clinician suspected OA.
Plain Films: A well-circumscribed distal left femoral metaphysis lesion is present. Internal 'arc-and-swirl' appearance is consistent with chondroid matrix.
Bone Scan: There is a focus of abnormal radiotracer uptake within the distal left femur both on pool and delayed images which coincides directly with the lesion seen on plain radiographs. Window and leveling of the whole body image demonstrates that the lesion is less intense than the ipsilateral anterior superior iliac spine. There are scattered degenerative changes. No metastases are present.
MRI: The lesion is well-circumscribed, T1 hypointense, T2 hyperintense and enhances following the administration of contrast. Eccentric posteriorly, the lesion touches the cortex without significant scalloping. There is no soft tissue mass.
How Was Dx Confirmed:
Treatment and Outcome:
The patient was referred to Orthopedics for further clinical evaluation and treatment. The distal femur enchondroma is unlikely to be the source of the patient's pain. However, Orthopedic surgeons at our institutions will sometimes inject local anesthetic into the joint to prove that pain is related to early degenerative changes. If pain is not relieved then a regional lesion could be the source of the patient's pain. The enchondroma in this case will be left alone unless symptomatic. New onset of pain is one feature suggestive of rare sarcomatous transformation of an enchondroma and should prompt reimaging by MRI to confirm stability.
This case is an excellent example of the bone scan findings discussed by Murphey et al in Enchondroma versus Chondrosarcoma in the Appendicular Skeleton: Differentiating Features. Radiographics 1998; 18: 1213-1237. With appropriate window and leveling of the whole-body delayed images, the abnormal high uptake within the lesion remains slightly less than the normal ipsilateral anterior superior iliac spine. While a 'rule-of-thumb' and not a major criteria in the determination of benign versus malignant lesion, this differentiation is a helpful suggestion of benignity.
A benign neoplasm composed of ectopic cartilage rests that have migrated into bonesâ€™ metaphysis from the growth plate. Enchondromas are usually singular, but multiple lesions may occur in enchondromatosis syndromes such as Ollierâ€™s, Maffucciâ€™s and metachondromatosis. Enchondromas are a benign finding seen incidentally on plain radiographs MRI, and/or CT while investigating other pathology.