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A patient, aged 10 years, presented with a 2‐day history of left ankle pain after a twisting injury during a field hockey game. She initially presented to an urgent care office the day of the injury, where x‐rays showed a large bone lesion in the calcaneus. No acute fractures were seen.
The patient was diagnosed with a lateral ankle sprain, was splinted, and was scheduled for orthopedic follow‐up. The patient denied having ankle pain prior to the recent injury.
On exam, the patient had tenderness over the lateral anterior talofibular ligament consistent with a lateral ankle sprain. The rest of the exam was unremarkable.
When reviewing the patient’s ankle x‐rays a large, round, well‐circumscribed radiolucent lesion in the calcaneus was observed. A lateral x‐ray of the calcaneus and a sagittal T1 MRI are shown. What is the most likely diagnosis?
Submit your diagnosis to see full explanation.
Osteoid osteomas, aneurismal bone cysts, non‐ossifying fibromas, unicameral bone cysts, and giant cell tumors are all benign bone tumors. Most benign tumors can be differentiated based on patient symptoms on presentation and x‐ray characteristics.
Osteoid osteomas are most commonly located in the cortices of long bones, occur most frequently in the second decade of life, and have a distinct nidus surrounded by sclerotic bone on imaging. Osteoid osteomas also have a distinct pain pattern of nocturnal pain that improves with nonsteroidal anti‐inflammatory drugs.
Aneurysmal bone cysts frequently occur in the spine (25%) and long bones (20%). X‐ray findings include a radiolucent, lytic lesion with an intact rim of cortex and bony septae or a “bubbly appearance.” Patients will present with pain, swelling, and with a pathologic fracture if large enough. MRI will show fluid filled levels that help make the diagnosis of aneurysmal bone cyst.
Non‐ossifying fibromas are the most common benign tumor in childhood. These are usually found incidentally on x‐ray, as they are asymptomatic lesions. However, large lesions may present as pathological fractures. X‐rays characteristics include an eccentric “bubbly” lytic lesion with a sclerotic outer rim.
Unicameral bone cysts are benign lesions that are often asymptomatic and found incidentally on x‐ray. X‐rays of unicameral bone cysts will show unilocular or septated lucency with thinning of the outer cortex. MRI characteristics include dark T1 images, bright T2 images, and rim enhancement with gadolinium contrast.
Giant cell tumors are locally aggressive benign tumors that typically present with pain, swelling, and joint stiffness. Giant cell tumors most commonly occur in adults aged 20 to 40 years with the distal femur and proximal tibia being the most common sites. X‐ray characteristics typically include an eccentric lytic lesion involving the epiphysis and metaphysis. Giant cell tumors can also extend through subchondral bone into the joint and cortical bone reaching the surrounding soft tissue.
References
- Lewis VO, Morris CD, Parsons TW 3rd. Instr Course Lect. 2013;62:535‐549.
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