Age / Sex : 16 / M

Age/Sex: 16/M

C.C.: Lt. foot pain (1YA)

osteoid osteoma in the calcaneus

Discussion

Findings:
 - Lateral ankle radiograph shows a radiolucent nidus with central calcification and surrounding sclerosis.
- Sagittal MR images show a subcortical nidus in the calcaneal sulcus. The nidus has a central calcification and is surrounded by sclerotic bone and extensive bone marrow edema in the calcaneus. Soft tissue edema is seen in the tarsal sinus and the planatar side of the calcaneus. Joint effusion and synovial hypertrophy are prominent in the posterior recess of the talocalcaneal joint.

Differential Diagnosis:
osteoid osteoma/ osteomyelitis/ stress fracture Diagnosis: osteoid osteoma in the calcaneus

Discussion:
Osteoid osteoma occurring in the foot is unusual and accounts for approximately 4% of cases. The most common site in the bone of the foot is the talus. The preoperative diagnosis of osteoid osteoma occurring in the foot may be delayed because of unusual location and atypical symptoms. On MRI, the nidus of osteoid osteoma shows low or intermediate signal intensity on spin echo T1-weighted images, variable signal intensity on T2-weighted images, and variable enhancement. Intra-articular lesions cause synovial thickening or inflammation and joint effusion, which may be readily apparent on MRIs. MRI may be misleading because of bone marrow and soft tissue changes associated with osteoid osteoma, which may sometimes be extensive. The misleading appearance of osteoid osteoma on MRI often leads to the diagnosis of osteomyelitis, stress fracture, inflammatory arthritis, or a more aggressive bone tumor. The mechanism that results in bone marrow and soft tissue edema is uncertain; however, prostaglandin, which is reported to be a cause of peritumoral edema on MRI, has been implicated because levels of this inflammatory mediator are elevated in osteoid osteoma.
References:
1. Lee GK, Kang IW, Lee ES, Min SJ, Cho SW, Hwang DH. Osteoid osteoma of the tarsal cuboid mimicking osteomyelitis. AJR 2004;183:341-342
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4. Ehara S, Rosenthal DI, Aoki J, et al. Peritumoral edema in osteoid osteoma on magnetic resonance imaging. Skeletal Radiol1999;28:265-270
5. Yamamura S, Sato K, Sugiura H, et al. Prostaglandin levels of primary bone tumor tissues correlate with peritumoral edema demonstrated by magnetic resonance imaging. Cancer 1997;79:255-261