What’s the Diagnosis – Case 138
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The prior images were from outside facilities and then the patient came to our institution. The patient had a subsequent procedure at our institution.
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Findings There is striking edema of the talus but no fracture line is identified and there is no collapse of the dome. Not perceived on the initial study was a round lesion of the medial aspect of the body of the talus. The patient subsequently underwent fixation of the talus but the round lesion is still present on the subsequent MRI. This lesion is shown well on the CT study as a radiolucent focus containing, dense, central mineralization.
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Diagnosis: Osteoid Osteoma I have presented a case of osteoid osteoma years ago and on the CT this is not a diagnostic dilemma as there is a radiolucent, round focus (nidus) containing central bone within the nidus. Osteoid osteoma are benign bone producing lesions which are most often found in children and young adults. This case highlights how this entity can unfortunately be missed. In this example the nidus is more conspicuous than in many cases on the MRI but still the correct diagnosis was not made. Over the years unfortunately we have seen this scenario many times and have probably fell victim to it as well. The inclination in the young, active patient is always to assume there is a stress fracture when massive edema is present. At times even, an osteoid osteoma may become aggravated with activity making it so the classic history of night time pain relieved by aspirin or NSAID may not be present or the history may not be as straight forward as we would like. The fixation in this case was for a presumed fracture but again no fracture is present. The lesion was ultimately treated by ablation. On an aside, the use of fat suppression after instrumentation, employed on this outside institution MRI, shows the marked artifact that chemical fat suppression produces and why IR or Dixon techniques are recommended for fat suppression with hardware in place.
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