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During the evaluation of a 15-year-old boy with an injury to the right foot, an unexpected radiographic finding was noted.
The lateral radiograph of the foot revealed a mostly round radiolucent area of about 1 cm in diameter in the anterior calcaneus. Additional views of the right calcaneus and radiographs of the left calcaneus showed no abnormalities. The patient had no tenderness or pain in the area of the anterior calcaneus.
A pseudocyst is a normal variant that looks like a lytic lesion but is actually a rarefaction of the normal trabecular pattern; the trabecular rarefaction is a low stress area of bone that becomes apparent when it is surrounded by more prominent higher stress areas. MRI scans of a pseudocyst show a normal bone marrow signal. In addition to the region of the anterior calcaneus, the greater tuberosity of the humerus is another common site for a pseudocyst.1
Comparing the radiograph with the abnormal finding with prior studies, when available, and films of the contralateral side can help distinguish a pseudocyst, which is usually of no clinical significance, from a true lytic lesion, which can be benign or malignant. ■
Bennett DL, El-Khoury GY. General approach to lytic bone lesions. Appl Radiol. 2004;33:8-17.