Intraosseous pneumatocysts are gas-containing cystic structures seen inside the bone.
They are of uncertain aetiology. These cysts do not communicate with the joint.
Most common site of involvement is sacroiliac joints. Other sites involved are cervical spine, scapula and other bones rarely.
Appear as very low density (i.e. air at approximately -1000 HU) cystic lesion with thin sclerotic margin, usually abutting a joint.
Low signal intensity on both T1 and T2 weighted MR images.
Imaging differential considerations include
- There is a risk of erroneously misdiagnosing intraosseous lipomas as intraosseous pneumatocysts, or vice-versa, if the lesion is only eye-balled on a soft tissue window. Therefore if unsure, one should either measure an ROI of the lesion to clarify if gas or fat density, or review the lesion on a lung window.
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- 3. Catalano O, De Rosa F, Muto M. Intraosseous pneumatocyst of the ilium: CT findings in two cases and literature review. European radiology. 7 (9): 1449-51. doi:10.1007/s003300050315 - Pubmed