Presentation
Incidental MRI finding of periarticular low signal abnormality on the medial aspect of the right sacroiliac joint
Patient Data
CT pelvis revealed: The lesion of interest noted on MRI appears as well-defined rounded gas-containing cystic structure inside the right sacrum in the periarticular medial aspect of the right sacroiliac joint. It measures about 1 cm in maximum dimension. It is not communicating with the adjacent sacroiliac joint. The overall density is about -980 HU.
Case Discussion
Acquired benign intraosseous pneumatocysts are findings with an incidence of about 9% in adults. They are commonly seen in the vertebral bodies, iliac bones, and sacrum (like our case). They are almost always asymptomatic although some cases may be associated with pain. In CT, they appear as well-defined cystic lesion with very thin wall and very low density (~ -1000 HU).