Summary: A 55-year-old patient presented with acute loin pain and hematuria, suggestive of right ureteric colic. Intravenous urogram showed adistal right ureteric calculus. His symptoms subsided and there was no calculus. On follow-up, noncontrast computed tomography (CT) indicated spontaneous passage. Incidentally, a well-defined lytic lesion was seen in the sacrum adjacent to the left sacroiliac joint consistent with a pneumatocyst.
Incidental intraosseous pneumatocyst
A radiograph of the pelvis showed a rounded well-defined lytic lesion in the sacrum, adjacent to the left sacroiliac joint in addition to the radio-opaque calculus in the distal ureter (Figure 1). It measured approximately 11 mm with a thin well-defined sclerotic margin.Axial and coronal CT showed the air density within the lesion (Figures 2 and 3). The sacroiliac joint was unremarkable.
Intraosseous pneumatocyst is a rare benign condition, commonly seen in iliac bone or sacrum.1,2 Locations like vertebral bodies, clavicle, acetabulum also have been mentioned.2,3,4,5 The etiology of pneumatocyst is unclear. Some have suggested that the cause is spontaneous development of intra-osseous gas or vacuum degeneration of an underlying intraosseous ganglion or synovial cyst. Laufer etal. speculated that the gas in the cyst is nitrogen released from the adjacent joints.6 Gas in the pneumatocyst may disappear spontaneously, and the cyst might change to a fluid-filled cyst. Subsequently, the cyst might be replaced with granulation tissue.4
Intraosseous pneumatocyst should be differentiated from bone neoplasms and osteomyelitis by its characteristic imaging findings. Intraosseous pneumatocysts are benign lesions, therefore biopsy and follow-up are unnecessary.
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- Linker CS, Peterfy CG, Helms CA. Case report 844. Intraosseous pneumatocyst of the clavicle. Skeletal Radiol. 1994;23:315-316.
- Laufer L, Schulman H, Hertzanu Y. Vertebral pneumatocyst: A case report. Spine. 1996;21:389 –391.