Incidental intraosseous pneumatocyst

Incidental intraosseous pneumatocyst

Findings

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.

Discussion

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

Conclusion

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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3. Kitagawa T, Fujiwara A, Tamai K, et al. Enlarging vertebral body pneumatocysts in the cervical spine. AJNR Am J Neuroradiol. 2003;24: 1707–1710.
4. Yamamoto T,Yoshiya S, Kurosaka M, et al. Natural course of an intraosseous pneumatocyst of the cervical spine. AJR Am J Roentgenol. 2002; 179:667–669.
5. Linker CS, Peterfy CG, Helms CA. Case report 844. Intraosseous pneumatocyst of the clavicle. Skeletal Radiol. 1994;23:315-316.
6. Laufer L, Schulman H, Hertzanu Y. Vertebral pneumatocyst: A case report. Spine. 1996;21:389 –391.