General Considerations

• Almost always found in the ilium or sacrum, near the sacroiliac joint
  • Also in the spine, especially cervical spine associated with degenerative disease
• Gas-containing
  • The gas is mostly nitrogen
• Uncertain etiology
• A communication with the joint is usually not visible

Imaging Findings

• They are rarely visible on conventional radiographs
• CT will identify the lesions as containing gas
  • Lesions have a sclerotic margin
• Low density on CT scans
  • -600 to -900 HU
• Decreased attenuation on both T1 and T2-weighted images
  • Do not contrast-enhance
• May be confusing on MR alone as they can be indistinguishable from blastic metastases

Differential Diagnosis

• Pathognomic on CT
• Osteomyelitis produced by a gas-forming organism
• Osteonecrosis

Complications

• Some pneumatocysts in the spine have been shown to enlarge
• Other have been shown over serial studies to fill in with fluid

 

 

           

Pneumatocysts. The white arrows point to two air-containing cyst-like structures
in the ilii adjacent to the sacroiliac joints on an axial CT image of the pelvis. The lesions have
a characteristic sclerotic margin.
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For this same photo without the annotations, click here

Vertebral pneumatocysts: uncommon lesions with pathognomonic imaging characteristics. Haithcock, J, with Layton, K andOpatowsky, M. Proc (Bayl Univ Med Cent). 2006 October; 19(4): 423–424.

 

Natural Course of an Intraosseous Pneumatocyst of the Cervical Spine. Yamamoto, T; Yoshiya1, S; Kurosaka1, M; Nagira, K; Takabatake, M; Hamamoto, H and Kazuo Mineo, K. AJR 2002; 179:667-669

 

Enlarging Vertebral Body Pneumatocysts in the Cervical Spine.  Kitagawaa, T; Fujiwaraa, A; Tamaia, K; Kobayashia, N; Saikia, K; Omataa, S and Saotomea, K. American Journal of Neuroradiology 24:1707-1710, September 2003