Incidental intraosseous pneumatocyst with gas-density-fluid level in an adolescent: a case report and review of the literature

Abstract

Intraosseous pneumatocyst is a gas containing lesion located within a bone. It is a relatively rare condition of unclear etiology and with an undetermined natural course. Gas-density-fluid level pneumatocyst is even rarer. Pneumatocyst is frequently seen in adults but rarely reported in pediatrics. The lesion is usually small and is seen in the vertebral bodies as well as around the sacroiliac joints. Rarely does it occur in other parts of the skeleton. We are reporting a case of large blood signal intensity containing intraosseous pneumatocyst in a 14 year old boy and reviewing other pediatric cases of pneumatocysts as well as those with gas-density-fluid level. The recognition of this incidental rare benign lesion is essential to avoid over investigation and an inappropriate aggressive intervention.

Keywords: CT; Gas-density-fluid level; Intraosseous pneumatocyst; MRI; Pediatrics.

Figure 1

Fourteen year-old boy with incidental left acetabular intraosseous pneumatocyst. Axial CT scan (a) soft tissue window (b) bone window. Coronal CT scan (c) soft tissue window (d) bone window. It shows a gas density - fluid level well circumscribed lobulated lesion with thin sclerotic margin (arrows) involving pubic bone portion of the left acetabulum. Note the normal appearance of adjacent bone, hip joint and surrounding soft tissue. [Technique CT, 106mAs, 120 KVP, 3mm SL, without contrast].

Figure 2

Fourteen year-old boy with incidental left acetabular intraosseous pneumatocyst. (A) Abdomen radiograph, anteroposterior view, supine. (B) Magnified view of left hip joint. It shows a well circumscribed, lobulated, expansile, lytic lesion with sclerotic margin and narrow zone of transition. It is seen at the projection of the left hip joint (arrows).

Figure 3

Fourteen year-old boy with incidental left acetabular intraosseous pneumatocyst. pelvic MRI axial cuts (a) T1WI [SL 3, TE 19, TR 778], (b) T1WI FAT SAT [SL 3, TE 19, TR 674], (c) T1WI FAT SAT post Contrast[SL 3, TE 19, TR 674, 4 ml of Gadolinium] and (d) GRE WI [SL 3, TE 9.84, TR 500] in supine position. The fluid component of the lesion (arrows) appears of intermediate signal on T1WI with no suppression upon fat saturation and no post contrast enhancement. On GRE WI the fluid inside the lesion shows two levels of low signal intensity at the upper part and high signal intensity at its dependant part.

Figure 4

Fourteen year-old boy with incidental left acetabular intraosseous pneumatocyst. Pelvic MRI axial cuts (a) T2WI supine [SL 3, TE 120, TR 5550] shows high T2WI signal intensity of the fluid with clear level (arrow). (b) T2WI prone [SL 3, TE 120, TR 5550] shows free movement of the fluid along the lesion wall (arrow). (c) DWI prone [SL 3, TE 104, TR 5719] and (d) ADC map (Apparent Diffusion Coefficient map) prone [SL 3, TE 104, TR 5719, ep_b0_1000] show restriction of diffusion (arrows).