We present a case of intraosseous pnematocyst of the right iliac bone, discovered incidentally in a 20-year-old gentleman who presented to the casualty following a road traffic accident, which to our knowledge is among the younger age group in which the entity has been reported in literature.
A healthy 20-year-old gentleman was brought into the casualty following a road traffic accident. His observations including GCS (15) were stable on scene and throughout his stay in the casualty. A CT was done to evaluate his abdomen following complain of right sided upper abdominal pain. The CT failed to reveal any injuries. However incidental note was made of gas attenuating cystic lesions in the right iliac bone in close proximity to the right sacroiliac joint, which by virtue of its typical appearance was diagnosed as a pneumatocyst. No communication with the adjacent joint or the bone margin was seen. The gentleman had no complains related to his back, pelvis or hips. There were no external signs of injury around the pelvis or lower abdomen and a complete orthopaedic examination of both lower extremities was normal. Once persistent clinical improvements were observed, the young gentleman was discharged home with simple analgesia.
Key words: Ileum, pneumatocyst Intraosseous pneumatocysts are rare, benign conditions, mostly described in ileum, sacrum or vertebrae.1-3 Occasionally cases have been described in humerus4, clavicle5, scapula5 acetabulum6 and ribs.7 Pneumatisation is a natural process in cranio-facial skeleton. Intraosseous gas elsewhere raises possibilities of infection, osteonecrosis, trauma, post surgical appearance or neoplasm. Intraosseous pnematocysts are gas containing described in proximity to joints, most commonly sacroiliac joint. The gas is nitrogen, from gaseous degeneration of subchondral cysts, by vacuum phenomenon when there is a communication with adjacent joint or disc space. However this is not universally accepted.1,4 With respect to ileum, they are common in males, may or may not be associated with degenerative disease of sacroiliac joint, intra-articular gas or communicate with joint space.9 Gas in disc spaces in degenerative spine disease is well recognised (vacuum phenomenon). Some cases have reported a communication between the intraosseous lesion and the disc space1 or the spinal canal.10 Secondary gas accumulation in an intraosseous ganglion is another possibility. They may be located adjacent to joint space resembling degenerative cysts.5 Subchondral cysts are described in osteoarthritis, rheumatoid arthritis, CPPD, osteonecrosis and neoplastia. However these produce associated radiological findings and are unlikely to be asymptomatic. Hence they were excluded from our differential. CT clinches the diagnosis by showing gas attenuation and a sclerotic rim.1,4 Intracystic fluid level or soft tissue may be seen but they are unlikely to represent infection.4 Pneumatocysts show hypo intensity in T1 and T2 weighted MR.1 Their natural history is unclear. They can disappear spontaneously, become fluid filled7,11 or be replaced by granulation tissue.11 As far as their management is concerned, one paper suggested pneumatocyst of the ileum as an unusual cause of back pain in healthy patient. CT guided puncture destruction of the cyst under local anaesthesia brought relief.12 Another suggested filling the cyst under imaging guidance as treatment.2 However, most lesions described are asymptomatic, discovered incidentally, do not require a routine biopsy or aggressive managenement.8 Pneumatocyst enlargement on follow-up has been described, but they were in the vertebrae. Clinical, radiological and common judgement needs to be exercised in deciding whether follow-up is necessary. The pneumatocyst we present was in a healthy young gentleman; younger than most cases described (i.e. 21 to 50 years)8. No bony or joint pathologies could be identified, and there was no family history of early onset arthropathy. There were no internal or external signs of trauma in the vicinity. A diagnosis of intraosseous pnematocyst was hence made. The cause of the pneumatocyst could not be determined with certainty. Early microscopic degenerative disease of the sacroiliac joint, secondary gaseous degeneration of an intraosseous ganglion5 or a primary cystic process could all be possibilities. Intraosseous pneumatocyst are benign innocuous lesions that do not require aggressive management or specific treatment. Their natural history is unclear. They can disappear spontaneously, become fluid filled or be replaced by granulation tissue. Most of them are discovered incidentally and they can be reliably differentiated from neoplasm or infection by their characteristic radiological appearance.
Intraosseous pnematocyst of the right ileum
The patient is a 20-year-old male. An incidental lesion in the right iliac bone was discovered during evaluation after a traffic accident. CT images show a localized low-density area containing gas within the lesion, adjacent to the sacroiliac joint. A sclerotic rim is visible around the lesion, which has clearly defined boundaries. No obvious cortical destruction or fracture signs are observed. There are no significant abnormalities or pathological destruction in the surrounding soft tissue, joint space, or bone structures.
If MRI (if performed) or additional imaging is done, T1 and T2 sequences are often low signal or show gas signal characteristics, consistent with the commonly seen “vacuum phenomenon” or a gas-filled cyst inside the bone.
Considering the patient's young age, the lesion's characteristics, and the normal appearance of the surrounding bone and soft tissue, an intraosseous pneumatocyst is highly suspected.
Taking into account the patient’s age (20 years), the imaging findings of a localized intraosseous gas-filled lesion with clearly defined margins and a surrounding sclerotic rim, as well as the lack of evidence for inflammatory or malignant changes, the most likely diagnosis is “Intraosseous Pneumatocyst” of the Right Iliac Bone.
Since the patient has no significant pain, functional impairment, or systemic discomfort, and the imaging findings are classic, it is clinically considered a benign, asymptomatic incidental finding. If symptoms develop or imaging findings change later, re-examination or further assessment may be warranted.
For asymptomatic or mildly symptomatic intraosseous pneumatocysts, no special intervention is typically required. General recommendations include:
Rehabilitation/Exercise Prescription Recommendations:
For currently asymptomatic or mildly symptomatic patients, exercise mainly aims to maintain joint flexibility and muscle strength. Follow the FITT-VP principles (Frequency, Intensity, Time, Type, Progression, Volume):
If the patient has other skeletal or cardiopulmonary issues, a more conservative approach to increasing activity is recommended, or consultation with a sports medicine or rehabilitation specialist may be advised to develop an individualized plan.
This report is a reference-based medical analysis created from the available data and imaging findings. It is not a substitute for a face-to-face clinical diagnosis or professional medical advice. If there are any concerns or changes in clinical symptoms, please seek medical evaluation and further investigation without delay.
Intraosseous pnematocyst of the right ileum
