Analysis of the early signs of septic sacroiliitis on computed tomography

Septic sacroiliitis is a difficult diagnosis rarely considered in an emergency in case of pelvic pain associated with fever. In these cases, a computed tomography (CT) is classically performed to exclude digestive or gynecological disorder, but the sacroiliac joint is not systematically analyzed. The aim of the present study was to detect the early signs of septic sacroiliitis on CT.

In a monocentric retrospective study, the characteristics, biology, and imaging of patients with septic sacroiliitis were analyzed.

Seven cases of septic sacroiliitis were included in the study. For all patients, a CT scan with contrast-enhanced acquisitions of the pelvis was performed. The 4 early signs of septic sacroiliitis frequently not evocated by a radiologist in an emergency were highlighted as follows: fat infiltration in front of the sacroiliac joint (83%), anterior bulging of the sacroiliac capsule (46%), and piriformis and iliac muscles swelling (71% for both). All patients had at least one of these signs; 86% had at least 2 signs. Magnetic resonance imaging was performed for 5 out of 7 patients and confirmed the aspect of infectious sacroiliitis.

Systematic analysis of the sacroiliac joint and adjacent muscles on pelvic CT scan is necessary to avoid the unrecognition of septic sacroiliitis in case of pelvic pain with fever.