Sacroiliac joint vacuum phenomenon—underreported finding

Background and purposeVacuum phenomenon (VP) is commonly found in sacroiliac joints, and its significance in patients with back pain has been debated. We investigated the prevalence of sacroiliac joint vacuum phenomenon (SJVP) and the rate at which it is reported on abdominopelvic and lumbosacral spine computed tomography (CT) images by body imagers and neuroradiologists. We hypothesized that it would be more common than not and that neuroradiologists would identify it more frequently than body imagers and on spine images more commonly than abdominopelvic studies due to the search for the source of back pain in the former.Materials and methodsCT images of the pelvis and lumbar spine from January to February 2009 were retrospectively reviewed. Six hundred fifty-two patients were studied during this period. Axial thin-section images were reviewed under default lung and bone window settings. Age, sex, and radiologist reports were assessed from electronic medical records.ResultsThe prevalence of SJVP on CT imaging was 34%, with higher rates found in female (41%, P<.001) and older (39%, P<.05) patients. Eighty-five percent of the phenomena were present bilaterally. Among the 223 patients with SJVP, only 17% were reported. There were no statistically significant differences between reporting rates for body radiologists and neuroradiologists.ConclusionSJVP is a prevalent condition with higher rates among older and female individuals. The phenomenon is underreported on CT images whether the studies performed are abdominopelvic scans or spine studies and whether they are interpreted by body imagers or neuroradiologists.