Objective: The purpose of this study was to evaluate the features of sigmoid volvulus on CT scanograms and cross-sectional images.
Materials and methods: We retrospectively reviewed 21 cases of sigmoid volvulus in 15 men and six women. Three radiologists evaluated scanograms and cross-sectional images for several classic and two novel imaging signs of volvulus: crossing sigmoid transitions (called the X-marks-the-spot sign) and folding of the sigmoid wall by partial twisting (called the split-wall sign). A general impression was assigned to scanograms and cross-sectional images. CT findings suggesting bowel compromise were compared with pathologic and endoscopic findings.
Results: The most sensitive scanogram findings were absence of rectal gas (19 of 21 cases, 90%) and an inverted-U-shaped distended sigmoid (18 of 21 cases, 86%) followed by the coffee bean sign and disproportionate sigmoid enlargement (both 16 of 21 cases, 76%). The most sensitive cross-sectional findings were one sigmoid colon transition point (20 of 21 cases, 95%) and disproportionate enlargement of the sigmoid (18 of 21 cases, 86%). The X-marks-the-spot and split-wall signs were present in nine of 21 (43%) and 11 of 21 (52%) patients, but one of the two signs was present in 18 of 21 patients (86%). Classic radiographic and definitive cross-sectional findings were seen in 11 of 21 (52%) and 16 of 21 (76%) patients. CT findings were definitive in five of seven patients (71%) with indeterminate scanogram findings. Imaging signs suggesting bowel compromise correlated poorly with clinical ischemia, but CT features were present in all three patients with frank necrosis.
Conclusion: Sigmoid volvulus has a spectrum of imaging findings. A classic appearance is absent on approximately one half of scanograms and one fourth of CT scans. Use of new signs that model the pathophysiologic characteristics of volvulus (X-marks-the-spot sign for more complete twisting and split-wall sign for less severe twisting) may improve diagnostic confidence.