Distinguishing pelvic phleboliths from distal ureteral stones on routine unenhanced helical CT: is there a radiolucent center?

OBJECTIVE: On radiographs of the abdomen and pelvis, phleboliths often have a characteristic radiolucent center that helps to distinguish them from ureteral stones. On unenhanced CT, the distinction between pelvic phleboliths and distal ureteral stones can be problematic. The objective of this study was to compare the appearance of phleboliths on routine clinical CT studies with their appearance on radiography and to determine if the radiolucent center seen on radiographs is revealed on CT. SUBJECTS AND METHODS: During a 3-month interval, we identified 50 patients with acute flank pain who underwent both unenhanced CT and abdominal radiography. Patients with a radiograph of the pelvis and an unenhanced CT scan obtained within 1 month of each other were included. CT was performed with a collimation of 5 mm and a pitch of 1. Each phlebolith was examined using soft-tissue and bone settings and was also retrospectively pixel mapped. RESULTS: Seventy-nine (66%) of 120 phleboliths revealed radiolucent centers on abdominal radiography. On CT, 119 (99%) of 120 phleboliths failed to reveal a low-attenuation center on both visual inspection and pixel mapping. CONCLUSION: Pelvic phleboliths were shown to lack a radiolucent center on routine clinical CT examinations despite their appearance on radiography. A radiolucent center therefore cannot be used to differentiate phleboliths from distal ureteral stones on unenhanced CT in patients with acute flank pain and suspected ureteral obstruction.