Venous thromboembolism: indirect CT venography during CT pulmonary angiography--should the pelvis be imaged?

To retrospectively determine the relative contribution of pelvic and lower-extremity indirect computed tomographic (CT) venography to the diagnosis of venous thromboembolism (VTE) in patients undergoing CT for pulmonary embolism (PE).

This HIPAA-compliant study was approved by the institutional review board, and informed consent was waived. The records of 2074 consecutive patients (890 men, 1184 women; mean age, 59 years; age range, 15-97 years) suspected of having PE who underwent combined CT pulmonary angiography and CT venography between May 2005 and March 2006 were reviewed. CT venograms from the iliac crests to the popliteal fossae were reviewed for presence and location of thrombi. Radiology reports were reviewed for CT pulmonary angiographic results. Thrombus detection rates with and without pelvic CT venography were compared by using the chi(2) test. Separate effective radiation doses for CT venography of pelvis and lower extremities were calculated.

On CT images of the 2074 patients, VTE was detected in 283 (13.6%) patients; PE, in 237 (11.4%); and deep vein thrombosis (DVT), in 121 (5.8%). Forty-six patients had DVT but no PE. Addition of CT venography to CT pulmonary angiography increased the detection of VTE by 19.4% (46 of 237). Isolated pelvic DVT was seen in two (0.1%) patients. There was no difference in the detection of VTE whether or not the pelvis was included (P = .92). Effective radiation dose for CT venography was 5.2 mSv +/- 0.5 (standard deviation) for the pelvis and 0.6 mSv +/- 0.2 for the lower extremities.

CT venography of the pelvis during CT pulmonary angiography does not significantly improve the detection of VTE. CT venography may be limited to the lower extremities, thus reducing radiation dose.