Identifying the Cause of Unilateral Hypoperfusion in Patients Suspected to Have Chronic Pulmonary Thromboembolism:Diagnostic Accuracy of Helical CT and Conventional Angiography

PURPOSE: To determine the prevalence of unilateral hypoperfusion in patients suspected to have chronic thromboembolism (CTE), to identify the most common cause of hypoperfusion, and to compare the accuracy of helical computed tomographic (CT) angiography with that of conventional angiography in helping to determine the cause. MATERIALS AND METHODS: Radionuclide lung scan reports showed asymmetric hypoperfusion in 47 of 410 consecutive patients referred because of suspected CTE. Twenty-seven patients had unilateral or predominantly unilateral perfusion abnormalities. Each pulmonary angiogram and CT angiogram in these patients was interpreted independently by two readers blinded to clinical information and surgical outcome. Surgical confirmation of the diagnosis was available in 39 of the 47 patients with asymmetric hypoperfusion. RESULTS: Unilateral (n = 11) or predominantly unilateral hypoperfusion (n = 16) was found in 6.6% (27 of 410 patients) of patients referred, and CTE was the most common cause. The accuracies of CT angiogram readers (reader 1, 83%; reader 2, 89%) were greater than those of conventional angiogram readers (reader 1, 73%; reader 2, 65%) for distinguishing CTE from other causes. CONCLUSION: Unilateral hypoperfusion occurred in 6.6% of our study population, most frequently because of CTE. CT angiography is an excellent diagnostic alternative to conventional angiography for distinguishing patients with CTE from those with other causes.