Conrad Wittram, MB, ChB ; Michael M. Maher, MD ; Albert J. Yoo, MD ; Mannudeep K. Kalra, MD ; Jo-Anne O. Shepard, MD ; Theresa C. McLoud, MD
1 From the Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Founders Building 202, 55 Fruit St, Boston, MA 02114. Recipient of a Certificate of Merit award for an education exhibit at the 2003 RSNA scientific assembly. Received January 13, 2004; revision requested March 10 and received April 16; accepted April 16. All authors have no financial relationships to disclose.
Computed tomographic (CT) pulmonary angiography is becoming the standard of care at many institutions for the evaluation of patients with suspected pulmonary embolism. This pathologic condition, whether acute or chronic, causes both partial and complete intraluminal filling defects, which should have a sharp interface with intravascular contrast material. In acute pulmonary embolism that manifests as complete arterial occlusion, the affected artery may be enlarged. Partial filling defects due to acute pulmonary embolism are often centrally located, but when eccentrically located they form acute angles with the vessel wall. Chronic pulmonary embolism can manifest as complete occlusive disease in vessels that are smaller than adjacent patent vessels. Other CT pulmonary angiographic findings in chronic pulmonary embolism include evidence of recanalization, webs or flaps, and partial filling defects that form obtuse angles with the vessel wall. Factors that cause misdiagnosis of pulmonary embolism may be patient related, technical, anatomic, or pathologic. The radiologist needs to determine the quality of a CT pulmonary angiographic study and whether pulmonary embolism is present. If the quality of the study is poor, the radiologist should identify which pulmonary arteries have been rendered indeterminate and whether additional imaging is necessary.