[Usefulness of dynamic computed tomography in the diagnosis of thoracic aortic aneurysms]

Five patients with thoracic aortic aneurysms, two saccular and three dissecting aneurysms, were examined by dynamic computed tomographic (CT) scanning. A Siemens Somatom 2 was employed. Dynamic scanning is the method by which plural serial images can be obtained in single operation. We used three serial images in a 5-second scan following a 3-second interval. After rapid manual injection of 30 ml of 76% megluminc amidotrizoate sodium into the right antecubital vein, scans of 4 mm section were performed three times and subsequently conventional scans four times. Serial changes in the same section and changes in the CT number against time in regions of interest in the image were investigated. Saccular aneurysms was difficult to distinguish from mediastinal tumors on the plain chest X-ray films. However, it was confirmed by the dynamic CT scanning demonstrating free communication between the aorta and the abnormal lumen, because the latter was filled with contrast medium, and the time of appearance, and the peak and washout of a contrast medium were almost the same between two lumens. In dissecting aneurysms, it was able to recognize both the false and true lumens as double channels in the aorta. We observed the different mode of dissection between the ascending and descending aorta in one case, and observed the twisting of an intimal flap in variable parts of the aorta in another case. Furthermore, it was possible to confirm the difference of blood flow pattern between the false and true lumens by dynamic CT. Because CT has a high quality image resolution, and especially, dynamic CT provides the serial changes in the same section after injection of contrast medium, both CT and dynamic CT are useful non-invasive imaging techniques for evaluating thoracic aortic aneurysms.