In patients with tortuous aortas due to aging or atherosclerotic disease, measurements of aneurysm on axial images can lead to falsely elevated aneurysm diameters. Figure 65.1 shows an axial CT image of the ascending thoracicaorta in a 64-year-old woman, which measured 3.9cm. However, when the aneurysm is evaluated on double oblique, sagittal, and coronal multiplanar reformatted images (MPRs), it becomes apparent that the actual size is 3.5cm. The thoracic aorta has a candycane configuration, which may necessitate measurements using MPRs to accurately determine the cross-sectional diameter. Similarly, Figure 65.2 shows a 64-year-old man with an abdominal aortic aneurysm, the course ofwhich is not entirely perpendicular to the z-axis of the scan. Accordingly, to accurately determine the diameter, themeasurements must be made on MPRs tailored to reflect the actual cross-sectional diameter perpendicular to the aorticcenterline. Importance One of the primary roles of CT in the patient with aortic aneurysm is aneurysm measurement, asthe risk of rupture directly correlates with aneurysm size. Surgical thresholds have been defined based on anatomic segment. For the ascending thoracic aorta it is 5.5cm, for descending thoracic aorta 6.5cm, and for abdominal aorta 5.5cm. Serial imaging is critical to evaluate for rate of growth, an additional risk factor that reflects an increased risk of rupture. Aneurysms that grow more than 5–7mm in 6 months or 1cm in one year are considered rapidly enlarging and may warrant repair. Accordingly, accurate methods of measurement are critical to patient management. As shown in this case, axial CT images should not be relied upon for thoracic aortic and abdominal aortic aneurysm measurements. Tortuosity of the aorta results in a course that is no longer directly perpendicular to the axial plane. In these cases, MPRs or 3D renderings are required to generate accurate bi-dimensional aneurysm measurements orthogonal tothe aortic lumen centerline. Either manual double oblique MPRs or short-axis images generated from software-based automated centerline tracking are recommended for the most reliable aneurysm measurement.
|Original language||English (US)|
|Title of host publication||Pearls and Pitfalls in Cardiovascular Imaging|
|Subtitle of host publication||Pseudolesions, Artifacts and Other Difficult Diagnoses|
|Publisher||Cambridge University Press|
|Number of pages||3|
|State||Published - Jan 1 2015|
ASJC Scopus subject areas