Abdominal Aortic Aneurysm:

Intervention or Conservative Management?

Patient History

The patient is a 76 year old male with a large AAA and intraperitoneal spread of colon cancer. The threshold diameter for elective repair, given his underlying condition, should be substantially greater than in an otherwise healthy patient. Standard two dimensional analysis could not determine whether this aneurysm was tortuous, and 6 cm in diameter, or eccentric, and 8 cm. Both extremes have been reported in recent CT examinations of this patient.

Consecutive 5 mm x 2 mm helical CT images are obtained through the abdominal aorta, and the diameter of the aneurysm is measured. The diameter was reported to be 6 x 8 cm, through the long ("A") and short ("B") axes.

Serial CT examinations reported that the aneurysm begins "just below" the renal arteries. From standard transverse images, it is unclear whether there is a sufficient "neck" to clamp the aorta above the aneurysm but below the renal arteries during repair.

Consecutive 5 mm x 2 mm helical CT images are obtained through the abdominal aorta.

Suspicion of suprarenal extension requires the surgeon to cross-clamp the aorta above the renal arteries, a technically more demanding procedure with increased operative morbidity and mortality. Incorrect assessment may alter the operative approach and increase the surgical risk for the patient.

Contribution of Volumetric Imaging to Case Outcome

Volumetric analysis of the aneurysm revealed that uncertainties of measurement were due to a combination of tortuosity and eccentricity. The greatest orthonormal diameter (6.7 cm), as determined by volumetric analysis.

Vessel tortuosity and tubular eccentricity degrade accuracy of standard two-dimensional measurements. Volumetric analysis allows examination perpendicular to the true centerline of the aneurysm, avoiding such errors.

Combined information from shaded surface display (SSD) and oblique coronal sections demonstrated an adequate neck for clamping below the renal arteries. This allows the surgeon an optimal approach, reducing operative time and surgical risk.

Shaded surface displays and multiplanar reformatting provided information not available, even in retrospect, from standard transverse two-dimensional images.

Volumteric Tools Applied

Movies

Original Reconstructed Helical CT data set

The original trans axial, 79 slice, 5mm thick Toshiba Helical CT data set of a patient with an abominal aortic aneurysm reconstructed with a 1:1 pitch at 2mm increments. No contrast was administered. Note: this scan could have been improved by instucting the patient not to breath during the scan. To obtain a good volumetric scan, instructing the patient not to move and not to breath is extremely important.

Shaded Surface Display (SSD)

Shaded Surface Displays (SSDs) are often useful to surgeons to gain preoperative knowledge about the aneurysm and its relationship to other important structures. Accurate depiction is dependent upon the accurate segmentation of the outer wall of the aneurysm and associated vessels.

Last modified: Tue Jun 1 13:44:51 CDT