Large ascending abdominal aortic aneurysm (AAA) in 82-year-old woman with history of lung cancer. Uniform physiologic 18F-FDG uptake is seen within lumen of aortic aneurysm on PET. Image source: J Nucl Med 2011;52:1–4.

In 1.7 percent of patients, aneurysm was found incidentally on PET/CT, and thrombus was present in 44 percent of these cases, according to a study in the September issue of the Journal of Nuclear Medicine. The overall prognosis for any cancer may be worsened by concurrent thrombosis, according to the study authors.

The most common type of aneurysm seen on PET/CT studies, the abdominal aortic aneurysm (AAA), is one that reaches an anteroposterior diameter of 3.0 cm. However, the incidence of AAA in the cancer population is not well known. The risk of rupture is greater in larger AAAs because they expand more rapidly than smaller AAAs, and a thrombus that is growing also has a greater risk of rupture, according to the study authors.

“[M]any incidental PET/CT findings have proven to be clinically significant,” they wrote. “Identifying asymptomatic patients and intervening before a major event continues to be a major concern.”

To evaluate the incidence of aneurysm and the frequency of thrombus within an aneurysm on unenhanced 18F-FDG PET/CT studies, Razi Muzaffar, MD, of the division of nuclear medicine at Saint Louis University in St. Louis, and colleagues reviewed 1,540 consecutive 18F-FDG PET/CT scans from 926 patients who were scanned because of known or suspected cancer. A log recorded whether each case of aneurysm had a suspected thrombus.

An aneurysm was found incidentally in 16 of the 926 patients, with 15 occurring in the abdominal aorta and one in the internal jugular vein. Seven of these 16 patients had shown suggestions of thrombus on unenhanced PET/CT, and in all seven, thrombi were confirmed on contrast-enhanced CT.

“The use of 18F-FDG PET has been gaining momentum in the diagnosis, staging and restaging of many cancers and is often better than anatomic imaging alone,” Muzaffar and colleagues wrote. “[E]ven in the absence of contrast enhancement, useful information can be gained by a skilled reader for 18F-FDG-avid or non-18F-FDG-avid abnormalities.”

To the best of the authors’ knowledge, this study was the first to determine the incidence of aneurysm in a population of cancer patients who underwent PET/CT.

Muzaffar et al wrote that their data suggest that one out of every 50 oncologic PET/CT studies will show an aneurysm, and about half of these will contain a thrombus.

Thus, the researchers concluded that “an incidental finding of 18F-FDG uptake within an aneurysm with a relatively cold area within the vessel is highly suggestive of a thrombus and requires further evaluation. These findings usually alter the prognosis and treatment of venous thrombosis and may do so for arterial aneurysmal thrombosis as well.”