Radiology: Digital subtraction CTA gets high marks for assessing intracranial aneurysms

One true-positive aneurysm in 62-year-old woman. Volume-rendered digital subtraction CT angiographic image. Source: Radiology

Digital subtraction CT angiography (CTA) should be the preferred noninvasive modality for evaluating intracranial aneurysms given the fact it has a high sensitivity and specificity, and is less invasive and time-consuming than 3D rotational digital subtraction angiography (DSA), according to a study published in the February issue of Radiology.

Approximately four in every five subarachnoid hemorrhages are caused by ruptured intracranial aneurysms, according to the study’s background information. In the U.S., it is estimated there are 27,000 to 30,000 annual cases of subarachnoid hemorrhage as a result of ruptured aneurysms. DSA is the standard for detecting intracranial aneurysms, but study author Guang Ming Lu, MD, of Nanjing University in Nanjing, China, and colleagues noted that improvements in multidetector CT techniques have led some institutions to use multidetector CTA in place of DSA.

To evaluate the diagnostic accuracy of the two approaches, the researchers conducted a retrospective study of 513 patients with suspected or known intracranial aneurysms and who underwent both digital subtraction CTA and 3D DSA.

Results showed that 79.3 percent of the patients had at least one aneurysm at 3D DSA. Digital subtraction CTA correctly depicted 99.3 percent of the aneurysms, and using 3D DSA as the standard of reference, the sensitivity of depicting intracranial aneurysms on a per-patient and per-aneurysm basis was 97.8 and 96.5 percent, respectively. Specificity was 88.7 percent on a per-patient basis and 87.8 percent on a per-aneurysm basis.

“Digital subtraction CTA had a sensitivity of greater than 90 percent, even in depicting aneurysms less than 3 mm in diameter,” wrote the authors. “To our knowledge, this is the largest cohort of patients in whom CT angiography for depicting intracranial aneurysms was compared with 3D DSA as the reference standard.”

The authors warned of weaknesses to both approaches based on some observed false results. Despite the 91.3 percent sensitivity for digital subtraction CTA in depicting aneurysms less than 3 mm, the authors found one overlooked aneurysm and said smaller aneurysms and those in uncommon locations can be easily overlooked at the initial CTA evaluation.

A false-positive based on 3D DSA findings was also diagnosed as thrombotic aneurysm at MR imaging and digital subtraction CTA. “This case indicates 3D DSA to be a suboptimal modality for the detection of thrombosed aneurysms,” wrote the authors.

“The detection of [intracranial] aneurysms was considered a challenging issue for multidetector CT angiography because of the presence of overlying bone structures and the complex vascular anatomy. However, in recent years, CT technology has been advancing rapidly…Digital subtraction CT angiography is becoming a choice in the detection of ruptured intracranial aneurysms and planning of therapeutic interventions,” the researchers concluded.