Misdiagnosis is a commonality when it comes to posterior inferior cerebellar artery aneurysms (PICAAs), but using thin, axial CT images for diagnosis could be a more effective and accurate option than depending on 3D volume rendering (VR) images, researchers have reported in Academic Radiology.

PICA aneurysms are relatively rare, accounting for just 0.5 percent to 1 percent of all intracranial aneurysms, but the nature of the condition means re-rupturing is easy after the acute phase of a first-time hemorrhage, lead author Yuan Zhang, MD, and colleagues wrote. The process can move quickly and result in death.

“Although the posterior inferior cerebellar artery is the last and largest branch of vertebral artery, its thin lumen makes it difficult to be shown on VR images of computed tomography angiography (CTA) under conventional or standard protocols,” Zhang et al. said. “The PICA aneurysm (PICAA), especially distal PICAA, is easily missed by a doctor, leading to misdiagnosis and treatment delays.”

The authors wrote that in their routine work at a Chinese hospital, they noticed most cases of PICAA were missed with CTA diagnosis, even if doctor diagnosis was correct. In an effort to assess the overall utility of CT angiography when it comes to PICAA—including the reasons CT imaging seems to misdiagnose the condition so regularly—the researchers reviewed 30 cases of confirmed PICAA within a six-year period.

The majority of patients enrolled for the study suffered subarachnoid hemorrhages alone. Five cases had both subarachnoid hemorrhage and cerebellar hematoma, and four cases presented neither condition and were discovered by chance.

Zhang and co-authors found that in 40 percent of patients with aneurysms, the exam lied on the proximal end of the posterior inferior cerebellar artery, though those same 12 cases of PICAA were displayed clearly in VR images of CTA and correctly diagnosed by doctors. Eighteen cases of aneurysm lied on the distal part of PICA, the researchers said, but only two were displayed on VR images and correctly diagnosed prior to surgery.

Post-op, Zhang’s team reviewed CTA images, determining that all aneurysms can be found on the thin axial images after “careful observation,” and are shown on VR images after adjusting the display threshold.

“Overdependence on three-dimensional VR images of CTA is the main cause of misdiagnosis,” the authors wrote. Thin axial CT images are most important and reliable for the detection of distal PICAA.”