Nonaneurysmal perimesencephalic subarachnoid hemorrhage: CT and MR patterns that differ from aneurysmal rupture

Area of Science:

• Neuroradiology
• Neurology
• Medical Imaging

Background:

• Subarachnoid hemorrhage (SAH) can originate from aneurysms or other causes.
• Nonaneurysmal perimesencephalic hemorrhage (NAPH) presents a unique cisternal blood distribution.
• Distinguishing NAPH from aneurysmal SAH is crucial for prognosis and management.

Purpose of the Study:

• To determine if the characteristic CT pattern of NAPH can reliably differentiate it from aneurysmal SAH.
• To assess the diagnostic accuracy and interobserver agreement for identifying NAPH on CT scans.

Main Methods:

• Retrospective review of 221 CT scans from patients with SAH who underwent angiography.
• Two neuroradiologists independently evaluated CT scans for the perimesencephalic hemorrhage pattern.
• Analysis of the predictive value of the CT pattern for a normal angiogram and interobserver agreement.

Main Results:

• A characteristic cisternal blood distribution anterior to the brainstem was observed in NAPH patients.
• The perimesencephalic CT pattern showed high predictive value for a normal angiogram (0.95 and 0.94).
• Excellent interobserver agreement (kappa 0.87) was achieved in identifying the NAPH pattern.

Conclusions:

• The perimesencephalic hemorrhage pattern on early CT scans is a reliable indicator of nonaneurysmal SAH.
• Recognition of this pattern is vital for accurate diagnosis and prognostication.
• Patients with NAPH identified by CT have an excellent prognosis, avoiding unnecessary aggressive interventions.