Study Supports Less-Strict Monitoring for Nonaneurysmal Perimesencephalic SAH Without Hydrocephalus

Digital subtraction angiography remains central to assessment of ‘benign’ PMSAH

brain scan showing perimesencephalic subarachnoid hemorrhage

Evaluation with digital subtraction angiography (DSA) to assess “benign” perimesencephalic subarachnoid hemorrhage (PMSAH) is still warranted in addition to computed tomography angiography (CTA) in the search for an underlying ruptured aneurysm. After complete assessment, a patient with nonaneurysmal PMSAH without hydrocephalus can be managed with a shorter hospital stay and less strict monitoring, as clinical outcomes tend to be favorable.


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So concluded Cleveland Clinic investigators after analysis of a 15-year institutional series of 81 patients with PMSAH, the largest published series of its kind that included patients within the last decade. It recently appeared in Stroke: Vascular and Interventional Neurology (Epub 2024 Feb 19)

“In our series, 6.2% of patients had an underlying ruptured aneurysm, more than half of which were detected only by DSA,” says Cleveland Clinic interventional neurologist Gabor Toth, MD, the study’s senior and corresponding author. “Although the number was small, consequences of an occult ruptured aneurysm can be grave, justifying the continued need for this conventional and more invasive test.”

Evaluating and managing PMSAH — unresolved issues

PMSAH is commonly referred to as benign because a source of bleeding often cannot be identified and recovery is usually uncomplicated. But in rare cases, an initially undetected ruptured aneurysm is the culprit. Investigation usually begins with CTA, often followed by DSA — a more invasive test considered to be the gold standard for detecting an intracranial vascular lesion. As CTA technology has advanced, the need for DSA investigation has been called into question.

Another controversy surrounding PMSAH is how intensively patients must be observed when no underlying ruptured aneurysm is found. The importance of other findings, such as vasospasm and hydrocephalus, is poorly understood. When vasospasm or hydrocephalus is symptomatic, patients may be hospitalized for extended times for monitoring and treatment.

This retrospective study was designed to help shed light on these issues by analyzing presentation, imaging findings and outcomes in a large series of patients with PMSAH.

Cohort characteristics and outcomes

The series consisted of 81 patients with PMSAH treated at Cleveland Clinic from 2007 to 2022. Mean age was 55.5 ± 10.3 years.

All patients had a baseline noncontrast head CT, CTA and DSA. CT was repeated for clinical deterioration. DSA was repeated for clinical deterioration or if vasospasm had been diagnosed. If no underlying ruptured aneurysm was detected by initial angiogram, repeat DSA was done after 7 to 10 days.

An underlying ruptured aneurysm was diagnosed in a total of five patients (6.2%). Of these, the aneurysm was detected only by DSA in three patients (3.7%) (two on the initial DSA and one on follow-up).

All aneurysms identified were in the posterior circulation (four were in the vertebrobasilar system and one was on the posterior communicating artery); four were saccular and one was a dissecting pseudoaneurysm. All aneurysms were small (< 5 mm in size).

Complications among the 81 patients included the following:

  • Vasospasm was seen in 31% of all patients, and most cases (84%) were asymptomatic. Symptomatic vasospasm was present in 40% of patients with underlying ruptured aneurysm versus only 2.6% of patients with nonaneurysmal PMSAH (P = .01).
  • Hydrocephalus was seen in 10% of all patients, and all cases were symptomatic and detected within one day. The presence of hydrocephalus trended higher in patients with underlying ruptured aneurysm (40%) versus others (8%) (P = .07).


The primary end point was favorable functional status at discharge, defined as a score of 0 to 2 on the modified Rankin scale, indicating no to slight disability. It was achieved by 40% of those with an underlying ruptured aneurysm versus 91% of those with nonaneurysmal PMSAH (P = .01).

Unfavorable clinical outcomes were associated with the following:

  • An underlying ruptured aneurysm (odds ratio [OR] = 14.7 [2.1 to 104]; P = .007)
  • Acute hydrocephalus (OR = 22.6 [4.2 to 123.5]; P < .001)
  • Symptomatic vasospasm (OR = 8.6 [1.1 to 69.9]; P = .04)

All patients who had asymptomatic vasospasm alone without underlying ruptured aneurysm achieved favorable outcomes.

Clinical applications

Dr. Toth emphasizes that this study provides support for two major practices in the assessment and care of patients with apparently benign PMSAH:

  • Without an underlying ruptured aneurysm or hydrocephalus, patients can be managed with less-strict monitoring and earlier hospital discharge, which may have a significant impact on patient comfort and healthcare costs. Although symptomatic vasospasm was associated with poorer outcomes, it was a very rare phenomenon in nonaneurysmal PMSAH, occurring in only two patients.
  • Complete diagnostic investigation should continue to include DSA. This series found that an underlying ruptured aneurysm was detected only with DSA in three out of five patients with aneurysmal PMSAH.

Dr. Toth adds that several baseline patient factors were significantly associated with having an underlying ruptured aneurysm: being a smoker, having a higher score on the Hunt and Hess scale, and having a higher modified Fisher grade. “For patients with such a profile, it is especially important to thoroughly investigate with DSA,” he notes.

He adds that there is currently insufficient evidence to forgo DSA in this patient population. “Unless the aneurysm detection rate with CTA reaches 100%, missing even one or two real aneurysms is a major concern with potentially life-threatening consequences,” Dr. Toth concludes.


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