Perimesencephalic Nonaneurysmal Subarachnoid Hemorrhage Research Articles

Aneurysmal Versus “Benign” Perimesencephalic Subarachnoid Hemorrhage

Background The rate of underlying ruptured aneurysms, complications, and their relevance to outcomes in “benign” perimesencephalic subarachnoid hemorrhage are not well known and underreported. Methods Retrospective analysis of patients with perimesencephalic subarachnoid hemorrhage from a large tertiary care center (2007–2022). Results Eighty‐one patients were included with mean age of 55.5 ± 10.3 years. An underlying ruptured aneurysm was diagnosed in 5 patients (6.2%); 3 (60%) had negative computed tomography angiography and they were detected only in digital subtraction angiography (2 on initial digital subtraction angiography and 1 on follow‐up digital subtraction angiography). The most common complication was vasospasm in 25/81 patients (31%), and the majority 21/25 (84%) were asymptomatic. Symptomatic vasospasm occurred at a significantly higher rate among patients with underlying aneurysm (40% versus 2.6%; P = 0.01). Hydrocephalus occurred in 10% of patients, all within 1 day, but at a higher rate in the aneurysmal group (40% versus 8%; P = 0.07). A total of 88% of patients had modified Rankin scale score 0–2 at discharge, but at a significantly higher rate in nonaneurysmal patients (91% versus 40%; P = 0.01). An underlying aneurysm, hydrocephalus, and symptomatic vasospasm were associated with poor functional status (odds ratio [OR] = 14.7 [2.1–104]; P = 0.007, OR = 22.6 [4.2–123.5]; P <0.001, OR = 8.6 [1.06–69.88]; P = 0.04), respectively. Conclusion “Benign” perimesencephalic subarachnoid hemorrhage pattern was associated with a ruptured aneurysm in 6.2% of patients, and 3.7% were detected only on cerebral angiogram. Underlying aneurysm, symptomatic vasospasm, and hydrocephalus were associated with lower rates of good clinical outcome. All hydrocephalus cases were symptomatic and occurred very early. Asymptomatic vasospasm alone was not associated with poor outcomes. Our findings suggest that patients with nonaneurysmal perimesencephalic subarachnoid hemorrhage without hydrocephalus can safely be managed with less strict monitoring and a shorter hospital stay.

Nonaneurysmal perimesencephalic subarachnoid hemorrhage on noncontrast head CT: An accuracy, inter-rater, and intra-rater reliability study

Background and purposeTo evaluate the reliability and accuracy of nonaneurysmal perimesencephalic subarachnoid hemorrhage (NAPSAH) on Noncontrast Head CT (NCCT) between numerous raters. Materials and methods45 NCCT of adult patients with SAH who also had a catheter angiography (CA) were independently evaluated by 48 diverse raters; 45 raters performed a second assessment one month later. For each case, raters were asked: 1) whether they judged the bleeding pattern to be perimesencephalic; 2) whether there was blood anterior to brainstem; 3) complete filling of the anterior interhemispheric fissure (AIF); 4) extension to the lateral part of the sylvian fissure (LSF); 5) frank intraventricular hemorrhage; 6) whether in the hypothetical presence of a negative CT angiogram they would still recommend CA. An automatic NAPSAH diagnosis was also generated by combining responses to questions 2–5. Reliability was estimated using Gwet's AC1 (κG), and the relationship between the NCCT diagnosis of NAPSAH and the recommendation to perform CA using Cramer's V test. Multi-rater accuracy of NCCT in predicting negative CA was explored. ResultsInter-rater reliability for the presence of NAPSAH was moderate (κG = 0.58; 95%CI: 0.47, 0.69), but improved to substantial when automatically generated (κG = 0.70; 95%CI: 0.59, 0.81). The most reliable criteria were the absence of AIF filling (κG = 0.79) and extension to LSF (κG = 0.79). Mean intra-rater reliability was substantial (κG = 0.65). NAPSAH weakly correlated with CA decision (V = 0.50). Mean sensitivity and specificity were 58% (95%CI: 44%, 71%) and 83 % (95%CI: 72 %, 94%), respectively. ConclusionNAPSAH remains a diagnosis of exclusion. The NCCT diagnosis was moderately reliable and its impact on clinical decisions modest.

Management of perimesencephalic nonaneurysmal subarachnoid hemorrhage: a national survey

Perimesencephalic nonaneurysmal subarachnoid hemorrhage (NASAH) is a rare type of subarachnoid hemorrhage (SAH), usually associated with minor complications compared to aneurysmal SAH. Up to date, data is scarce and consensus on therapeutic management and follow-up diagnostics of NASAH is often missing. This survey aims to evaluate the clinical management among neurosurgical departments in Germany. 135 neurosurgical departments in Germany received a hardcopy questionnaire. Encompassing three case vignettes with minor, moderate and severe NASAH on CT-scans and questions including the in-hospital treatment with initial observation, blood pressure (BP) management, cerebral vasospasm (CV) prophylaxis and the need for digital subtraction angiography (DSA). 80 departments (59.2%) answered the questionnaire. Whereof, centers with a higher caseload state an elevated complication rate (Chi2 < 0.001). Initial observation on the intensive care unit is performed in 51.3%; 47.5%, 70.0% in minor, moderate and severe NASAH, respectively. Invasive BP monitoring is performed more often in severe NASAH (52.5%, 55.0%, 71.3% minor, moderate, severe). CV prophylaxis and transcranial doppler ultrasound (TCD) are performed in 41.3%, 45.0%, 63.8% in minor, moderate and severe NASAH, respectively. Indication for a second DSA is set in the majority of centers, whereas after two negative ones, a third DSA is less often indicated (2nd: 66.2%, 72.5%, 86.2%; 3rd: 3.8%, 3.8%, 13.8% minor, moderate, severe). This study confirms the influence of bleeding severity on treatment and follow-up of NASAH patients. Additionally, the existing inconsistency of treatment pathways throughout Germany is highlighted. Therefore, we suggest to conceive new treatment guidelines including this finding.

A Case of Quadrigeminal Variant of Perimesencephalic Nonaneurysmal Subarachnoid Hemorrhage

AbstractThe incidence of perimesencephalic subarachnoid hemorrhage (PMSAH) is rare, 0.5 in 100,000 adults. It comprises 5 to 10% of all SAHs and approximately 33% of all nonaneurysmal SAH. Quadrigeminal SAH is a variant of perimesencephalic nonaneurysmal subarachnoid hemorrhage (PMNASAH) that is not well described in the literature. It may comprise up to one-fifth of PMNASAH cases and carries a similar benign prognosis. This variant of PMSAH is characterized by blood centered in the quadrigeminal cistern and limited to the superior vermian and posterior perimesencephalic cisterns. Noncontrast computed tomography of the brain is the initial investigation of choice, while four-vessel cerebral angiogram is the gold standard for the diagnosis of SAH.We report a case at our institute.

Non-Traumatic Non-Aneurysmal Perimesencephalic Subarachnoid Hemorrhage as a Primary Presentation of Acute Myeloid Leukemia: an Uncommon Case Report

Non-Traumatic Non-Aneurysmal Perimesencephalic Subarachnoid Hemorrhage as a Primary Presentation of Acute Myeloid Leukemia: an Uncommon Case Report

Current status of perimesencephalic non-aneurysmal subarachnoid hemorrhage.

Perimesencephalic nonaneurysmal subarachnoid hemorrhage (PNSAH) is a distinctive disease, representing SAH centered in perimesencephalic cisterns, with negative angiography findings. In recent years, the number of patients with PNSAH has increased significantly; however, the knowledge of PNSAH is insufficient. Therefore, we performed a review of the literature from a PubMed search and recounted our understanding of PNSAH. In this review, we summarized that current high-resolution computed tomography angiography is an acceptable replacement for digital subtraction angiography to rule out aneurysms in PNSAH with strict criteria. The current hypothesis about the etiology of PNSAH is that there is deep vein rupture from aberrant venous anatomy and increased intracranial venous pressure. PNSAH is associated with mild symptoms and lower rates of hydrocephalus and symptomatic vasospasm. For PNSAH, conservative treatment has been the mainstream treatment. PNSAH has a benign clinical course and an excellent prognosis; in long-term follow-up, re-bleeding and death were uncommon.

Physical exertion as a risk factor for perimesencephalic nonaneurysmal subarachnoid hemorrhage

BackgroundPerimesencephalic and nonperimesencephalic nonaneurysmal subarachnoid hemorrhage (PM‐naSAH and NPM‐naSAH) have a different bleeding pattern and clinical course. The etiology and risk factors for PM‐naSAH and NPM‐naSAH are unclear. The objective of this study was to compare risk factors and triggering events between PM‐naSAH and NPM‐naSAH.MethodsWe reviewed retrospectively all patients (n = 3475) who had undergone cerebral digital subtraction angiography between 2003 and 2020 at our tertiary hospital. Of these, 119 patients had 6‐vessel angiography negative subarachnoid hemorrhage (47 (39%) PM‐naSAH and 72 (61%) NPM‐naSAH) and accurate information about the triggering event was available in 42 (89%) PM‐NASAH and 64 (89%) NPM‐naSAH patients.ResultsPM‐naSAH were younger compared to NPM‐naSAH (mean age [SD]; 55.3 [11.1] years vs. 59.6 [12.2] years, p = .045. PM‐naSAH was triggered during the physical exertion in 79% of patients and 16% of patients with NPM‐naSAH (relative risk 5.4; 95% CI, 2.9‐10.1, p < .0001). There were no significant difference in sex, smoking, alcohol abuse, hypertension, diabetes, hyperlipidemia, or anticoagulation/antithrombotic usage between PM‐naSAH and NMP‐naSAH, p > .05.ConclusionPhysical exertion was a triggering factor in most of the PM‐naSAH cases and the risk was five times greater than in NMP‐naSAH. More studies are needed to confirm our results and to study pathophysiology of PM‐naSAH and NPM‐naSAH.

Baseline characteristics and outcome for aneurysmal versus non-aneurysmal subarachnoid hemorrhage: a prospective cohort study

This study aims to investigate the characteristics of patients with mild aneurysmal and non-aneurysmal perimesencephalic and non-perimesencephalic subarachnoid hemorrhage (aSAH, pmSAH, npmSAH) with emphasis on admission biomarkers, clinical course, and outcome. A prospective cohort of 115 patients with aSAH (Hunt and Hess 1–3) and of 35 patients without aneurysms (16 pmSAH and 19 npmSAH) admitted between January 2014 and January 2020 was included. Demographic data, blood samples on admission, complications (hydrocephalus, shunt dependency, delayed cerebral ischemia DCI, DCI-related infarction, and mortality), and outcome after 6 months were analyzed. Demographic data was comparable between all groups except for age (aSAH 55 [48–65] vs. npmSAH 60 [56–68] vs. pmSAH 52 [42–60], p = 0.032) and loss of consciousness (33% vs. 0% vs. 0%, p = 0.0004). Admission biomarkers showed poorer renal function and highest glucose levels for npmSAH patients. Complication rate in npmSAH was high and comparable to that of aSAH patients (hydrocephalus, shunt dependency, DCI, DCI-related infarction, mortality), but nearly absent in patients with pmSAH. Favorable outcome after 6 months was seen in 92.9% of pmSAH, 83.3% of npmSAH, and 62.7% of aSAH (p = 0.0264). In this prospective cohort of SAH patients, npmSAH was associated with a complicated clinical course, comparable to that of patients with aSAH. In contrast, such complications were nearly absent in pmSAH patients, suggesting fundamental differences in the pathophysiology of patients with different types of non-aneurysmal hemorrhage. Our findings underline the importance for a precise terminology according the hemorrhage etiology as a basis for more vigilant management of npmSAH patients. NCT02142166, 05/20/2014, retrospectively registered.

Non-aneurysmal Perimesencephalic Subarachnoid Hemorrhage in A COVID-19 Patient: Case Report and Review on Subarachnoid Hemorrhage Patterns in COVID-19

Background and Importance: The novel SARS-CoV-2 virus has had an undeniable effect worldwide in different aspects. Although cerebrovascular diseases, especially subarachnoid hemorrhage (SAH), have already been reported in COVID-19 patients, little is known about various types and patterns of SAH in these patients. Case Presentation: A 63-year-old woman was admitted to the emergency department with a headache. Her headache was severe (Hunt and Hess score, grade 2). She was diagnosed with COVID-19 by a positive nasopharyngeal swab PCR test. Her CT scan revealed a perimesencephalic hemorrhage, thick SAH without any signs of hydrocephalus or intraventricular hemorrhage. Conclusion: Regarding the different associations of SAH with COVID-19, the perimesencephalic hemorrhage in our case is a novel type. Although not uncommon among non-infected populations, SAH occurrence in COVID-19 patients has not been reported before and needs further investigation.

Long-term global and focal cerebral atrophy in perimesencephalic subarachnoid hemorrhage-a case-control study.

Non-aneurysmal perimesencephalic subarachnoid hemorrhage (PmSAH) represents 6.8% of spontaneous subarachnoid hemorrhage, and usually has a benign clinical course. However, patients might have early cerebral ischemic lesions and long-term neurocognitive complaints. Cerebral atrophy has been described in patients after aneurysmal SAH, but not in PmSAH. We aimed to investigate if PmSAH associates with increased brain volume loss. In this prospective study, we included consecutive patients with PmSAH that performed MR in the first 10days after hemorrhage, and follow-up MR 6-7years later. Automated volumetric measurements of intracranial, white matter, gray matter, whole brain, lateral ventricles, hippocampus, and amygdala volumes were performed. Volumes were compared to a normal population, matched for age. Eight patients with PmSAH were included, with a mean age of 51.5 (SE 3.6) at baseline. The control group included 22 patients with a mean age of 56.3 (SE 2.0). A relative reduction of all volumes was found in both groups; however, PmSAH patients had significant reductions in intracranial, white and gray matter, whole brain, and hippocampal volumes when compared to controls. These changes had a higher magnitude in whole brain volume, with a significant absolute decrease of 6.5% in PmSAH patients (versus 1.9% in controls), and a trend for an increase in lateral ventricle volume (absolute 21.3% increase, versus 3.9% in controls). Our cohort of PmSAH patients showed significant long-term parenchymal atrophy, and higher global and focal parenchymal volume loss rates when compared to a non-SAH population.

CT perfusion-guided endovascular treatment of symptomatic cerebral vasospasm in a patient with perimesencephalic non-aneurysmal subarachnoid hemorrhage

Symptomatic vasospasm represents an uncommon complication of perimesencephalic nonaneurysmal subarachnoid hemorrhage (SAH) which is a benign form of SAH without any recognizable source of bleeding accounting for about 15% of non-traumatic SAH [1,2].

Persistent primitive hypoglossal artery presenting with perimesencephalic nonaneurysmal subarachnoid hemorrhage: A case report and review of literature

BackgroundPersistent primitive hypoglossal artery (PPHA) is a rare remnant of the congenital carotid-basilar artery anastomosis, sometimes associated with subarachnoid hemorrhage (SAH), and aneurysms are the more common cause. However, the association of PPHA with perimesencephalic nonaneurysmal subarachnoid hemorrhage (PNSAH) is extremely rare. This report is the first to describe the occurrence of PNSAH concerning PPHA. Case descriptionA 53-year-old man suffered from subarachnoid hemorrhage with a sudden severe headache. An emergency brain computed tomography (CT) disclosed a perimesencephalic pattern of SAH. CT angiography (CTA) revealed a right PPHA entering the posterior fossa through the right enlarged hypoglossal canal. No source of the hemorrhage was identified in the imaging examinations, even with the performance of a 4-vessel angiography. ConclusionWe present a case of PPHA associated with PNSAH and review the literature. The main cause for the PPHA related to SAH is an aneurysm. The four vessels angiography helped rule out an aneurysm that is associated with a poorer prognosis and requires immediate active management. It is, therefore, essential for physicians to be aware of the increased incidence of aneurysms in PPHA to make the correct diagnosis.

Central Pontine Myelinolysis After Non-Aneurysmal Perimesencephalic Subarachnoid Hemorrhage: Case Report and Review of the Literature

Central pontine myelinolysis (CPM) is one of the encephalopathy that results from extreme fluctuations in serum sodium concentration and plasma osmolality. CPM after non aneurysmal perimesencephalic subarachnoid hemorrhage (NPSAH) is very rare. A 53-year-old female patient aggravated her instabilty 3 weeks after treatment of after NPSAH. Brain CT showed a prominent low-density lesion in the central pons. Vasospasm, pontine infarct, multiple sclerosis must be excluded after subarachnoid hemorrhage. Her brain magnetic resonance imaging (MRI) of the brainstem revealed CPM. The peripheral fiber sparing, central trident appearance was observed. Peripheral fiber sparing is more prominent, but central trident is disappearing at long-term follow-up MRI. CPM can develop even after NPSAH as well as aneurysmal subarachnoid hemorrhage. Trident pattern in pons area and peripheral fiber sparing is differential diagnosis with vasospasm, cerebral infarct and multiple sclerosis after NPSAH. Keywords: Subarachnoid hemorrhage; Hyponatremia; Central pontine demyelination; Demyelination.

Midterm Follow-Up of 20 Consecutive Patients with Nonaneurysmal Subarachnoid Hemorrhage of Unknown Origin in a Single-Center: Two Cases of De Novo Development of Dural Arteriovenous Fistula

The mechanisms and prognosis of underlying subarachnoid hemorrhage of unknown origin remain unclear. Previous investigators have suggested a relationship between nonaneurysmal perimesencephalic subarachnoid hemorrhage and venous abnormalities like a primitive venous drainage of the basal vein of Rosenthal. We report the outcome of a midterm follow-up of 20 consecutive patients with nonaneurysmal subarachnoid hemorrhage of unknown origin, and 2 patients in whom the development of new dural arteriovenous fistulas after subarachnoid hemorrhage of unknown origin were detected during follow-up. All patients who were admitted to our hospital for nontraumatic subarachnoid hemorrhage between April 2008 and March 2016 were retrospectively analyzed. Of 705 patients included in the study, 20 (2.8%) were diagnosed with nontraumatic subarachnoid hemorrhage of unknown origin. During the follow-up periods, there was no rebleeding. Although 18 patients did not show any vascular abnormalities, the other 2 patients were diagnosed with dural arteriovenous fistula. Both fistulas were successfully treated with endovascular embolization. Subarachnoid hemorrhage of unknown origin had a low incidence rate, and its clinical course was excellent without rebleeding. Although no vascular abnormalities were observed during the patients' initial admission, venous lesions might have been involved in both subarachnoid hemorrhages and delayed dural arteriovenous fistulas. Here, the possible pathogenesis is discussed with a review of the literature.

Delayed Onset Transient Pupillary Involving Third Cranial Nerve Palsy in Perimesencephalic Nonaneurysmal Subarachnoid Hemorrhage (P2.289)

Delayed Onset Transient Pupillary Involving Third Cranial Nerve Palsy in Perimesencephalic Nonaneurysmal Subarachnoid Hemorrhage (P2.289)

Perimesencephalic Hemorrhage: Yield of Single versus Multiple DSA Examinations-A Single-Center Study and Meta-Analysis.

Purpose To quantify the rate of detection of aneurysms at follow-up digital subtraction angiography (DSA) after initial DSA with results negative for aneurysms in subjects with perimesencephalic (PM) nonaneurysmal subarachnoid hemorrhage. Materials and Methods This single-center retrospective study and meta-analysis was approved by the institutional review board. At a single institution from 2000 to 2013, 252 consecutive patients with subarachnoid hemorrhage at computed tomography (CT) and two DSA examinations negative for aneurysm within 10 days were evaluated for inclusion in the study, and 131 met CT criteria for PM nonaneurysmal subarachnoid hemorrhage (53 women; mean age, 53 years [range, 33-88 years]). DS angiographic reports were reviewed for causative abnormalities. Three reviewers searched MEDLINE and electronic databases for studies that reported detection of aneurysm in subjects with PM hemorrhage who had undergone multiple DSA examinations. Main inclusion criteria were PM hemorrhage at CT per van Gijn classification, head CT performed within 72 hours of symptom onset, initial DS angiographic results negative for aneurysm, and two DSA examinations within 10 days. Studies with fewer than 25 subjects were excluded. Methodology was assessed by using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The summary rate of aneurysm detection for subsequent DSA was calculated by using a fixed-effects model. Results Six studies with 298 subjects and a single-institution study with 131 subjects were included. No aneurysms were seen at follow-up DSA in the single-center study (0.0%). Three aneurysms were detected at follow-up DSA in three of six studies from the literature (one of 29 [3.4%], one of 65 [1.5%], and one of 34 [2.9%] patients). Two occurred in cases that likely preceded the use of the current DSA technique. The summary aneurysm detection rate at subsequent DSA was 1.6% (95% confidence interval: 0.7%, 3.8%; range of individual study detection rate: 0.0%-3.4%). Conclusion In patients with PM nonaneurysmal subarachnoid hemorrhage and initial DSA negative for aneurysms, the yield of follow-up DSA for detection of causative aneurysms is very low. © RSNA, 2016 Online supplemental material is available for this article.

Transient unilateral facial paralysis induced by perimesencephalic non-aneurysmal subarachnoid hemorrhage: A case report and review of the literature.

The present study is, to the best of our knowledge, the first report of a rare, transient form of unilateral facial paralysis induced by perimesencephalic non-aneurysmal subarachnoid hemorrhage. The paralysis may have resulted from the compression of a part of the facial nerve by the flow of the hemorrhage into the cavum subarachnoidale; alternatively, the paralysis may have been caused by disorder of the blood supply of the facial nucleus, with the hemorrhage leading to brainstem vasospasm. The patient underwent hemostatic therapy, administration of a symptomatic antiemetic and dehydration. The facial nerve compression was released due to the absorption of the hemorrhage or the rapid improvement of the facial nucleus blood supply following the resolution of the vasospasm. Consequently, the facial nerve function was fully recovered, and the facial paralysis disappeared.

CT within 6 hours of headache onset to rule out subarachnoid hemorrhage in nonacademic hospitals.

To investigate whether staff radiologists working in nonacademic hospitals can adequately rule out subarachnoid hemorrhage (SAH) on head CT <6 hours after headache onset. In a multicenter, retrospective study, we studied a consecutive series of patients presenting with acute headache to 11 nonacademic hospitals. Inclusion criteria were (1) normal level of consciousness without focal deficits, (2) head CT <6 hours after headache onset and reported negative for the presence of SAH by a staff radiologist, and (3) subsequent CSF spectrophotometry. Two neuroradiologists and one stroke neurologist from 2 academic tertiary care centers independently reviewed admission CTs of patients with CSF results that were considered positive for presence of bilirubin according to local criteria. We investigated the negative predictive value for detection of SAH by staff radiologists in nonacademic hospitals on head CT in patients scanned <6 hours after onset of acute headache. Of 760 included patients, CSF analysis was considered positive for bilirubin in 52 patients (7%). Independent review of these patients' CTs identified one patient (1/52; 2%) with a perimesencephalic nonaneurysmal SAH. Negative predictive value for detection of subarachnoid blood by staff radiologists working in a nonacademic hospital was 99.9% (95% confidence interval 99.3%-100.0%). Our results support a change of practice wherein a lumbar puncture can be withheld in patients with a head CT scan performed <6 hours after headache onset and reported negative for the presence of SAH by a staff radiologist in the described nonacademic setting.

The relationship between perimesencephalic subarachnoid hemorrhage and deep venous system drainage pattern and calibrations

Background and purposeThe purpose of this study is to investigate the relationship between Rosenthal basal vein (BVR) type and diameter and perimesencephalic nonaneurysmal subarachnoid hemorrhage (P-SAH). Materials and methodsAneurysmal subarachnoid hemorrhage (A-SAH), P-SAH, and control groups were evaluated, and BVRs were classified by type. BVR diameters in patients were measured. ResultsThere was a statistically significant difference of BVR drainage types between groups (P=.002). BVR diameters of patients with normal drainage pattern in P-SAH group were significantly smaller than those in both other groups (P<.001). ConclusionThere is a relationship between P-SAH and BVR primitive drainage type. P-SAH risk increases in parallel with decreasing caliber of BVR in patients with normal drainage pattern.

Description of the Vasospasm Phenomena following Perimesencephalic Nonaneurysmal Subarachnoid Hemorrhage

Background. Perimesencephalic nonaneurysmal subarachnoid hemorrhage (PM-NASAH) is characterized by a benign course compared with aneurysmal SAH. While vasospasm (VS) after aneurysmal SAH is considered responsible for serious complications, VS post-PM-NASAH is not well documented. Our purpose was to characterize the incidence and course of VS among 63 patients—one of the largest databases of PM-NASAH patients with documented blood flow velocities in the literature. Methods. Data from 63 patients that were admitted with PM-NASAH from 2000 to 2012 and underwent transcranial Doppler tests to assess cranial vessel flow velocity was analyzed. Results. On average, the maximal flow velocity was measured on the 7th day after hemorrhage. Higher risk for VS was associated with younger age, female sex, and higher Hunt and Hess scores, a lower risk for patients treated with statins (P < 0.05). Using velocity thresholds for diagnosis of VS, 49.2% showed evidence of VS. This is the first description of blood flow velocities in PM-NASAH. VS average onset was on the 4th day, average cessation on day 15 after hemorrhage. No patients showed clinical manifestation of VS. Conclusions. VS post-PM-NASAH is not as rare as previously believed. However, its lack of clinical significance raises questions regarding the need for diagnosis and may suggest a less intensive treatment protocol.