Nonaneurysmal Perimesencephalic Hemorrhage Is Associated with Deep Cerebral Venous Drainage Anomalies: A Systematic Literature Review and Meta-Analysis

Delayed appearance of basilar trunk small atypical aneurysms in nontraumatic, initially angiogram-negative subarachnoid hemorrhage: A report of three patients

BACKGROUND

Repeat angiography will identify vascular pathology in approximately 10% of cases following angiogram-negative subarachnoid hemorrhage (anSAH), but small atypical aneurysms of the basilar artery are very uncommon.

OBJECTIVE

To report a case series of delayed appearance of nontraumatic basilar artery small atypical aneurysms.

METHODS

IRB approval was obtained for this retrospective case series and patient consent was waived.

RESULTS

Herein we report three cases of spontaneous anSAH, all of whom had a negative digital subtraction angiogram (DSA) on admission and all of whom had appearance of a small atypical aneurysms of the upper basilar trunk/apex on follow-up imaging (two during the initial admission and one in a delayed fashion). All three patients were ultimately treated with flow diversion (although one patient underwent attempted coiling that was abandoned due to inability to catheterize the aneurysm).

CONCLUSION

This report highlights the importance of a repeat DSA in cases of anSAH as well as the importance of scrutinizing the basilar trunk for these very small atypical aneurysms that may go unnoticed.

Physical exertion as a risk factor for perimesencephalic nonaneurysmal subarachnoid hemorrhage

BACKGROUND

Perimesencephalic 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.

METHODS

We 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.

RESULTS

PM-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.

CONCLUSION

Physical 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.

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.

Reversible cerebral vasoconstriction syndrome: review of neuroimaging findings

Reversible cerebral vasoconstriction syndrome (RCVS) is a group of disorders characterized by segmental narrowing and dilatation of medium-to-large cerebral arteries, clinically presenting with recurrent episodes of sudden-onset thunderclap headaches, with or without focal neurological deficits. Cerebral vasoconstriction is typically reversible, with spontaneous resolution within 3 months. Although the syndrome has generally a benign course, patients with neurological deficits may experience worse outcome. The main imaging finding is segmental constriction of intracranial arteries, which can be associated with subarachnoid hemorrhage and/or ischemic foci. Other possible findings are intracranial hemorrhage, subdural bleeding and cerebral edema. The latter may have a pattern which can resemble that of posterior reversible encephalopathy syndrome, a condition that can overlap with RCVS. New imaging techniques, such as vessel wall imaging and arterial spin labeling, are proving useful in RCVS and are giving new insights into the pathophysiology of this condition. In this paper, we aim to review neuroimaging findings of RCVS.

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.

Dural Venous Sinus Variations in Idiopathic Subarachnoid Hemorrhage: A New Indicator of the Venous Origin with Diagnostic Usefulness?

OBJECTIVE

Venous hypertension associated with a primitive basal vein of Rosenthal (BVR) has been noted as the most likely cause of idiopathic subarachnoid hemorrhage (iSAH). Other types of venous drainage variations have been scarcely studied but may further explain the cases not associated with a BVR anomaly. Our aim was to investigate if dural venous sinus (DVS) anomalies are related with iSAH.

METHODS

A total of 76 patients diagnosed with iSAH were identified from a prospectively maintained database and their angiographic findings compared with 76 patients diagnosed with aneurysmal subarachnoid hemorrhage.

RESULTS

On top of the BVR variations, our data showed a higher prevalence of transverse sinus hypoplasia (47.4% vs. 28.9%; P = 0.019), superior petrosal sinus hypoplasia (32.9% vs. 13.2%; P = 0.003), and clival plexus hyperplasia (65.8% vs. 43.4%; P = 0.005) in patients with iSAH. Analyzing by total number of angiograms, the iSAH group showed also a higher prevalence of inferior petrosal sinus hyperplasia (36.2% vs. 25%; P = 0.003). Of the patients with iSAH without a primitive BVR, 84% harbored ≥1 perimesencephalic DVS variation and the overall number of venous drainage variations was significantly higher in patients with iSAH.

CONCLUSIONS

In addition to the well-documented BVR anomalies, there seems to be a significant relationship of other DVS variations in patients with iSAH. Transverse sinus hypoplasia, superior petrosal sinus hypoplasia, inferior petrosal sinus hyperplasia, and clival plexus hyperplasia were significantly more frequent in patients with iSAH. The presence of ≥3 of those variations would increase the suspicion of a nonaneurysmatic subarachnoid hemorrhage and could help avoid a second angiogram.

Repeat Catheter Angiography in Patients with Aneurysmal-Pattern Angiographically Negative Subarachnoid Hemorrhage

BACKGROUND

A significant proportion of patients with subarachnoid hemorrhage have a normal cerebral angiogram. Patients with angiographically negative subarachnoid hemorrhage (anSAH) with either perimesencephalic- (panSAH) or aneurysmal-pattern hemorrhage (aanSAH, also known as diffuse anSAH) have an excellent prognosis, but only if underlying vascular abnormalities are completely excluded. The rate of occult aneurysms in patients with aanSAH varies widely across studies. The purpose of this study was to quantify the value of repeat DSA in these patients.

METHODS

We reviewed the records of all patients initially diagnosed with aanSAH after a screening DSA at a single tertiary neurovascular referral center from January 2006-April 2018. Patients with panSAH and traumatic SAH were excluded. We also performed a systematic review and meta-analysis of positive second DSAs in previously published case series of patients with aanSAH who underwent two serial DSAs. For meta-analysis, PubMed Central, MEDLINE and Cochrane Library databases were searched for pertinent studies up to November 2019. The rate of aneurysm detection on repeat angiography was extracted from each study. Pooled rates for positive second angiogram were calculated as untransformed proportions in a binary random-effects model meta-analysis. Inter-study heterogeneity was calculated using an I² statistic.

RESULTS

Three of 27 patients (11.1%) with aanSAH and at least two DSAs were subsequently found to have a cerebral aneurysm in our institutional dataset. Twenty-six studies in our systematic review met inclusion criteria, and the pooled rate of positive second angiogram was 10.4% (95% CI 7.3%-13.5%, P < 0.001). Substantial inter-study heterogeneity was observed in the meta-analysis (I² = 61.7%, P < 0.001).

CONCLUSIONS

One in 10 patients with aanSAH has an occult ruptured aneurysm. A second-look DSA should be strongly considered in these cases.

Recurrent perimesencephalic nonaneurysmal subarachnoid hemorrhage within a short period of time: A case report

BACKGROUND

Spontaneous subarachnoid hemorrhage (SAH) is primarily caused by a ruptured intracranial aneurysm. Perimesencephalic nonaneurysmal SAH (PNSAH) accounts for approximately 5% of all spontaneous SAH. PNSAH displays favorable prognosis. The risk of hemorrhage recurrence is low. We report a case of PNSAH recurrence, occurring within a short time after the initial episode in a patient not receiving antithrombotic or antiplatelet drugs.

CASE SUMMARY

A 66-year-old male, without any history of recent trauma or antithrombotic/ antiplatelet medication, suffered two similar episodes of sudden onset of severe headache, nausea, and vomiting. A plain head computed tomography (CT) scan showed subarachnoid blood confined to the anterior part of the brainstem. Platelet count and coagulation function were normal. PNSAH was diagnosed by repeated head CT, magnetic resonance imaging, and cerebral angiography, none of which revealed the source of SAH. The patient was discharged without focal neurological deficits. At 6-mo follow-up, the patient had experienced no sudden onset of severe headache and presented favorable clinical outcome. Studies have reported a few patients with recurrent PNSAH, originating frequently from venous hemorrhage and conventionally associated with venous abnormalities. PNSAH recurs within a short time following the initial onset of symptoms, although the possibility of re-hemorrhage is extremely rare.

CONCLUSION

PNSAH recurrence should arouse vigilance; however, the definite source of idiopathic SAH in this case report deserves further attention.

Subarachnoid Hemorrhage of Unknown Cause: Distribution and Role of Imaging

Subarachnoid hemorrhage of unknown cause represents approximately 10% to 15% of nontraumatic subarachnoid hemorrhages. The key factors in determining the management strategy for a presumed nonaneurysmal subarachnoid hemorrhage are the distribution, location, and amount of subarachnoid blood. Hemorrhage distribution on computed tomography can be categorized as follows: perimesencephalic, diffuse, sulcal, and primary intraventricular. The extent of the workup required in determining the cause of hemorrhage depends on the distribution of blood. The authors review the potential causes, differential diagnoses, and acute and long-term follow-up strategies in patients with subarachnoid hemorrhage of unknown cause.

Evaluating thunderclap headache

PURPOSE OF REVIEW

Thunderclap headache (TCH) is an abrupt-onset of severe headache that needs to be thoroughly investigated because the most common secondary cause is subarachnoid hemorrhage (SAH). There has been no consensus guideline regarding the diagnostic workup. This review aims to provide an update on the evaluation of TCH.

RECENT FINDINGS

The most important update in the 2019 American College of Emergency Physicians guideline for evaluation of acute headache in the emergency department is that negative noncontrast brain computed tomography (CT) findings within 6 h from ictus essentially excludes SAH. Additionally, the updated guideline recommends that after a negative brain CT, CT angiogram is a reasonable alternative to lumbar puncture if clinical suspicion of an intracranial source of SAH is high. An important update of reversible vasoconstriction syndrome (RCVS), the second most common etiology of TCH, is the RCVS2 score development based on clinical and radiological features, providing high specificity and sensitivity for distinguishing RCVS from other intracranial arteriopathies.

SUMMARY

Although the evaluation of TCH is exhaustive, the potentially catastrophic consequence of a missed diagnosis of sentinel headache justifies the efforts. Awareness of the clinical features and application of diagnostic tools specific for different pathological conditions can facilitate the diagnostic workup.

Deep venous drainage variant rate and degree may be higher in patients with perimesencephalic than in non-perimesencephalic angiogram-negative subarachnoid hemorrhage

OBJECTIVES

The basal vein of Rosenthal (BVR) variant is a potential origin of bleeding in angiogram-negative subarachnoid hemorrhage (AN-SAH). We compared the rate and degree of BVR variants in patients with perimesencephalic AN-SAH (PAN-SAH) and non-perimesencephalic AN-SAH (NPAN-SAH).

METHODS

We retrospectively reviewed the records of AN-SAH patients admitted to our hospital between 2013 and 2018. The associations between variables (baseline characteristics, clinical and radiological data, and outcome) with bleeding patterns and degree of BVR variants were analyzed. Additionally, potential predictors of positive findings on repeated digital-subtracted angiogram (DSA), rebleeding, delayed cerebral infarction (DCI), and poor outcome were further studied.

RESULTS

A total of 273 patients with AN-SAH were included. The incidence rate and degree of BVR variants were significantly higher in PAN-SAH patients compared with those in NPAN-SAH patients (p < 0.001). Patients with normal bilateral BVRs are more likely to have a severe prognosis and diffused blood distribution (p < 0.05). We found an increased rate of positive findings on repeated DSA, DCI, rebleeding, and poor outcome at 3 months and 1 year after discharge (all p < 0.05) in patients with bilateral normal BVRs. Bilateral normal BVRs were considered a risk factor (predictor) of positive findings on repeated DSA, rebleeding, and poor outcome (all p < 0.05).

CONCLUSIONS

PAN-SAH patients have a higher rate and degree of BVR variants compared with patients with NPAN-SAH. Those AN-SAH patients with bilateral normal BVRs are more likely to be of arterial origin and are at risk of suffering from rebleeding and a poor outcome.

KEY POINTS

• Patients with PAN-SAH have a higher rate and degree of BVR variants compared with patients with NPAN-SAH, which suggested that AN-SAH patients with normal BVRs are more likely to originate from arterial bleeding. • AN-SAH patients with normal BVRs are more likely to have positive findings on repeated DSA examinations, as well as an increased incidence of rebleeding and poor outcome, which may assist and guide neurologists in selecting treatment.

Acute Hydrocephalus Requiring External Ventricular Drainage Following Perimesencephalic Nonaneurysmal Subarachnoid Hemorrhage in a Pediatric Patient: Case Report and Review of the Literature

BACKGROUND

Perimesencephalic nonaneurysmal subarachnoid hemorrhage (PNSAH) is a well-described subset of subarachnoid hemorrhage with an excellent prognosis in adults. However, its characteristics in the pediatric population have not yet been fully understood. We present a case of acute hydrocephalus requiring external ventricular drainage following pediatric PNSAH.

CASE DESCRIPTION

A previously healthy 10-year-old girl was admitted to our neurosurgical department after sudden onset of severe headache with vomiting during exercise. Cerebral non-contrast computed tomography detected subarachnoid hemorrhage filling all perimesencephalic cisterns. However, digital subtraction angiography could not locate the hemorrhage source. Her consciousness deteriorated within 7 hours of onset, and a computed tomography scan revealed acute hydrocephalus. We subjected the patient to external ventricular drainage for 10 days. She was discharged after 38 days of hospitalization, when she was physically and neuropsychologically healthy. Repeated digital subtraction angiography performed at the 6-month follow-up did not show any obvious source of hemorrhage except for a variant drainage pattern of the basal vein of Rosenthal. Based on the observations, we diagnosed the patient with PNSAH of a venous origin.

CONCLUSIONS

We propose that acute hydrocephalus be suspected in pediatric patients with nonaneurysmal subarachnoid hemorrhage filling all perimesencephalic cisterns, as in adults. We also propose that one of the possible causes of pediatric PNSAH as of venous origin and related to the abnormal drainage pattern of basal vein of Rosenthal and elevation of venous pressure with exercise. Immediate surgical drainage could obtain a good outcome in a symptomatic case.

Recurrent Bleeding After Perimesencephalic Hemorrhage: Case Report and Review of the Literature

BACKGROUND

Perimesencephalic hemorrhage (PMH), a subtype of nonaneurysmal subarachnoid hemorrhage, is characterized by a typical pattern of localized hemorrhage on head computed tomography. PMH is usually associated with a benign clinical course, and a lower incidence of complications such as vasospasm and rebleeding.

CASE DESCRIPTION

We present the cases of a man aged 28 years and a woman aged 21 years with no relevant medical history who experienced recurrent, spontaneous episodes of PMH within the course of 7 days and 29 months. No precipitating causes were identified.

CONCLUSIONS

There are only a couple of case reports of recurrent PMH, some of which were defined questionably. We review the reported cases and discuss the possible causes and long-term outcomes. Neurointerventionalists and neurosurgeons should be aware that the risk of recurrent hemorrhage of PMH does exist, although it is rather low. Even after early or late rebleeding, prognosis of PMH is excellent.

The Acute Phase of Experimental Subarachnoid Hemorrhage: Intracranial Pressure Dynamics and Their Effect on Cerebral Blood Flow and Autoregulation

Clinical presentation and neurological outcome in subarachnoid hemorrhage (SAH) is highly variable. Aneurysmal SAH (aSAH) is hallmarked by sudden increase of intracranial pressure (ICP) and acute hypoperfusion contributing to early brain injury (EBI) and worse outcome, while milder or non-aneurysmal SAH with comparable amount of blood are associated with better neurological outcome, possibly due to less dramatic changes in ICP. Acute pressure dynamics may therefore be an important pathophysiological aspect determining neurological complications and outcome. We investigated the influence of ICP variability on acute changes after SAH by modulating injection velocity and composition in an experimental model of SAH. Five hundred microliters of arterial blood (AB) or normal saline (NS) were injected intracisternally over 1 (AB₁, NS₁), 10 (AB_10, NS₁₀), or 30 min (AB₃₀) with monitoring for 6 h (n = 68). Rapid blood injection resulted in highest ICP peaks (AB₁ median 142.7 mmHg [1.Q 116.7-3.Q 230.6], AB₃₀ 33.42 mmHg [18.8-38.3], p < 0.001) and most severe hypoperfusion (AB₁ 16.6% [11.3-30.6], AB₃₀ 44.2% [34.8-59.8]; p < 0.05). However, after 30 min, all blood groups showed comparable ICP elevation and prolonged hypoperfusion. Cerebral autoregulation was disrupted initially due to the immediate ICP increase in all groups except NS₁₀; only AB₁, however, resulted in sustained impairment of autoregulation, as well as early neuronal cell loss. Rapidity and composition of hemorrhage resulted in characteristic hyperacute hemodynamic changes, with comparable hypoperfusion despite different ICP ranges. Only rapid ICP increase was associated with pronounced and early, but sustained disruption of cerebral autoregulation, possibly contributing to EBI.

Analysis of biochemical laboratory values to determine etiology and prognosis in patients with subarachnoid hemorrhage: a clinical study

OBJECTIVES

The aim of this study was to establish prognostic and predictive markers in patients with subarachnoid hemorrhage (SAH) using simple laboratory methods.

METHODS

A retrospective examination was made of patients with SAH diagnosed secondary to isolated head trauma, isolated anterior communicating artery aneurysm rupture, and angiography-negative SAH. Age, gender, Glasgow Coma Scale (GCS) scores, and Fisher's grade scores, Glasgow Outcome Scale (GOS) scores, leukocyte count, neutrophil count, lymphocyte count, platelet count, neutrophil-lymphocyte ratio (NLR) and platelet-lymphocyte ratio results (PLR) were evaluated.

RESULTS

NLR and PLR values, which were similar in patients with spontaneous SAH, were significantly high in patients with traumatic SAH. NLR and PLR values could be 80% sensitive and 75% specific for distinguishing traumatic SAH from spontaneous SAH. Eosinophil count was lower in patients with angiography-negative SAH and patients with aneurysmal SAH than in patients with traumatic SAH. Initially measured GCS score, Fisher's grade score, eosinophil, neutrophil and lymphocyte counts could be prognostic in all patients with SAH. Moreover, it was concluded that the initially measured number of eosinophils might be directly related to patient prognosis. The eosinophil count was generally found to be high in traumatic SAH patients and it was observed that this parameter could be predictive for these patients. Lymphocyte count and NLR values could be prognostic markers in patients with angiography-negative SAH.

CONCLUSION

NLR, PLR and eosinophil count values could be predictive for etiological factors (traumatic SAH or spontaneous SAH) of patients who were admitted unconscious to the emergency room with SAH detected on radiological imaging.

The Incidence of Hydrocephalus and Shunting in Patients with Angiogram-Negative Subarachnoid Hemorrhage: An Updated Meta-Analysis

OBJECTIVE

To evaluate the incidence of hydrocephalus and implanted shunts in angiogram-negative subarachnoid hemorrhage (SAH) according to hemorrhage patterns: perimesencephalic SAH (PMH) versus non-PMH.

METHODS

The online database literature from January 1990 to November 2017 was systematically reviewed. A fixed-effect model was used when heterogeneity was <50%. A Begg funnel plot was used to assess publication bias. An additional trim and fill method was used to estimate the number of missing studies. A subgroup analysis with studies, which defined angiogram-negative SAH using repeated angiography or computed tomography angiography, was further performed.

RESULTS

A total of 28 articles including 2577 patients were enrolled. Patients with PMH showed a significantly decreased incidence of hydrocephalus (odds ratio [OR], 0.269; 95% confidence interval [CI], 0.208-0.348) and shunts (OR, 0.263; 95% CI, 0.169-0.411) than did patients without PMH. A subgroup analysis of 7 studies with 675 patients showed less hydrocephalus in patients with PMH than in patients without PMH (OR, 0.358; 95% CI, 0.161-0.793), with possible publication bias. Shunt procedures were marginally less common in patients with PMH compared with those patients without PMH (OR, 0.490; 95% CI, 0.236-1.018) with possible publication bias. After correction of the forest plot, the adjusted OR was 0.617 (95% CI, 0.251-1.513) for hydrocephalus and 0.618 (95% CI, 0.310-1.232) for shunts, suggesting no significant relationships between PMH and the risk of hydrocephalus or shunting.

CONCLUSIONS

Hydrocephalus and shunts were more evident in non-PMH than PMH. However, subgroup analyses did not show significant associations between PMH and lower risks of these events after correction for possible publication bias. Further meta-analyses based on individual patient data are necessary.

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

BACKGROUND AND PURPOSE

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.

METHODS

All patients who were admitted to our hospital for nontraumatic subarachnoid hemorrhage between April 2008 and March 2016 were retrospectively analyzed.

RESULTS

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.

CONCLUSIONS

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.

Perimesencephalic nonaneurysmal subarachnoid hemorrhage caused by transverse sinus thrombosis: A case report and review of literature

RATIONALE

Perimesencephalic nonaneurysmal subarachnoid hemorrhage (PNSAH) is characterized by a pattern of extravasated blood restricted to the perimesencephalic cisterns, normal angiographic findings, and an excellent prognosis with an uneventful course and low risks of complication. The precise etiology of bleeding in patients with PNSAH has not yet been established. The most common hypothesis is that PNSAH is venous in origin. Intracranial venous hypertension has been considered as the pivotal factor in the pathogenesis of PNSAH. The underlying venous pathology such as straight sinus stenosis, jugular vein occlusion may contribute to PNSAH. We describe a patient in whom transverse sinus thrombosis preceded intracranial venous hypertension and PNSAH. These findings supported that the source of the subarachnoid hemorrhage is venous in origin.

PATIENT CONCERNS AND DIAGNOSES

A 45-year-old right-handed man was admitted to the hospital with a sudden onset of severe headache associated with nausea, vomiting, and mild photophobia for 6 hours. The patient was fully conscious and totally alert. An emergency brain computed tomography (CT) revealed an acute subarachnoid hemorrhage restricted to the perimesencephalic cisterns. CT angiography revealed no evidence of an intracranial aneurysm or underlying vascular malformation. Digital subtraction angiography of arterial and capillary phases confirmed the CT angiographic findings. Assessment of the venous phase demonstrated right transverse sinus thrombosis. Magnetic resonance imaging confirmed the diagnosis of cerebral venous sinus thrombosis (CVST). Lumbar puncture revealed an opening pressure of 360 mmH2O, suggestive of intracranial venous hypertension. Grave disease was diagnosed by endocrinological investigation.

INTERVENTIONS

Low-molecular-weight heparin, followed by oral warfarin, was initiated immediately as the treatment for cerebral venous sinus thrombosis and PNSAH.

OUTCOMES

The patient discharged without any neurologic defect after 3 weeks of hospital stay. MR venography revealed recanalization of right transverse sinus at the 6-month follow-up. No clinical or neuroimaging evidence of relapse was detected at 12 months follow-up.

LESSONS

Hyperthyroidism may contribute to the development of CVST. The presence of acute transverse sinus thrombosis, as a cause of PNSAH, provides further support for the hypothesis that the source of PNSAH is venous in origin and intracranial venous hypertension plays a critical role in the pathogenesis of PNSAH.