Non-Aneurysmal Subarachnoid Hemorrhage & Vascular Malformations

ABPN Neurocritical Care Study Guide Exam

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1 Chapter 1: Neurologic Examination & Coma Assessment in the ICU

Current Examination, Blueprint & Preparation Neurologic Examination in Critically Ill Patients Coma Evaluation & Consciousness Alterations Delirium & Toxic-Metabolic Encephalopathy in the ICU

2 Chapter 2: Cerebral Physiology & Intracranial Dynamics

Cerebral Blood Flow, Metabolism & Autoregulation Intracranial Pressure & Compliance Cerebral Edema & Herniation Syndromes

3 Chapter 3: Intracranial Hypertension & Cerebral Perfusion Management

Tiered ICP Management Protocols Hyperosmolar Therapy & Fluid Management Advanced & Refractory ICP Interventions

4 Chapter 4: Airway, Mechanical Ventilation & Pulmonary ICU Management

Emergency Airway Management & Neuro-Intubation Mechanical Ventilation Strategies in Acute Brain Injury Tracheostomy & Ventilator Weaning in Neurocritical Care Pulmonary Complications in the Neuro-ICU Obstructive Lung Disease, Pulmonary Hypertension & Bronchoscopy

5 Chapter 5: Hemodynamics, Shock & Cardiovascular Management

Hemodynamic Monitoring & Blood Pressure Targets Vasoactive Agents: Inotropes, Vasopressors & Antihypertensives Cardiac Complications of Brain Injury

6 Chapter 6: Neuropharmacology, Analgesia & Sedation

ICU Sedation & Analgesia Neuromuscular Blockade & Monitoring Propofol Infusion Syndrome & Drug Toxicities Antiseizure Drug Pharmacology in the ICU

7 Bleeding, Thrombosis & Hematologic Emergencies

Warfarin & Heparin Reversal Direct Oral Anticoagulant (DOAC) Reversal Antiplatelet Management & Platelet Dysfunction Venous Thromboembolism Prophylaxis & Management Transfusion, Coagulopathy, TMA & Cellular-Therapy Neurotoxicity

8 Chapter 8: Systemic ICU Care, Fluids, Electrolytes & Endocrine

Hyponatremia & Osmoregulation: SIADH vs Cerebral Salt Wasting Diabetes Insipidus, Hypernatremia & Endocrine Crises Critical Care Prophylaxis, Nutrition & Infection Prevention

9 Systemic Trauma & Environmental Injury

Polytrauma, Chest Injury & Abdominal Hemorrhage Burns, Electrical Injury & Hanging

10 Cardiac Emergencies & Mechanical Support

IABP, Ventricular Devices & ECMO Acute Coronary, Valvular, Rhythm & Aortic Emergencies

11 Kidney Injury, Acid–Base & Renal Replacement

Acute Kidney Injury & Renal Drug Clearance Acid–Base Disorders, Electrolytes & Renal Replacement

12 Systemic Infection & Endocrine Emergencies

Sepsis, Endocarditis & Antimicrobial Principles Thyroid, Adrenal & Dysglycemic Emergencies

13 Gastrointestinal & Hepatic Emergencies

Acute Abdomen, GI Bleeding & Abdominal Compartment Syndrome Acute Liver Failure, Cirrhosis & Hepatic Drug Effects

14 Chapter 9: Neuroimaging in the Neuro-ICU

Non-Contrast CT & CT Angiography CT Perfusion & Advanced Perfusion Imaging Magnetic Resonance Imaging in Critical Illness

15 Chapter 10: Electrophysiology & Neuromonitoring

Continuous EEG & ACNS Standardized Critical Care Terminology Invasive Neuromonitoring: ICP & External Ventricular Drains Multimodal Monitoring: PbtO2, Microdialysis & Transcranial Doppler

16 Angiography, Electrodiagnosis & CSF Analysis

Conventional Angiography & Cranial–Spinal Shunts EMG, Nerve Conduction & Acute Muscle Disease CSF Analysis: Infection, Inflammation & Hemorrhage

17 Chapter 11: Bedside Procedures, Ultrasound & Death by Neurologic Criteria

Critical Care Procedural Skills Critical Care Ultrasound & Echocardiography Determination of Death by Neurologic Criteria

18 Chapter 12: Acute Ischemic Stroke & Reperfusion Therapies

Acute Ischemic Stroke Management & Thrombolysis Endovascular Thrombectomy & Large Vessel Occlusion Malignant Hemispheric & Cerebellar Infarction

19 Chapter 13: Spontaneous Intracerebral Hemorrhage & Intraventricular Hemorrhage

Acute Intraparenchymal Hemorrhage Management Intraventricular Hemorrhage & Hydrocephalus Surgical Evacuation & Minimally Invasive Surgery in ICH

20 Chapter 14: Aneurysmal Subarachnoid Hemorrhage & Delayed Cerebral Ischemia

Aneurysmal Subarachnoid Hemorrhage: Acute Resuscitation & Securing Delayed Cerebral Ischemia & Cerebral Vasospasm Non-Aneurysmal Subarachnoid Hemorrhage & Vascular Malformations

21 Venous, Spinal & Traumatic Vascular Disease

Cerebral Venous Thrombosis & Spinal Cord Infarction Traumatic Dissection, Carotid–Cavernous Fistula & Penetrating Injury

22 Chapter 15: Traumatic Brain & Spinal Cord Injury

Severe Traumatic Brain Injury & Contusions Acute Traumatic Spinal Cord Injury & Neurogenic Shock Spine Trauma, Fractures & Cord Syndromes

23 Chapter 16: Status Epilepticus, Seizures & Neuromuscular Emergencies

Status Epilepticus: Convulsive & Non-Convulsive Refractory & Super-Refractory Status Epilepticus Acute Neuromuscular Respiratory Failure

24 Chapter 17: Post-Cardiac Arrest Care, CNS Infections & Encephalitis

Targeted Temperature Management & Post-Cardiac Arrest Care Post-Cardiac Arrest Neuroprognostication Acute CNS Infections, Encephalitis & Inflammatory Emergencies

25 Neuroinflammation & Neurooncology

Fulminant Demyelination & Autoimmune Encephalitis Brain, Spinal & Leptomeningeal Cancer Emergencies

26 Pregnancy, Transplantation & Pediatric Care

Pregnancy, Postpartum & Post-Transplant Neurologic Care Pediatric Neurocritical Care

27 Chapter 18: Neurosurgical & Perioperative Emergencies

Postoperative Neurosurgical Complications Device Complications: EVDs, Shunts & ICP Monitors Cerebral Hyperperfusion Syndrome & Post-Interventional Emergencies

28 Chapter 19: Ethics, Palliative Care & Organ Donation in the Neuro-ICU

Communication, Surrogate Decision-Making & Conflict Resolution Neuroprognostication Ethics, Withdrawal of Life Support & Palliative Care Organ Donation & Management of the Deceased Donor

Non-Aneurysmal Subarachnoid Hemorrhage & Vascular Malformations

Key Takeaways Explain This Topic AI

A strictly perimesencephalic pattern with an adequate negative vascular evaluation generally has a favorable course; reassess atypical findings.

Angiogram-negative diffuse SAH can hide a vascular lesion and often needs specialist-directed repeat investigation.

ARUBA favored medical care over intervention during its follow-up in selected unruptured AVMs, with limits to applying one result to every lesion.

AVM size, eloquence, and deep drainage inform microsurgical risk; rupture status and patient factors affect treatment.

Cortical venous reflux increases dAVF concern; preserve functional venous drainage when treating an associated cavernoma and DVA.

Last updated: October 2026

Non-Aneurysmal Subarachnoid Hemorrhage & Vascular Malformations

Approximately 15 % 15\% 15% of spontaneous subarachnoid hemorrhages occur in the absence of an identifiable intracranial aneurysm on initial catheter angiography. Furthermore, intracranial vascular malformations—including arteriovenous malformations ( A V M s AVMs A V M s ), dural arteriovenous fistulas ( d A V F s dAVFs d A V F s ), and cavernous malformations—represent critical neurovascular entities that present with subarachnoid or intraparenchymal hemorrhage, seizures, and progressive focal deficits. Neurocritical care clinicians must distinguish benign non-aneurysmal hemorrhage patterns from high-risk structural vascular malformations that demand targeted surgical or endovascular interventions.

Perimesencephalic Non-Aneurysmal SAH (PM-SAH)

Perimesencephalic non-aneurysmal subarachnoid hemorrhage ( P M - S A H PM\text{-}SAH PM - S A H ) accounts for approximately 10 – 15 % 10\text{--}15\% 10 – 15% of all spontaneous SAH presentations and up to two-thirds of all angiogram-negative cases.

Diagnostic Criteria (The van Gijn Criteria)

To be classified as true perimesencephalic SAH, the initial non-contrast head CT obtained within 72 hours of symptom onset must fulfill strict topographic anatomical criteria:

Epicenter of Hemorrhage: Blood is located immediately anterior to the midbrain or upper pons (interpeduncular, prepontine, or chiasmatic cisterns).

Limited Cisternal Extension: Clot may extend symmetrically or asymmetrically into the ambient cisterns, crural cisterns, or basal portions of the Sylvian fissures.

Absence of Frank Intraventricular Hemorrhage ( I V H IVH I V H ): No frank intraventricular casting (minor sedimentation of red cells in the occipital horns of the lateral ventricles is permissible).

Absence of Lateral Sylvian or Interhemispheric Clot: No blood pooling in the lateral Sylvian fissures and no anterior interhemispheric fissure clot (findings that strongly indicate a ruptured middle cerebral or anterior communicating artery aneurysm).

No Intraparenchymal Hematoma: Absence of brain parenchymal clot. [ Acute Non-Traumatic SAH on NCCT ]
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[ True Perimesencephalic ] [ Non-Perimesencephalic Pattern ]
Blood anterior to midbrain • Thick cisternal, lateral Sylvian,
No frank IVH/ICH or interhemispheric clot
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[ Initial 3D-CTA / DSA: Neg ] [ Initial 3D-CTA / DSA: Neg ]
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Venous origin proposed • High occult aneurysm risk (~10-15%)
Rebleeding rate ~0% • Repeat vascular workup considered
Vasospasm/DCI < 1% in 7–14 days
Excellent prognosis • Full SAH ICU surveillance bundle
Repeat DSA rarely needed
Etiology, Angiographic Workup & Prognosis

Etiology: A venous mechanism has been proposed for classic perimesencephalic SAH, but a single mechanism is not established for every case. Confirm that the imaging pattern and vascular evaluation adequately exclude an aneurysm or another cause before using a lower-risk label.

Brain Arteriovenous Malformations (AVMs)

Brain arteriovenous malformations are high-flow congenital vascular anomalies comprising direct fistulous connections between feeding cerebral arteries and draining veins through a central dysplastic vascular tangle—the nidus —without an intervening capillary bed.

Clinical Presentation & Hemodynamics

Hemorrhage ( 50 % 50\% 50% ): Intraparenchymal hemorrhage ( I C H ICH I C H ), intraventricular hemorrhage ( I V H IVH I V H ), or subarachnoid hemorrhage ( S A H SAH S A H ).

Seizures ( 30 % 30\% 30% ): Secondary to cortical gliosis, hemosiderin irritation, or localized ischemia.

Arterial Steal Syndrome: High-volume, low-resistance arteriovenous shunting diverts blood away from surrounding normal brain parenchyma, precipitating progressive focal neurological deficits.

The Spetzler-Martin Grading Scale

The Spetzler-Martin scale predicts the morbidity and mortality associated with microsurgical resection of brain AVMs:

Variable Clinical Feature Points Assigned
Nidus Size Small ( < 3 cm < 3\text{ cm} < 3 cm ) 1
Medium ( 3 – 6 cm 3\text{--}6\text{ cm} 3 – 6 cm ) 2
Large ( > 6 cm > 6\text{ cm} > 6 cm ) 3
Eloquence of Adjacent Cortex Non-eloquent brain tissue 0

Eloquent brain tissue (sensorimotor, language, visual, hypothalamus, thalamus, internal capsule, brainstem, cerebellar peduncles/deep nuclei) 1

Venous Drainage Pattern Superficial cortical veins only (sagittal/transverse sinuses) 0
Deep venous drainage (internal cerebral veins, basal vein of Rosenthal, straight sinus) 1

Grades I–II (Low Risk): Low surgical morbidity ( < 1 – 3 % < 1\text{--}3\% < 1 – 3% ); complete microsurgical resection is the definitive standard of care.

Grade III (Intermediate Risk): Heterogeneous cohort requiring individualized multimodal management (microsurgery, preoperative embolization, or radiosurgery).

Grades IV–V (High Risk): Significant surgical morbidity and mortality ( 20 – 40 % 20\text{--}40\% 20 – 40% ); microsurgical resection is generally contraindicated unless the patient presents with a life-threatening, accessible hematoma.

The ARUBA Trial: Unruptured AVMs

The landmark ARUBA trial (A Randomized Trial of Unruptured Brain Arteriovenous Malformations) compared medical management alone (antiepileptic drugs, blood pressure control) versus interventional therapy (microsurgery, endovascular embolization, stereotactic radiosurgery, or combinations) in adults with unruptured AVMs.

Primary Endpoint: The trial was halted prematurely after enrolling 226 patients due to overwhelming superiority of medical management alone: the risk of stroke or death was significantly higher in the interventional therapy arm ( 30.7 % 30.7\% 30.7% ) compared to the medical management arm ( 10.1 % 10.1\% 10.1% ) , with a hazard ratio of 0.27 0.27 0.27 for medical management relative to intervention.

Long-Term Evidence: Extended 5-year follow-up confirmed persistent disparity. Consequently, guideline-directed neurocritical practice avoids routine prophylactic interventional eradication for unruptured brain AVMs.

Ruptured AVM Management: In contrast, patients presenting with a ruptured AVM face a rebleeding hazard of 6 – 18 % 6\text{--}18\% 6 – 18% in the first year post-bleed (compared to 1 – 3 % 1\text{--}3\% 1 – 3% /year for unruptured AVMs). Ruptured AVMs require specialist planning for hemorrhage management and possible definitive treatment; timing and modality depend on anatomy, clinical stability, and treatment risk.

Dural Arteriovenous Fistulas (dAVFs)

Dural arteriovenous fistulas are acquired, pathological arteriovenous shunts located entirely within the dural leaflets, commonly fed by branches of the external carotid artery (middle meningeal, occipital, ascending pharyngeal arteries) and draining into dural venous sinuses or cortical leptomeningeal veins. They often arise following dural sinus thrombosis, head trauma, or prior craniotomy.

The Borden and Cognard Classifications

Borden Type Cognard Type Venous Drainage Architecture Clinical Risk & Hemorrhage Potential

Type I Type I / IIa Anterograde drainage directly into dural venous sinus; no Cortical Venous Reflux ( C V R CVR C V R ) Benign: Low hemorrhage risk ( < 1 % < 1\% < 1% /year); presents with pulsatile tinnitus or ocular symptoms (chemosis/proptosis)

Type II Type IIb / IIa+b Drainage into dural venous sinus with retrograde Cortical Venous Reflux ( C V R CVR C V R ) Aggressive / Malignant: High hemorrhage risk ( 8 – 10 % 8\text{--}10\% 8 – 10% /year); progressive neurological deficits

Type III Often Cognard III / IV; classifications are not identical Direct cortical venous drainage; Cognard V specifically describes spinal perimedullary drainage Malignant: Highest hemorrhage risk ( 15 – 20 % 15\text{--}20\% 15 – 20% /year) and rapid neurological decline

Important

Cortical Venous Reflux ( C V R CVR C V R ) is the single most critical prognostic determinant. High-pressure arterial shunting directed retrogradely into thin-walled cortical leptomeningeal veins causes severe venous hypertension, venous infarction, and intraparenchymal or subarachnoid hemorrhage. The presence of CVR mandates urgent endovascular embolization (e.g., transarterial/transvenous Onyx or PHIL) or surgical disconnection.

Cerebral Cavernous Malformations (Cavernomas)

Cerebral cavernous malformations ( C C M s CCMs CCM s ) are low-flow vascular anomalies consisting of compact clusters of dilated, hyalinized endothelial-lined capillary-like sinusoidal channels ("caverns") devoid of intervening neural parenchyma or mature vessel wall architecture (lacking smooth muscle and internal elastic lamina).

Neuroimaging Hallmarks

MRI T2-Weighted / FLAIR: Pathognomonic "popcorn" or "mulberry" appearance , with a central core of heterogeneous mixed signal intensity representing hemorrhages of varying ages (thrombosis, methemoglobin, hemosiderin), encapsulated by a complete circumferential rim of profound T2 hypointensity due to hemosiderin deposition.

Gradient Echo ( G R E GRE GRE ) and Susceptibility-Weighted Imaging ( S W I SWI S W I ): Displays prominent, extensive "blooming" artifact due to magnetic susceptibility from iron breakdown products.

Catheter Angiography ( D S A DSA D S A ): Angiographically occult. Cavernomas have low, sluggish internal blood flow without arteriovenous shunting and are invisible on catheter digital subtraction angiography. [ Cerebral Cavernous Malformation ]

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[ MRI Pathognomonic Appearance ] [ Associated DVA Alert ]
Central mixed-signal "popcorn" core • Found in 30-40% of cases
Complete hypointense hemosiderin rim • Provides functional venous
Marked blooming on SWI/GRE drainage of normal brain

Angiographically occult on DSA • DO NOT RESECT OR OCCLUDE DVA!

Developmental Venous Anomalies (DVAs) & Surgical Principles

In 30 – 40 % 30\text{--}40\% 30 – 40% of sporadic cavernomas, a Developmental Venous Anomaly ( D V A DVA D V A ) ("caput medusae" draining into a collector vein) is intimately associated with the lesion.

Warning

The DVA provides essential functional venous drainage for the surrounding normal brain tissue. During surgical resection of a cavernoma, the associated DVA must never be coagulated, occluded, or resected . Obliteration of a functional DVA can lead to severe venous infarction, massive cerebral edema, and intracranial hemorrhage.

Natural History and Indications for Intervention

Hemorrhage Rates:

Unruptured incidental cavernomas: Annual bleeding rate of 0.5 – 1 % 0.5\text{--}1\% 0.5 – 1% per year .

Previously ruptured cavernomas: Annual rebleeding rate increases to 4 – 5 % 4\text{--}5\% 4 – 5% per year (clustering phenomenon within the first 2–3 years post-hemorrhage).

Brainstem cavernomas carry significantly higher neurological morbidity with each bleeding episode due to the high density of cranial nerve nuclei and tracts.

Surgical Indications: Microsurgical resection is indicated for: (1) surgically accessible cavernomas causing medically refractory epilepsy, (2) progressive focal neurological deficits, or (3) recurrent symptomatic hemorrhages. Stereotactic radiosurgery is reserved as a second-line consideration for deep, surgically inaccessible brainstem lesions with multiple life-threatening hemorrhages.

Angiographic strategy: Interpret the blood pattern, initial CTA/DSA quality, clinical course, and residual suspicion together. Strictly perimesencephalic bleeding with an adequate negative evaluation has a low subsequent diagnostic yield. Nonperimesencephalic diffuse bleeding has a greater occult vascular-lesion risk and often warrants repeat catheter angiography. The timing and modality are specialist decisions rather than an inflexible universal 7–14-day rule.

Surveillance: An aneurysmal pattern with a negative first angiogram remains concerning. Thrombosis, vasospasm, technical limitations, or obscuring blood can hide a lesion. Continue appropriate monitoring while completing the diagnostic plan; do not discharge solely because the first angiogram was negative.