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🧠 INTRACRANIAL ANEURYSMS, BRAIN AVMs & DAVFs — Comprehensive Neurosurgery Viva Guide

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PART 1: INTRACRANIAL ANEURYSMS

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1.1 CLASSIFICATION OF INTRACRANIAL ANEURYSMS

• Small: < 10 mm
• Large: 10–24 mm
• Giant: ≥ 25 mm

• Anterior circulation (85–90%): ACoA (30%), PCoA (25%), MCA (20%), ICA (including ophthalmic, cavernous)
• Posterior circulation (10–15%): Basilar tip, PICA, vertebral artery

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1.2 EPIDEMIOLOGY & DEMOGRAPHICS

⚠️ Viva point: Rupture in childhood is rare. Rupture risk markedly increases for aneurysms >6 mm; those ≥10 mm are especially high risk.

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1.3 PATHOGENESIS (Saccular Aneurysm)

1. Congenital theory: Developmental defect in tunica media and internal elastic lamina at bifurcations
2. Acquired theory (Ferguson): Hemodynamic stress at apex of bifurcations → focal destruction of internal elastic membrane → intima bulges → adventitia-covered sac → gradually enlarges → rupture at dome
3. Average size at rupture: 10 mm (but can rupture at smaller sizes)
4. Site of rupture: Dome (may have secondary sacculations)

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1.4 CLINICAL PRESENTATION

A. UNRUPTURED ANEURYSM (Incidental / Mass Effect)

B. RUPTURED ANEURYSM (SAH)

• "Thunderclap headache" — "worst headache of my life," sudden onset, peaks in seconds (sentinel headache in 30–50% before major rupture)
• Meningism: nuchal rigidity, Kernig's sign, Brudzinski's sign
• Photophobia, phonophobia
• Nausea, vomiting
• Transient/prolonged loss of consciousness
• Focal neurological deficits (cranial nerve palsy)
• Subhyaloid hemorrhage (Terson syndrome — vitreous hemorrhage)
• Seizures (early)

1. Rebleeding — Highest risk day 1; 20–30% within 2 weeks without treatment (fatal in 78%)
2. Vasospasm — Days 4–14 post-SAH (peak day 7); symptomatic in 30%; DCI (delayed cerebral ischemia)
3. Hydrocephalus — Acute (obstructive) or chronic (communicating/normal pressure)
4. Hyponatremia — SIADH or Cerebral Salt Wasting Syndrome (distinction critical!)
5. Cardiac dysfunction — Neurogenic stunned myocardium, T-wave inversions, QT prolongation
6. Neurogenic pulmonary edema

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1.5 GRADING SCALES 📊

Hunt & Hess Scale (1968) — Clinical Severity

Grade I/II → Operate early. Grade IV/V → Consider delayed surgery or medical stabilization first.

WFNS Scale (GCS-based)

Fisher Grade (CT — Predicts Vasospasm Risk)

Modified Fisher Grade (more commonly used now): adds IVH as a separate variable.

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1.6 INVESTIGATIONS

CT HEAD (Non-contrast) — FIRST LINE

• Indication: Sudden-onset severe headache ("thunderclap"), meningism, LOC
• Positive findings:
  • Hyperdensity (white) in basal cisterns, Sylvian fissures, interhemispheric fissure = SAH
  • "Star-shaped" pattern at Circle of Willis
  • Sensitivity: >90% within 6 hours of bleeding; drops to ~85% at 24h, ~50% at 1 week
  • Can show hydrocephalus, ICH, location of maximum clot (localizes the aneurysm)

LUMBAR PUNCTURE — If CT negative but clinical suspicion high

• Indication: CT negative + symptoms >6 hours old (allows xanthochromia to develop)
• Wait ≥12 hours after headache onset (time for RBC lysis → oxyhaemoglobin → xanthochromia)
• Positive findings:
  • Xanthochromia (yellow CSF) — gold standard for LP diagnosis
  • RBCs not clearing across 3 tubes (vs. traumatic tap)
  • Elevated opening pressure
  • Spectrophotometry detects oxyhaemoglobin/bilirubin

CT ANGIOGRAPHY (CTA)

• Indication: SAH confirmed on CT → next step to identify aneurysm
• Positive findings: Saccular outpouching at vessel bifurcation, aneurysm neck/dome morphology
• Sensitivity >95% for aneurysms >3 mm
• Used for operative planning when DSA not immediately available

DIGITAL SUBTRACTION ANGIOGRAPHY (DSA) — GOLD STANDARD

• Indication: CTA inconclusive; pre-operative planning; SAH with negative CTA (10% of SAH have negative initial CTA); follow-up after coiling
• Positive findings: Aneurysm neck, dome, feeding vessels, relationship to parent artery, multiplicity, vasospasm
• 4-vessel study (bilateral ICA + vertebral arteries)
• Repeat DSA at 2 weeks if initial is negative (angiographically negative SAH may be perimesencephalic or aneurysm missed due to spasm/thrombosis)

MRI/MRA

• Indication: Incidental aneurysm screening; follow-up of coiled aneurysms; subacute SAH (FLAIR detects blood >24h)
• Positive findings: Flow-void; FLAIR hyperintensity in subarachnoid space; T2* GRE for chronic bleeds

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1.7 MANAGEMENT

Medical Management (Acute SAH)

1. Airway/breathing/circulation — Secure airway if GCS ≤8
2. Bed rest in HDU/ICU
3. Blood pressure control: Systolic ≤150 mmHg (until aneurysm secured); avoid hypotension
4. Nimodipine — START IMMEDIATELY

💊 NIMODIPINE

• Drug class: Dihydropyridine calcium channel blocker (CCB)
• MOA: Blocks L-type voltage-gated Ca²⁺ channels in cerebral vascular smooth muscle → prevents Ca²⁺ influx → reduces sustained arterial spasm. Also has direct neuroprotective action via Ca²⁺-mediated neuronal death pathways
• Dose: 60 mg oral/NG every 4 hours × 21 days (or 0.5–2 mg/h IV in SIADH/unable to swallow)
• Special points:
  • Only FDA-approved drug for reducing neurological deficits from vasospasm after SAH
  • Does NOT decrease angiographic vasospasm but reduces DCI and improves neurological outcomes
  • Must be given enterally (oral capsule or NG); IV preparation had risk of fatal errors if given as bolus — use IV preparation cautiously with infusion pump
  • Reduces systemic BP — monitor for hypotension
  • Statins (simvastatin, pravastatin) as adjunct — pleiotropic effects may reduce vasospasm (not first-line; evidence limited)

1. Euvolemia — Maintain normal circulating blood volume (avoid hypovolemia → worsens vasospasm)
2. Analgesia: Codeine, paracetamol (avoid NSAIDs)
3. Antiepileptics: Short-term phenytoin or levetiracetam (prophylactic — controversial; not routine)
4. DVT prophylaxis: Compression stockings; subcutaneous heparin after aneurysm secured
5. Stool softeners (prevent Valsalva)
6. Treat hyponatremia: If SIADH → fluid restriction; if CSWS → isotonic fluid replacement + fludrocortisone
7. Hydrocephalus: EVD (External Ventricular Drain) if acute obstructive; VP shunt for chronic

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1.8 SURGICAL & ENDOVASCULAR OPTIONS

A. SURGICAL CLIPPING

• Principle: Craniotomy + microsurgical placement of titanium clip across aneurysm neck, excluding it from circulation while preserving parent artery flow
• Indications (prefer clipping over coiling):
  • Young patient with good grade (H&H I–III)
  • Wide-necked aneurysm (dome:neck ratio <2, or neck >4 mm)
  • MCA aneurysms (particularly good surgical access)
  • Associated large ICH requiring evacuation
  • Failed or recurrent after coiling
  • Fusiform aneurysm
• Timing: Within 24–72 hours of SAH (early surgery to prevent rebleeding)
• Key surgical steps: Standard pterional craniotomy (most common), CSF drainage, sylvian fissure dissection, proximal control, clip application, intraoperative angiography/ICG to confirm complete exclusion

B. ENDOVASCULAR COIL EMBOLIZATION (GDC — Guglielmi Detachable Coils)

• Principle: Microcatheter navigated into aneurysm sac via femoral arterial access → platinum coils deployed → thrombosis fills the sac → excluded from circulation
• Indications (prefer coiling over clipping):
  • Posterior circulation aneurysms (basilar tip, PICA) — hard surgical access
  • Elderly or poor-grade patients (H&H IV–V)
  • Narrow-necked aneurysm (dome:neck ratio >2)
  • Medical comorbidities precluding craniotomy
  • Patient preference
• ISAT Trial (2002): In patients suitable for both, coiling → better neurological outcome at 1 year vs. clipping (23.7% vs. 30.6% dependency/death); but higher rebleeding rate at 7 years
• BRAT Trial: Similar findings; favoured coiling for posterior circulation

• Balloon-assisted coiling — remodelling technique for wide-necked aneurysms
• Stent-assisted coiling — intracranial stent deployed across neck + coils
• Flow-diverter devices (Pipeline Embolization Device — PED): Redirects flow away from aneurysm into parent vessel → progressive thrombosis; used for large/giant fusiform aneurysms, wide-necked aneurysms (especially ICA)

C. GIANT ANEURYSMS — Special Considerations

• Parent artery occlusion (PAO) with bypass (EC-IC bypass)
• Trapping (proximal + distal occlusion)
• Wrapping with muslin (palliative)
• Intraluminal stent stabilization (investigational)

D. MYCOTIC ANEURYSMS

• Treatment: Antibiotics (target organism for 4–6 weeks) first
• Surgery/coiling if: enlarging on serial angiography despite antibiotics, rupture, size >10 mm
• Serial DSA every 2 weeks while on antibiotics

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1.9 UNRUPTURED INTRACRANIAL ANEURYSMS (UIA) — Management

• Aneurysms <7 mm with no prior SAH → very low annual rupture risk (~0.05%)
• Aneurysms ≥7 mm, posterior circulation location, or growth on serial imaging → treat
• Shared decision-making: Patient age, aneurysm size/location/morphology, comorbidities

• First-degree relative of patient with SAH + aneurysm (especially ≥2 affected relatives)
• ADPKD patients (5–10% harbor aneurysms)
• Connective tissue disease

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1.10 VASOSPASM MANAGEMENT (Triple-H Therapy — now modified)

• Target SBP 160–200 mmHg after aneurysm secured
• If refractory: Intra-arterial verapamil or nicardipine via cerebral angiography
• Transluminal balloon angioplasty for large vessel proximal vasospasm
• TCD (Transcranial Doppler) daily to monitor for vasospasm: MCA velocity >120 cm/s (mild), >200 cm/s (severe), Lindegaard ratio >3

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PART 2: BRAIN ARTERIOVENOUS MALFORMATIONS (AVMs)

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2.1 DEFINITION & PATHOLOGY

• Abnormal cluster of arteries connected directly to veins without intervening capillary bed (nidus)
• High-pressure arteriovenous shunting
• Associated aneurysms in ~5% of cases (on main feeding artery)
• Somatic KRAS mutations in endothelial cells identified in ~50% of specimens

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2.2 EPIDEMIOLOGY

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2.3 CLINICAL PRESENTATION

• Young patient with ICH in unusual location (not basal ganglia/thalamus — which is hypertensive)
• No hypertension
• Recurrent hemorrhage in the same location
• Seizure disorder + unusual headaches

• Pulsatile carotid in the neck (large AVM)
• Retinal vascular malformation (coextensive with optic nerve lesion)
• Vein of Galen enlargement → hydrocephalus in children

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2.4 SPETZLER-MARTIN GRADING SCALE (Surgical Risk Stratification)

• Grade I–II: Low surgical risk → recommend surgery
• Grade III: Intermediate → individualized decision
• Grade IV–V: High surgical risk → consider SRS or embolization; surgery rarely recommended

• Age (<20, 20–40, >40), prior bleed, nidus compactness

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2.5 INVESTIGATIONS

MRI Brain

• Indication: Screening, diagnosis, pre-operative mapping
• Positive findings:
  • T2: Serpiginous flow voids (high-velocity arterial flow) = hallmark
  • T1: Hemosiderin from old bleeds (dark rim)
  • T2*/GRE/SWI: Microbleeds, old hemorrhage
  • FLAIR: Perilesional gliosis (from chronic ischemia/"steal")
  • Dilated feeding arteries and draining veins

CT (non-contrast)

• Positive findings: ICH, calcifications within AVM (35%), hyperdense nidus

DSA (Gold Standard)

• Indication: Diagnosis confirmation; pre-treatment planning (surgical, embolization, SRS)
• Positive findings: Nidus (tangle of abnormal vessels), feeding arteries, draining veins (early venous filling = AV shunting), associated aneurysms
• 4D DSA (3D rotational) for pre-operative planning

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2.6 MANAGEMENT OF BRAIN AVMs

Conservative (Observation)

• Small, deep, unruptured AVMs in elderly
• ARUBA Trial (2014): For unruptured AVMs, medical management alone may be superior to intervention in the short term — controversial, ongoing debate

A. MICROSURGICAL RESECTION

• Indications: Grade I–III AVMs; ruptured AVM in accessible location; lesion causing progressive deficits
• Steps: Craniotomy → identify and control feeding arteries first → circumferential dissection of nidus → coagulate feeding arteries → remove nidus en bloc → ligate draining veins last (ligate veins early → hemorrhagic infarction!)
• Intraoperative DSA to confirm complete resection
• Grade IV–V → rarely operated; morbidity very high

B. STEREOTACTIC RADIOSURGERY (SRS — Gamma Knife / CyberKnife / LINAC)

• Indications: Small AVMs (≤3 cm / <10 ml), deep/eloquent location (thalamus, brainstem), Grade III–IV, residual after embolization
• Mechanism: Ionizing radiation → endothelial injury → progressive thrombosis and fibrosis → obliteration over 2–3 years
• Obliteration rates: ~80% for small AVMs at 3 years
• Limitation: Latency period of 2–3 years during which AVM still bleeds; radiation necrosis (3–5%)

C. ENDOVASCULAR EMBOLIZATION (ONYX / NBCA)

• Indications: Rarely curative alone; used as adjunct to surgery (reduce blood loss) or SRS (reduce nidus volume)
• ONYX (Ethylene-vinyl alcohol copolymer): Liquid embolic agent; controlled injection; forms cast in nidus
• NBCA (n-butyl cyanoacrylate): Older liquid embolic; faster polymerization
• Pre-operative embolization 24–48 hours before surgery

D. MULTIMODALITY APPROACH

• Embolization → SRS (reduce nidus volume to <3 cm for SRS)
• Embolization → Surgery (reduce blood loss, easier resection)

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PART 3: DURAL ARTERIOVENOUS FISTULAS (DAVFs)

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3.1 DEFINITION

• Dural sinus thrombosis (most important — angiogenesis-related recanalization)
• Trauma
• Prior surgery/craniotomy
• Infection
• Idiopathic

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3.2 EPIDEMIOLOGY

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3.3 CLASSIFICATION

COGNARD CLASSIFICATION (Venous Drainage Pattern — Hemorrhage Risk)

BORDEN CLASSIFICATION (Simpler, 3 types)

Viva pearl: Borden III = Cognard III/IV = HIGH RISK → needs treatment

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3.4 CLINICAL FEATURES

• ICH, SAH
• Focal neurological deficits
• Dementia (venous congestion)
• Seizures
• Papilledema

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3.5 INVESTIGATIONS

MRI Brain

• Dilated cortical veins
• T2 hyperintensity in white matter (venous hypertension/congestion)
• Prominent superficial vessels on MRA
• GRE/SWI: Hemosiderin from old bleeds

CT/CTA

• Early venous filling
• Dilated cortical veins
• Venous ectasia (varix)

DSA (Gold Standard)

• Indication: Definitive diagnosis; pre-treatment planning; defines fistula point, feeding arteries (ECA/ICA dural branches), venous drainage
• Positive findings: Early arteriovenous shunting; retrograde cortical venous filling; venous varices; fistula point

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3.6 MANAGEMENT OF DAVFs

Conservative Management

• Borden I (antegrade sinus drainage only) — low risk; observe or treat symptoms
• Cavernous sinus DAVF: 50% spontaneous closure; manual carotid compression (patient compresses ipsilateral carotid with contralateral hand × 10 min 3× daily for 4 weeks — Halbach technique) — effective in some CCF/DAVF

A. ENDOVASCULAR EMBOLIZATION (PREFERRED for most)

• ONYX injected via microcatheter into feeding arteries → occludes fistula point
• Used for anterior cranial fossa DAVF, transverse/sigmoid DAVF

• Microcatheter navigated via venous route into sinus/vein near fistula → coils/ONYX → occlude fistula
• Particularly effective for cavernous sinus DAVF (via inferior petrosal sinus)
• Transvenous coiling of involved sinus segment for sigmoid/transverse sinus DAVF

B. SURGICAL TREATMENT

• Indications: Failed endovascular; anterior cranial fossa DAVF (ethmoidal — surgical disconnection preferred due to proximity to ophthalmic artery); accessible Borden III DAVFs
• Technique: Craniotomy → identify and interrupt cortical draining vein at fistula point → sinus skeletonization → coagulation/clip of fistulous connection

C. STEREOTACTIC RADIOSURGERY

• Adjunct or alternative for small DAVFs; slower obliteration
• Suitable for deep/inaccessible locations

Cavernous-Carotid Fistula (CCF) — Special Type of DAVF

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PART 4: FOLLOW-UP PROTOCOLS

Aneurysm Follow-Up

AVM Follow-Up

DAVF Follow-Up

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QUICK VIVA SUMMARY TABLE

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Key Viva Tips:

1. Nimodipine does NOT prevent vasospasm angiographically — it prevents the neurological consequences (DCI)
2. Ligate AVM veins LAST during surgery — ligating early causes hemorrhagic infarction
3. Anterior cranial fossa DAVF has no benign form — all drain to cortical veins → always treat surgically
4. ISAT Trial favoured coiling; BRAT Trial confirmed coiling for posterior circulation
5. Spetzler-Martin Grade ≥ IV → surgery carries unacceptably high morbidity; consider SRS or observation
6. Cerebral salt wasting vs SIADH — both cause hyponatremia post-SAH; CSWS requires volume replacement (not restriction!)
7. 20% of aneurysm patients have multiple aneurysms — identify the ruptured one by the clot location on CT

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• Full classification (saccular/fusiform/mycotic/traumatic/giant) with size categories
• Demographics: peak age 35–65, F>M, 20% multiple
• Pathogenesis: congenital defect in media + hemodynamic theory (Ferguson)
• Clinical: thunderclap headache, CN III palsy patterns, mass effect
• 3 Grading Scales: Hunt & Hess (clinical), WFNS (GCS-based), Fisher (CT/vasospasm risk)
• Investigations: CT → LP (xanthochromia) → CTA → DSA with indications and positive findings
• Management: Nimodipine (MOA + dose + special points), general ICU care
• Surgery: Clipping vs. Coiling with ISAT/BRAT evidence, flow diverters, indications for each
• Vasospasm management (Triple-H → evolved to induced HTN + euvolemia)
• Unruptured aneurysm (ISUIA criteria)

• Epidemiology: age 10–30, 3%/year bleed risk
• Spetzler-Martin Scale (full table with scoring)
• MRI findings (flow voids), DSA planning
• Surgical resection, SRS (Gamma Knife), ONYX embolization with clear indications
• ARUBA Trial mention

• Acquired (sinus thrombosis) vs. congenital AVM
• Cognard Classification (I–V) + Borden Classification (I–III) with hemorrhage risk
• Location-specific symptoms (cavernous → proptosis; transverse → tinnitus; anterior fossa → ICH)
• Endovascular (transarterial/transvenous ONYX), surgical, SRS options
• Carotid-Cavernous Fistula (Barrow A–D types)