🧠 HYDROCEPHALUS & ICP MONITORING — Comprehensive Neurosurgery Viva Guide

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PART 1: HYDROCEPHALUS

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1. DEFINITION & OVERVIEW

⚠️ Viva Point: Not all ventriculomegaly = hydrocephalus. Hydrocephalus ex vacuo (atrophic enlargement) must be distinguished — it does NOT benefit from intervention.

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2. CLASSIFICATION

A. By Communication of Ventricular System (Dandy & Blackfan, 1914)

B. By Pathophysiology

• Obstructive (non-communicating): aqueductal stenosis, posterior fossa tumour, colloid cyst of 3rd ventricle
• Communicating: post-meningitis, post-SAH, post-haemorrhagic (neonates), leptomeningeal metastases
• Over-productive: choroid plexus papilloma

C. By Age Group

• Congenital/Infantile (before suture fusion, <2–3 years)
• Childhood (sutures fusing)
• Adult/NPH (idiopathic, elderly)

D. By Onset

• Acute vs. chronic vs. arrested/compensated

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3. CSF PHYSIOLOGY (Essential for Viva)

• Production: 0.3–0.35 mL/min (≈ 500 mL/day); mainly by choroid plexus of lateral ventricles
• Total volume: 150 mL (adults); turnover 3–4×/day
• Absorption: Primarily arachnoid granulations → dural venous sinuses; also spinal cord, brain parenchyma
• Flow path: Lateral ventricles → Foramen of Monro → 3rd ventricle → Aqueduct of Sylvius → 4th ventricle → Foramina of Luschka & Magendie → Basal cisterns → Convexity subarachnoid space → Arachnoid granulations
• Monro-Kellie Doctrine: Brain (80–90%) + Blood + CSF = constant volume. Expansion of one = compression of others.

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4. ALL TYPES OF HYDROCEPHALUS — IN DETAIL

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TYPE 1: CONGENITAL / INFANTILE HYDROCEPHALUS

Demographics

• Age: Neonate to 3 years (before suture fusion)
• M = F (congenital causes); M > F (aqueductal stenosis — X-linked form)

Causes

Clinical Presentation

• Macrocephaly — head circumference crossing centiles (>97th); most reliable early sign
• Tense, bulging anterior fontanelle (even in upright position)
• Sutural diastasis (widened sutures on palpation)
• Frontal bossing; scalp vein distension; calvarial thinning
• "Setting sun sign" — downward deviation of eyes, sclerae visible above iris; due to pressure on midbrain tectum (Parinaud's phenomenon)
• Lateral rectus palsy (CN VI) — false localizing sign
• Leg spasticity (stretching of corticospinal tracts around dilated ventricles)
• Fretfulness, poor feeding, vomiting
• Advanced: flexed posture, feeble movements, optic atrophy

⚠️ Viva Trap: No papilledema in infants — the fontanelle acts as a safety valve.

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TYPE 2: CHILDHOOD HYDROCEPHALUS (Sutures fusing, >2 years)

Causes

• Posterior fossa tumours (most common): Medulloblastoma (#1 in children), Ependymoma, Cerebellar astrocytoma
• Aqueductal stenosis (acquired: gliosis, ependymitis, tumour)
• Pineal region tumours → compress aqueduct

Clinical Presentation (sutures rigid/fusing)

• Headache — worse in the morning (due to lying flat → increased ICP), vomiting (projectile)
• Papilledema (present — skull cannot expand)
• CN VI palsy (false localizing)
• Leg spasticity, ataxia
• Altered conscious level
• Parinaud's syndrome (loss of upward gaze) — from tectal compression
• Cushing's triad (hypertension + bradycardia + irregular respirations) — terminal, indicates herniation

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TYPE 3: NORMAL PRESSURE HYDROCEPHALUS (NPH)

Named after: Adams, Fisher & Hakim (1965)

Demographics

• Age: >60 years (idiopathic NPH); can be younger in secondary NPH
• Prevalence: ~0.2% in 70–79 years; ~5.9% in >80 years

Classic Hakim-Adams Triad (order of appearance):

1. Gait disturbance (earliest & most prominent) — "magnetic gait," short shuffling steps, widened base, difficulty on stairs, cannot lift feet; mimics Parkinsonism but without rigidity/tremor
2. Dementia — "frontal" type: apathy, dullness, slowed thinking, memory impairment; may mimic Alzheimer's
3. Urinary incontinence — urgency initially → frank incontinence; bowel incontinence late; "frontal incontinence" (patient indifferent)

Mnemonic: "Wet, Wobbly, and Wacky"

Causes:

• Idiopathic (most common)
• Secondary: SAH, meningitis, TBI, craniotomy, Paget's disease of skull

CSF Pressure in NPH:

• Normal (70–200 mm H₂O on LP) by definition — but may be intermittently elevated (Lundberg B waves may be present on continuous monitoring)

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TYPE 4: HYDROCEPHALUS EX VACUO

• Ventricular enlargement secondary to brain parenchymal loss (atrophy, infarct, surgery)
• NOT true hydrocephalus — NO increased ICP
• Does NOT require treatment
• Key differentiator: prominent sulci and cortical atrophy accompanying ventricular enlargement

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TYPE 5: ARRESTED/COMPENSATED HYDROCEPHALUS

• Longstanding hydrocephalus where a new equilibrium has been reached
• Ventricles may be large but ICP is normal or near-normal
• May decompensate with minor insults

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TYPE 6: EXTERNAL HYDROCEPHALUS (Benign External Hydrocephalus of Infancy)

• Enlarged subarachnoid spaces over hemispheres + mild ventricular enlargement
• Usually self-limiting
• Must exclude subdural hygroma/hematoma, arachnoid cyst

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5. INVESTIGATIONS

A. NEUROIMAGING

Non-Contrast CT Head (First Line)

MRI Brain (Preferred for Detailed Assessment)

• FLAIR: Periventricular hyperintensity (transependymal edema)
• T2: Dilated ventricles, aqueductal flow void (absent = stenosis, present = patent)
• Sagittal T1: Aqueduct morphology, floor of 3rd ventricle, site of obstruction
• Callosal angle (coronal view): Angle between roof of lateral ventricles at posterior commissure
  • NPH: <90° (typically 50–80°)
  • Atrophy: >100°
• DESH sign in NPH: Disproportionately Enlarged Subarachnoid-space Hydrocephalus — tight sulci at high convexity + Sylvian fissure enlargement

CT of NPH (Adams & Victor, Fig. 29-4):

Skull X-ray

• Beaten silver / copper-beaten appearance (chronic ICP — children)
• Sutural diastasis
• Shunt series: assess tubing integrity, disconnection, calcification

B. LUMBAR PUNCTURE

• Remove 20–50 mL CSF
• Assess gait before and 1–4 hours after (formal timed 10-metre walk)
• Improvement in gait = positive tap test → high predictive value for shunt response
• Negative tap test does NOT exclude NPH or shunt benefit

• NPH: Opening pressure usually 150–200 mm H₂O (can be lower); normal composition
• Post-meningitis: elevated protein, pleocytosis
• SAH: xanthochromia

C. PATHOLOGICAL INVESTIGATIONS

D. SCORES & INDICES

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6. MANAGEMENT APPROACH

Step 1: Resuscitation & Emergency Management

• Elevate HOB 30°
• Normocapnia (PaCO₂ 35–40 mmHg; hyperventilate briefly to 30–35 if herniation imminent)
• Osmotherapy: Mannitol 0.5–1 g/kg IV over 20 min (draws water out of brain)
• Hypertonic saline (3% NaCl) 1–2 mL/kg — alternative if hypotension present
• Avoid hypotension; maintain CPP >60–70 mmHg
• Dexamethasone 10 mg IV loading dose then 4 mg every 6h — if oedema around tumour (NOT for TBI or ischaemic stroke)
• Levetiracetam 2000 mg IV loading → 1000 mg BD — seizure prophylaxis (especially post-SAH)
• Emergency EVD if acute obstructive HCP causing herniation

Step 2: Medical Management (temporizing)

Step 3: Surgical Management

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SURGERY OPTION 1: EXTERNAL VENTRICULAR DRAIN (EVD)

• Acute/obstructive hydrocephalus (emergency decompression)
• SAH (Hunt-Hess grade III–V), IVH with HCP
• Monitoring ICP while awaiting definitive surgery
• Post-haemorrhagic HCP in neonates (bridging)
• Suspected CSF infection (diagnostic + therapeutic)

• Burr hole at Kocher's point (mid-pupillary line, 1 cm anterior to coronal suture; = 11 cm from nasion, 3 cm from midline on right side)
• Catheter passed ~6–7 cm perpendicular to skull → lateral ventricle (aimed at medial canthus of ipsilateral eye in coronal plane + just anterior to ear in sagittal plane)
• External drainage bag set at 15 cm H₂O above foramen of Monro (level of tragus)

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SURGERY OPTION 2: VENTRICULOPERITONEAL (VP) SHUNT

• Communicating hydrocephalus of all types
• NPH (VP shunt is first line)
• Post-obstructive HCP where cause cannot be removed
• Communicating post-haemorrhagic/post-infective HCP
• Failed or ineligible for ETV

• Active infection
• Peritoneal pathology (previous surgery, ascites, obesity — consider VA shunt)
• Significant coagulopathy

1. Burr hole at Kocher's point (right frontal preferred)
2. Ventricular catheter placed in frontal horn of right lateral ventricle
3. Tunnelling under skin: neck → chest → abdomen (subcostal)
4. Distal catheter placed in peritoneal cavity (leave 15–20 cm extra for growth in children)
5. Valve (differential pressure/programmable) interposed between ventricular and peritoneal catheters

• Fixed pressure: Low (1–4 cm H₂O), medium (4–8), high (8–12) — chosen based on clinical need
• Programmable/adjustable (e.g. Codman Hakim, Medtronic Strata): Allows non-invasive adjustment post-op via magnet; preferred in NPH to prevent overdrainage
• Anti-siphon device (ASD): Prevents overdrainage in upright position

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SURGERY OPTION 3: ENDOSCOPIC THIRD VENTRICULOSTOMY (ETV)

• Non-communicating (obstructive) hydrocephalus with intact CSF absorption
• Aqueductal stenosis (best indication — ETV Success Score >80)
• Posterior fossa tumour with aqueduct obstruction (after tumour removal)
• Post-infective HCP in older children (>1 year)
• ETV Success Score (ETVSS) guides patient selection: age, aetiology, prior shunt → score 0–90

• Communicating hydrocephalus (absorptive failure) — ETV won't help
• Infants <6 months (high failure rate; consider ETV+CPC)
• Very small 3rd ventricle, unfavourable anatomy

1. Right frontal burr hole near Kocher's point
2. Endoscope passed through right frontal lobe → right lateral ventricle → foramen of Monro → 3rd ventricle
3. Floor of 3rd ventricle perforated at the tuber cinereum (anterior to mammillary bodies, posterior to infundibulum)
4. Stoma dilated with Fogarty balloon catheter
5. Liliequist's membrane may need fenestration to allow CSF into interpeduncular/prepontine cistern
6. CSF flows: 3rd ventricle → stoma → interpeduncular cistern → basal cisterns → subarachnoid space → absorbed

• Haemorrhage (basilar artery injury — catastrophic)
• CSF leak
• Stoma closure/failure (early failure in <6 months; late failure years later)
• Memory deficit (fornix injury)
• Diabetes insipidus (hypothalamic injury — rare)

• Used in infants <2 years, especially in sub-Saharan Africa settings
• Cauterizes choroid plexus to reduce CSF production
• Success rate >70% in myelomeningocele-related HCP

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SURGERY OPTION 4: VENTRICULOATRIAL (VA) SHUNT

• Distal catheter placed in right atrium (via internal jugular vein)
• Used when peritoneal cavity unavailable/unsuitable
• Additional complications: bacteraemia, shunt nephritis (immune complex deposition), pulmonary embolism, arrhythmia, superior vena cava obstruction
• Catheter must be repositioned as child grows

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SURGERY OPTION 5: TUMOUR RESECTION (ADDRESSING CAUSE)

• Posterior fossa tumour → surgical excision → may resolve HCP
• Colloid cyst of 3rd ventricle → endoscopic/microsurgical excision
• Pineal tumour → biopsy + radiosurgery or open resection
• Often requires EVD pre-operatively, with reassessment post-resection

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PART 2: ICP MONITORING

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7. PHYSIOLOGY OF ICP

• Target CPP: 60–70 mmHg (TBI guidelines)
• Normal CPP: 70–90 mmHg

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8. ICP WAVEFORMS

⚠️ Pathological sign: When P2 > P1 → reduced intracranial compliance (exhausted compensatory reserve)

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9. LUNDBERG ICP WAVES

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10. ICP MONITORING DEVICES

Indications for ICP Monitoring:

• Severe TBI (GCS ≤8) with:
  • Abnormal CT (haemorrhage, contusion, oedema, herniation)
  • Normal CT + age >40 years + SBP <90 mmHg + abnormal posturing (any 2 of 3)
• SAH Hunt-Hess Grade III–V
• Acute bacterial meningitis (selected cases)
• Hydrocephalus requiring monitoring during EVD
• Post-operative monitoring after major neurosurgery
• Hepatic encephalopathy with raised ICP

Types of Monitors:

Viva Point: Intraventricular = most accurate = gold standard. Intraparenchymal = most commonly used in practice (easier, safer). The trade-off: can't drain CSF with intraparenchymal.

Antibiotic Prophylaxis for EVD:

• Cefazolin 2 g IV every 8 hours from insertion until 24–48 hours after removal
• OR antibiotic-impregnated catheters (rifampicin/clindamycin or minocycline/rifampicin)
• DO NOT routinely change catheter every 5 days (no benefit; increased risk with multiple insertions)

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11. NON-INVASIVE ICP ESTIMATION

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12. ICP MANAGEMENT ALGORITHM

Raised ICP >20–25 mmHg sustained >5 min
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TIER 1 (Basics — must do first):
  • HOB 30°
  • Head neutral (avoid venous obstruction)
  • Normothermia
  • Normoglycaemia
  • Avoid hypotension (MAP >80)
  • Normovolaemia
  • Adequate sedation & analgesia (propofol/midazolam + morphine)
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TIER 2:
  • Drain CSF via EVD (if present)
  • Mannitol 0.5–1 g/kg or Hypertonic saline 3% 1–2 mL/kg
  • Brief hyperventilation (PCO₂ 30–35) — bridge only
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TIER 3 (Refractory raised ICP):
  • Barbiturate coma (thiopental/pentobarbital)
  • Decompressive craniectomy
  • Hypothermia (controversial)

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13. CEREBROVASCULAR PRESSURE REACTIVITY INDEX (PRx)

• Moving correlation between mean ICP and slow MAP fluctuations
• PRx < 0 (negative) → intact autoregulation → arterioles constrict when MAP rises → ICP falls
• PRx > 0 (positive) → impaired autoregulation → ICP passively follows MAP
• PRx guides optimal CPP ("sweet spot" where PRx is most negative)

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14. FOLLOW-UP

Post-VP Shunt:

Viva Point: Always compare with baseline imaging. Absolute ventricular size less important than CHANGE from baseline.

Post-ETV:

NPH (post-shunt):

• Follow-up at 1, 3, 6, 12 months post-shunt
• Assess gait (timed 10m walk), cognition (MMSE/MoCA), continence
• CT at 3 months to assess ventricular decompression
• Programmable valve adjustment guided by clinical response and CT

Congenital HCP (paediatric):

• More frequent follow-up: every 3 months in first 2 years, then 6-monthly
• Monitor: head circumference, fontanelle, developmental milestones
• CT or MRI (prefer MRI for repeat studies to avoid radiation)
• Ultrasound through fontanelle in neonates — no radiation, bedside

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15. QUICK VIVA RECAP

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1. All types of HCP — Non-communicating, Communicating, NPH (Hakim-Adams), Ex vacuo, External (benign infantile), Arrested/Compensated, and Overproduction type — each with age/demographics, causes, and clinical features
2. Clinical presentations by age group — Infant (setting sun sign, macrocephaly, fontanelle bulge) vs. Child (papilledema, morning headache) vs. Adult/NPH ("Wet, Wobbly, Wacky")
3. Investigations — CT (Evans Index, bicaudate index, periventricular lucency), MRI (callosal angle, DESH, flow voids for ETV), LP tap test for NPH, CSF analysis
4. Management — Stepwise: emergency medical (mannitol, dexamethasone, acetazolamide with full MOA and doses) → surgical (EVD at Kocher's point, VP shunt with valve types and complications including slit ventricle, ETV with exact technique and Fogarty balloon, VA shunt)
5. ICP Monitoring — Monro-Kellie, normal values, P1/P2/P3 waveforms, Lundberg A/B/C waves, all device types with pros/cons, PRx index
6. Scores — Evans Index, Callosal Angle, ETVSS, Hunt-Hess, Modified Fisher, GCS thresholds
7. Follow-up protocols — by modality and frequency for each surgical approach