Hydrocephalus & CSF Diversion
Hydrocephalus & CSF Diversion
Bottom Line
Hydrocephalus is classified as obstructive (non-communicating) or communicating — the distinction drives treatment: obstructive → ETV candidate; communicating → VP shunt. NPH presents with the Hakim triad (wet, wacky, wobbly) — gait is first and most shunt-responsive. Shunt complications: obstruction is most common (proximal > distal); infection is usually Staph epidermidis within 6 months — requires hardware removal. IIH surgery: vision-threatening disease drives intervention — ONSF or CSF diversion for progressive visual loss or fulminant IIH; for headache-only IIH, use weight loss + acetazolamide/topiramate + headache-directed therapy (shunting for headache alone is controversial and highly selected). Venous sinus stenting is a selected option for medically refractory IIH with vision threat, venous sinus stenosis, and a significant manometric gradient (requires antiplatelets); NOT for headache alone. Always try acetazolamide + weight loss first (IIHTT trial).
HighYield Pearls
- NPH Hakim triad: gait apraxia (magnetic, broad-based) + urinary incontinence + subcortical cognitive impairment — gait is first and most shunt-responsive (“wet, wacky, wobbly”).
- LP tap test: large-volume LP (30–50 mL) with gait improvement predicts NPH shunt response; if ambiguous, do external lumbar drain trial 3–5 days.
- NPH imaging: ventriculomegaly out of proportion to atrophy + Evan’s index >0.3 + callosal angle <90° + DESH (disproportionately enlarged subarachnoid space hydrocephalus).
- Obstructive → ETV; communicating → VP shunt — classification drives surgery; ETV creates ostomy in floor of 3rd ventricle for aqueductal-level (or below) obstruction.
- Colloid cyst at foramen of Monro: ball-valve obstruction → acute bilateral lateral ventricle dilation → sudden death — classic board scenario.
- Shunt infection: S. epidermidis within 6 months — fever + abdominal pain + meningitis signs; treat with hardware removal + EVD + IV antibiotics + reinsertion only after CSF sterile.
- Shunt malfunction triad: headache + vomiting + lethargy (often mimicking original symptoms); image → increased ventricular size OR slit ventricles (overdrainage).
- Overdrainage syndromes: slit ventricle syndrome, chronic subdural hematoma, postural headache — address with programmable valve adjustment or anti-siphon device.
- IIH (pseudotumor cerebri): young obese woman + headache + transient visual obscurations + papilledema + pulsatile tinnitus; LP OP >25 cm with normal CSF; treat weight loss + acetazolamide/topiramate + headache-directed therapy; vision-threatening / fulminant IIH → ONSF or CSF diversion; venous sinus stenting reserved for medically refractory IIH with vision threat + venous stenosis + significant manometric gradient (requires antiplatelets); shunting for headache alone is controversial and highly selected.
- EVD infection risk rises sharply after >1 week — use antibiotic-impregnated catheters; CSF rhinorrhea confirmed with β-2 transferrin or β-trace protein.
🔍 Quick ReferenceClinical · Imaging · CSF diversion / complications
Clinical phenotype
- Magnetic gait + urinary incontinence + subcortical dementia → NPH (Hakim triad — wet, wacky, wobbly)
- Young obese woman + headache + transient visual obscurations + pulsatile tinnitus + papilledema → IIH (pseudotumor cerebri)
- Infant with macrocephaly, bulging fontanelle, “sunset sign” (forced downgaze) → Congenital obstructive hydrocephalus (often aqueductal stenosis)
- Sudden positional headache + drop attack in young adult → Colloid cyst at foramen of Monro
- Morning headache + Valsalva-worsened + N/V + papilledema + decreased LOC → Raised ICP from obstructive hydrocephalus
- Shunt patient with fever + abdominal pain + meningismus → Shunt infection (S. epidermidis)
- Postural (upright) headache in shunted patient → Overdrainage / slit ventricle syndrome
Imaging
- Evan’s index >0.3 + callosal angle <90° + DESH → NPH
- Dilated lateral & 3rd ventricles with normal 4th ventricle → Aqueductal stenosis
- Periventricular transependymal CSF flow (T2/FLAIR cap) → Active hydrocephalus (vs ex vacuo)
- Hyperdense round mass at foramen of Monro → Colloid cyst
- Empty sella + flattened posterior globes + tortuous optic nerve sheaths + transverse sinus stenosis → IIH
- Proportionate sulcal & ventricular enlargement, no transependymal edema → Hydrocephalus ex vacuo (do NOT shunt)
CSF diversion / complications
- ETV (endoscopic third ventriculostomy) → Bypasses aqueductal-level obstruction; avoids shunt hardware; ETV Success Score predicts outcome
- VP shunt with programmable valve → NPH (preferred; non-invasive pressure adjustment)
- VA shunt (atrial) → Used when abdomen contraindicated; risk of endocarditis & pulmonary hypertension
- LP shunt → Communicating hydrocephalus or IIH refractory to medical therapy
- EVD >1 week → Rising infection risk — use antibiotic-impregnated catheter
- Proximal obstruction → Choroid plexus into ventricular catheter (most common shunt failure site)
- Distal obstruction → Peritoneal pseudocyst
- β-2 transferrin or β-trace protein positive → CSF rhinorrhea / otorrhea
- IVH grade III–IV in premature neonate → Post-hemorrhagic hydrocephalus → temporize with reservoir taps or ventriculosubgaleal shunt; permanent VP shunt once medically stable and large enough
Types of Hydrocephalus
CSF Physiology
- CSF production: ~500 mL/day (0.35 mL/min; ~20 mL/hr); total volume ~150 mL; turns over 3–4× per day
- Primary source: choroid plexus (70%) in lateral, third, and fourth ventricles; remainder from ependymal lining and brain interstitial fluid
- Flow pathway: lateral ventricles → foramen of Monro → 3rd ventricle → aqueduct of Sylvius → 4th ventricle → foramina of Luschka (lateral) and Magendie (midline) → subarachnoid space → arachnoid granulations → dural venous sinuses
- Absorption: primarily via arachnoid granulations (villi) into the superior sagittal sinus; driven by pressure gradient between CSF and venous sinus
Classification
| Type | Mechanism | Common Causes | Treatment |
|---|---|---|---|
| Obstructive (non-communicating) | Blockage within ventricular system — CSF cannot exit ventricles | Aqueductal stenosis, posterior fossa tumor, colloid cyst (foramen of Monro), tectal glioma, pineal region tumor | ETV preferred; VP shunt if ETV fails |
| Communicating | Impaired absorption at arachnoid granulations; ventricles communicate freely with subarachnoid space | Post-SAH, post-meningitis, post-IVH, carcinomatous meningitis, choroid plexus papilloma (overproduction — rare) | VP shunt |
| Normal pressure (NPH) | Communicating; ICP intermittently elevated (B-waves) but normal on single measurement | Idiopathic (iNPH); secondary to SAH, meningitis, TBI | VP shunt with programmable valve |
| Ex vacuo | Ventricular enlargement from brain parenchymal loss — NOT true hydrocephalus | Alzheimer disease, stroke, diffuse atrophy | No treatment (no elevated pressure) |
Causes of Obstructive Hydrocephalus
- Aqueductal stenosis: most common cause of congenital obstructive hydrocephalus; congenital (X-linked L1CAM mutation) or acquired (post-infection, tectal glioma); lateral and 3rd ventricles dilated, 4th ventricle normal
- Posterior fossa tumors: medulloblastoma, pilocytic astrocytoma, ependymoma — compress 4th ventricle or aqueduct
- Pineal region tumors: germinoma, pineoblastoma — compress aqueduct from dorsal aspect; Parinaud syndrome (upgaze palsy, convergence-retraction nystagmus)
- Colloid cyst at foramen of Monro: ball-valve obstruction → acute bilateral lateral ventricle dilation; can cause sudden death — classic board scenario
Causes of Communicating Hydrocephalus
- Post-SAH: blood products impair CSF absorption at arachnoid granulations; acute (~20–30%) and chronic (~10–20%). Acute post-SAH hydrocephalus is often OBSTRUCTIVE (IVH blocking aqueduct/outflow), while chronic post-SAH hydrocephalus is COMMUNICATING (arachnoid granulation impairment)
- Post-meningitis: inflammatory debris and fibrosis of arachnoid granulations
- Choroid plexus papilloma: CSF overproduction — rare cause; tumor produces CSF at >normal rate
- Carcinomatous meningitis: tumor cells clog arachnoid villi
Special Types
- Hydrocephalus ex vacuo: NOT true hydrocephalus; brain atrophy with proportionate ventriculomegaly and sulcal enlargement; no periventricular edema; no elevated ICP; do NOT shunt
- External hydrocephalus (benign enlargement of subarachnoid spaces): infants with macrocephaly; enlarged subarachnoid spaces over frontal convexities; normal or mildly enlarged ventricles; self-resolves by age 2; distinguished from subdural collections by cortical veins traversing the fluid space
Board Pearls
- Obstructive vs. communicating — determines treatment: obstructive → ETV; communicating → VP shunt
- Ex vacuo ventriculomegaly is NOT hydrocephalus — sulcal enlargement proportionate to ventricular enlargement; no periventricular transependymal edema; do NOT shunt
- Colloid cyst at foramen of Monro: can cause acute obstructive hydrocephalus and sudden death — classic board scenario
- Choroid plexus papilloma — the only cause of hydrocephalus from CSF overproduction
- External hydrocephalus in infants is benign and self-resolving — do NOT shunt
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