Hydrocephalus (HCP)

Definition

An abnormal accumulation of cerebrospinal fluid within the ventricles of the brain

Numbers

Prevalence 1%

Incidence of congenital HCP: 1/1000 births (0.2-3.5/1000)

Hydrocephalus may occur with the frequency of 1 in every 500 children.

Classification

Flow

Obstructive

Hyperacute

Sudden (< hours)

Ventricles not much change

Reduced arterial perfusion

Compression of draining veins

No periventricular oedema

No macrocephaly

Progressively acute

Weeks or months

Enlarged ventricles

+/- macrocephaly

Periventricular interstitial oedema

Chronic

Months to yrs

Progressively enlarged ventricles

Parenchymal loss

No periventricular interstitial oedema

May decompensate

Decompensation of chronic hydrocephalus

Development of high ICP in patient with compensated chronic HCP
An impairment of both compliance and absorption
Due to

Ventriculomegaly beyond threshold
Closure of sutures
Trauma
Infection

Arrested (compensated hydrocephalus)

Definition

No progression or deleterious sequelae due to hydrocephalus that would require the presence of a CSF shunt.
No sequalae here will refer to

Near normal ventricular size
Normal head growth curve
Continued psychomotor development

Mechanism

CSF is reabsorbed through other routes (glymphatic)

Decompensates when shows symptoms of intracranial hypertension (headaches, vomiting, ataxia or visual symptoms)

Communicating (might be still obstructive just that we don't know where it is obstructing)

No blockage of CSF flow seen
Progressive ventricular dilatation
Responsive to shunt placement
Eg

Fibrosis post meningitis or haemorrhage or reduce elasticity spinal dura

Greitz model

Impaired propagation of pulse pressure waves
Loss of craniospinal meningeal compliance
Increased pulsation waves on prenchyma

Age

Prenatal

Ventriculomegally vs hydrocephalus can be challenging

Small head-probably not HCP

Associated anomalies are common

Myelomeningocele
Callosal anomalies

Normal measurements

Atrium of lateral ventricles ≤ 10mm

Size of atrium of lateral ventricle	Outcomes
<12mm	93% normal
12-15mm	21-25% developmental delay

Coronal diameter 3rd ventricle : <4mm

Sagittal diameter 4th ventricle: <7mm

Post natal

<2yrs old

Usually progressive head enlargement.
80% chiari II or aqueduct stenosis/gliosis

>2yrs old

Signs of elevated ICP
Most common cause Post Fossa tumour

Mechanism

Classical

Reduced CSF reabsorption

Communicating hydrocephalus (non-obstructive)

Defect in CSF reabsorption by the AG

Increased CSF reduction (rare)

Choroid plexus papillomas

A type of communicating HCP
Even here, reabsorption is probably defective in some as normal individuals could probably tolerate the slightly elevated CSF production rate of these tumors

Obstruction of CSF circulating pathways

Obstructive hydrocephalus (non-communicating)

Block proximal to the arachnoid granulations (AG).
Enlargement of ventricles proximal to block (e.g. obstruction of aqueduct of Sylvius → lateral and 3rd ventricular enlargement out of proportion to the 4th ventricle, sometimes referred to as triventricular hydrocephalus)

Pulsatile

Issues the classical theory cant explain

Increasing the amplitude of CSF pulse pressure without changing mean CSF pressure can cause HCP
Transmantle pressure gradients have not been demonstrated in communicating HCP and as such is not the cause of ventricular dilation
Normal pressure HCP cannot be explained

Dec. In intracranial compliance results in increasing in systolic pressure transmission to the brain parenchyma and as a results ventricular dilation occurs

Aetiology

Congenital

Primary (31%)

Communicating hydrocephalus,
Aqueductal atresia,
Foramen atresia
X-linked inherited disorder: rare

Dysgenetic (56%)

Chiari Type 2 + myelomeningocele (MM)
Bifid cranium
Dandy Walker malformation/Variant

Atresia of foramina of Luschka & Magendie.
Incidence of pts with HCP: 2.4%

Holoprosencephaly
Chiari Type 1 malformation

HCP may occur with 4th ventricle outlet obstruction

Primary aqueductal stenosis

Usually presents in infancy, rarely in adulthood

Secondary (13%)

Brain tumour
Haemorrhage
Infection

TORCH infection can increase risk of HCP

Trauma
Secondary aqueductal gliosis

Due to intrauterine infection or germinal matrix hemorrhage

Acquired

Infectious

Most common cause of communicating HCP
Post-meningitis

Especially purulent and basal,

Organism

TB
Cryptococcus
Cysticercosis

Post-hemorrhagic (2nd most common cause of communicating HCP)

Post-SAH
Post-intraventricular hemorrhage (IVH): many will develop transient HCP. 20–50% of patients with large IVH develop permanent HCP, requiring a shunt

Secondary to masses

Non neoplastic

Vascular malformation

Neoplastic

Most produce obstructive HCP by blocking CSF pathways, especially tumors around aqueduct (e.g. medulloblastoma).
A colloid cyst can block CSF flow at the foramen of Monro.
Pituitary tumor

Suprasellar extension of tumor
Expansion from pituitary apoplexy

Post-op

20% of paediatric patients develop permanent hydrocephalus (requiring shunt) following p-fossa tumor removal.
May be delayed up to 1 yr

Neurosarcoidosis

“Constitutional ventriculomegaly”

Asymptomatic.
Needs no treatment

Associated with spinal tumors

? due to ↑ protein?,
⬆️ venous pressure?,
Previous hemorrhage in some?

Special forms of hydrocephalus

Normal pressure hydrocephalus (NPH)
Entrapped fourth ventricle
Arrested hydrocephalus

Clinical features

People with rigid cranial vault (adults and older children)

Papilledema

Gait changes

Upgaze and/or abducens palsy

Slowly enlarging ventricles may initially be asymptomatic

Tinnitus

Trullen 1996

Due to venous noise resulting from the turbulence created when the blood flows from the hypertensive intracranial portion to the low-pressure zone of the jugular bulb.
Noise is unilateral owing to the asymmetry of the right and left jugular flow (anatomical variant of normality).
Tinnitus is located on the side with the greater venous flow.
This theory is supported by its direct relationship with intracranial pressure (when the intracranial pressure decreases, so does the tinnitus), its occurrence in front of the external auditory canal, its pulsating character, and its attenuation by manoeuvres that decrease jugular flow (ipsilateral jugular compression, Valsalva manoeuvre and ipsilateral head movement).
The finding of a pulsating tinnitus responding to jugular compression or to the Valsalva manoeuvre, may suggest Intracranial hypertension.

Children

Abnormalities in head circumference (OFC)

As a rule of thumb, the OFC of a normal infant should equal the distance from crown to rump.
Measurement technique

Using a non-stretchable tape
Measure the circumference of the head just above the supraorbital ridge anteriorly and around the most prominent part of the occiput posteriorly (keeping above the ears).
Pull the tape snug to compress hair (exclude any braids or hairclips).
Take 2 separate measurements (reposition the tape each time)
If the measurements are within 2mm, record the largest value.
If the measurements disagree by>2mm, take a third measurement and record the average of the 2 closest measures

Worrying signs or part of catch up phase of brain growth in premature infants after they recover from their acute illnesses

Progressive upward deviations from the normal curve (crossing curves)
Continued head growth of more than 1.25cm/wk
OFC approaching 2 standard deviations (SD) above normal
Head circumference out of proportion to body length or weight, even if within normal limits for age

Deviations below the curves or head growth in the premature infant in the neonatal period of less than 0.5 cm/wk (excluding the first few weeks of life) may indicate microcephaly.

Cranium enlarges at a rate > facial growth

Irritability,

Poor head control,

Fontanelle full and bulging

Frontal bossing (protuberance of the frontal bone manifesting as a prominent forehead)

Enlargement and engorgement of scalp veins

Inc. Icp → due to reversal of flow from intracerebral sinuses

MacEwen’s sign

Tapping (percussion) the skull near the junction of the frontal, temporal and parietal bones will produce cracked pot sound.
Positive test is indication of separated sutures.

6th nerve (abducens) palsy

The long intracranial course is postulated to render this nerve very sensitive to pressure

“Setting sun sign” (upward gaze palsy)

Parinaud’s syndrome from pressure on region of suprapineal recess

Damage of the vertical gaze center (rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) and the interstitial nucleus of Cajal (INC))

Both are in close proximity to the cerebral aqueduct and decussate in the posterior commissure

Hyperactive reflexes

Irregular respirations with apnoeic spells

Splaying of cranial sutures (may be seen on plain skull X-ray)

Visual defects from hydrocephalus

Ocular motility or visual field defects

More common with shunt malfunction than is blindness.

Types of visual disturbance

Blindness

Blindness is a rare complication of hydrocephalus and/or shunt malfunction.
Aetiology

Posttraumatic oedema
Tumour
Abscess
SDH
Unshunted hydrocephalus
Shunt malfunction

Pathophysiology

Occlusion of posterior cerebral arteries (PCA caused by downward transtentorial herniation)
Chronic papilledema causing injury to optic nerve at the optic disc
Dilatation of the 3rd ventricle with compression of optic chiasm

Classification

Pregeniculate (anterior visual pathway) blindness

64.3%

Pathophysiology

Elevated ICP transmits pressure → elevated Intraocular pressure → reduce blood flow to retina
Enlarging third ventricle → compress optic chiasm

Causing bitemporal hemianopia

Clinical features

Marked optic nerve atrophy (early)
Reduced pupillary light reflexes.

Also, if hypotension and anaemia were present, consider the possibility of ischemic optic neuropathy, which may be anterior, or posterior (the latter of which carries a poorer prognosis).

Postgeniculate (cortical) blindness

35.7%

Due to

Lesions posterior to lateral geniculate bodies (LGB),
Hypoxic injuries
Trauma.

Macular sparing is not expected in traumatic occipital lobe injury.

Occasionally associated with Anton’s syndrome (denial of visual deficit) and with Ridoch’s phenomenon (appreciation of moving objects without perception of stationary stimuli).

Pathophysiology In patients with occipital lobe infarction

Occipital lobe infarctions (OLI)

In PCA distribution are seen either bilaterally, or if unilateral are associated with other injuries to optic pathways posterior to LGB.
More likely with a rapid rise in ICP (doesn’t allow compensatory shifts and collateral circulation to develop).
Herniation of brain through tentorial notch → compression of PCA →

PCA or its branches lie on the surface of the hippocampal gyrus and tend to cross the free edge of the tentorium

(Some authors implicate parahippocampal gyral compression in tentorial notch directly injuring LGBs; this may never produce permanent blindness).

Upward cerebellar herniation (e.g. from ventricular puncture in face of a p-fossa mass) may impinge on PCA or branches with the same results.
Macular sparing is common

Due to

Potential dual blood supply of occipital poles (sometimes filled both by PCA and MCA collaterals);
The calcarine cortex may be supplied by a distinct branch of the PCA that fortuitously escapes compression.

The occipital poles are also particularly vulnerable to diffuse hypoxia

Cortical blindness after cardiac arrest.

Hypotension superimposed on compromised PCA circulation (from herniation or elevated ICP) may thus increase the risk of post-geniculate blindness.

Clinical features

Normal light responses
Minimal or no optic nerve atrophy (or atrophy late).

Presentation

These deficits are frequently unsuspected (altered mental state and the youth of many of these patients makes detection difficult);
An examiner must persevere to detect homonymous hemianopsias in an obtunded patient.
Pregeniculate blindness is less often associated with depressed sensorium than is postgeniculate (where direct compression and vascular compromise of midbrain are more likely).

Prognosis

Cortical blindness after diffuse anoxia frequently improves (occasionally to normal); usually slowly (weeks to years quoted; several mos usually adequate).
As with infarcts elsewhere, younger patients fare better, but extensive calcarine infarcts are probably incompatible with significant visual recovery.
Many reports of blindness after shunt malfunction are pre-CT era; thus, the presence or extent of occipital lobe infarction cannot be ascertained.

Some optimistic outcomes are reported;
However, permanent blindness or severe visual handicap are also described;
No reliable predictor has been identified.

Imaging

CT/MRI criteria for hydrocephalus

HCP best seen on CT or MRI

MRI sq

How do you want to deal with this image????

Special consideration in young infants

Longer T1 and T2 values of the parenchyma

Inc TR in T1WI
Inc. TR and TE in T2WI
May increase echo train length

Skull expandable, spinal canal small no flow void in aqueduct
Greater diffusivity of interstitial water

Flow voids: see MRI on flow

Flow voids form when fluid that have low signal in one 3d space flows into the acquired (scanned) 3d space

Strong flow void do not mean no HCP

Absence of flow void does refer to occlusion

CISS/FIESTA not good at judging flow void

Inc. Flow voids potential sign of foraminal or aqueduct stenosis

Due to: stenosis → increase flow for same volume of fluid → greater amount of flow voids

Specific imaging criteria for hydrocephalus HCP is suggested when either

The size of both temporal horns (TH) is ≥ 2mm in width (Normally the temporal horns should be barely visible), and the Sylvian & interhemispheric fissures and cerebral sulci are not visible OR

Most sensitive sign is temporal horns visible

Things to watch out for is not misdiagnose temporomesial atrophy: trisomy 21 and Alzheimer disease

Both TH are ≥ 2mm, and the ratio FH/ID > 0:5 (where FH is the largest width of the frontal horns, and ID is the internal diameter from inner-table to inner-table at this level

Other features

“Mickey Mouse” ventricles

Ballooning of frontal horns of lateral ventricles + 3rd ventricle
The 3rd ventricle should normally be slit-like

Periventricular changes

Low density on CT
High intensity signal on T2WI on MRI
Due to

Stasis of fluid in brain adjacent to ventricles
Not transependymal absorption of CSF (note: a misnomer: CSF does not actually penetrate the ependymal lining, proven with CSF labelling studies)

Used alone, the ratio is

FH/ID ratio	Suggestion
< 40%	Normal
40–50%	Borderline
> 50%	Suggests hydrocephalus

Evans ratio or index

Ratio of FH to maximal biparietal diameter (BPD) measured in the same CT slice
Originally described for ventriculography
> 0.3 suggests hydrocephalus.
Measurements that rely on the frontal horn diameter tend to underestimate hydrocephalus in paediatrics

Possibly because of disproportionate dilatation of the occipital horns in paediatrics

Sagittal MRI may show thinning of the corpus callosum (generally present with chronic HCP) and/or upward bowing of the corpus callosum

BPD= maximal biparietal diameter on the same imaging slice as FH; FH= largest width of the frontal horns; ID = internal diameter from inner-table to inner-table at this level; OH= occipital horns; TH= temporal horns

Rounding of the temporal horns of the lateral ventricles (more specific than frontal horns)

Inferomedial compression of the hippocampi, enlargement of the choroidal fissure (blue arrows)

Dilatation of the third ventricle recesses (orange stars)

Separation of fornix from splenium, stretched corpus callosum (blue arrow)

Lowering of the floor of the third ventricle (green arrow)

Treatment

Recommendation on whether to repair or remove a disconnected or non-functioning shunt

When in doubt, shunt

Indications for shunt repair (vs. removal)

Marginally functioning shunts
The presence of any signs or symptoms of increased ICP (vomiting, upgaze palsy, sometimes H/A alone…)
Changes in cognitive function, ↓ attention span, or emotional changes
Patients with aqueductal stenosis or spina bifida: most are shunt-dependent

Shunt only to be removed (+ temporizing EVD placement) when infected due to risk with removal

Patients with a non-functioning shunt should be followed closely with serial CTs, and possibly with serial neuropsychological evaluations

ETV

ETV success score = age score + etiology score + previous shunt score ≈ percentage probability of ETV success

High score predicts a high chance of early ETV success

Best candidates for ETV

>6 mos of age
Aqueductal stenosis or tectal tumor
No prior shunting

When is ETV is considered successful?

Clinical success

Clinical improvement
No further surgical intervention required

Imaging

⬇️ vents (different than VP shunts)
Rebound cortical mantle
⬇️ or stable HC/macrocephaly
Patent ventriculostomy

Failure rate is 30%
Can cause endocrine dysfunction

Precocious puberty

VPS

Truth

There is insufficient evidence to recommend the routine use of endoscopic guidance in ventricular shunt placement
Antibiotics impregnated shunts better than no antibiotics and silver shunts
Prophylactic antibiotics reduces infection risk
Frontal better than occipital
There is insufficient evidence to recommend the routine use of endoscopic guidance in ventricular shunt placement

Evidence

Baird LC, Mazzola CA, Auguste KI, Klimo P Jr, Flannery AM; Pediatric Hydrocephalus Systematic Review and Evidence-Based Guidelines Task Force. Pediatric hydrocephalus: systematic literature review and evidence-based guidelines. Part 5: Effect of valve type on cerebrospinal fluid shunt efficacy. J Neurosurg Pediatr 2014;14 Suppl. 1:35-43. Review. PubMed PMID: 25988781. Baird et al 2014
Kemp J, et al. Pediatric hydrocephalus: systematic literature review and evidence-based guidelines. Part 9: Effect of ventricular catheter entry point and position. J Neurosurg Pediatr 2014;14 Suppl. 1:72-6. PubMed PMID: 25988785. Kemp et al 2014
Flannery AM, et al. Pediatric hydrocephalus: systematic literature review and evidence-based guidelines. Part 3: Endoscopic computer-assisted electromagnetic navigation and ultrasonography as technical adjuvants for shunt placement. J Neurosurg Pediatr 2014;14 Suppl. 1:24-9. PubMed PMID: 25988779. Flannery et al 2014
Klimo P Jr, et al. Pediatric hydrocephalus: systematic literature review and evidence-based guidelines. Part 6: Preoperative antibiotics for shunt surgery in children with hydrocephalus: a systematic review and meta-analysis. J Neurosurg Pediatr 2014;14 Suppl. 1:44-52. PubMed PMID: 25988782. Klimo et al 2014
Klimo P Jr, et al. Pediatric hydrocephalus: systematic literature review and evidence-based guidelines. Part 7: Antibiotic-impregnated shunt systems versus conventional shunts in children: a systematic review and meta-analysis. J Neurosurg Pediatr 2014;14 Suppl. 1:53-9. Review. PubMed PMID: 25988783. Klimo et al 2014

Post treatment

Width of the lateral ventricles does not necessarily correlate with ICP

Intraindividual change in ventricular size may be indicative

Large interindividual variations

Shunt failure with normal / no change in ventricle size

Look for fluid along shunt catheter or reservoir, consider clinical symptoms

Hygromas

Subdural hematoma / hygroma sign of overdrainage
Pressure-regulating shunts prone to overdrainage
Flow-regulating valves prone to obstruction

Differential diagnosis

“Pseudohydrocephalus”: Conditions that may mimic HCP but are not due to inadequate CSF absorption

“Hydrocephalus ex vacuo”

Enlargement of the ventricles due to loss of cerebral tissue (cerebral atrophy),
Due to

Normal aging
Alzheimer’s disease,
Creutzfeldt-Jakob disease,
Traumatic brain injury

Differentiating from true hydrocephalus hard

Developmental anomalies where the ventricles or portions of the ventricles appear enlarged

Agenesis of the corpus callosum

Can be associated with HCP BUT
More often merely represents expansion of the third ventricle and separation of the lateral ventricles

Septo-optic dysplasia
Hydranencephaly: a post-neurulation defect.

Total or near-total absence of the cerebrum
Due to bilateral ICA infarcts.
It is critical to differentiate this from severe (“maximal”) hydrocephalus (HCP) since shunting for true HCP may produce some re-expansion of the cortical mantle; see means to differentiate

Conditions that have been dubbed “hydrocephalus” but do not actually mimic the appearance of HCP

Otitic hydrocephalus: obsolete term used to describe the increased intracranial pressure seen in patients with otitis media; see Idiopathic intracranial hypertension (IIH)
External hydrocephalus: seen in infancy, enlarged subarachnoid space with increasing OFCs and normal or mildly dilated ventricles

EVOH (extraventricular hydrocephalus ) vs BESS (benign enlargement of subarachnoid spaces: aka benign external hydrocephalus)