Module Hydrocephalus

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Online Module:

Hydrocephalus


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Hydrocephalus

Derived from Greek words: Hydro water

Cephalus head

As the name implies, it refers to a generalcondition whereby there is excess Cerebro-Spinal Fluid (CSF) within the intracranial space

and, specifically, the intraventricular spaceswithin the braincausing dilation of theventricles, and a wide range of symptoms.


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Sidebar

For our purposes, we will be dealing withhydrocephalus in the older child/adultpopulation. Hydrocephalus in the younger

population, especially neonates and childrenwithout fixed sutures, represents an excellentavenue for further reading, in case you are asked

to elaborate on it for extra points!


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Facts and Physiology

The majority of CSF is produced by the choroidplexuswithin the brain through a metabolicallyactive process (i.e. requires ATP) whereby

sodium is pumped into the subarachnoid space,and water follows from the blood vessels.

Choroid plexus is primarily located in the lateralventricles (temporal horn roofs, and floors ofbodies), posterior 3rd ventricle roof, and caudal4th ventricle roof.


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Facts and Physiology

The average adult brain produces between 450and 600 ccs of CSF every day. Normally, production = resorption.

At any given moment, there is only ~150 ccs ofCSF present in the average adult; of this, only~25 ccs is within the brain ventricles!

So, the CSF volume turns over three to four timesevery day, with only a very small fraction of the CSFbeing in the ventricles at any given time, eventhough the majority of it is produced there!


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Important concept to build on

The CSF production/resorption system exists ina delicate balance under normal conditions.


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The CSF pathway

From the lateral ventricle (remember, there aretwoone on each side), CSF travels throughthe foramen of Monro into the 3rd ventricle

(midline), then passes through the CerebralAqueduct [of Sylvius] into the 4th ventricle. Itthen exits the 4th ventricle through either of two

Foramina of Luschka (L is forLateral/Luschka) or the single Foramen ofMagendie (M is for Midline/Magendie).


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CSF pathway (contd)

After exiting the 4th ventricle, the CSF flowsthrough the subarachnoid space over andaround the brain and spinal cord, and is

eventually reabsorbed into the venous (blood)system through numerous arachnoidgranulations along the dural venous sinuses

(especially the superior sagittal sinus).


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CSF pathway (contd)

Arachnoid granulations contain arachnoid villi,which function as pressure-dependent one-wayvalves that open when the ICP is ~3 to 5 cm

H20 greater than dural venous sinus pressure. RememberCSF production is a metabolically

active process which uses ATP, whereas CSFresorption is a passive process that is driven bythe pressure gradient between the intracranialspace (ICP) and the venous system (~CVP).


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Hydrocephalus

Two major distinctions:

Communicating Hydrocephalus (CoH)

Also known as non-obstructive hydrocephalus

Non-communicating Hydrocephalus (NCH)

Also known as obstructive hydrocephalus


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Hydrocephalus terminology

It is important to understand the differencebetween Communicating and Non-communicating hydrocephalus.

If the CSF pathway is open from start to finish,meaning CSF can travel freely from the choroidplexus to the arachnoid granulations, then you haveno obstruction and a communicatinghydrocephalus.

If the CSF cant travel freely from start to finish,then youve got an obstruction and non-communicatinghydrocephalus.


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Lets look first at

Communicating

Hydrocephalus


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CoH

In the vast, vast majority of cases, this representsa problem with CSF resorption; simply put, itcannot keep the pace with CSF production.

Normal CSF production = resorption

Comm. Hydrocephalus CSF production >resorption

As a result, the ventricular system dilatesuniformly, and ICP rises.


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Still building

Remember that the normal system exists in afairly delicate balance. A major insult is notrequired to upset this balance; sometimes, a very

slight disturbance is enough to tip the scalessuch that, over time, communicatinghydrocephalus results.


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CoH

Very rarely, there is overproduction of CSF(rather than under-absorption) which leads todisruption of this balance, and development of

communicating hydrocephalus.

This is rare, but Choroid Plexus Papillomas havebeen known to present this way.


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CoH

Signs/Symptoms In young children whose cranial sutures have not yet

fused, you can see disproportional increase in head

circumference compared to the rest of theface/body.

In children with fused sutures/adults, hydrocephalusmanifests with symptoms of increased intracranial

pressure; H/A, N/V, papilledema, gait disturbance, 6th cranial nerve

palsy, upgaze difficulty, etc.


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CoH etiology

Infection (incidence after bacterial meningitiscan approach 30%)

Subarachnoid Hemorrhage (blood and bloodbreakdown products cause scarring of arachnoidgranulations)

Post-operative

Head trauma

Etc.


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Still building

Although we usually think of CommunicatingHydrocephalus as being a gentle disruption ofthe balance between CSF production and

resorption that occurs over time, sometimesthere can be a sizeable insult that causes an acutedisruption of the balance, and CSF resorption is

suddenly (and dramatically) reduced.


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Still building

Given the high turnover of CSF in the normalindividual, you should quickly recognize that adramatic decline in CSF resorption ability can

represent an emergency. If a significant numberof arachnoid granulations are impaired, say, bysubarachnoid blood (such as from a rupturedaneurysm), hydrocephalus can develop very

quickly. Neurological decline in such a situationcan be rapid, with patients becoming sleepy,then obtunded, then requiring intubation.


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Lets pause the CoH

discussion, now, and turn

our focus to Non-

communicating

Hydrocephalus (NCH)


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NCH

Non-communicating hydrocephalus occurswhenever there is ANY physical obstruction tothe normal flow of CSF before it leaves the

ventricles.


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NCH causes

Many, many causes:

Aqueductal stenosis

Tumors/Cancers/Masses

Cysts

Infection

Hemorrhage/hematoma

Congenital malformations/conditions

Etc.


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The bottom lineNCH

Non-communicating hydrocephalus can resultfrom CSF flow obstruction at any point alongthe intraventricular pathway.

Processes that have developed over longerperiods of time (i.e. masses, etc) usually causegradual development of symptoms.

Acute processes (i.e. intraventricular bleed) cancause acute obstruction with rapid mental statusdecline (just like we discussed previously).


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Radiography

The earliest consistentradiographical findingindicative ofdevelopment ofhydrocephalus is dilationof the temporal horns ofthe lateral ventricles(arrows). In most

younger and middle-agedpatients, these should bealmost invisible.

This is an abnormal scan!


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Hydrocephalus treatment

Treatment for Hydrocephalus remains surgical.Acute hydrocephalus, whether communicating or

not, usually necessitates urgent or emergent

placement of an External Ventricular Drain (EVD -catheter passed through the patients scalp and skullinto lateral ventricle, that drains CSF to a collectionsystem kept at the patients bedside).

EVD cannot be maintained indefinitely; usually, if thepatient is unable to tolerate weaning/clamping of theEVD prior to removal, a permanent shunt will berequired.


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Hydrocephalus treatment

For communicating hydrocephalus, the mainstayof treatment is shunt placement.Ventriculo-peritoneal is most used.

Lumbar-peritoneal sometimes utilized, thoughoverdrainage is a problem.

Acute communicating hydrocephalus patients (i.e.SAH) can sometimes be managed with EVD with

successful weaning and no shunt placement, but asignificant number of these patients eventually needshunt placement weeks or months later.


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Non-communicating Hydrocephalus

NCH treatment also surgical, but sometimesshunt can be avoided by removing theobstructing lesion.

Colloid cyst at anterior 3rd ventricle causingball/valve obstruction of Foramen of Monro.

Pineal region tumor causing compression of cerebral

aqueduct. Ependymoma blocking 4th ventricular CSF outlets.

Many, many more!


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NCH treatment

In addition to surgical removal of obstructivelesion and shunt placement, ThirdVentriculostomy is an option for non-

communicating hydrocephalus. Often performed in conjunction with VP shunt

placement.

Hole is surgically opened in floor of third ventricleso CSF flows out into the interpeduncular cisternand pre-pontine space (bypasses cerebral aqueduct).


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Previously shunted patients

Take note: Every patient with a history of VPshunt placement who presents with a headacheis NOT automatically having a shunt

malfunction/infection.Yes, you should consider that in your differential,

but still work it up appropriately. After all, the vast

majority of patients with headaches dont have VPshunts.


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Previously shunted patients

Nevertheless, VP shunts can and do fail for anyof a number of reasons.

The incidence of shunt failure is as much as 40% the

first year (most in the first few months), and then5% per year after the first year.

50% of shunts fail by 5 years from placement.

Mechanical failure from occlusion/disconnection,migration, overdrainage/underdrainage, infection, skinerosion, etc.


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One last thing to

discuss


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Normal Pressure Hydrocephalus

Normal Pressure Hydrocephalus (NPH) - Thisis a distinct clinical entity that was first describedin 1965.

This is important and you MUST know itbecause it is one of the rare preventable and/orreversible causes of dementia.

Under-recognition leads many patients with NPH tobe diagnosed with Alzheimers or age-relateddementia and they never seek (or receive) treatment.


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NPH

Classic triad: Wet, Wobbly, and Wacky!

Urinary incontinence

Gait disturbance (usually the first symptom to

present)wide stance; short, shuffling steps Rather quickly-progressive dementia

Communicating hydrocephalus on CT/MRI

Lumbar Puncture (LP) Normal opening pressure

Symptoms improve with CSF removal


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NPH treatment

Procedure of choice for patients felt to besuffering from NPH is VP shunt placement.

LP shunts tend to overdrain.


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NPH prognosis

Chance of outcome is improved if symptomshave been present for shorter period of time Meaning that failure to recognize these patients

delays their treatment and lessens their chances! Least likely symptom to improve with shunting

is dementia Its always a worse sign once mentation gets

involved!

Most likely symptom to improve is incontinence


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NPH: Bottom Line

Good history taking and time with patients andfamily is key to nailing this diagnosis. Justbecause theyve got the classic triad doesnt

mean it may not be Alzheimers (it often willbe); but if you keep NPH on your differentialand consider it rather than writing off all

dementia as Alzheimers, you will have theopportunity to make a fantastic difference in thelives of many patients.

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