CSF, Hydrocephalus, Lumbar Puncture Flashcards
What is hydrocephalus?
a general condition whereby there is excess Cerebro-Spinal Fluid (CSF) within the intracranial space and, specifically, the intraventricular spaces within the brain…causing dilation of the ventricles, and a wide range of symptoms
an accumulation of cerebrospinal fluid (CSF) occurs within the brain. This typically causes increased pressure inside the skull
Where and how is CSF made?
The majority of CSF is produced by the choroid plexus within the brain through a metabolically active 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 lateral ventricles (temporal horn roofs, and floors of bodies), posterior 3rd ventricle roof, and caudal 4th ventricle roof
How much CSF is ther ein the brain every day?
The average adult brain produces between 450 and 600 cc’s of CSF every day
At any given moment, there is only ~150 cc’s of CSF present in the average adult; of this, only ~25 cc’s is within the brain ventricles
So, the CSF volume turns over three to four times every day, with only a very small fraction of the CSF being in the ventricles at any given time, even though the majority of it is produced there
The CSF ________/________system exists in a delicate balance under normal conditions
The CSF production/resorption system exists in a delicate balance under normal conditions
Describe the CSF pathway
From the lateral ventricle, CSF travels through the foramen of Monro into the 3rd ventricle, then passes through the Cerebral Aqueduct [of Sylvius] into the 4th ventricle. Then exits the 4th ventricle through either of two Foramina of Luschka (“L” is for Lateral/Luschka) or the single Foramen of Magendie (“M” is for Midline/Magendie)
After exiting the 4th ventricle, the CSF flows through the subarachnoid space over and around the brain and spinal cord, and is eventually reabsorbed into the venous (blood) system through numerous arachnoid granulations along the dural venous sinuses (especially the superior sagittal sinus)
How is CSF absorbed?
Arachnoid granulations contain arachnoid villi, which function as pressure-dependent one-way valves that open when the ICP is ~3 to 5 cm H20 greater than dural venous sinus pressure
Remember - CSF production is a metabolically active process which uses ATP, whereas CSF resorption is a passive process that is driven by the pressure gradient between the intracranial space (ICP) and the venous system (~CVP)
What are the 2 types of hydrocephalus?
Communicating Hydrocephalus (CoH) - also known as “non-obstructive” hydrocephalus
Non-communicating Hydrocephalus (NCH) - also known as “obstructive” hydrocephalus
What is the difference between “Communicating” and “Non-communicating” hydrocephalus?
If the CSF pathway is “open from start to finish,” meaning CSF can travel freely from the choroid plexus to the arachnoid granulations, then you have “no obstruction” and a communicating hydrocephalus
If the CSF can’t travel freely from start to finish, then you’ve got an “obstruction” and non-communicating hydrocephalus
What tends to be the reason for communicating hydrocephalus being caused?
In the vast, vast majority of cases, this represents a problem with CSF resorption; simply put, it cannot keep the pace with CSF production
Normal CSF production = resorption
Comm. Hydrocephalus CSF production > resorption
As a result, the ventricular system dilates uniformly, and ICP rises
The normal CSF system exists in a dleicate balance, what can disrupt this?
A major insult is not required to upset this balance; sometimes, a very slight disturbance is enough to tip the scales such that, over time, communicating hydrocephalus results
In communicating hydrocephalus, the main cause is the CSF not being absorbed fast enough but what may be the other rarer cause of communicating hydrocephalus?
Very rarely, there is overproduction of CSF (rather than under-absorption) which leads to disruption of this balance, and development of communicating hydrocephalus
This is rare, but Choroid Plexus Papillomas have been known to present this way
Do NOT say this as the first answer!
What are the symptoms and signs of communicating hydrocephalus?
In young children whose cranial sutures have not yet fused, you can see disproportional increase in head circumference compared to the rest of the face/body or failure to thrive
In children with fused sutures/adults, hydrocephalus manifests with symptoms of increased intracranial pressure; H/A, N/V, papilledema, gait disturbance, 6th cranial nerve palsy, upgaze difficulty, etc.
What is the aetiology of communicating hydrocephalus?
Infection (incidence after bacterial meningitis can approach 30%)
Subarachnoid Hemorrhage (blood and blood breakdown products cause scarring of arachnoid granulations)
Post-operative
Head trauma
Etc.
Although we usually think of Communicating Hydrocephalus as being a “gentle” disruption of the balance between CSF production and resorption that occurs over time, sometimes there can be a sizeable insult that causes an ______ disruption of the balance, and CSF resorption is suddenly (and dramatically) reduced
acute
a dramatic decline in CSF resorption ability can represent an __________
emergency
When may hydrocephalus develop rapidly?
If significant number of arachnoid granulations are impaired, say, by subarachnoid blood (from a ruptured aneurysm), hydrocephalus can develop very quickly
Neurological decline in such a situation can be rapid, with patients becoming sleepy, then obtunded, then requiring intubation
When does non-communicating hydrocephalus occur?
Non-communicating hydrocephalus occurs whenever there is ANY physical obstruction to the normal flow of CSF before it leaves the ventricles
What are the causes of non-communicating hydrcephalus?
Many causes:
Aqueductal stenosis
Tumors/Cancers/Masses
Cysts
Infection
Hemorrhage/hematoma
Congenital malformations/conditions
Etc.
Non-communicating hydrocephalus can result from CSF flow obstruction at ________ along the intraventricular pathway
any point
Processes that have developed over longer periods of time (i.e. masses, etc) usually cause _________ development of symptoms
gradual
Acute processes (i.e. intraventricular bleed) can cause acute obstruction with ______ mental status decline (just like we discussed previously)
rapid
The earliest consistent radiographical finding indicative of development of hydrocephalus?
dilation of the temporal horns of the lateral ventricles (arrows)
In most younger and middle-aged patients, these should be almost invisible
What other changes can be seen on a radiograph in hydrocephalus?
The third ventricle will become ballooned
Lateral ventricle size increase
Peripheral sulci effaced
Evans Ratio ->30% /Ventricular index >50%
What is the treatment of hydrcephalus?
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 patient’s scalp and skull into lateral ventricle, that drains CSF to a collection system kept at the patient’s bedside)
What are the negatives of EVD
Common procedure but infection risk is high
EVD cannot be maintained indefinitely; usually, if the patient is unable to tolerate weaning/clamping of the EVD prior to removal, a permanent shunt will be required
What is the treatment ofr communicating hydrocephalus?
For communicating hydrocephalus, the mainstay of treatment is shunt placement
Ventriculo-peritoneal is most used
Lumbar-peritoneal sometimes utilized, though overdrainage is a problem
Ventriculo-atrial can also be considered in cases of peritoneal failure
Acute communicating hydrocephalus patients (i.e. SAH) can sometimes be managed with EVD with successful weaning and no shunt placement, but a significant number of these patients eventually need shunt placement weeks or months later
What is the treatment of non-communicating hydrocephalus?
NCH treatment also surgical, but sometimes shunt can be avoided by removing the obstructing lesion:
Colloid cyst at anterior 3rd ventricle causing ball/valve obstruction of Foramen of Monro
Pineal region tumor causing compression of cerebral aqueduct
Ependymoma blocking 4th ventricular CSF outlets
Many, many more!
When treating non-communicating hydrocephalus, in addition to surgical removal of obstructive lesion and shunt placement, what else may be done?
Third Ventriculostomy is an option for non-communicating hydrocephalus
Often performed in conjunction with VP shunt placement
Hole is surgically opened in floor of third ventricle so CSF flows out into the interpeduncular cistern and pre-pontine space (bypasses cerebral aqueduct)
Every patient with a history of VP shunt placement who presents with a headache is NOT automatically having what?
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 don’t have VP shunts
Do VP shunts fail?
VP shunts can and do fail for any of a number of reasons
The incidence of shunt failure is as much as 40% the first year
What is Normal Pressure Hydrocephalus (NPH)?
This is important and you MUST know it because it is one of the rare preventable and/or reversible causes of dementia
Under-recognition leads many patients with NPH to be diagnosed with Alzheimer’s or age-related dementia and they never seek (or receive) treatment
What is the classic triad seen in NPH
Classic triad: “Wet, Wobbly, and Wacky!”
What is seen on investigation of NPH?
Communicating hydrocephalus on CT/MRI
Lumbar Puncture (LP):
- Normal opening pressure
- Symptoms improve with CSF removal
- Gait assessment (time walk and turns) and MMSE
What is the treatment of NPH?
Procedure of choice for patients felt to be suffering from NPH is Programmable VP shunt placement
What is the prognosis of NPH?
Chance of outcome is improved if symptoms have 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 - It’s always a worse sign once mentation gets involved!
Most likely symptom to improve is gait>incontinence>memory
Overall what is it you do with NPH patients?
Good history taking and time with patients and family is key to nailing this diagnosis. Just because they’ve got the classic triad doesn’t mean it may not be Alzheimer’s (it often will be); but if you keep NPH on your differential and consider it rather than writing off all dementia as Alzheimer’s, you will have the opportunity to make a fantastic difference in the lives of many patients
What are the indications for doing a lumbar puncture?
To obtain CSF for the diagnosis of:
Meningitis
Meningoencephalitis
Subarachnoid hemorrhage
Malignancy - diagnosis and treatment
Idiopathic Intracranial Hypertension
Other neurologic syndromes
Infusion of Drugs or contrast
What are the contraindications for a lumbar puncture?
Unstable patient with cardiovascular or respiratory instability
Localized skin/soft tissue infection over puncture site
Evidence of unstable bleeding disorder
Platelets < 50,000 or clotting factor deficiency
Increased intracranial pressure:
- Head CT before study if focal neurologic findings present to rule out impending cerebral mass herniation
- Normal CT does not preclude intracranial HTN
- Do not delay antibiotics to obtain imaging studies when bacterial meningitis is strongly suspected
Neurologic deterioration can occur if LP is done below the level of a complete spinal subarachnoid block
Caution in patients with Chiari malformations
What position is required for a LP?
Spinal cord usually ends at L1-L2(check!), so sites for puncture are located at L3-L4 or L4-L5
Restrain patient in lateral lying down position
Maximally flex spine without compromising airway
Keep alignment of feet, knees and hips
Position head to left if right handed or vice versa
What is the procedure of alumbar puncture?
Cleanse skin with povidone iodine from puncture site radially out to 10 cm and ALLOW TO DRY
Drape below patient and around site with fenestrated drape
Anesthetize with lidocaine if topical not used by
Careful not to inject into a blood vessel or spinal canal
Insert spinal needle with stylet with bevel up to keep cutting edge parallel with nerve and ligament fibers
Aim towards umbilicus directing needle slightly cephalad
Hold needle firmly
A “pop” of sudden decrease in resistance indicates that ligamentum flavum and dura are punctured
Remove stylet and check for flow of spinal fluid
If no fluid, then: Rotate needle 90°, Reinsert stylet and advance needle slowly checking frequently for CSF
Jugular vein compression can increase CSF pressure in low flow situations
If bony resistance is felt immediately then you are not in the spinal interspace
If bony resistance is felt deeply, then withdraw needle to the skin surface and redirect more cephalad and increase patient flexion
If bloody fluid that does not clear or that clots results, then withdraw needle and reattempt at a different interspace
What is manometry used in a LP?
When CSF flows, attach manometer to obtain opening pressure if desired
Pressure can only be accurately measured in lateral decubitus position and in the relaxed patient
Attach manometer with a 3-way stopcock when free flow of CSF is obtained
Read column when highest level is achieved and respiratory variation is noted
How do you end a LP?
Collect 1ml of CSF in each of 3 vials for:
◦ Tube 1: culture & gram stain
◦ Tube 2: glucose, protein
◦ Tube 3: cell count & differential
◦ and extra CSF if desired for other lab tests
Check closing pressure with manometer, if desired
Reinsert stylet and remove needle in one quick motion
Cleanse back and cover puncture site
What posiiton is a LP done is a child
sitting
