4. CSF Formation
Average intracranial volume : 1400 to 1700 ml
CSF occupies about 150 ml : 10 percent approx.
Rate of formation : 0.35ml/min = ~20ml/hour = ~500ml/day
Renewed 3 – 4 times a day
5. Sites of production
Choroidal plexus : 70-80 percent
Extra-choroidal : 20-30 percent
Ependyma
Capillaries
Brain Interstitial fluid
6. AQP1
Mechanism of choroidal production
Tight junction
Epithelial cells
Active process :
Uses ATP
movement of ions
osmotic
gradient
secretion of H2O
high expression of
AQP1 on apical
membrane
7. Factors affecting CSF production
Endogenous Exogenous
CSF Pressure Acetazolamide
Choroid plexus ischemia Frusemide
Hypoxia Amiloride
Acidosis/ Alkalosis Omeprazole
Hypoglycemia Glycosides
Neural Cholera toxins
Johnston, I et al. Child's Nerv Syst. 2000
8. Pathway of CSF Flow
Lateral ventricles
Foramen of Monro Third ventricle
Aqueduct of Sylvius
Fourth ventricle
Foramina of Magendie and Luschka
Subarachnoid space of brain & spinal
cord
Reabsorption into venous sinus
11. Mechanism of CSF flow
The pressure gradient is highest in the lateral ventricles and diminishes
successively along the subarachnoid space
b, the negative venous pressure
(dark blue) produced during
inspiration causes temporary
pressure decrease in intracranial
compartment, resulting in CSF
outflow (Dreha-Kulaczewski et al.
2017)
Delaidelli, A et al. Journal of Neuroscience 2017
a. Arterial pulse wave (red) causes
temporary pressure increase in
intracranial compartment, resulting
in CSF outflow (O'Connell, 1943)
13. Mechanism of absorption
Hydrostatic pressure in
subarachnoid space (11 mmHg)
> dural sinuses (5 mmHg)
Arachnoid villi open : pressure
in SAS ~1.5 mm Hg > pressure
in dural sinuses
Passive process
Papaiconomou,C.et al News Physiol Sci 2002
14. Possible alternative sites of CSF absorption
Arachnoid endothelium &
membrane
Adventitia of blood vessels
and lymphatics
Cranial/ spinal nerve roots
sleeves/ lymphatics
Capillary endothelium
Spinal arachnoid
projections
Johnston, I et al. Child's Nerv Syst. 2000
Papaiconomou,C.et al News Physiol Sci 2002
15. The functions of the CSF
Support: wt. of brain ~1500 gm ~50 gm
Shock absorber : protects brain during head trauma
Homeostasis
Maintains stable intrinsic CNS temperature
Maintains osmotic pressure normal CSF pressure normal cerebral
perfusion
Removes biochemical waste products
Nutrition : glucose/proteins/lipids/electrolytes essential CNS nutrition
Immune function : contains immunoglobulins and mononuclear cells
16. Intra Cranial Pressure (ICP)
≤ 15 mmHg in adults
Intracranial hypertension (ICH) : pressure ≥ 20 mmHg
Normally lower in children than adults
Homeostatic mechanisms stabilize ICP
Intracranial contents include :
Brain parenchyma — 80 %
Cerebrospinal fluid — 10 %
Blood — 10 %
17. Compliance
Compliance is the
interrelationship between
changes in the volume of
intracranial contents and
changes in ICP
The compliance relationship is
nonlinear
Compliance decreases as the
combined volume of the
intracranial contents increases
Point of exhaustion
of compliance
18. The Monroe-Kellie doctrine
Sum of volumes of the 3 components
is constant an increase in volume
of any one component
accompanied by a reduction in
volume of at least one of the
remaining two components
ICP : Function of the volume and
compliance of each component of the
intracranial compartment
The magnitude and the rate of
change in the volume of each
component determines its effect on
ICP
19. Factors that influence ICP
Arterial pressure
Venous pressure
Intra-abdominal and intra-thoracic pressure
Posture
Temperature
Blood gases (hypoxia / hypercapnia)
The degree to which these factors ↑ ICP depends on the ability of the
brain to accommodate to the changes.
20. Cerebral Perfusion Pressure (CPP)
The pressure needed to overcome ICP in order to deliver O2 &
nutrients.
Clinical surrogate for the adequacy of cerebral perfusion.
MAP is the DRIVING FORCE ---------- ICP is the RESISTENCE
CPP = MAP – ICP = 100 mmHg – 15 mmHg = 85 mmHg (Normal)
CPP < 50 mmHg → cerebral ischemia
CPP < 30 mmHg → brain death
21. Consequences of altered CSF hydrodynamics
Abnormal fluid movement (transependymal/transparenchymal)
Effects of raised ICP
Circulatory changes (micro and macro) Ischemia
Changes in brain morphology/parenchymal damage
Changes in CSF circulatory path : obstruction/ shunt/ surgery
Effects of loss or misdistribution of CSF
Post-shunt or other post-surgical changes
Johnston, I et al. Child's Nerv Syst. 2000
25. Definition
Hydrocephalus : derived from two Greek words: hydro = water, and
cephalus = head
Condition wherein excess of CSF accumulates within ventricular system
and cisterns of the brain leading to increased ICP and related
consequences
26. Types & causes
Functional
Time of onset
of the lesion
Rate of
appearance
of clinical
symptoms
Clinical
symptoms
Intracranial
pressure
Non-
communicating
(obstructive)
Congenital Acute (within
days)
Active Normal pressure
hydrocephalus
(NPH)
Communicating
(non-
obstructive)
Acquired Subacute
(within
weeks)
Occult /
Arrested
Increasing pressure
hydrocephalus
Chronic
29. Clinical features
Clinical features of hydrocephalus are influenced by:
Patient's age
Cause
Location of obstruction
Duration
Rapidity of onset
30. In infants
Symptoms Signs
Poor feeding Head enlargement
Vomiting Disjunction of sutures
Irritability Dilated scalp veins
Reduced activity/
lethargy
Tense fontanels
Setting sun sign
Increased limb tone
31. In children / adults
Symptoms Signs
Cognitive decline Papilledema
Headache Failure of upward gaze &
accommodation
Vomiting -- morning U/L or B/L sixth nerve palsy
Neck pain Lower limb spasticity
Blurred / double vision Gait apraxia
Difficulty in walking Other signs of raised ICP
Stunted growth and sexual
maturation in children
Macewen sign : A "cracked
pot" sound on percussion of
head in children
32. Diagnostic techniques
USG
in infants (due to open fontanel)
and in utero
CT/MRI scanning : the mainstay of diagnosis
CSF Flow study
CSF pressure measurement
33. CT/MRI features
Increased frontal horn radius
(Mickey mouse ventricle)
Dilatation of the temporal horns
(>2mm)
Acute ventricular angles
34. CT/MRI features
Periventricular interstitial edema
from the transependymal flow :
high T2 signal on MRI or low-
density change on CT
Intra-ventricular flow void from
CSF movement
35. CT/MRI Features
Inferior displacement of the
floor of the 3rd ventricle
Outward bowing / ballooning
of the lateral walls & recesses
of the third ventricle
(infundibular, optic and pineal
recesses)
Ballooning of the suprapineal
recess
36. CT/MRI Features
On mid-sagittal plane :
Upward displacement of corpus
callosum
Thinned out corpus callosum
Depression of the posterior
fornix
Decreased mamillopontine
distance ( normal >5.5mm)
37. CSF flow study
To qualitatively assess and quantify pulsatile CSF flow
MC technique : time-resolved 2D phase contrast MRI with velocity
encoding (VENC)
CSF flow in the context of imaging : pulsatile to-and-fro flow due to
vascular pulsations NOT bulk transport of CSF
Typical CSF flow is 5-8 cm/s
Hyperdynamic circulation : much higher velocities : up to 25 cm/s
38. CSF flow study
Images are typically presented in sets of 3 for each plane and velocity
obtained.
The set comprises of
re-phased image (magnitude of flow compensated signal)
• flow is of high signal
• background is visible
39. CSF flow study
magnitude image (magnitude of difference signal)
• flow is of high signal (regardless of direction)
• background is suppressed
phase image (phase of difference signal)
• signal is dependent on direction:
forward flow is of high signal;
reverse flow is of low signal
• background is mid-grey
40. CSF flow study
Clinical applications
aqueduct stenosis
normal pressure hydrocephalus (NPH)
patency of third ventriculostomy
flow at the cervicomedullary junction (foramen magnum)
Chiari I malformation
41. CSF pressure measurement
Direct assessment of elevated ICP
Surgical placement of ventricular /
intraparenchymal pressure transducer
Intraparenchymal transducer : more
invasive /real time data/ accurate
determination of ICP
Helps in management decisions
42. Management
The main goal is to minimize or prevent brain damage by decreasing ICP
and improving CSF flow.
Medical management
Temporary procedures
External ventricular drainage
Spinal tap
Surgical management
Shunt
Endoscopic Third Ventriculostomy (ETV)/other endoscopic procedure
Eliminating the cause of obstruction
43. Medical management
Acetazolamide:
Carbonic anhydrase inhibitor
Reduces CSF production
Cannot be used as a long-term treatment modality
Diuretics therapy – tried in infants with bloody CSF : resumption of
normal CSF reabsorption.
Watch for electrolyte imbalance and acetazolamide side effects:
Lethargy , tachypnea, diarrhea , paresthesias
44. External Ventricular Drainage (EVD)
Acute hydrocephalus, whether communicating or not : necessitates
urgent or emergent placement of EVD
It is temporary drainage of CSF
from the lateral ventricles or
the lumbar space of the spine
into an external collection bag.
An EVD system drains CSF
by using a combination of
gravity and ICP
45. External Ventricular Drainage (EVD)
Cannot be maintained indefinitely
Unable to tolerate weaning/clamping of the EVD : permanent shunt
Acute communicating hydrocephalus patients (i.e. SAH) can
sometimes be managed with EVD with successful weaning and no
shunt placement
Additional benefits:
ICP monitoring
Intraventricular antibiotics
CSF sampling
46. Spinal tap
Hydrocephalus after IVH may be transient
Serial taps (ventricular or LP) may temporize until resorption resumes
LPs only for Communicating HCP
No reabsorption when the protein content of the CSF is < 100 mg/dl
Spontaneous resorption unlikely
SHUNTING
47. Shunt surgery
Recommended for communicating hydrocephalus, including NPH
Can be used in obstructive hydrocephalus f/b ventriculostomy
Purpose : to divert CSF flow to another area of the body, where it can be
absorbed
Ancillary testing before shunt surgery:
Radionuclitide cisternography
CSF flow study
Intracranial pressure measurement
CSF tap test - 40-50ml of CSF and assessment of gait & cognition.
48. Shunt system & types
Shunt systems include three components:
a ventricular catheter (with reservoir)
a one way valve and
a distal catheter.
The ventricular catheter is a straight piece of tubing, closed on the
proximal end with multiple holes for the entry of CSF
Shunts are composed of a material called Silastic (polymerized
silicone).
50. Shunt system & types
Preferred location for the distal catheter : peritoneal cavity
ease of access
fewer complications.
Previous abdominal surgery or peritonitis: ventriculoatrial shunt /
ventriculopleural shunt
More complications risk of emboli, pleural effusion, pneumothorax,
respiratory distress, and endocarditis with ventriculoatrial /
ventriculopleural shunt
51. Rare types of shunts
Torkildsen shunt:
Shunting ventricle to cisternal space
Lumbo-peritoneal shunt:
Only for communicating hydrocephalus
If proximal catheter cannot be placed in ventricle
Not used in children due to risk of scoliosis
Cyst/Subdural-Peritoneal shunt:
Draining arachnoid cyst/subdural hygroma cavity
52. Complications of shunt surgery
Shunt malfunction:
caused by infection or mechanical failure
Approx. 40 percent malfunction : within the first year after placement
5 percent per year malfunction in subsequent years
Possible shunt malfunction : development of new or worsening signs
or symptoms of elevated ICP
Urgent evaluation with detailed neurologic examination and
neuroimaging : CT scan
53. Complications of shunt surgery
Infection:
common complication
5 to 15 percent of procedures
Can lead to ventriculitis
Contribute to impaired cognitive outcome and death
Max risk : first 6 months after shunt placement
54. Complications of shunt surgery
Common presentation in VP shunt : increasing abdominal pain
associated with peritoneal signs and/or fever
Only fever in children
Antibiotics : often not effective alone
Infected shunt must be removed placement of EVD
Perioperative antibiotic prophylaxis / use of antibiotic-impregnated
catheters : lowers risk of infection
55. Complications of shunt surgery
Mechanical failure :
Most common : first year after shunt placement
Major cause : obstruction at the ventricular catheter
Fractured tubing : approx. 15 % of cases.
Other causes include
shunt migration (partial or complete) and
excessive CSF drainage (over drainage)
Requires prompt recognition and surgical intervention
56. Complications of shunt surgery
Over drainage:
Functional shunt failure
Causes subnormal ICP (particularly in the upright position)
Associated with characteristic symptoms : postural headache and
nausea
Can lead to slit-ventricle syndrome : small or slit-like ventricles, coupled
with transient episodes of symptoms of raised ICP
57. Endoscopic Third Ventriculostomy
Involves creating an opening in the
floor of third ventricle to allow CSF to
flow into pre-pontine cistern and
subarachnoid space
All patients with obstruction between
the third ventricle and the cortical
subarachnoid spaces are potential
candidates for ETV
Absolute contraindication :
obstruction at the level of the
arachnoid villi or the venous flow in
the superior sagittal sinus
59. Endoscopic Third Ventriculostomy
Indications:
Aqueductal stenosis
Posterior fossa tumors and cysts with hydrocephalus
Postinfectious hydrocephalus
Tuberculous meningitis with hydrocephalus
Hydrocephalus associated with myelomeningocoele and Chiari
malformation
Hydrocephalus secondary to intracerebral / intraventricular hemorrhage
Shunt dysfunction
60. Endoscopic Third Ventriculostomy
Complications:
infection
CSF leak
Surgical complications : subdural, intracerebral, and epidural
hematoma
hemiparesis, gaze palsy, memory disorders, altered
consciousness, and/or hypothalamic dysfunction
Postoperative mortality (0.2 percent)
Delayed sudden death (i.e., >2 years following ETV) due to acute
hydrocephalus from stoma occlusion
61.
62. Recent studies
Endoscopic third ventriculostomy was found to be safe and effective in TBM
hydrocephalus (Yadav YR et al. Neurology India 2011)
The evidence at the moment is not sufficient to recommend ETV in the routine
management of TBM related hydrocephalus especially in the early stage ( Misra
UK et al., Ann Indian Acad Neurol. 2012)
ETV should be considered as treatment of choice in chronic phase of tubercular
meningitis associated obstructive hydrocephalus (Yadav R. et al., Asian J
Neurosurg. 2016)
ETV gives comparable results in pediatric hydrocephalus with the distinct
advantage of freedom from hardware and its associated risks ( Deopujari et al., J
Korean Neurosurg Soc. 2017)
Early surgical outcome following ETV is better than VPS surgery in patients with
obstructive hydrocephalus ( Rehman MM et al. Asian J Neurosurg. 2018)
64. Definition
Refers to a condition of pathologically enlarged ventricular size with
normal opening pressure on lumbar puncture
A form of communicating hydrocephalus
65. Types
Idiopathic NPH : When no obvious cause is identified
Secondary NPH : Impaired absorption of CSF is the suspected
mechanism in most cases of secondary NPH.
The MC causes are :
Intra-ventricular or subarachnoid hemorrhage
Prior acute or ongoing chronic meningitis
Paget disease at the skull base, mucopolysaccharidosis of the meninges,
and achondroplasia are other rarely reported causes of secondary NPH
66. Clinical features
Three cardinal features:
Gait difficulty : most prominent clinical feature, a magnetic or "glue-
footed" gait
Cognitive impairment with subcortical and frontal features, including:
• Psychomotor slowing
• Decreased attention and concentration
• Impaired executive function
• Apathy
Urinary incontinence
Absence of signs and symptoms related to increased ICP : headaches,
nausea and vomiting, visual loss or papilledema
67. Additional Radiological findings
The Evans' index
Ratio of maximum width of the frontal horns of the lateral ventricles (A)
and maximal internal diameter of skull (B) at the same level
Employed in axial CT / MRI images
Varies with the age and sex
Marker of ventricular volume
A/B > 0.3 - Hydrocephalus
68. Narrow callosal angle :
Angle measured on a coronal image perpendicular to the anterior
commissure - posterior commissure (AC-PC) plane at the level of the
posterior commissure
Normal = 100-120°
NPH = 50-80°
69. Cingulate sulcus sign :
Denotes the posterior part of the cingulate sulcus being narrower than
the anterior part.
Divider b/w anterior and posterior parts of the sulcus : line drawn parallel
to the floor of 4th ventricle
70. Cerebral aqueduct flow void
Loss of signal in the aqueduct of Sylvius
Represents higher-than-normal flow velocity of CSF in the aqueduct
71. DESH (Disproportionately
enlarged subarachnoid space
hydrocephalus)
Characterized by:
• Ventriculomegaly
• Tight high-convexity and medial
subarachnoid spaces
• Disproportionate enlargement of
the Sylvian fissures
• Focally dilated or entrapped sulci
without adjacent cortical atrophy
• Acute callosal angle
72. Feature of idiopathic NPH = DESH-iNPH
May be complete or incomplete
Predicts favorable outcome after shunt surgery
Akiguchi I.et al, Annals of Clinical and Translational Neurology 2014
Shinoda N. et al, Journal of Neurosurg 2017
74. Hydrocephalus ex vacuo
Compensatory enlargement of the CSF spaces
Seen in :
asymptomatic elderly people : aging brain with related volume loss
pathological conditions that promote brain shrinkage:
• generalised brain degeneration (e.g. Alzheimer disease and
leukodystrophies)
• encephalomalacia due to focal damage (e.g. stroke and traumatic
injuries)
75. Benign external hydrocephalus
Enlargement of the subarachnoid space
frontal or
frontoparietal regions
Ventriculomegaly : absent or mild.
Clinically, infants have macrocephaly but otherwise well-appearing and
have normal development.
Presentation : progressive increase in the head circumference with normal
anterior fontanel.
Family history of macrocephaly : Frequent
Self-limited
Do not require any intervention
76. Arrested hydrocephalus
Asymptomatic/ occult/ compensated/ long
standing overt ventriculomegaly of adulthood/
late onset idiopathic aqueductal stenosis
Moderate to severe tri-ventricular enlargement
No evidence of periventricular fluid
accumulation on imaging
Stable for years
Incidental diagnosis
Conservative approach with serial imaging
May be associated with cognitive decline or
sudden decompensation
78. Definition & Types
Defined as CSF pressure < 60 mm H2O in patients with clinical
presentation compatible with intracranial hypotension
Most commonly results from a CSF leak somewhere along the neuraxis
Intracranial hypotension can broadly be divided into:
primary: referred to as spontaneous intracranial hypotension (SIH)
secondary:
• iatrogenic (lumbar puncture or surgery)
• over-shunting due to diversion devices,
• traumatic
79. Causes
SIH : usually result from CSF leak in the spine.
Causes include :
spontaneous dural dehiscence of meningeal diverticula (perineural
cyst)
degenerative dural tears
congenital focal absence of dura (nude nerve root) - rare
CSF-venous fistula
80. Presentation
Presentation : positional headache
relieved by lying in recumbent position within 15-30 minutes
Nausea/vomiting/vertigo/neck pain
Traumatic or iatrogenic intracranial hypotension : history of
abundant, clear rhinorrhea or otorrhea present.
Occasionally, presentation is more sinister, with reported cases of
decreased level of consciousness and coma
81. Radiographic features
Imaging is crucial both for confirming the diagnosis of intracranial
hypotension and identifying the location of the leak
CT
subdural collection
acquired tonsillar ectopia
dural venous sinus distention
84. Management
Conservative
Avoidance of the upright position : strict bed rest and the possible
addition of analgesics.
Restoring CSF volume : oral or i.v. hydration, high oral caffeine intake,
and high salt intake
Epidural blood patches : first line
infusion of 10 to 20 cc of autologous blood into the epidural space
may be repeated
Adverse effects : back pain, radiculopathy, leg paresthesias, and fever
Epidural fibrin glue
Surgical repair