HYDROCEPHALUS Flashcards
WHAT IS HYDROCEPHALUS?
Hydrocephalus refers to a disorder where the is a disturbance in the production, flow or reabsorption of CSF resulting in accumulation of CSF pathway and cerebral ventricles, causing ventricular enlargement due that discrepancy
Accumulation of CSF within its pathway (ventricles) result in their dilatation and subsequent increase in ventricular pressure which is transmited to the adjuscent brain parenchymal causing impairment of of such structures as the corticobulbar and corticospinal tracts
A progressive loss of motor function ensues
OUTLINE THE FLOW OF CSF
70% of CSF is produced by the choroid plexus of the lateral, 3rd and 4th ventricles by an active transport process across the endothelium of capillaries in the villus processes of the choroid plexus and 30% is secreted by the brain parenchymal across ependymal (single layer of ciliated columnar epithelium cells lining the ventricular system)
After its production it enters the ventricles
The formation is an active process involving the enzyme carbonic anhydrase and specific transport mechanisms which transport Na+and Mg2+ into CSF and remove K+ and Ca2+
Normally, rate of formation of CSF is about 20 mL/hour (≈ 500 mL/day) and total volume of CSF is 90 to 150 mL, of which about 23 mL is in ventricles, and remaining is in the subarachnoid space.
CSF has similar osmotic pressure to that of plasma but its viscosity is similar to H2O
Movement of CSF is pulsatile.
It flows from lateral ventricles into 3rd ventricle through foramina of Monro (interventricular foramen).
Then, from 3rd ventricle it flows via cerebral aqueduct (aqueduct of Sylvius) into 4
th ventricle.
CSF leaves 4th ventricle via 2 lateral foramina of Luschka and midline foramen of Magendie and enters cerebellomedullary cistern (cisterna magna).
From cisterna magna, CSF then travels rostrally over the cerebral hemisphere and absorbed by arachnoid villi into dural venous sinuses in one direction because the pressure in SAS is higher (about 200 mmH2O) than that in dural venous sinuses (about 80 mmH2O).
Some CSF from cisterna magna also flows downward into spinal SAS and then ascends along the ventral surface of the spinal cord into the basal part of the brain then courses dorsally to empty into the dural sinuses
WHICH LAYERS MAKE UP THE CHOROID PLEXUS?
A choroid plexus consists of 3 layers of membranes:
(1) An endothelial layer of the choroidal capillary wall, which has fenestrations
(2) A pial membrane, and
(3) A layer of choroidal epithelial cells with numerous mitochondria and many basal infoldings and microvilli on the surface facing the inside of the ventricle
WHAT ARE THE FUNCTIONS OF CSF?
Functions of CSF
1) Brain and spinal cord float in CSF whose buoyant effect results in reduction of traction exerted upon the nerves and blood vessels connected to these CNS structures.
2) Provides a cushioning effect on the CNS and dampens the effects of trauma.
3) Removal of metabolites from the CNS.
4) Provides a stable ionic environment for the CNS under normal conditions.
WHAT ARE THE CAUSES OF HYDROCEPHALUS?
Causes of hydrocephalus
Results from
d) An excess of CSF production (in rare condition of choroid plexus papilloma and choroid plexus Ca),
e) From CSF flow obstruction (an obstructive hydrocephalus) - aqueductal stenosis, brain lesion and tumour, infections (meningitis), intraventricular bleeds, Dandy Walker cyst
f) Failure of reabsorption (a communicating hydrocephalus) - obstruction at the arachnoid granulations, otitic hydrocephalus, sinus thrombosis, arachnoiditis,
g) Familial causes; Bicker’s Adam syndrome, an X-linked recessive abnormality
h) Associated abnormalities
i. Dandy-Walker syndrome
ii. Arnold-Chiari malformation
iii. Spina bifida
iv. Aqueductal stenosis
LIST THE CLASSIFICATIONS OF HYDROCEPHALUS
Classification I of Hydrocephalus
1. Communicating Hydrocephalus
2. Noncommunicating hydrocephalus
Classification II of hydrocephalus
1. Congenital Hydrocephalus
2. Acquired hydrocephalus
DIFFERENTIATE BETWEEN COMMUNICATING AND NON-COMMUNICATING HYDROCEPHALUS
- Communicating Hydrocephalus (Non obstructive hydrocephalus): Ventricles communicate freely into the subarachnoid space.
Movement of CSF in dural venous sinuses is impeded or blocked by defective absorption at the arachnoid villi e.g. following any inflammation, subarachnoid haemorrhage or trauma.
Also excess production of CSF such as in choroid plexus papillioma - Noncommunicating hydrocephalus (aka obstructive hydrocephalus): Obstruction is in the ventricle or its exit, due to tumours or any inflammatory process.
Mvt of CSF out of the ventricular system is impeded (e.g. blockage at cerebral aquaduct/foramina of 4th ventricle- foramina of luschka and magedie)
A tracer dye injected in the lateral ventricles does not appear in the lumber CSF due to obstruction
WHAT IS NORMAL PRESSURE HYDROCEPHALUS?
a) Normal pressure hydrocephalus- Form of communicating hydrocephalus
A dye injected in the lateral ventricles appear in lumbar CSF.
Occur in cerebral atrophy, ventricles are dilated but the pressure is not raised.
Aka Hydrocephalus ex vacuo.
Cause of NPH may be known but most often it’s idiopathic.
Its characterized by a triad of 3w; Wacky (dementia/cognitive decline), wobbly (gait apraxia /gait disturbance) and wet (incontinence)
May occur de novo or on a background of previous brain insults including SAH, head injury, meningitis and tumour.
Ventriculomegaly is evident on imaging
WHAT IS CONGENITAL HYDROCEPHALUS
Congenital Hydrocephalus - Presents at birth caused by complex interaction of genetic and environmental factors during fetal development
Dsis by US
WHAT ARE THE CAUSES OF CONGENITAL HYDROCEPHALUS?
Causes
a) Intrauterine infections/conditions: Rubella, cytomegalovirus, toxoplasmosis, intracranial bleeds, intraventricular hemorrhage
b) Intracranial haemorrhage - IVH
c) Congenital malformations:
i. Aqueduct stenosis – x-linked conditions in males
ii. Dandy-Walker syndrome (posterior fossa cyst continuous with fourth ventricle), its characterized by cystic dilatation of 4th ventricle and cerebellum hypoplasia
iii. Arnold-Chiari syndrome (portions of cerebellum and brainstem herniating into cervical spinal canal, blocking the flow of CSF to the posterior fossa)
iv. Midline tumors obstructing CSF flow
v. Neural tube defects- Myelomeningocele usually leads to Arnold Chairi II malformation which causes part of the cerebellum and the 4th ventricle to be pushed downwards via the magnum foramen blocking the flow of CSF
vi. Arachnoid cysts – commonly located in the back of the brain (posterior fossa). The cysts are filled
with CSF and lined with arachnoid membrane and these may block CSF pathway.
vii. Encephalocoele
viii. Incompetent arachnoid villi
ix. Atresia of foramen of Monro
WHAT ARE THE CAUSES OF ACQUIRED HYDROCEPHALUS?
- Acquired hydrocephalus – develops after birth due to neurological conditions e.g. head trauma,
i. Infection: Tuberculosis, chronic and pyogenic meningitis, infectious and chemical ventriculitis, chemical arachnoiditis
ii. Head Trauma – cause damage to the brain tissue, nerves and blood vessels. Blood can then enter CSF pathway causing inflammation. Scarred meninges at the level arachnoid villi/ granulation can block CSF absorption
iii. Post-intraventricular hemorrhage
iv. Subarachnoid haemorrhage
v. Posterior fossa tumors: Medulloblastoma, astrocytoma, ependymoma
Brain tumours—(pineal/cerebellar/craniopharyngiomas)
vi. Arteriovenous malformation, intracranial hemorrhage, ruptured aneurysm (Berry aneurysm)
vii. Hydrocephalus ex vacuo
viii. Rarely choroid plexus papilloma - cause excessive production of CSF
DESCRIBE THE PATHOPHYSIOLOGY OF HYDROCEPHALUS
As a results of an imbalance between production, circulation and absorption of CSF, CSF continues to accumulate leading to progressive dilatation of the subarachnoid channels,
Increase in CSF pressure is transmitted to the venticular system resulting in ventriculomegaly.
Ependymal lining of ventricles is disrupted resulting in periventricular ooze and hence periventricular compression of adjuscent white matter.
Ventricular enlargement causes displacement of primary cerebral arteries and a reduction in the calibre and number of secondary and tertiary vessels causing diminished blood flow and ischaemia
Cortex is generally preserved due to better blood supply until late and so atrophy involving primarily axons and neurons of the grey matter are selectively spared.
WHAT ARE THE EFFECTS OF INCREASED INTERCRANIAL PRESSURE ON THE DEVELOPING BRAIN?
Effects of increased ICP on the developing brain include:
a) White matter atrophy
b) Stretching and damage of ependymal epithelium with formation of ventricular diverticulae
c) Spongy oedema of the brain parenchyma
d) Fenestration of septum pellucidum and thinning of interhemispheric commisure
WHAT ARE THE CLINICAL FEATURES OF HYDROCEPHALUS IN NEWBORNS AND INFANTS?
Newborn and Infant
Large head often causes obstructed labour.
Presents with raised head circumference > 2 cm/month and craniofacial disproportion- Head circumference (Macrocrania) > 97th percentile for GA is suggestive.
Discrepancy between head & chest circumference may also be suggestive (normally head measures about 1 cm > chest circumference until late in 1st year when it reverses).
Bulging anterior fontanelle, more prominent on crying.
Poor feeding and failure to thrive
Lethargy, somnolence and irritability.
Sutural diastasis particularly the squamoparietal suture.
Dilated scalp vein, scalp is thin and shiny,
Parinauds phenomenon (sunset sign caused by pressure on tectal plate) decreased upward gaze
May have divergent strabismus
Macewen’s sign (cracked pot resonance)- on percussion cracked pot sound due to dilated ventricle
Delayed milestones and difficulty in head control.
Apneic bouts and bradycardia are usually associated with posterior fossa anomalies due to distortion of brain stem. Also associated with systemic hypertension and altered respiration rate
Cranial nerve palsies and stridor may also be seen in infants.
Exclude spasticity of the lower extremeties
WHAT ARE THE CLINICAL FEATURES OF HYDROCEPHALUS IN OLDER CHILDREN?
Older Child
Older children have a more acute presentation due to inability of fused cranium to expand
Presents with a triad of: severe headache, vomiting and lethargy.
Papilloedema on fundoscopy due to ↑ICP
Skull contour becomes abnormal and forehead is prominent
Delayed motor and cognitive development and subtle behavioural changes are noted.
A mild spastic diplegia (pyramidal tract signs) with positive Babinski sign can also be elicited.
Decreased active leg motion, poor placing and positive support reflexes.
Features of raised ICP mainly in adult, lethargy, irritability, ataxia, papilloedema, blindness, ophthalmoplegia, abducens palsy and respiratory failure
