= excess of CSF ← increased intraventricular pressure ← imbalance of CSF formation and absorption
Pathophysiology:
- Overproduction (rare)
- Impaired absorption
- Blockage of CSF flow within ventricular system, cisterna magna, basilar cisterns, cerebral convexities
- Blockage of arachnoid villi / lymphatic channels of cranial nerves, spinal nerves, adventitia of cerebral vessels
Signs of raised intracranial pressure (skull film):
- young infant / newborn
- increase in craniofacial ratio
- bulging of anterior fontanel
- sutural diastasis
- macrocephaly + frontal bossing
- “beaten brass” = “hammered silver” appearance = prominent digital impressions (wide range of normals in 4–10 years of age)
- adolescent / adult → changes in sella turcica:
- atrophy of anterior wall of dorsum sellae
- shortening of the dorsum sellae producing pointed appearance
- erosion / thinning / discontinuity of floor of sella
- depression of floor of sella with bulging into sphenoid sinus
- enlargement of sella turcica
DDx: osteoporotic sella (aging, excessive steroid hormone)
Signs favoring hydrocephalus over white matter atrophy:
- commensurate dilatation of temporal horns of lateral ventricles (most reliable sign)
- narrowing of ventricular angle (= angle between anterior / superior margins of frontal horns at level of foramen of Monro) ← concentric enlargement:
- Mickey Mouse ears on axial scan
- enlargement of frontal horn radius (= widest diameter of frontal horns taken at 90° angle to long axis of frontal horn):
- rounding of frontal horn shape
- enlargement of ventricular system disproportionate to enlargement of cortical sulci (← compression of brain tissue against skull + consequent sulcal narrowing)
- interstitial edema from transependymal flow of CSF:
- periventricular hypodensity
- rim of prolonged T1 + T2 relaxation times surrounding lateral ventricles
- hydrocephalic distortion of ventricles + brain:
- atrial diverticulum = herniation of ventricular wall through choroidal fissure of ventricular trigone into supracerebellar and quadrigeminal cisterns
- dilatation of suprapineal recess expanding into posterior incisural space resulting in inferior displacement of pineal gland / shortening of tectum in rostral-caudal direction / elevation of vein of Galen
- enlargement of anterior recess of 3rd ventricle extending into suprasellar cistern
= new equilibrium established at higher intracranial pressure ← opening of alternate pathways (arachnoid membrane / stroma of choroid plexus / extracellular space of cortical mantle = transependymal flow of CSF)
= obstruction to normal CSF flow ← impaired absorption
NUC: radioisotope cisternography
- delay (up to 48 hours) for tracer to surround convexities + reach arachnoid villi
- positive “w” sign
Communicating Hydrocephalus
= EXTRAVENTRICULAR HYDROCEPHALUS
= elevated intraventricular pressure ← blockade beyond outlet of 4th ventricle within subarachnoid pathways
Incidence: 38% of congenital hydrocephaly
Pathophysiology: unimpeded CSF flow through ventricles; impeded CSF flow over convexities by adhesions / impeded reabsorption by arachnoid villi
Cause:
repetitive subarachnoid microhemorrhage (most common cause), immaturity of arachnoid villi, meningeal carcinomatosis (medulloblastoma, germinoma, leukemia, lymphoma, adenocarcinoma), purulent / tuberculous meningitis, subdural hematoma, craniosynostosis, achondroplasia, Hurler syndrome, venous obstruction (obliteration of superior sagittal sinus), absence of Pacchioni granulations
- symmetric enlargement of lateral, 3rd + often 4th ventricles
- dilatation of subarachnoid cisterns
- normal / effaced cerebral sulci
- symmetric low attenuation of periventricular white matter (transependymal CSF flow)
- delayed ascent of radionuclide tracer over convexities
- persistence of radionuclide tracer in lateral ventricles for up to 48 hours
Changes after successful shunting:
- diminished size of ventricles + increased prominence of sulci
- cranial vault may thicken
Cx: subdural hematoma ← precipitous decompression
Noncommunicating Hydrocephalus
= INTRAVENTRICULAR HYDROCEPHALUS
= blockade of CNS flow within ventricular system with dilatation of ventricles proximal to obstruction
Pathogenesis: increased CSF pressure causes ependymal flattening with breakdown of CSF-brain barrier → myelin destruction + compression of cerebral mantle (brain damage)
Location:
- Lateral ventricular obstruction
Cause: ependymoma, intraventricular glioma, meningioma - Foramen of Monro obstruction
Cause: 3rd ventricular colloid cyst, tuber, papilloma, meningioma, septum pellucidum cyst / glioma, fibrous membrane (post infection), giant cell astrocytoma - Third ventricular obstruction
Cause: large pituitary adenoma, teratoma, craniopharyngioma, glioma of 3rd ventricle, hypothalamic glioma - Aqueductal obstruction
Cause: Congenital web / atresia (often associated with Chiari malformation), fenestrated aqueduct, tumor of mesencephalon / pineal gland, tentorial meningioma, S/P intraventricular hemorrhage or infection - Fourth ventricular obstruction
Cause: Congenital obstruction, Chiari malformation, Dandy-Walker syndrome, inflammation (TB), tumor within 4th ventricle (ependymoma), extrinsic compression of 4th ventricle (astrocytoma, medulloblastoma, large CPA tumor, posterior fossa mass), isolated / trapped 4th ventricle
- enlarged lateral ventricles (enlargement of occipital horns precedes enlargement of frontal horns)
- effaced cerebral sulci
- periventricular edema with indistinct margins (especially frontal horns)
- change in RI indicates increased intracranial pressure (ΔRI 47–132% versus 3–29% in normals)
- radioisotope cisternography: no obstruction if tracer reaches ventricle
= rapid CSF production
Cause: Choroid plexus papilloma
- ventricle near papilloma enlarges
- intense radionuclide uptake in papilloma
- enlarged anterior / posterior choroidal artery and blush
= multifactorial CNS malformation during the 3rd / 4th week after conception
Etiology:
- Aqueductal stenosis (43%)
- Communicating hydrocephalus (38%)
- Dandy-Walker syndrome (13%)
- Other anatomic lesions (6%):
- Genetic factors: spina bifida, aqueductal stenosis (X-linked recessive trait with a 50% recurrence rate for male fetuses), congenital atresia of foramina of Luschka and Magendie (Dandy-Walker syndrome; autosomal recessive trait with 25% recurrence rate), cerebellar agenesis, cloverleaf skull, trisomy 13–18
- Nongenetic etiology: tumor compressing 3rd / 4th ventricle, obliteration of subarachnoid pathway due to infection (syphilis, CMV, rubella, toxoplasmosis), proliferation of fibrous tissue (Hurler syndrome), Chiari malformations, vein of Galen aneurysm, choroid plexus papilloma, vitamin A intoxication
Incidence: 0.3–1.8÷1,000 pregnancies
Associated with:
- intracranial anomalies (37%): hypoplasia of corpus callosum, encephalocele, arachnoid cyst, arteriovenous malformation
- extracranial anomalies (63%): spina bifida in 25–30% (with spina bifida hydrocephalus present in 80%), renal agenesis, multicystic dysplastic kidney, VSD, tetralogy of Fallot, anal agenesis, malrotation of bowel, cleft lip / palate, Meckel syndrome, gonadal dysgenesis, arthrogryposis, sirenomelia
- chromosomal anomalies (11%): trisomy 18 + 21, mosaicism, balanced translocation
- elevated amniotic α-fetoprotein level
OB-US (assessment difficult prior to 20 weeks GA as ventricles ordinarily constitute a large portion of cranial vault):
- “dangling choroid plexus” sign:
- choroid plexus not touching medial + lateral walls of lateral ventricles
- downside choroid plexus falling away from medial wall + hanging from tela choroidea
- upside choroid falling away from lateral wall
- lateral width of ventricular atrium ≥10 mm (size usually constant between 16 weeks MA and term)
- 88% of fetuses with sonographically detected neural axis anomalies have an atrial width >10 mm
- BPD >95th percentile (usually not before 3rd trimester)
- polyhydramnios (in 30%)
Recurrence rate:<4%
Mortality:
- Fetal death in 24%
- Neonatal death in 17%
Prognosis: poor with
- Associated anomalies
- Shift of midline (porencephaly)
- Head circumference >50 cm
- Absence of cortex (hydranencephaly)
- Cortical thickness <10 mm
- ocular disturbances: paralysis of upward gaze, abducens nerve paresis, nystagmus, ptosis, diminished pupillary light response
- spasticity of lower extremities (from disproportionate stretching of paracentral corticospinal fibers)
Etiology:
mnemonic:A VP-Shunt Can Decompress The Hydrocephalic Child
- Aqueductal stenosis
- Vein of Galen aneurysm
- Postinfectious
- Superior vena cava obstruction
- Chiari II malformation
- Dandy-Walker syndrome
- Tumor
- Hemorrhage
- Choroid plexus papilloma
Doppler:
- RI >0.8 (sign of increased ICP) in neonate:
- RI of 0.84 ± 13% decreasing to 0.72 ± 11% after shunting
- RI >0.65 (sign of increased ICP) in older children
= NPH = ADAM SYNDROME
= pressure gradient between ventricle + brain parenchyma in spite of normal CSF pressure
- Potentially treatable cause of dementia in elderly!
Cause: communicating hydrocephalus with incomplete arachnoidal obstruction from neonatal intraventricular hemorrhage, spontaneous subarachnoid hemorrhage, intracranial trauma, infection, surgery, carcinomatosis
mnemonic:PAM the HAM
- Paget disease
- Aneurysm
- Meningitis
- Hemorrhage (from trauma)
- Achondroplasia
- Mucopolysaccharidosis
Pathophysiology of CSF:
(?) brain pushed toward cranium from ventricular enlargement; brain unable to expand during systole thus compressing lateral + 3rd ventricles + expressing large CSF volume through aqueduct; reverse dynamic during diastole; “water-hammer” force of recurrent ventricular expansion damages periventricular tissues
Age: 50–70 years
- normal opening pressure at lumbar puncture
- dementia, gait apraxia, urinary incontinence
mnemonic:wacky, wobbly and wet
- communicating hydrocephalus with prominent temporal horns
- ventricles dilated out of proportion to any sulcal enlargement
- upward bowing of corpus callosum
- flattening of cortical gyri against inner table of calvarium (DDx: rounded gyri in generalized atrophy)
MR:
- pronounced aqueductal flow void ← diminished compliance of normal pressure hydrocephalus
- periventricular hyperintensity ← transependymal CSF flow
NUC: radioisotope cisternography
- reversal of normal CSF flow dynamic = tracer moves from basal cisterns into 4th, 3rd and lateral ventricles
- loss of “w” sign
Rx: CSF shunting (only in 50% improvement)