Hydrocephalus Flashcards
Epidemiology of Hydrocephalus
Estimated prevalence: 1-1.5%
Incidence of congenital hydrocephalus ~0.9-1.8/1000 births (reported range from 0.2-3.5/1000)
Two functional classifications of hydrocephalus
Obstructive (AKA non-communicating): block is proximal to arachnoid granulations
Communicating (AKA non-obstructive): CSF blocked at level of arachnoid granulations
Hydrocephalus ex vacuo
“Pseudohydrocephalus” condition with enlargement of ventricles due to cerebral atrophy, usually as function of normal aging, but accelerated or accentuated by certain disease processes (eg AD, CJD, TBI)
Otitic hydrocephalus
Obsolete term describing “pseudohydrocephalus” condition where there is increased intracranial pressure in pts with otitis media
External hydrocephalus
“Pseudohydrocephalus” condition seen in infancy with enlarged subarachnoid space with increaseing occipital-frontal head circumference (OFCs) and normal or mildly dilated ventricles
- Enlarged subarachnoid space (usually over the cortical sulci of the frontal poles) seen in infancy (primarily in first year of life)
- Usually accompanied by abnormally increasing head circumference with normal or mildly dilated ventricles
- Often enlarged basal cisterns and widening of the anterior interhemispheric fissure
- NO other S/Sx should be present (although there may be slight delay in motor milestones due to large head)
- Eti is unclear; defect in CSF resorption is postulated
- External hydrocephalus may be variant of communicating hydrocephalus
- May be associated with some craniosynostoses (esp plagiocephaly), but no predisposing factor found in some cases
- May follow intraventricular hemorrhage or superior vena cava obstruction
- DDx: must be distinguished from symptomatic chronic extra-axial fluid collections (or chronic subdural hematoma) which may be accompanied by seizure, vomiting, headache, and may be result of child abuse
- Cortical vein sign may be present in external hydrocephalus where CT or MRI shows cortical veins extending from surface of brain to inner table of skull coursing through the fluid collection; whereas the collections in subdural hematomas compress subarachnoid space which apposes the veins to the surface of the brain
Hydranencephaly
“Pseudohydrocephalus” condition where there is post-neurulation defect, total or near-total absence of cerebrum most commonly due to bilateral ICA infarcts; critical to differentiate this from severe (“maximal”) hydrocephalus since shunting for true hydrocephalus may produce some re-expansion of the cortical mantle
CT/MRI Criteria of Hydrocephalus
A. size of both temporal horns is ≥ 2 mm in width (normally, TH are barely visible) and the sylvian and interhemispheric fissures and cerebral sulci are not visible
OR
B. both TH are ≥ 2 mm and the ratio of FH/ID > 0.5
- FH = largest width of frontal horns
- ID = internal diameter from inner-table to inner-table at level of where FH have largest width)
Other features suggestive of hydrocephalus
- Ballooning of frontal horns of lateral ventricles (Mickey Mouse Ventricles) and/or 3rd ventricle (normally the 3rd ventricle is slit-like)
- Periventricular low density on CT or periventricular high intensity on T2WI on MRI suggesting transependymal absorption of CSF
- FH/ID ratio: < 40% is normal; 40-50% is borderline; >50% suggests hydrocephalus
- Evans ratio (or index): ratio of FH to maximal biparietal diameter measured in same CT slice > 0.3 suggests hydrocephalus
- Sagittal MRI may show thinning and/or upward bowing of corpus callosum
DDx of hydrocephalus
Congenital: chiari 2 and/or myelomeningocele, chiari 1, primary aqueductal stenosis, secondary aqueductal gliosis, Dandy walker malformation, x-linked inherited disorder
Acquired: infectious (most common cause of communicating hydrocephalus) post meningitis (esp purulent and basal, including TB and cryptococcus), cysticercosis; post-hemorrhagic (2nd most common cause of communicating hydrocephalus) post SAH, post-interventricular hemorrhage; secondary to masses (non-neoplastic, eg vascular malformation; neoplastic, esp tumors around the aqueduct such as medulloblastoma; colloid cyst at foramen of monroe; pituitary tumor)
Post-Op: 20% of peds pts develop permanent hydrocephalus requiring shunt after p-fossa tumor removal
Neurosarcoidosis
Constitutional ventriculomegaly
Associated with spinal tumors
Atrophy (hydrocephalus ex vacuo)
Hydranencephaly
Developmental abnormalities where ventricles appear enlarged (agenesis of corpus callosum, septo-optic dysplasia)
Congenital etiologies of hydrocephalus
- Chiari 2 and/or myelomeningocele
- Chiari 1: hydrocephalus may occur secondary to 4th ventricle outlet obstruction
- Primary aqueductal stenosis: usually presents in infancy (rarely in adulthood)
- Secondary aqueductal gliosis: due to intrauterine infection or germinal matrix hemorrhage
- Dandy-Walker malformation: atresia of foramina of Luschka and Magendie (incidence of this in pts with hydrocephalus is 2.4%)
- X-linked inherited disorder (rare)
Acquired Etiologies of hydrocephalus
- Infectious (most common cause of communicating hydrocephalus): post-meningitis (esp purulent and basal, such as TB or cryptococcus), cysticercosis
- Post-hemorrhagic (2nd most common cause of communicating hydrocephalus): post SAH, post intraventricular hemorrhage (many will develop transient hydrocephalus and 20-50% with large IVH will develop permanent HCP)
- Secondary to masses: non-neoplastic (vascular malformation), neoplastic (tumors around aqueduct such as medulloblastoma; colloid cyst can block foramen of Monroe; pituitary tumor with suprasellar extension or expasion from pituitary apoplexy)
- Post-op: 20% of Peds pts develop hydrocephalus after surgery for p-fossa tumor (may be delayed up to 1 year)
- Neurosarcoidosis
- “Constitutional ventriculomegaly”: asymptomatic and needs no treatment
- Associated with spinal tumors
S/Sx of active hydrocephalus in young children
- Cranium enlarges at rate greater than facial growth
- Irritability, poor head control, N/V
- Fontanelle full and bulging
- Enlargement/engorgement of scalp veins due to reversal of flow from intracerebral sinuses due to increased intracranial pressure
- Macewen’s sign: cracked pot sound on percussing over dilated ventricles
- 6th nerve palsy: thought to be very sensitive to pressure due to long intracranial course
- “Setting sun sign” (upward gaze palsy): Parinaud’s syndrome from pressure on region of suprapineal recess
- Hyperactive reflexes
- Irregular respirations with apneic spells
- Splaying of cranial sutures (seen on plain film of skull)
*When child is older with rigid cranial vault: symptoms of increased ICP (papilledema, H/A, N/V, gait changes, upgaze and/or abducens palsy); slowly enlarging ventricles may initially be asymptomatic
Clinical features of chronic hydrocephalus
- Beaten copper cranium (some reger to beaten silver appearance) on plain skull film; by itself, does not correlate with increased ICP, but when combined with #3 and 4 below, it does correlate; may be seen in craniosynostosis
- 3rd ventricle herniating into sella (seen on CT/MRI)
- Erosion of sella turcica which sometimes produces an empty sella and erosion of the dorsum sella
- Temporal horns may be less prominent on CT than in acute hydrocephalus
- Macrocrania: by convention, occipital-frontal head circumference > 98th percentile
- Atrophy of corpus callosum: best appreciated on sagittal MRI
- In infants: sutural diastasis, delayed closure of fontanelles, failure to thrive/developmental delay
Tx of External Hydrocephalus
- Usually compensates by 12-18 months without shunting
- Recommend serial US and/or CT to rule out ventricular enlargement
- Emphasize to parents that this does NOT represent cortical atrophy
- There is increased risk of positional molding, so parents may need to periodically reposition head while kid is sleeping
- Shunt may be rarely indicated when collections are bloody (consider child abuse) or for cosmetic reasons for severe macrocrania or frontal bossing
X-Linked Hydrocephalus
- Eponym
- Description
- Epi
- Genetics
- Pathophys
- Eponym: Bickers-Adam syndrome
- Description: inherited hydrocephalus with phenotypic expression in males passed on through carrier females who are phenotypically normal (classic phenotypic expression will skip generations)
- Epi: incidence 1/25000-60000; prevalence 2/100 cases of hydrocephalus
- Genetics: gene located on Xq28
- Pathophys: L1CAM membrane bound receptor plays significant role in CNS development for axonal migration to appropriate target locations through Integrin cell adhesion molecules and MAP kinase signal cascade; with abnormal gene expression, there is poor differentiation and maturation of cortical neurons resulting in macroscopic anatomical abnormalities (bilateral absence of pyramidal tracts); cytoplasmic domain loss of function mutations result in severe L1 syndrome, whereas mutations retaining expression of some functional protein (component imbeded in cell membrane) leads to mild L1 syndrome
