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Extraventricular Obstructive Hydrocephalus
KEY FACTS
Terminology
-
Extraventricular obstructive hydrocephalus (EVOH): Enlarged ventricles due to mismatch between cerebrospinal fluid (CSF) formation, absorption
-
Synonym: “Communicating” hydrocephalus
Imaging
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Impaired absorption of CSF distal to 4th ventricle outlet foramina
-
Ventricular size varies with duration of obstruction
-
All ventricles enlarged with no intraventricular obstructive cause
-
Lateral, 3rd, and 4th ventricles dilated
-
± periventricular white matter interstitial edema
-
± abnormal density/intensity of cisternal CSF ± leptomeningeal enhancement
Top Differential Diagnoses
-
Intraventricular obstructive hydrocephalus
-
Ventricular enlargement secondary to parenchymal loss
-
Normal pressure hydrocephalus
Pathology
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Hemorrhage → fibrosis/obstruction of subarachnoid space
-
Most common cause of EVOH
-
-
Other etiologies include suppurative meningitis, neoplastic or inflammatory exudates
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Subarachnoid hemorrhage, exudates may fibrose/occlude subarachnoid space, reduce CSF pulsations
Clinical Issues
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Headache, papilledema
-
Nausea, vomiting, diplopia (cranial nerve palsy)
Diagnostic Checklist
-
EVOH: Generalized ventricular enlargement with abnormal density/intensity in basal cisterns ± leptomeningeal enhancement
Axial NECT shows acute subarachnoid hemorrhage in the basal cisterns
and sylvian fissures
. There is early extraventricular obstructive hydrocephalus with mild periventricular hypodensity
due to interstitial edema.
and sylvian fissures . There is early extraventricular obstructive hydrocephalus with mild periventricular hypodensity due to interstitial edema.
Axial T1WI C+ MR shows extensive leptomeningeal enhancement of the basal cisterns in neurosarcoidosis
. Notice the early communicating hydrocephalus with the dilated 3rd ventricle
and temporal horns
.
. Notice the early communicating hydrocephalus with the dilated 3rd ventricle and temporal horns .
Axial T2 MR in a 21-year-old patient with a remote history of meningitis shows chronic “compensated” extraventricular communicating hydrocephalus with marked dilatation of the lateral
and 3rd ventricles
.
and 3rd ventricles .
Sagittal T1 MR in the same patient shows a patent widened cerebral aqueduct
and foramen of Magendie
with dilatation of 4th ventricle
. In long-standing “compensated” hydrocephalus, there is no periventricular interstitial edema around the ventricles, as in this case.
and foramen of Magendie with dilatation of 4th ventricle . In long-standing “compensated” hydrocephalus, there is no periventricular interstitial edema around the ventricles, as in this case.
TERMINOLOGY
Abbreviations
-
Extraventricular obstructive hydrocephalus (EVOH)
Synonyms
-
“Communicating” hydrocephalus
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