Keywords: Hydrocephalus, CSF shunt malfunction, ventriculomegaly, Evans' ratio (PubMed Search)
Hydrocephalus is a disorder of cerebrospinal fluid (CSF) accumulation. Acute obstructive hydrocephalus such as in subarachnoid hemorrhage and CSF shunt malfunction can cause a rapid rise in intracranial pressure. Nonobstructive hydrocephalus is associated with subacute symptoms. Clinical features of acute obstructive hydrocephalus include headache, blurred vision, papilledema, ocular palsies, nausea and vomiting, and decreased level of consciousness.
Evaluation of hydrocephalus in the ED should include neuroimaging, typically noncontrast head CT given its wide availability. CT characteristics of hydrocephalus can be seen in Figure 1: ventriculomegaly with dilated 3rd ventricle, dilated 4th ventricle, and presence of temporal horns.
When evaluating patients with pre-existing hydrocephalus for worsening symptoms, such as in the evaluation of CSF shunt malfunctions, it is helpful to compare the head CT or MRI for interval ventricular enlargement. Two simple measurements can be taken on a CT or MRI for objective comparisons (Figure 2).
Evans' ratio = A/B = Maximum width of frontal horns (A) divided by maximum width of inner skull (B) at the same CT/MRI level
C = Width of 3rd ventricle
Use of acetazolamide to decrease CSF production is not effective in long-term treatment of hydrocephalus. About 75% of patients with hydrocephalus require CSF shunt placement.
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