In humans, the epidemiology of hydrocephalus is shown to exhibit a bimodal age curve. The first peak in incidence occurs in infancy and is commonly associated with congenital malformations. A second peak is seen during later adulthood, secondary to normal-pressure hydrocephalus, and is diagnosed when enlarged ventricles are seen in the context of a clinical triad of gait disturbance, dementia, and urinary incontinence. In the United States, the incidence of congenital hydrocephalus is 3 cases per 1000 live births; the incidence of acquired hydrocephalus is not known. Males and females appear to be equally affected by the disease, although normal-pressure hydrocephalus has a slight predominance in males.
The presentation of obstructive hydrocephalus varies according to the age of the patient and the etiology of the obstruction. Adults frequently complain of headaches that are worse in the morning and that are relieved by sitting up; however, the headaches become continuous as the condition progresses. Nausea and vomiting in the morning are also common symptoms. Increasing confusion, blurred vision, double vision from a sixth nerve palsy, neck pain, difficulty walking, and incontinence may also be present. On physical examination, adult patients may have papilledema, truncal and limb ataxia, failure of upward gaze (Parinaud sign), and a unilateral or bilateral sixth nerve palsy. If hydrocephalus is left untreated, death may occur. Accumulation of the CSF causes elevated intracranial tension, resulting in tonsillar herniation, compression of the brain stem, and subsequent respiratory arrest.
In adults, the diagnosis of hydrocephalus is made by either CT scanning or MRI of the brain. The criteria for diagnosing acute hydrocephalus by diagnostic imaging are as follows: The ratio between the largest width of the frontal horns and the internal diameter, from inner-table to inner-table at this level, should be greater than 0.5; the ratio of the largest width of the frontal horns to the maximum biparietal diameter should be greater than 0.3; the temporal horns are enlarged (this is helpful in distinguishing hydrocephalus from atrophy, wherein the temporal horns are typically normal in size); the sulci and interhemispheric and sylvian fissures are narrowed (in atrophy, these are widened); transependymal absorption of CSF is seen as periventricular low density; and, on sagittal images, upward bowing of the corpus callosum and decreased distance between the pons and the mammillary bodies are seen.
Common imaging findings for chronic hydrocephalus include less prominent temporal horn dilation, third ventricle herniation, erosion of the sella turcica, macrocrania, and an atrophied corpus callosum. In infants, ultrasonography can be used via the anterior fontanelle to assess for intraventricular hemorrhage and progressive hydrocephalus. Although a lumbar puncture is useful in diagnosing and treating nonobstructive hydrocephalus, the procedure is contraindicated in obstructive hydrocephalus, as the sudden loss of CSF in the spinal column could potentially exacerbate tonsillar herniation.
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