A 43-year-old man comes to the office due to progressive memory loss and cognitive decline over the past several years. Medical history includes HIV infection diagnosed 11 years ago. Highly active antiretroviral therapy was prescribed, but he is nonadherent. The patient describes concerns with attention, concentration, and speech. In the past few months, he has become more apathetic and increasingly lethargic. More recently, he has had difficulty with balance and has fallen on multiple occasions. The patient has had no headache, tremor, vision change, fever, nausea, vomiting, or urinary incontinence. His brother has a history of severe intellectual disability and epilepsy. The patient scores 18/30 on the Mini-Mental State Examination and appears emotionally blunted. He also has postural instability and difficulty performing fine motor tasks. Noncontrast CT scan of the head is shown in the Image 1 , Image 2 . This patient's condition can best be characterized as which of the following?
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This patient with a long history of inadequately treated HIV infection has memory impairment with evidence of subcortical dysfunction (eg, inattention, impaired psychomotor function and speed), which is characteristic of HIV-associated dementia.
CT scan reveals dramatic enlargement of the ventricles (ie, ventriculomegaly) consistent with hydrocephalus. In addition, there is increased prominence of the sulci consistent with cortical atrophy. Therefore, the compensatory increased cerebrospinal fluid (CSF) volume is due to significant loss of neuronal volume rather than a CSF disorder (hydrocephalus ex vacuo).
Any advanced neurodegenerative disease (eg, HIV-associated dementia, Alzheimer disease) or other condition that leads to neuronal loss (eg, trauma, stroke) can progress to hydrocephalus ex vacuo. Associated clinical manifestations are typically those associated with the primary cause of the neuronal loss rather than those specifically related to hydrocephalus.
(Choices A and D) Many forms of hydrocephalus are due to an inappropriate increase in CSF volume. These forms of hydrocephalus can be classified by whether there is obstruction of flow within the ventricular system (communicating vs noncommunicating). Although this patient has no obstruction of flow within the ventricular system, the increased CSF volume is compensatory due to a decrease in neuronal volume, which is better characterized as hydrocephalus ex vacuo.
(Choice C) Lissencephaly (agyria) is a congenital absence of gyri. This condition is typically accompanied by severe intellectual disability and seizures. On gross examination and imaging, the brain surface has a smooth appearance.
(Choice E) Pseudotumor cerebri (idiopathic intracranial hypertension) refers to elevated intracranial pressure in the absence of ventricular enlargement on imaging. This disorder classically presents in young, obese women with headache, papilledema, and possible vision loss due to optic neuropathy.
(Choice F) Transtentorial (uncal) herniation can occur due to an intracranial mass (eg, tumor, hemorrhage) or cerebral edema. The herniation may lead to compression of the ipsilateral oculomotor nerve (CN III) and posterior cerebral artery. A fixed, dilated pupil on the same side as the lesion is often the first sign of uncal herniation.
Educational objective:
Hydrocephalus ex vacuo can occur due to neurodegenerative disease (eg, HIV infection) when significant neuronal loss leads to a compensatory increase in the volume of cerebrospinal fluid.