A 45-year-old woman comes to the emergency department due to sudden-onset, severe headache. On arrival, the patient is alert and oriented and has no focal neurological deficits. CT scan of the head reveals subarachnoid hemorrhage, and she is admitted to the critical care unit. Over the next several hours, the patient gradually becomes somnolent and less responsive. She opens her eyes to painful stimuli only and does not follow commands. Repeat imaging of the brain shows no new hemorrhage, but there is enlargement of the entire ventricular system compared to the previous CT scan. Which of the following is the most likely cause of this patient's neurologic deterioration in the hospital?
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This patient with a worsening neurologic status has enlargement of the ventricles on CT scan, consistent with hydrocephalus, a common complication of subarachnoid hemorrhage (SAH). Blood in the subarachnoid space can acutely obstruct and impair absorption of cerebral spinal fluid (CSF) by the arachnoid granulations. Later, blood-induced inflammation can cause fibrosis of the arachnoid granulations that perpetuates the absorption impairment and leads to chronic hydrocephalus.
Impaired CSF absorption creates a communicating hydrocephalus. Because the blockage to flow is distal to the entire ventricular system, enlargement of all 4 ventricles occurs. The ventricular enlargement stretches adjacent nerve fibers and, in the acute setting, leads to deteriorating mental status (eg, somnolence, unresponsiveness). Treatment involves the placement of an external ventricular drain to relieve pressure in the ventricular system and subarachnoid space.
(Choice A) Blockage of the cerebral aqueduct (aqueduct of Sylvius) is less common with SAH and more typically occurs with intracerebral hemorrhage complicated by intraventricular bleeding. The resulting hydrocephalus is noncommunicating because there is no free passage of CSF from the ventricular space into the subarachnoid space. Enlargement of only the lateral and third ventricles is expected; the fourth ventricle is distal to the obstruction and remains normal in size.
(Choice B) Cerebral vasospasm is a common complication of SAH; however, it is typically delayed, occurring 4-14 days following the initial bleed, and leads to localized stroke with focal neurologic deficits rather than deteriorating mental status. Dilated ventricles are not seen.
(Choice C) Edema that occurs due to disruption of the blood-brain barrier (vasogenic cerebral edema) collects within the brain parenchyma and can result from stroke or trauma. It is not expected following SAH.
(Choice D) Excessive CSF production is a rare cause of communicating hydrocephalus that may result from a choroid plexus papilloma. Enlargement of all 4 ventricles is expected, but this patient's SAH makes impaired absorption of CSF far more likely.
Educational objective:
Communicating hydrocephalus is a common complication of subarachnoid hemorrhage that presents with deteriorating mental status. It typically results from blood-induced impairment of absorption of cerebrospinal fluid by the arachnoid granulations.