Continuous quantitative electroencephalography for early detection of acute low-pressure obstructive hydrocephalus in aneurysmal subarachnoid hemorrhage: illustrative case.

backgroundAneurysmal subarachnoid hemorrhage (aSAH) is often associated with acute high-pressure hydrocephalus. Less commonly, an acute low-pressure hydrocephalus (ALPH) variant can develop and contribute to increased morbidity. ALPH is particularly challenging to diagnose and manage, as patients present with symptoms of increased intracranial pressure (ICP) despite the absence of corroborating evidence from ICP measurements. Misdiagnosis or delayed recognition can result in increased morbidity. OBSERVATIONS: The authors describe a patient with aSAH who developed neurological deterioration from ALPH. Despite normal ICP readings, the patient displayed symptoms of increased ICP. Significant electroencephalography (EEG) changes preceded the neurological deterioration by many hours. In addition, these EEG changes reversed with cerebrospinal fluid removal and eventual hydrocephalus resolution. LESSONS: ALPH presents with paradoxical ICP dynamics, complicating its diagnosis. Careful monitoring, including EEG, can provide an early indication of neurological deterioration and guide timely intervention. This case underscores the importance of considering ALPH in patients with aSAH who show clinical worsening without corresponding increases in ICP. Tailoring management to address the atypical pressure dynamics is crucial for improving outcomes. https://thejns.org/doi/10.3171/CASE24612.