• Michael B Keough, Albert M Isaacs, Geberth Urbaneja, Jarred Dronyk, Andrew P Lapointe, and Mark G Hamilton.
• 1Department of Surgery, University of Alberta, Edmonton.
• J. Neurosurg. 2021 Jul 1; 135 (1): 300308300-308.

ObjectiveAcute low-pressure hydrocephalus (ALPH) is characterized by clinical manifestations of an apparent raised intracranial pressure (ICP) and ventriculomegaly despite measured ICP that is below the expected range (i.e., typically ≤ 5 cm H2O). ALPH is often refractory to standard hydrocephalus intervention protocols and the ICP paradox commonly leads to delayed diagnosis. The aim of this study was to characterize ALPH and develop an algorithm to facilitate diagnosis and management for patients with ALPH.MethodsEMBASE, MEDLINE, and Google Scholar databases were searched for ALPH cases from its first description in 1994 until 2019. Cases that met inclusion criteria were pooled with cases managed at the authors' institution. Patient characteristics, presenting signs/symptoms, precipitating factors, temporizing interventions, definitive treatment, and patient outcomes were recorded.ResultsThere were 195 patients identified, with 42 local and 153 from the literature review (53 pediatric patients and 142 adults). Decreased level of consciousness was the predominant clinical sign. The most common etiologies of hydrocephalus were neoplasm and hemorrhage. While the majority of ALPH occurred spontaneously, 39% of pediatric patients had previously undergone a lumbar puncture. Prior to ALPH diagnosis, 92% of pediatric and 39% of adult patients had a ventricular shunt in situ. The most common temporizing intervention was subatmospheric CSF drainage. The majority of patients underwent a shunt insertion/revision or endoscopic third ventriculostomy as definitive ALPH treatment. Although the mortality rate was 11%, 83% of pediatric and 49% of adult patients returned to their pre-ALPH neurological functional status after definitive treatment. Outcomes were related to both the severity of the underlying neurosurgical disease causing the hydrocephalus and the efficacy of ALPH treatment.ConclusionsALPH is an underrecognized variant phenotype of hydrocephalus that is associated with multiple etiologies and can be challenging to treat as it frequently does not initially respond to standard strategies of CSF shunting. With early recognition, ALPH can be effectively managed. A management algorithm is provided as a guide for this purpose.

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