What is the difference between communicating and non-communicating hydrocephalus?

From the Guidelines

Communicating hydrocephalus should be managed with cerebrospinal fluid diversion, such as ventriculoperitoneal shunt, as it is the most effective treatment for reducing morbidity and mortality, and improving quality of life, as supported by the American Heart Association/American Stroke Association guidelines 1. The key difference between communicating and non-communicating hydrocephalus lies in the flow of cerebrospinal fluid (CSF) through the ventricular system.

• Communicating hydrocephalus is characterized by the free flow of CSF through the ventricular system, but inadequate absorption in the subarachnoid space, often due to problems with the arachnoid granulations.
• Non-communicating (obstructive) hydrocephalus occurs when there is a physical blockage preventing CSF flow between ventricles, commonly at the level of the cerebral aqueduct, fourth ventricle, or foramen of Monro. The management of hydrocephalus depends on the type, with communicating hydrocephalus typically requiring a ventriculoperitoneal shunt to divert CSF, as recommended by the guidelines 1. In contrast, non-communicating hydrocephalus may be treated with either a shunt or endoscopic third ventriculostomy (ETV) to create an alternative CSF pathway. Diagnosis involves neuroimaging (CT or MRI) to visualize ventricular size and identify potential obstructions, and clinical symptoms are similar in both types, including headache, nausea, vomiting, visual disturbances, cognitive changes, gait abnormalities, and urinary incontinence, though presentation varies by age and progression rate. The guidelines also recommend that aSAH-associated acute symptomatic hydrocephalus should be managed by cerebrospinal fluid diversion (EVD or lumbar drainage, depending on the clinical scenario) 1. Furthermore, weaning EVD over >24 hours does not appear to be effective in reducing the need for ventricular shunting, and routine fenestration of the lamina terminalis is not useful for reducing the rate of shunt-dependent hydrocephalus 1.

From the Research

Communicating vs Non-Communicating Hydrocephalus

• Hydrocephalus is a neurological pathology linked to high morbidity from neurocognitive and motor impairment, and it is classified as either communicating or non-communicating 2.
• Communicating hydrocephalus is understood as a deficit at cranial arachnoid villi and granulation absorption sites, while non-communicating hydrocephalus is often caused by an obstruction in the cerebrospinal fluid (CSF) pathway 2.
• Treatment options for hydrocephalus include endoscopic third ventriculostomy (ETV) and ventriculoperitoneal shunt (VPS), with ETV being an effective long-term treatment for selected adult patients with hydrocephalus 3.
• The success rate of ETV varies depending on the underlying pathology, with a proposed hydrocephalus grading system predicting the outcome of ETV based on the extent of downward bulging of the floor of the third ventricle, presence of directly visualised CSF pathway obstruction, and progression of clinical symptoms 4.

Treatment Outcomes

• A systematic review and meta-analysis found no significant differences in failure rate between ETV and VPS, but ETV was found to have lower complication rates than VPS in prospective cohort studies 5.
• Another systematic review and meta-analysis compared ETV to VPS for the treatment of idiopathic normal pressure hydrocephalus (iNPH) and found no statistically significant difference concerning failure rate of CSF diversion method, but ETV showed a significantly lower complication rate compared to VPS 6.
• The overall ETV success rate when it was the primary treatment modality for adult hydrocephalus was approximately 87%, and 99% of patients experienced symptomatic improvement after 2 ETVs 3.

Classification and Grading

• A proposed hydrocephalus grading system predicts the outcome of ETV based on the extent of downward bulging of the floor of the third ventricle, presence of directly visualised CSF pathway obstruction, and progression of clinical symptoms, with a high correlation between the grade and the outcome of ETV 4.
• The grading system consists of five different grades, with grade 1 showing no downward bulged floor of the 3rd ventricle, no obstruction of the CSF pathway, and no progressive symptoms of hydrocephalus, and grade 5 showing a markedly downward bulged floor of the 3rd ventricle and direct detection of the CSF pathway obstruction with progressive clinical deterioration 4.