New Research Reconsiders the Cause of Hydrocephalus

Hydrocephalus, commonly referred to as "water on the brain," is a dangerous and potentially deadly condition that can harm the brain. For more than a century, physicians have believed that the buildup of cerebrospinal fluid (CSF) within the brain and the organ's inability to absorb CSF is the main cause of hydrocephalus.

Now, new research led by Stony Brook Medicine neurosurgeon Michael Egnor, MD, suggests this process is not the cause, and if proved true, the finding could revolutionize treatments for hydrocephalus.

The research is detailed in a paper published in the Journal of Neurosurgery: Pediatrics (JNS Pediatrics), the leading international journal on the research of neurological conditions in children, including hydrocephalus.

Hydrocephalus is prevalent worldwide and can affect people of any age. According to the Hydrocephalus Association, one million Americans suffer from the condition and some 25 million worldwide. The most common medical conditions that can lead to hydrocephalus are children who are born with hydrocephalus or develop it from brain hemorrhage of prematurity, people with head trauma, aneurysms, strokes or tumors, and elderly who can develop normal pressure hydrocephalus.

Some people with hydrocephalus have a severe build-up of pressure in the brain that can be life-threatening. Others who are elderly can have hydrocephalus that causes difficulty with walking, bladder control and memory loss.

For nearly all patients, hydrocephalus is an incurable disease that requires lifelong medical care and operations. Hydrocephalus can only be treated with surgery, which usually consists of the insertion of a CSF shunt from the brain into the abdomen. As medical devices, shunts have high malfunction rates, which complicates hydrocephalus management and can lead to many operations for patients to keep shunts working.

"For a century, neurosurgeons and scientists have believed that hydrocephalus is caused by a blockage to CSF absorption that causes a buildup of cerebrospinal fluid in the ventricles of the brain," said Egnor, lead author and professor of Neurosurgery and Pediatrics in the Renaissance School of Medicine (RSOM) at Stony Brook University. "We showed that the conventional understanding of the cause of hydrocephalus is not correct. Hydrocephalus is caused by the failure of the brain to absorb pulsatile energy from the heartbeat, not by the failure of the brain to absorb CSF."

The research team illustrated through their work that the salient features of hydrocephalus are explained better as the result of malabsorption of pulsatile energy from the heartbeat than the malabsorption of CSF. They used an electrical circuit model of the pulsatile CSF dynamics of the cerebral windkessel system - which removes the heartbeat pulsations from the blood entering the brain so that capillary blood flow is smooth and safe - to simulate hydrocephalus caused by subarachnoid obstruction.

"This new understanding of hydrocephalus points to new treatment approaches based on the diversion of pulsatile energy," the authors wrote.

They added that "the theory that hydrocephalus is caused by CSF malabsorption is inconsistent with a broad spectrum of experimental and clinical evidence." And therefore, "We propose that hydrocephalus is a disorder of pulsatile dynamics, i.e., hydrocephalus is impairment of the cerebral windkessel system caused by high impedance of pulsatility in the CSF pathways."

Egnor and colleagues stress that the windkessel theory is a new approach to the study of intracranial dynamics. The theory is a direct challenge to the traditional theory (Monro-Kellie doctrine), which obscures the pulsatile cause because of neuroscientists' misguided century-long preoccupation with CSF formation and absorption.

The authors say they welcome scrutiny of the windkessel theory of hydrocephalus, which will add to the body of research for a better understanding and treatment of the condition, which they emphasize is long overdue. They also hope that future investigators study the windkessel dynamics and electrical circuit theory, just as past hydrocephalus researchers studied bulk CSF flow and pressure-volume curves.

Editorial supports the new theory

An editorial in the same edition of JNS Pediatrics, titled "Hydrocephalus, pulsatility and the windkessel effect," by a team of neurosurgery investigators not involved in the study, believes the new research is essential to advancing physicians' understanding of hydrocephalus.

They wrote that despite some key questions remaining, "The authors are to be commended for this readable and understandable summary of CSF physiology according the windkessel theory. The electrodynamic model corresponds nicely to the physical conditions that the authors have chosen for this experiment."

The editorial further endorsed the direction of the groundbreaking work, particularly in the context that hydrocephalus treatment with shunts to drain CSF - which did change hydrocephalus treatment from an often fatal disease to a manageable one - are also problematic.

Egnor says that he and colleagues will continue studying various forms of hydrocephalus and will include imaging studies as part of future research. They will also investigate new shunt designs for hydrocephalus. The research will involve multiple departments from the RSOM and Stony Brook University.

Co-authors for the JNS Pediatrics paper include Nahid Shirdel Abdolmaleki, Yicun Wang, Anand Ravishankar and Petar M. Djurić of the Department of Electrical and Computer Engineering at Stony Brook University; Racheed Mani, MD, of the Department of Neurology; and Susan Fiore of the Department of Neurosurgery in the RSOM.