Cerebrospinal fluid (CSF) is the clear liquid that surrounds your brain and spinal cord. It cushions both structures, delivers nutrients, and removes waste. In a healthy brain, CSF flows freely through hollow chambers called ventricles and around the outside of the brain before draining back into the bloodstream. The whole system depends on those pathways staying open.
A high-grade glioma can interrupt that flow. As the tumor grows, it may press on or narrow the channels CSF uses to travel. Fluid backs up, the ventricles swell, and pressure inside the skull rises. That condition is called hydrocephalus. In brain tumor patients, it can appear at any point: at first diagnosis, after surgery, or during later treatment phases. Research shows that roughly 7% of glioma patients develop postoperative hydrocephalus after resection. For a smaller group, the problem arises even without surgery, just from tumor size alone.
Recognizing the warning signs early matters. So does understanding your treatment options. This article explains why hydrocephalus develops in high-grade glioma, how it is diagnosed, and what your surgical team will likely recommend. Options include a ventriculoperitoneal (VP) shunt or a shunt-free endoscopic alternative.
How a High-Grade Glioma Disrupts CSF Flow
Your brain produces roughly 500 milliliters of CSF every day. That fluid circulates through four connected ventricles and through the space surrounding your brain and spinal cord before being absorbed by tissue near large veins. The route involves several narrow passages, and a tumor in or near any of them can cause trouble.
High-grade gliomas include glioblastoma (GBM), anaplastic astrocytoma, and anaplastic oligodendroglioma. These tumors can disrupt CSF flow in two main ways. A tumor positioned near the aqueduct of Sylvius (a narrow channel connecting the third and fourth ventricles) or near the exit points of the fourth ventricle can physically block CSF drainage. Tumors that spread along the brain's lining (a process called leptomeningeal dissemination) can prevent the body from reabsorbing CSF even when no single blockage exists.
The American Brain Tumor Association notes that increased intracranial pressure drives many of the most disruptive brain tumor symptoms. Pressure rises due to tumor size, surrounding swelling (edema), or CSF backup. This pressure causes headache, nausea, drowsiness, and vision changes. Hydrocephalus is one of the most direct and treatable causes of that pressure spike.
Two Types of Hydrocephalus in High-Grade Glioma
Neurosurgeons classify hydrocephalus into two categories. The distinction shapes which procedure your team recommends.
- Obstructive (non-communicating) hydrocephalus happens when the tumor physically blocks a CSF pathway. Fluid cannot circulate past the blockage, so it backs up and the ventricles upstream enlarge. This is most common when tumors sit near the aqueduct of Sylvius, posterior fossa structures, or the fourth ventricle. It tends to appear at or shortly after diagnosis when the tumor is biggest.
- Communicating hydrocephalus happens when the ventricles remain connected to each other, but fluid is not being reabsorbed properly at the end of the circuit. In glioma patients, this form often develops later: after surgery, radiation, or leptomeningeal spread. Its symptoms can be harder to notice and more gradual.
A study in the Journal of Neuro-Oncology examined VP shunting in glioblastoma patients. It found that patients can develop either type. Obstructive hydrocephalus is more common at initial presentation because the tumor takes up space. Communicating hydrocephalus tends to appear later in the disease and is the more common reason for shunt placement. Understanding which type you have guides whether an implanted shunt or a shunt-free surgical bypass is the right choice for you.
Warning Signs That Suggest a CSF Problem
Some symptoms of hydrocephalus overlap with chemotherapy side effects or steroid changes, making them easy to attribute to treatment rather than a new problem. The following signs warrant prompt evaluation by your care team. Do not wait for your next scheduled appointment if you notice them.
- New or worsening headache especially one that is worst in the morning, when lying flat, or with bending forward
- Nausea or vomiting particularly without a clear dietary cause
- Excessive sleepiness or difficulty staying awake during the day
- Visual changes blurred vision, double vision, or a sense that your peripheral vision has narrowed
- Unsteady gait or worsening balance problems a common feature of communicating hydrocephalus
- Worsening confusion or cognitive slowing a change that feels different from your usual treatment-related fog
- Urinary urgency or incontinence particularly in the communicating form, which can mimic normal-pressure hydrocephalus
Cognitive symptoms that overlap with hydrocephalus can be hard to distinguish from treatment-related changes. For a closer look at how chemo and radiation affect thinking and memory, see our article on cognitive changes during glioblastoma treatment. If any of the symptoms above are sudden, severe, or rapidly worsening, call your neuro-oncology team the same day.
How the Diagnosis Is Confirmed
Hydrocephalus in brain tumor patients is diagnosed with imaging. An MRI is the most helpful: it shows enlarged ventricles, fluid tracking through the ventricular walls (called transependymal flow), and the position of the tumor relative to CSF pathways. In an acute or emergency setting, a CT scan can confirm ventricular enlargement quickly without the wait for an MRI slot.
Your team will also look at the full picture: how fast symptoms developed, your tumor's current location and size on imaging, and whether you have recently had surgery, radiation, or new leptomeningeal findings. This context helps rule out other causes of neurological decline. Radiation necrosis and tumor recurrence can both produce swelling that looks like hydrocephalus on scans. To understand that difference, see our piece on distinguishing radiation necrosis from tumor recurrence.
Treating Hydrocephalus: The VP Shunt
Once hydrocephalus is confirmed, the goal is to relieve CSF pressure. A ventriculoperitoneal (VP) shunt is the most widely used approach for brain tumor patients. It is a small, flexible tube system that reroutes excess CSF away from the ventricles and delivers it to the abdominal (peritoneal) cavity, where the body can safely reabsorb it.
The system has three components: a ventricular catheter placed inside the enlarged ventricle, a one-way valve that controls flow and prevents backflow, and a distal catheter that tunnels under the scalp and skin down to the abdomen. Most modern valves are programmable from outside the skin. Pressure settings can be adjusted without returning to the operating room.
The Memorial Sloan Kettering Cancer Center patient guide on VP shunt surgery explains that CSF protects the brain and spinal cord by acting as a cushion and carrying nutrients in and waste out. Restoring normal drainage through a shunt returns that protective function and reduces the symptoms caused by increased pressure.
A study in the Journal of Neuro-Oncology examined VP shunt outcomes in glioblastoma. The procedure relieved symptoms in most patients who received it, with few serious complications. It is now a well-established part of supportive care across all stages of glioma treatment.
An Alternative: Endoscopic Third Ventriculostomy (ETV)
For patients with obstructive hydrocephalus, where one blockage prevents CSF flow, a procedure called endoscopic third ventriculostomy (ETV) may avoid the need for a permanent implant. During ETV, a neurosurgeon uses a thin endoscope (a tiny camera-guided tube) to create a small opening in the floor of the third ventricle. That opening bypasses the blockage, allowing CSF to flow directly into the surrounding space where it is naturally reabsorbed.
Because ETV involves no implanted hardware, it removes the lifetime risk of shunt blockage, mechanical failure, or device-related infection. A review of several studies found that ETV had lower infection rates and fewer CSF leaks than VP shunts. However, ETV only relieves obstructive hydrocephalus. It does not address communicating hydrocephalus, where the problem is with reabsorption rather than a physical blockage. Your neurosurgeon will determine which approach matches your anatomy, tumor location, and current disease status.
What VP Shunt Surgery Involves
VP shunt placement typically takes about one to two hours under general anesthesia. The surgeon makes a small incision in the scalp and drills a small opening in the skull to insert the ventricular catheter. A second incision is made in the abdomen. The distal catheter is then passed under the skin from the head, down the neck and chest, to the belly. No large openings or craniotomies are required.
Most patients stay in the hospital for one to two days after the procedure. Before you leave, the team does imaging to confirm correct catheter placement and check that ventricular size is decreasing. Headache and nausea often improve within hours to a few days as pressure falls. More complex symptoms like unsteady gait, fatigue, or cognitive slowing may take days to weeks to resolve as the brain adjusts to normal pressure.
Living with a Shunt During Active Glioma Treatment
A VP shunt does not prevent you from continuing tumor-directed therapy. Patients with shunts routinely undergo radiation, temozolomide chemotherapy, and in eligible cases, tumor treating fields (TTFields). Certain MRI protocols may require minor adjustments to reduce imaging artifacts near the catheter hardware, but the shunt generally does not interfere with standard follow-up imaging. If your shunt valve is programmable, the MRI magnetic field may reset its pressure setting. Your team will check and re-program the valve after any scan.
Seizures sometimes occur with the elevated intracranial pressure that accompanies hydrocephalus. If you are managing both, our article on seizures in glioblastoma and anti-seizure medication options covers that overlap in more detail.
Risks and Complications to Know
VP shunts are generally safe and well-tolerated, but they carry specific risks that patients and caregivers need to understand before and after surgery.
- Shunt failure or blockage: A long-term study in the Journal of Neurosurgery reported shunt survival rates of approximately 77% at 1 year, 71% at 5 years, and 67% at 10 years in brain tumor patients. This means some patients will need revision surgery over time.
- Infection: Shunt infections are uncommon but serious. Signs include fever above 100.4°F (38°C), redness or swelling along the catheter tract from head to abdomen, and neck stiffness.
- Over-drainage: If CSF drains too rapidly, pressure can drop below normal, causing low-pressure headaches that worsen when sitting or standing upright. Programmable valves help prevent this.
- Abdominal complications: Rarely, the peritoneal catheter causes a fluid collection (pseudocyst) in the abdomen, or the distal tip becomes displaced and stops working.
- Revision surgery: Some patients will need one or more revision procedures during their illness to replace or reposition a malfunctioning component.
Studies of CSF shunting in glioblastoma patients show that tumor growth makes shunt function more complicated over time. Disease progression, leptomeningeal spread, and the effects of prior radiation can all affect how well the shunt works. You need regular neuro-oncology and neurosurgery follow-up. This is essential not just in the weeks after surgery, but through your treatment.
Signs That Your Shunt May Not Be Working
Knowing the warning signs before they escalate can prevent shunt failure from becoming an emergency. Contact your care team promptly, the same day if possible, if you notice:
- Return of the headaches, nausea, or drowsiness that the shunt initially relieved
- Fever or redness along the shunt tubing from your scalp down to your abdomen
- New swelling or a tender fluid collection at the scalp incision or along the abdominal catheter track
- New or suddenly worsening neurological symptoms: arm or leg weakness, speech changes, or confusion
- Sudden changes in vision
Shunt malfunction can produce symptoms that closely mimic tumor progression or a new bleed. Your team will likely order an urgent CT scan of the head and a shunt series. A shunt series is a set of plain X-rays that shows the entire path of the catheter from skull to abdomen. These images look for hardware problems before drawing other conclusions.
When to Talk to Your Doctor
If you are experiencing new morning headaches, unexplained nausea, unusual fatigue, balance problems, or trouble thinking clearly during or after high-grade glioma treatment, bring it up with your neuro-oncology team at your next appointment. Or call the same day if symptoms are sudden or severe. Hydrocephalus is a manageable, treatable condition. Timely diagnosis and the right surgical approach can stabilize symptoms and allow your tumor-directed treatment to continue without interruption. Your neuro-oncologist and neurosurgeon work together on these decisions. You don't have to handle this alone.
This article is for general information and is not a substitute for medical advice. Always consult your oncologist or care team about your specific situation.