What Is an Ommaya Reservoir and How Is It Used?

An Ommaya reservoir is a small, dome-shaped device implanted under the scalp that allows doctors to deliver chemotherapy and other medications directly into the cerebrospinal fluid surrounding the brain. Developed by the Pakistani-American neurosurgeon Ayub Khan Ommaya, the device bypasses the blood-brain barrier, a biological shield that blocks most drugs given by vein from ever reaching the central nervous system. Since its introduction, the reservoir has become a standard tool in treating cancers that spread to the brain’s lining, certain leukemias, severe central nervous system infections, and a handful of other conditions where getting medication into the brain is the whole challenge.

How the Device Works

The brain and spinal cord float in cerebrospinal fluid, which circulates through a series of internal chambers called ventricles and around the outer surfaces of the brain and spinal cord. A tough set of membranes and the blood-brain barrier keep most bloodborne substances out of this fluid. That protection is normally a good thing, but it becomes a serious obstacle when cancer cells or infections settle in the cerebrospinal fluid. Drugs injected into a vein achieve far lower concentrations in the brain and spinal fluid than they do in the rest of the body.¹ The Ommaya reservoir solves that problem by providing a permanent port directly into the ventricular system.

The device itself has two parts: a silicone dome roughly the size of a quarter that sits in a shallow pocket carved into the skull bone, and a thin catheter that threads from the dome down into one of the brain’s lateral ventricles. Once healed, the dome sits just beneath the scalp and can be felt as a soft bump. A clinician accesses it by inserting a small needle through the scalp and into the dome, then injects medication or withdraws a sample of cerebrospinal fluid. Because the catheter tip rests inside the ventricle, the drug disperses through the entire cerebrospinal fluid circulation rather than pooling at a single spot.

Surgical Placement

Implanting the reservoir is a relatively brief neurosurgical procedure, usually performed under general anesthesia. The surgeon makes a small incision on the scalp, drills a burr hole through the skull, and guides the catheter into the frontal horn of the lateral ventricle, typically on the right side. The silicone dome is then secured over the burr hole beneath the scalp, and the incision is closed.

Accuracy of catheter placement matters a great deal. If the tip lands outside the ventricle or migrates afterward, the reservoir cannot distribute drugs properly and may need surgical revision. In a retrospective review of 109 consecutive adults who had their catheters placed using stereotactic guidance, accurate ventricular placement was achieved in 99% of cases, with the only poor catheter position caused by migration after surgery rather than a placement error. Perioperative complications occurred in about 6% of patients, and bleeding complications were concentrated in those who had low platelet counts or were on blood-thinning medications.²

Guidance technology has evolved over the decades. A comparison of 145 patients found that frameless stereotactic navigation and traditional fluoroscopy produced similar overall accuracy, with revision rates under 5% in both groups.³ More recently, some centers have combined electromagnetic neuronavigation with a flexible endoscope, allowing the surgeon to visualize the ventricle in real time and confirm catheter position before closing. Early reports suggest this approach improves tip accuracy compared with blind or fluoroscopy-guided methods.⁴

Why Not Just Use a Lumbar Puncture?

The traditional alternative for putting drugs into the cerebrospinal fluid is a lumbar puncture, the familiar “spinal tap.” A needle goes between the vertebrae in the lower back, enters the spinal fluid space, and delivers the medication. Lumbar punctures do not require surgery or a permanent implant, so they sound simpler. The catch is that drug injected at the base of the spine has to travel upward through the spinal canal and eventually into the brain’s ventricles, and the distribution is uneven. By contrast, medication instilled through the Ommaya reservoir starts at the top of the system and flows downward, covering the brain surfaces more reliably.

A review at St. Jude Children’s Research Hospital confirmed that intraventricular delivery through an Ommaya reservoir improves drug distribution in the central nervous system compared with the more commonly used lumbar route.⁵ Whether better distribution translates into longer survival has been tested in several studies, and the results lean in the reservoir’s favor. A systematic review and meta-analysis found that patients with leptomeningeal metastases who received intrathecal chemotherapy through an Ommaya reservoir had significantly better overall survival than those treated by lumbar puncture, with no significant difference in disease control rates between groups.⁶

A separate retrospective study focused on patients who also had hydrocephalus (excess fluid buildup in the brain) alongside their leptomeningeal cancer. In that population, the Ommaya group achieved a substantially higher overall response rate (roughly 87% versus 48%) and a higher clinical response rate (100% versus about 52%), with better relief of elevated intracranial pressure. Complication rates were comparable between the two approaches.⁷ For patients who need repeated treatments, the reservoir also spares them the discomfort and risks of repeated lumbar punctures, which can involve headache, back pain, and occasional failed attempts.

Common Indications

The largest group of patients who receive an Ommaya reservoir are those with leptomeningeal metastases, a condition in which cancer cells from a tumor elsewhere in the body seed the membranes covering the brain and spinal cord. Breast cancer, lung cancer, and melanoma are among the most frequent culprits. Median survival for patients treated with reservoir-delivered chemotherapy for leptomeningeal metastases has been reported at about nine months.⁸ That number is modest, but the disease itself carries a grim prognosis regardless of treatment approach, and the reservoir enables symptom relief and intracranial pressure management alongside chemotherapy.

In pediatric oncology, the reservoir has a long track record. Children with acute lymphoblastic leukemia (ALL) and non-Hodgkin lymphoma sometimes develop central nervous system involvement that demands direct cerebrospinal fluid treatment. An early study of 39 children with meningeal leukemia described using an Ommaya reservoir to deliver chemotherapy into the cerebrospinal fluid after initial remission was induced through lumbar punctures.⁹ That approach has since become standard at major pediatric cancer centers. The reservoir spares children from repeated spinal taps, which can be especially traumatic for young patients.

Beyond cancer, Ommaya reservoirs have been used for severe central nervous system infections that do not respond adequately to intravenous antibiotics or antifungals. Cryptococcal meningitis in immunocompromised patients is one example. In a report of children with cryptococcal meningitis managed with an Ommaya reservoir, patients experienced rapid symptom reversal and remained asymptomatic after discharge.¹⁰ These cases are uncommon but illustrate the device’s versatility when conventional drug routes fall short.

Less Familiar Uses

Craniopharyngiomas, slow-growing tumors that arise near the pituitary gland, sometimes form large fluid-filled cysts that press on the optic nerves and surrounding brain tissue. Rather than performing repeated open surgeries to drain these cysts, some neurosurgeons place an Ommaya reservoir directly into the cyst cavity. This lets them aspirate fluid through a simple needle tap whenever the cyst refills, and in some cases they instill a sclerosing agent to shrink the cyst wall. In a series of 11 adults with cystic craniopharyngiomas treated this way, visual function and elevated intracranial pressure improved after decompression, and local tumor control was achieved in about 73% without the need for additional treatments.¹¹

In neonatology, extremely premature infants who develop bleeding inside the brain’s ventricles can go on to develop posthemorrhagic hydrocephalus. These babies are often too small and fragile for a permanent shunt. An Ommaya reservoir can serve as a temporizing measure, allowing nurses to tap the dome and drain small amounts of cerebrospinal fluid daily until the infant grows large enough for definitive shunt surgery, or occasionally until the hydrocephalus resolves on its own. A small series of seven infants weighing under 1,000 grams at birth found that two of the seven ultimately avoided permanent shunt surgery altogether, though the complication rate was relatively high in this fragile population.¹²

Infection Risk and Management

Any implanted device that breaches the skin barrier repeatedly is vulnerable to infection, and the Ommaya reservoir is no exception. Each time a needle is inserted through the scalp into the dome, bacteria from the skin surface can hitch a ride. The infection rate varies across institutions and patient populations, but the range in published studies gives a reasonable picture. A 16-year retrospective analysis identified infections in about 5.5% of patients, translating to 0.74 infections per 10,000 device-days. Nearly a third of these infections occurred within the first 30 days of placement, and the majority of late infections were linked to a reservoir access in the preceding month. The most common organisms were skin bacteria: coagulase-negative staphylococci accounted for over half of infections, followed by Propionibacterium acnes.¹³

Other studies have reported higher rates. A Japanese single-center analysis of 136 adults found that about 13% developed reservoir-related bacterial meningitis, at a rate of 5.9 infections per 10,000 device-days.¹⁴ A separate review of 501 reservoir placements reported an 8% infection rate, again dominated by gram-positive skin flora (over 80% of pathogens).¹⁵ The differences likely reflect variations in patient populations, how aggressively the reservoirs were accessed, and local sterile technique protocols.

When infection does occur, the traditional teaching held that the reservoir had to come out, the way an infected joint prosthesis usually does. But evidence has accumulated that many infections can be cleared with antibiotics alone, administered both intravenously and directly into the reservoir, without removing the device. An early case series found that all eight episodes of reservoir infection responded to systemic antibiotics with or without intraventricular treatment, and none relapsed after at least 40 days of follow-up. The authors argued that removal of the reservoir was not always necessary, challenging the prevailing assumption at the time.¹⁶ Today, the decision is individualized. If the patient still needs the reservoir for ongoing treatment, trying antibiotics first makes sense; if the device is no longer needed or the infection is resistant, removal may be the cleaner path.

What Living with a Reservoir Is Like

Once healed, the reservoir is largely invisible to an observer, though the patient can feel the dome as a soft bump under the scalp. Hair typically regrows over the incision site. There are no external tubes or drainage bags. Between treatments, the reservoir sits dormant, and most patients can carry on with daily life without restrictions, though contact sports and activities that risk a direct blow to the head are generally discouraged.

When it is time for a treatment or a fluid sample, the patient sits up or reclines, the scalp over the dome is cleaned, and a small-gauge butterfly needle is pushed through the skin into the silicone reservoir. The procedure takes a few minutes and is done at the bedside or in a clinic room. Some patients report a brief feeling of pressure or mild headache during or after the tap, but the discomfort is generally less than that of a lumbar puncture. The frequency of taps depends entirely on the treatment protocol and can range from weekly to every few months.

One quality-of-life advantage that patients often appreciate is predictability. Lumbar punctures sometimes fail on the first attempt, especially in patients with obesity, spinal arthritis, or prior lumbar surgery. The Ommaya dome is always in the same place, always accessible, and almost never fails to yield cerebrospinal fluid. For patients facing months of repeated treatments, that consistency reduces both physical discomfort and anxiety around each visit.

Cost and Access Considerations

The Ommaya reservoir requires a neurosurgical procedure for placement, which adds upfront costs compared with lumbar punctures, where no surgery is needed. A conference abstract estimated typical placement costs at roughly $29,000 for a standard intraventricular Ommaya reservoir. However, some centers have explored a lumbar variant placed into the spinal fluid space rather than the brain’s ventricle, which came in at about $17,350, representing approximately a 40% cost reduction.¹⁷ Whether the lumbar variant offers equivalent drug distribution remains an open question, but it points to ongoing efforts to make the technology more accessible.

In practice, the decision about whether to place a reservoir depends on how many intrathecal treatments the patient is expected to need. If someone needs only one or two doses, the cost and risk of surgery are hard to justify when lumbar puncture is available. If the treatment plan calls for weekly or biweekly injections over several months, the reservoir becomes not just more convenient but often cheaper in total when you factor in the cost of repeated hospital visits for lumbar punctures, each of which may require imaging guidance and a proceduralist.

The Person Behind the Device

Ayub Khan Ommaya was born in 1930 in what is now Pakistan and trained in neurosurgery in the United Kingdom and the United States. His career spanned clinical neurosurgery, research into traumatic brain injury, and medical device innovation. The reservoir that bears his name was one of several contributions; he was also known for work on the biomechanics of head injury and served as a medical officer at the National Institutes of Health.¹⁸ The reservoir was developed in the 1960s, and while neurosurgical tools from that era have largely been replaced, the Ommaya reservoir’s fundamental design has endured with remarkably few modifications. The dome-and-catheter concept was sound enough that six decades of advances in materials and imaging have mostly refined the placement technique rather than the device itself.

That longevity is unusual in medicine, where devices tend to be redesigned or supplanted within a generation. Part of the explanation is the simplicity of the concept: there are no moving parts, no electronics, nothing to break or run out of battery. The dome is made of medical-grade silicone, which the body tolerates well for years. As long as the catheter remains in the ventricle and the dome remains intact, the reservoir can function indefinitely. Some patients have had functioning reservoirs in place for over a decade without trouble.