Overview of Ommaya Reservoir
The Ommaya reservoir is a medical device that doctors use to gain ongoing access to a space within your spinal cord called the intrathecal space. It’s named after its creator, Pakistani neurosurgeon Ayub Khan Ommaya, who invented it in 1963. Its original purpose was for inserting anti-fungal medications directly into the cerebrospinal fluid (CSF), which is the fluid in your brain and spine. Today, the device is commonly used for inserting chemotherapy drugs to treat brain and spinal cord diseases and also to take samples of the CSF.
Before the Ommaya reservoir, doctors had to repeatedly inject drugs or take fluid samples directly from the spinal cord. This device has made the process easier and allows doctors to give chemotherapy drugs more consistently and without needing to perform a lumbar puncture, which is a procedure to remove fluid from the spinal canal.
For a long time, the Ommaya reservoir was inserted using a freehand technique (without using medical imaging). It worked well, but if the brain chambers, also known as ventricles, were too small, placing the device correctly was challenging. But incorrect placement could lead to complications like bleeding, brain infection, and seizures.
These issues led to the development of methods to assist in placing the Ommaya reservoir using medical imaging technology called computed tomography. This development paved the way for future brain navigation techniques.
Since then, there have been major advancements in inserting this device. It’s now facilitated by high-resolution imaging techniques and advancements in brain navigation including optical tracking, frameless stereotactic approach (a minimally invasive form of surgery), electromagnetic tracking, fluoroscopy-assisted (a type of x-ray), ultrasound-guided, robot-guided, and endoscope-guided implantations.
Anatomy and Physiology of Ommaya Reservoir
The Ommaya reservoir is a device that consists of a tube-like catheter with a small, silicone reservoir or pouch that sits under the scalp. The catheter’s end is placed into the part of the brain called the anterior horn during surgery, and the other end connects to the reservoir.
Brain specialists require specific skills and knowledge to perform this procedure, which is similar to another common brain procedure called a frontal ventriculostomy. In a ventriculostomy, the goal is to reach the center of the anterior horn in the brain.
According to Kocher, a neurosurgeon, the entry point for this procedure is a few centimeters from the centerline of the head, and a few centimeters before a gap in the brain called the precentral fissure. Scientists have different opinions about the exact location of this entry point, but the main goal is to avoid damaging important parts of the brain, like the sagittal sinus (a large blood vessel), the basal ganglia (a group of structures in the brain involved in movement), the frontal eye fields (which control eye movements), and the motor cortex (which controls voluntary movements).
Now, it’s generally accepted that the Kocher point is 11 cm above and behind the nasion (the point where the nose meets the forehead), 3 cm to the side of the centerline of the face, and 1 to 2 cm before a ridge in the skull called the coronal suture.
The recommended direction for the catheter during surgery is down and back, aiming for the external auditory meatus (the opening of the ear) or 1 to 1.5 cm before the tragus (a small pointed part of the outer ear). When seen from the side, the direction varies: it can be straight towards the corner of the eye on the other side, towards the nasion, or towards the corner of the eye on the same side. The most reliable entry point and direction follow the 3-2-1 rule: enter 3 cm beside the centerline and 2 cm before a part of the skull called the bregma, aiming for the corner of the opposite eye and 1 cm before the tragus.
Why do People Need Ommaya Reservoir
An Ommaya reservoir is a medical device that is placed under the skin on your scalp and coupled with a tube into a brain ventricle to help deliver medication directly to the brain or to remove fluids like cerebrospinal fluid (CSF), which surrounds the brain and spinal cord, or fluid from brain tumor cysts. Its use can vary depending on patient’s specific health conditions. Here are the primary reasons why a doctor might use an Ommaya reservoir:
1. To administer chemotherapy drugs directly into the brain for treating cancers in the head or blood cancers that have spread to the brain, such as acute lymphoblastic leukemia.
2. To inject antibiotics directly into the cerebrospinal fluid in cases of difficult-to-treat or recurrent brain infections.
3. To regularly remove CSF in infants who have suffered a brain bleed, which can cause a harmful buildup of this fluid.
4. To continuously drain fluid from brain tumor cysts, particularly when the tumor is craniopharyngioma, a rare type of benign brain tumor.
5. To deliver powerful pain-relieving medication, such as opioids, to the brain.
6. To take out residual blood or fluid under the outer covering of the brain following a head injury or surgery.
The Ommaya reservoir may also be used to administer specific medications such as Nusinersen, a drug for treating spinal muscular atrophy, a genetic disorder lead to muscle weakness and atrophy. Similarly, it may be used in research studies for administering rituximab, a medication under investigation for treating progressive multiple sclerosis, a chronic disease that affects brain and spinal cord.
When a Person Should Avoid Ommaya Reservoir
There are a few reasons why certain people might not be able to undergo certain medical procedures:
One reason could be a scalp infection. This means that a person’s scalp has bacteria or other germs causing it to become inflamed or irritated. Performing a procedure on an infected area could lead to further complications.
Another reason could be a brain abscess, which is a pocket of pus in the brain. This can be caused by an infection and can be quite serious. Because of the risks associated with operating near or on this infection, some procedures might not be safe.
Finally, if someone has a previously known allergy to silicone, they may not be able to have certain procedures. Silicone is often used in medical devices or tools, and an allergic reaction could cause serious problems.
Equipment used for Ommaya Reservoir
For some types of brain surgery, doctors might use a specialized drill set, called a Cranial perforator drill set or Hudson drill with a perforator bit. This helps them make precise holes in the skull. Another tool they often use is a Mayfield clamp holder for neuronavigation, which helps secure and position your head during surgery.
Part of the procedure might involve inserting a system made up of a reservoir implant and an intraventricular catheter. A reservoir implant is a small device placed under the skin that holds medication. The intraventricular catheter is a thin tube that delivers this medicine directly into the fluid-filled spaces in the brain, called ventricles.
Sometimes, your doctors also might use additional technology during surgery. These can include an image-guided navigation system, which helps them navigate through the brain using detailed images. Or a C-arm fluoroscopy, a special type of X-ray machine, to double-check the position of the catheter. In certain cases, they might use an endoscope for ventriculoscopy. An endoscope is a thin instrument with a light and a camera on the end, and ventriculoscopy is a procedure that lets doctors look at the inside of the ventricles.
Who is needed to perform Ommaya Reservoir?
To insert something called an Ommaya reservoir, a specialist team is needed. This team is composed of a neurosurgeon, who is a highly trained doctor that operates on the brain and nerves, a nurse who helps care for patients, an operating practitioner that aids in the procedure, and an anesthetist, who is a professional that puts patients to sleep during surgeries.
Preparing for Ommaya Reservoir
The operation is carried out under general anesthesia, which means the patient is completely asleep and won’t feel the procedure happening. This is unless it is not suitable for the patient due to other health reasons. The patient is laid on their back (this is what ‘supine position’ means) and their head is secured in a special kind of head holder called a Mayfield clamp holder. Before the surgery, doctors use imaging techniques, such as a CT scan or MRI, to take pictures of the affected areas inside the patient’s body. This lets them see any abnormal areas or any differences in the brain’s ventricles (fluid-filled spaces).
Doctors usually choose to make the incision in the right frontal region of the head, unless a cyst or tumor requires them to make the incision elsewhere, or if the ventricles in the brain are unevenly sized, which would make a left-side incision better. It is recommended that the reservoir system (a device used to manage fluid levels in the body) be soaked in a saline solution mixed with antibiotics. This helps to prevent infection.
The surgery is done with the help of special imaging techniques. Before the surgery, a CT scan or MRI with markers that stick to the skin is performed. These markers help the surgeon to accurately locate the surgical site. These images are then uploaded into a computer system that guides the surgery. This computer system helps to plan the surgery, showing the best site for the incision (which is usually at the top of a ridge of brain tissue, keeping important blood vessels safe), and aiming for a particular point in the brain called the foramen of Monro. A tracking system is attached to the arm of the head holder to guide this process. The system is then checked to make sure it’s working accurately before the surgery begins.
How is Ommaya Reservoir performed
The surgery process begins with the preparation of the surgical area. This involves cleaning and covering up the surrounding areas for infection control. A small U-shaped cut will be made on your scalp, a little larger than the size of the Ommaya reservoir (a small device used for administering medicine or drainage). The cut is made at a specific location called the Kocher point, which is 3 cms away from the middle of the forehead at eye level and 1 cm in front of the coronal suture (the joint where the two halves of the skull meet in front).
After the cut is made, a small flap of the scalp is lifted. A small hole is then made in your skull and the tough membrane that covers your brain (dura mater) is cut in a cross shape. The surgeon will make sure they do as little damage as possible to your brain by identifying and avoiding any blood vessels on the brain’s surface.
A special needle linked to a navigation system will then be introduced. This allows the surgeon to accurately identify the entry point into the brain using images. This needle is carefully inserted into the brain. If the placement is done without pre-set markers, the needle will be inserted straight down into the skull, or angled towards a specific point that is predetermined by the doctor.
The entry into the brain’s ventricles (fluid-filled cavities in your brain) is indicated by a change in resistance (“pop sensation”) and the flow of cerebrospinal fluid (the fluid around your brain and spine). A catheter (a thin, flexible tube) is then inserted along the same path as the needle. The catheter is cut to a specific length based on your brain imaging and is then attached to the Ommaya reservoir. This results in the catheter tip positioned near the bottom of one of the front cavities of your brain. The correct placement of the catheter can be double-checked with the navigation system.
After the installation of the reservoir, the flap of scalp tissue is put back in place and sewn. The scalp cut is also stitched up. The surgeon can make a skin marking to show where the top of the reservoir is. After the operation, a CT scan of your head will be done to check the position of the catheter and to check for any bleeding in the brain.
When the reservoir needs to be accessed in the future, the scalp over the reservoir is cleaned. A small needle is used to access the reservoir to either draw fluid out or to inject medication. This needle is inserted at an angle into the reservoir. The reservoir can hold up to 2.4 ml of liquid. Once the necessary fluid has been removed or medication injected, the needle is removed. For brain tumor cases, the excess fluid from the tumor is slowly drawn out until the desired amount of fluid is collected. After this procedure, you will be asked to stay lying down for about 2 hours to monitor for any neurological changes.
Possible Complications of Ommaya Reservoir
Some people who undergo a procedure to get an Ommaya reservoir, which is a device inserted into the brain for treatment, could face certain challenges. An infection related to this surgery can occur in about 5.5% to 8% of patients, with most appearing within 10 days of the operation. Clear signs of these infections can be redness and swelling of the skin, inflammation of the brain’s protective membranes, or a combined inflammation of both the brain and its protective membranes.
The tube that drains fluid from the brain can sometimes be placed incorrectly. This could lead to direct harm or internal bleeding, but these issues usually don’t have significant health impacts. This tube can accidentally injure several areas in the brain and its blood vessels. While internal bleeding can happen in about 7% of the surgeries, only 0.8% actually lead to serious health concerns. If the tube is placed past a certain point in the brain, it could be blocked by a part called the choroid plexus. Almost 22.4% of these tube placements miss the intended spaces in the brain and need multiple attempts for correct placement.
Then there are two other complications that can happen right after surgery or later on. These are Subdural Hematoma and Subdural Hygroma, which are generally abnormal collections of fluid in and around the brain due to recurrent aspirations.
The original series of cases reported by Ommaya and Ratcheson noted that the most common problem was the tube not working properly, affecting 23.5% of cases. But today, such issues are extremely rare. Other possible complications can include damage to the white matter of the brain and the formation of a destructive type of cyst due to chemotherapy medications administered directly into the fluid surrounding the brain and spinal cord.
What Else Should I Know About Ommaya Reservoir?
The Ommaya reservoir is a specially designed device that is implanted in the body for easy access to the brain’s fluid, known as cerebrospinal fluid (CSF). This device has made it much simpler to directly give essential medications like antibiotics, antifungal, cancer-fighting drugs, and painkillers into the brain. It provides a long-term solution for medication delivery effectively.
