Ommaya Reservoir

Anatomy and Physiology

The Ommaya reservoir comprises an indwelling ventricular catheter with a dome-shaped, collapsible silicone reservoir port under the scalp. The tip of the catheter is surgically positioned into the ipsilateral anterior horn of the lateral ventricle, with the proximal open end of the catheter connected to the reservoir. The prerequisite knowledge and skill required for successful performance of this procedure are an extension of a frontal ventriculostomy procedure. A frontal ventriculostomy is 1 of the most common neurosurgical procedures performed worldwide. A ventriculostomy catheter's optimal placement is at the center of the anterior horn. Kocher described the entry point for the ventriculostomy as "2.5 to 3 cm from the median line and 3 cm anterior to the precentral fissure."[9] The recommendations for the entry point in the literature vary from 1.5 to 4 cm from the skull's midline, 10 to 12.5 cm posterior to the nasion, and 1 to 2 cm anterior to the coronal suture. Although there have been numerous descriptions of the location of Kocher point in literature, the common concept governing the safe entry site involves avoiding injury to the sagittal sinus, bridging veins, basal ganglia, frontal eye fields, and the motor cortex.

Today, the Kocher point is better described as an entry point that is 11 cm superior and posterior to the nasion, 3 cm lateral to the midline of the skull, aligned with the midpupillary line, and 1 to 2 cm anterior to the coronal suture.[10] The recommended trajectory for the catheter in the sagittal plane is downward and posterior, targeting the external auditory meatus or a point 1 cm to 1.5 cm anterior to the tragus. In the coronal plane, the targets vary from the perpendicular puncture directed toward the contralateral medial canthus, nasion, or ipsilateral medial canthus. The most robust entry point and trajectory with the highest rate for successful catheter placement follows the 3-2-1 rule, ie, enter at a point 3 cm lateral to the midline and 2 cm anterior to bregma by directing the catheter toward the contralateral medial canthus and 1 cm anterior to the tragus.

Indications

An Ommaya reservoir can be used to administer several medications into the intrathecal space, aspirate CSF, or to remove intratumoral cyst fluid if necessary.[11] The primary indications are listed below:

• Administration of intrathecal (IT) chemotherapeutic agents for intracranial neoplasms, as well as hematological conditions with central nervous system (CNS) involvement, such as in acute lymphoblastic leukemia
• Administration of IT antibiotics for chronic relapsing meningitis and multidrug-resistant CNS infections [12]
• Chronic drainage of CSF for infants with intraventricular hemorrhage
• Chronic aspiration of fluid from recurrent tumor cysts that have been unresponsive to treatment, such as craniopharyngiomas [13]
• Administration of opioid pain medications
• Aspiration for resolving residual subdural hematoma
• Administration of IT drugs for spinal muscular atrophy and progressive multiple sclerosis [14][15]

Contraindications

The contraindications to placement of an Ommaya reservoir include: 

• Scalp infection
• Brain abscess
• Previously known allergy to silicone

Equipment

The following equipment is needed to place an Ommaya reservoir: 

• Cranial perforator drill or Hudson brace drill with perforator bit 
• Mayfield clamp head holder for neuronavigation
• Reservoir implant and intraventricular catheter system

Optional intraoperative technology that can also be used includes: 

• Image-guided navigation system [16][17]
• C-arm fluoroscopy to verify the position of the catheter
• Endoscope for ventriculoscopy [6]

Personnel

A complete team for insertion of an Ommaya reservoir would include:

• Trained neurosurgeon
• Nurse
• Surgical technologist
• Anesthesiologist

Preparation

The procedure is performed under general anesthesia unless contraindicated. The patient is placed in a supine position with the head fixed in a Mayfield clamp holder. Preoperative computed tomography (CT) scan or magnetic resonance imaging (MRI) is assessed for any lateralizing lesions or ventricular asymmetry. The preferred insertion site is the right frontal region unless the treatment indication is for placement in a tumor cyst or if there is an anterior horn asymmetry that favors a left-sided approach. Presoaking the reservoir system in an antibiotic saline solution is often practiced.

The image-guided technique is as follows: 

• Preoperative neuronavigation CT scan or MRI with adhesive fiducial markers is performed before surgery.[18] Preoperative imaging is loaded into the image guidance navigation system and delineates the entry and target points on the surgical planning software. The entry point is through the surface of a gyrus, avoiding cortical vessels; the target point is directed toward the ipsilateral foramen of Monro. The passive reference frame of the image guidance system is attached to the articulating arm of the Mayfield clamp holder. Fiducial registration is performed, and image-guidance accuracy is checked.[16][17]

Technique or Treatment

Operation

The surgical site is prepared and then cleaned and draped under aseptic precautions.[19] An inverted U-shaped scalp incision slightly larger than the diameter of the Ommaya reservoir (3.4 cm) is made around the entry point. The center of the incision overlies the Kocher point, located 3 cm lateral to the midline at the midpupillary line and 1 cm anterior to the coronal suture.[9][10] A pericranial flap is raised to surround the full extent of the Ommaya reservoir. A burr hole is made, followed by a cruciate durotomy. Minimal bipolar coagulation of the cortical surface is performed. A cortical incision through the pia arachnoid is made to avoid any surface vessels.

Image-guided navigation can significantly improve the accuracy of the target point.[6] The image guidance system registers a Dandy needle with an optical tracker. The trajectory of insertion is planned using the image guidance system. If the freehand placement technique is used, the catheter trajectory for accurate insertion is placed perpendicular to the calvarium in the coronal plane, 2 cm anterior to the external auditory meatus, and directed toward the contralateral medial canthus.[20] Entry into the ventricle can often be identified by a "pop sensation" as the ependyma is perforated and free flow of CSF is confirmed. The catheter is inserted parallel to the brain needle trajectory. The catheter length is estimated according to preoperative imaging; when measured from the inner table of the calvarium and secured to the base of the reservoir with a silk tie, it is approximately 5 to 5.5 cm in length. This length allows the tip of the catheter to be positioned near the floor of the anterior horn of the lateral ventricle. The correct catheter placement can be verified with the image guidance system.

The pericranial flap is repositioned over the reservoir and sutured closed. The scalp is closed in 2 layers: 1 layer represents the galea, and the other the skin. Skin marking with Indian ink could be used to identify the correct position of the dome for others not present during the surgery. In the postoperative period, a head CT scan is performed to evaluate the catheter placement and to exclude any evidence of hemorrhage.

Reservoir Aspiration

The scalp is prepared with an antiseptic scrub.[21] The dome of the reservoir is palpated to confirm the location of the apex. Using a 25-gauge needle, the reservoir apex is punctured obliquely and then gently aspirated. The internal fluid volume of the reservoir for adults varies from 1.5 to 2.4 mL. After the CSF is aspirated to confirm adequate flow through the catheter, the therapeutic medication is slowly injected before withdrawing the needle. The cyst contents are aspirated slowly for tumors until the desired amount is obtained.[22][23][24] The patient is monitored for 2 hours in a supine position to rule out any neurological deterioration.

Complications

Possible complications of an Ommaya reservoir placement include: 

• Infection
  • A small proportion of patients develop Ommaya reservoir-related infections, varying from 5.5% to 8%.[25][26][27] Approximately 60% of these infections occur within 10 days of accessing the device.
  • The most common manifestations are cellulitis, meningitis, or meningoencephalitis.[28]
• Suboptimal positioning
  • Misplacement of the ventricular catheter is not uncommon. This occurrence can lead to direct injury of the brain tissue or hemorrhage, though it is rarely clinically relevant. Direct injury can occur to the basal ganglia, internal capsule, fornix, thalamus, choroid plexus, and vessels (such as the superior thalamostriate vein).
  • Periprocedural hemorrhage can occur in up to 7% of reservoir placements, although only 0.8% are deemed clinically relevant.[29] 
  • A position beyond the foramen of Monro into the third ventricle is suboptimal because the catheter can become occluded by the choroid plexus.
  • Approximately 22.4% of freehand catheter placements occur outside the ventricular system and require several passes for successful placement.[20]
• Subdural hematoma or subdural hygroma
  • Either may occur acutely during the implantation or later due to recurrent aspirations.[30]
• Mechanical failure of the device
  • In the original case series by Ommaya and Ratcheson, catheter malfunction was the most common complication, involving 23.5% of cases.[3] However, catheter malfunction is extremely rare currently.
• Leukoencephalopathy and encephaloclastic cyst development
  • These are due to the use of intrathecal chemotherapeutic agent administration.[31][32]

Clinical Significance

An Ommaya reservoir is a highly effective implant that provides long-term access to the CSF and has simplified the administration of antimicrobial, antifungal, antineoplastic, and analgesic medications directly into the CSF of the brain.[5]

Enhancing Healthcare Team Outcomes

Caring for patients with an Ommaya reservoir requires a coordinated interprofessional approach to ensure safety and therapeutic effectiveness. Clinicians must demonstrate strong procedural and clinical assessment skills, including patient selection, reservoir access, and monitoring for complications such as infection, obstruction, or cerebrospinal fluid leakage. Nurses play a critical role in daily care, including sterile technique during reservoir access, vigilant monitoring for early signs of infection or neurologic decline, and patient education on self-monitoring and when to seek urgent care. Pharmacists contribute by ensuring the accurate preparation, dosing, and safe administration of intraventricular medications, while guiding drug interactions and neurotoxicity.

Effective interprofessional communication and care coordination are essential to optimize patient outcomes. Regular team discussions between neurosurgeons, oncologists, infectious disease specialists, pharmacists, and nursing staff support timely treatment adjustments, clear documentation of drug administration protocols, and rapid recognition of complications. Standardized care pathways, checklists, and shared decision-making strategies enhance patient safety and reduce errors. By combining clinical expertise with collaborative practice, the healthcare team can provide patient-centered care that improves treatment success, minimizes risks, and supports patients and families throughout the therapeutic course.

Nursing, Allied Health, and Interprofessional Team Interventions

Nurses and allied health staff involved in the care of patients with Ommaya reservoirs need to be aware of the following:

• Assisting and performing CSF sampling from the Ommaya reservoir under aseptic techniques
• Administering drugs via the Ommaya reservoir under the supervision of the treating clinician
• Collecting and sending CSF samples for biochemical and microbiological tests
• Identifying signs of increased intracranial pressure secondary to excessive tumor cyst fluid accumulation to arrange for the timely aspiration of the reservoir [33]

Nursing, Allied Health, and Interprofessional Team Monitoring

The nurses involved in the surveillance of patients with an Ommaya reservoir should monitor for:

• Signs of surgical site infection, such as redness or wound dehiscence, in the postoperative period
• Signs and symptoms of meningitis arising after the device is implanted
• Early signs of elevated intracranial pressure after excluding other causes of neurological deterioration [34]