Ommaya Reservoir

Anatomy and Physiology

Ommaya reservoir consists of an indwelling ventricular catheter with a dome-shaped collapsible silicone reservoir port positioned under the scalp. The distal end of the catheter is surgically positioned into the ipsilateral anterior horn with the proximal end connected to the reservoir.

The prerequisite knowledge and skill required for this procedure is an extension of a frontal ventriculostomy procedure. A frontal ventriculostomy is one of the most common neurosurgical procedures. The target of an ideal ventriculostomy is at the center of the anterior horn. Kocher described the entry point for the ventriculostomy as "2.5 cm to 3 cm from the median line and 3 cm anterior to the precentral fissure."[8] The recommendations for the entry point in the literature vary from 1.5 cm to 4 cm from the midline, and from 10 cm to 12.5 cm posterior to the nasion (1 cm to 2 cm anterior to the coronal suture). Though there have been numerous definitions of the Kocher point in literature, the common principles governing the site of entry involve avoiding injury to the sagittal sinus, bridging veins, basal ganglia, frontal eye fields, and the motor cortex. Nowadays, the Kocher point is better described as an entry point that is 11 cm superior and posterior from the nasion, 3 cm lateral to midline along the mid pupillary line, and 1 cm to 2 cm anterior to the coronal suture.[9] The recommended trajectory in the sagittal plane is downward and backward, targetting the external auditory meatus or 1 cm to 1.5 cm anterior to the tragus. In the coronal plane, the targets vary from either perpendicular puncture towards contralateral medial canthus, nasion, or ipsilateral medial canthus. The most robust entry point and trajectory with the highest hit rate follow the 3-2-1 rule, i.e., entering at a point 3 cm lateral to the midline and 2 cm anterior to the bregma by targetting the contralateral medial canthus and 1 cm anterior to the tragus.

Indications

Ommaya reservoir can be used for several procedures where medications are injected into the intrathecal space, CSF is aspirated, or where tumoral cyst fluid is removed.[10] The major indications are enumerated below.

1. Administration of intrathecal (IT) chemotherapeutic agents for intracranial neoplasms as well as hematological conditions with CNS involvement such as in acute lymphoblastic leukemia
2. Administration of IT antibiotics for chronic relapsing meningitis and multi-drug resistant central nervous system infections[11]
3. Chronic drainage of CSF for infants with intraventricular hemorrhage
4. Chronic aspiration of fluid from tumor cysts not amenable to treatment such as craniopharyngiomas
5. Administration of opioid pain medications
6. Aspiration of residual subdural hematoma or effusion
7. Administration of IT drugs such as Nusinersen for spinal muscular atrophy,[12] and rituximab for progressive multiple sclerosis (phase 1b study)[13]

Contraindications

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

Equipment

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

Optional Intraoperative Technology 

• Image-guided navigation system[14][15]
• C-arm fluoroscopy to verify the position of the catheter
• Endoscope for ventriculoscopy[6]

Personnel

A complete team for insertion of Ommaya reservoir would include a trained neurosurgeon, nurse, operating practitioner, and anesthetist.

Preparation

The procedure is performed under general anesthesia unless contraindicated. The patient is placed in a supine position with the head fixed on 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 site of insertion is the right frontal region unless indicated for a tumor cyst or if there is an anterior horn asymmetry that favors a left-sided approach. Pre-soaking the reservoir system in an antibiotic saline solution is recommended.

Image-guided Technique: Preoperative neuronavigation CT scan or MRI with adhesive fiducial markers is performed before surgery. Preoperative imaging is loaded into the image guidance system, followed by a delineation of entry and target points on the surgical planning software. The entry point is through the crown of a gyrus avoiding cortical vessels. The target point is directed to 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.[14][15]

Technique or Treatment

Operation

The surgical site is prepared and then cleaned and draped under aseptic precautions. An inverted U-shaped scalp incision slightly larger than the diameter of the Ommaya reservoir (3.4 cm) is made over the entry point. The center of the incision overlies the Kocher point, located 3 cms lateral to the midline at the mid pupillary line and 1 cm anterior to the coronal suture.[8][9] A pericranial flap is raised to fit the size of the Ommaya reservoir. A burr hole is made, followed by a cruciate durotomy. Minimal bipolar coagulation of the cortical surface is encouraged. A pial/cortical incision is made, avoiding any surface vessel. Image-guided navigation can significantly improve the accuracy of the target point.[6] A Dandy needle with an optical tracker is registered with the image guidance system. The trajectory of insertion is as planned via the image guidance system. If done via freehand placement, the trajectory of insertion is placed perpendicular to the calvarium or towards a coronal plane 2 cm anterior to the external auditory meatus and directed towards the contralateral medial canthus.[16] Entry into the ventricle can be identified by a "pop sensation" and free flow of CSF. The catheter is inserted along the brain needle trajectory. The length of the catheter is cut as estimated according to preoperative imaging (roughly 5 cm to 5.5 cm when measured at the inner table of the calvarium) and attached to the base of the reservoir with a silk tie. This length allows the tip of the catheter to be positioned near the floor of the anterior horn of the lateral ventricle. The correct placement of the catheter can be verified with an image guidance system. The pericranial flap is repositioned over the reservoir and sutured back. The scalp is closed in two layers. Skin marking with Indian ink could be used to identify the correct position of the dome. In the postoperative period, a head CT scan is performed to evaluate the catheter placement and any evidence of hemorrhage.

Reservoir Aspiration

The scalp is prepared with antiseptic scrub.[17] The dome of the reservoir is palpated and ascertained. Using a 25 gauge or thinner needle, the reservoir is pierced in an oblique fashion and then aspirated. The internal capacity of the reservoir for adults varies from 1.5 ml to 2.4 ml. After the aspiration, the therapeutic medication is injected, and the needle is withdrawn. For tumors, the cyst contents are aspirated slowly until the desired amount is obtained.[18][19][20] The patient is monitored for 2 hours in a supine position to rule out any neurological deterioration.

Complications

1. Infection: A low proportion of patients get Ommaya reservoir-related infections, varying from 5.5% to 8%.[21][22] Approximately 60% of them occur within 10 days of accessing the device. The most common manifestations are cellulitis, meningitis, or meningoencephalitis.[23]
2. Suboptimal Position: Misplacement of a ventricular catheter is common. This can lead to direct injury or hemorrhage, though it is rarely clinically relevant. Direct injury can occur to 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 placements, but only 0.8% are deemed clinically relevant.[24] A position beyond the foramen of Monro is suboptimal as the catheter can get blocked by the choroid plexus. Approximately 22.4% of freehand placements occur outside the ventricular spaces and required several passes for successful placement.[16]
3. Subdural Hematoma or Subdural Hygroma: May occur acutely during the implantation or later due to the recurrent aspirations.
4. Mechanical Failure of Device: In the original case series by Ommaya and Ratcheson, catheter malfunction was the most common complication, involving 23.5% of cases.[3] However, in present times, catheter malfunction is extremely rare.
5. Leucoencephalopathy and encephaloclastic cyst due to the use of intrathecal chemotherapeutic agents[25][26]

Clinical Significance

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

Enhancing Healthcare Team Outcomes

Ommaya reservoirs are used for the administration of drugs into the intrathecal space, primarily for CNS hematological malignancies and also for drainage of intracranial cystic tumors. These devices are implanted by neurosurgeons under general anesthesia. Immediate postoperative care and repeated tumor cyst drainage would involve coordination between the neurosurgeons and the neurosurgical nursing team. These reservoirs are accessed by hematologists and oncologists for the administration of chemotherapeutic drugs and CSF sampling for the dose titration, as early as the day of operation. Radiologists play a part in their management as these patients often require imaging to assess for intracranial disease/tumor staging or, rarely, for malfunctioning of the device. General practitioners and community nursing staff should be aware and able to identify early signs of infection. Once the skin heals, these devices do not require any special care. They can remain in place for months to years. [Level 5]

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:[27]

• Assisting and performing CSF sampling from Ommaya reservoir under aseptic techniques
• Administration of drugs via Ommaya reservoir under the supervision of the treating physician
• Collection and sending of CSF samples for biochemical and microbiological tests
• Identify signs of increased intracranial pressure secondary to excessive cyst fluid accumulation and arrange for timely aspiration of the reservoir

Nursing, Allied Health, and Interprofessional Team Monitoring

The nurses involved in the surveillance of patients with an Ommaya reservoir should monitor for:[28]

• Signs of surgical site infection such as redness or wound dehiscence in the postoperative period
• Signs and symptoms of meningitis arising from the implanted device
• Early signs of raised intracranial pressure and arrange for urgent aspiration after ruling out other causes of neurological deterioration