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

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 which 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.[10][11]

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.[7][8] 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 contralateral medial canthus.[12] 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 India 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.[13] 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.[14][15][16] The patient is monitored for 2 hours in a supine position to rule out any neurological deterioration.

1. Infection: A low proportion of patients get Ommaya reservoir related infections, varying from 5.5% to 8%.[17][18] Approximately 60% of them occur within 10 days of accessing the device. The most common manifestations are cellulitis, meningitis, or meningoencephalitis.[19]
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 superior thalamostriate vein. Periprocedural hemorrhage can occur in up to 7% of placements, but only 0.8% are deemed clinically relevant.[20] 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.[12]
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.

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.[3][4][5]

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 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]

Nurses and allied health staff involved in the care of patients with Ommaya reservoirs need to be aware of the following:[21]

• 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

The nurses involved in the surveillance of patients with an Ommaya reservoir should monitor for:[22]

• 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