What is an Ommaya reservoir, when is it indicated, and how does it compare to Ventriculoperitoneal (VP) shunting and extraventricular drain placement in terms of uses and duration?

Ommaya Reservoir: Comprehensive Overview and Clinical Decision-Making

What is an Ommaya Reservoir?

An Ommaya reservoir is a small, dome-shaped subgaleal reservoir connected to an intraventricular catheter that provides reliable access to the cerebrospinal fluid (CSF) for repeated intrathecal chemotherapy administration and CSF sampling. 1

• The device consists of a subcutaneous reservoir placed under the scalp with a catheter tip positioned in the lateral ventricle, typically at the foramen of Monro 2
• It allows direct intraventricular drug delivery, bypassing the blood-brain barrier 3

Primary Indications for Ommaya Reservoir Placement

Place an Ommaya reservoir when patients with leptomeningeal metastases require repeated intrathecal chemotherapy administration or frequent CSF sampling for cytologic monitoring. 1

Specific Clinical Scenarios:

• Leptomeningeal metastases from solid tumors requiring intrathecal chemotherapy (most common indication in adults) 1
• Hematologic malignancies (acute lymphoblastic leukemia, diffuse large B-cell lymphoma) requiring intraventricular chemotherapy 4
• Leptomeningeal carcinomatosis requiring repeated CSF access 2
• Patients requiring frequent CSF cytology monitoring for therapeutic response 1

Key Advantages Over Lumbar Puncture:

• Improved survival: Intraventricular drug delivery has been associated with improved survival compared to lumbar drug delivery 1
• Superior drug distribution: Drug exposure in ventricular CSF after intraventricular administration is ten times higher than after lumbar administration 1
• Better CSF flow dynamics: Intraventricular administration improves drug dissemination through pulsatile CSF flow and gravitational influences 1
• Patient comfort: Reduces anxiety, avoids post-dural puncture headaches, low back pain, and radiculopathy 1
• Anticoagulation management: Obviates need for anticoagulation holds 1

Duration of Use

Ommaya reservoirs remain in place for the duration of intrathecal chemotherapy treatment, which typically ranges from months to years depending on disease response and patient survival. 1

• Median survival for patients with leptomeningeal metastases treated via Ommaya reservoir is approximately 9 months 2
• The device remains functional as long as needed, with revision required in less than 5% of patients 1
• Infection incidence is 0.74 per 10,000 Ommaya reservoir-days 1

Clinical Decision Algorithm: Ommaya vs. VP Shunt vs. EVD

When to Place an Ommaya Reservoir:

Choose Ommaya reservoir placement when the patient requires repeated intrathecal chemotherapy delivery WITHOUT elevated intracranial pressure or hydrocephalus. 1, 2

• Normal or mildly elevated intracranial pressure 2
• Need for frequent CSF sampling and drug delivery 1
• Expected survival sufficient to justify surgical placement (typically >3 months) 1
• No evidence of CSF flow obstruction 1

When to Place a VP Shunt Instead:

Convert to or initially place a VP shunt when patients develop hydrocephalus with elevated intracranial pressure that requires permanent CSF diversion. 2

• Critical distinction: VP shunts divert CSF away from the intracranial compartment, precluding delivery of intrathecal chemotherapy 1, 2
• In the Memorial Sloan-Kettering series, 8 patients (7.5%) required conversion from Ommaya to VP shunt due to hydrocephalus development 2
• An additional 11 patients initially referred for Ommaya placement required VP shunt instead due to elevated intracranial pressure 2
• Key pitfall: Once a VP shunt is placed, intrathecal chemotherapy cannot be effectively delivered through the ventricular system 1

When to Place an External Ventricular Drain (EVD):

Place an EVD for temporary CSF diversion in acute hydrocephalus, intracranial pressure monitoring, or as part of infected CSF shunt management. 1

Specific EVD Indications:

• Acute hydrocephalus requiring temporary CSF diversion 1
• Intracranial pressure monitoring in critically ill patients 1
• Infected CSF shunt management as part of treatment approach 1
• Temporary measure: EVDs are short-term devices, not for chronic chemotherapy administration 1

EVD vs. Ommaya Distinction:

• EVDs have higher infection rates (11.4 per 10,000 EVD-days vs. 0.74 per 10,000 Ommaya-days) 1
• EVD infections occur at 8% vs. 6% for Ommaya reservoirs 1
• EVDs are removed once acute condition resolves; Ommaya reservoirs remain for chronic therapy 1

Surgical Technique and Complication Avoidance

Optimal Placement Technique:

Use intraoperative image guidance (fluoroscopy or frameless stereotactic navigation) to confirm catheter tip position at the foramen of Monro, which significantly reduces malposition rates. 2, 4, 5

• Catheter malposition rates: 37.5% without image guidance vs. 2.1% with image guidance 4
• Fluoroscopy shows slight advantage in proximity to foramen of Monro (8.6 mm vs. 10.2 mm with stereotaxy, p=0.03) 5
• Robot-assisted placement achieves radial error of 2.14±0.99 mm and axial error of 1.69±1.24 mm 3
• Median surgical time: 36-41 minutes with modern techniques 6, 3

Infection Prevention Protocol:

Administer preprocedural cefazolin, use perioperative chlorhexidine shampoo with hair clipping (avoiding skin abrasions), and place the reservoir under a skin flap at safe distance from the incision site. 1

• Modern infection rates: 1.8-9.8% (perioperative 0.9-2.7%, delayed 2.8-3.8%) 1
• Main risk factor for infection: frequency of CSF sampling 1
• Common organisms: Staphylococcus species and Cutibacterium acnes 1
• Critical practice point: Only highly qualified personnel should access the device using strict sterile technique 1

Contemporary Complication Rates:

• Overall complications: 1.8-9.8% (substantially lower than historical 10-15%) 1
• Perioperative hemorrhage: 0.9-6.4% 1
• Ommaya malfunction: 1.1-2.8% perioperative, 0.9% delayed 1
• Wound dehiscence: 1.8% 1
• Catheter tract leukoencephalopathy: 1.8% 1
• Revision required: <5% of patients 1

Special Considerations for Slit Ventricles

For patients with slit ventricles, perform preoperative pneumoencephalography for ventricular dilation before Ommaya placement. 2

• In the Memorial Sloan-Kettering series, 25 of 107 patients (23%) required this approach 2
• This technique facilitates accurate catheter placement in challenging anatomy 2

Post-Operative Management

Obtain postoperative CT scan before initiating intraventricular chemotherapy to confirm proper catheter position and rule out hemorrhage. 2

• Treatment-related imaging abnormalities occur in 8.4% of patients 2
• Most (7 of 9 patients) remain asymptomatic 2
• Two patients may develop symptomatic leukoencephalopathy 2

Critical Pitfall to Avoid

Never place an Ommaya reservoir in patients with elevated intracranial pressure requiring CSF diversion—these patients need VP shunts, which precludes effective intrathecal chemotherapy delivery. 2

• Assess for hydrocephalus and elevated intracranial pressure before Ommaya placement 2
• If hydrocephalus develops after Ommaya placement, conversion to VP shunt becomes necessary but eliminates the chemotherapy delivery route 2