Optimal implantation of Ommaya reservoirs for cystic metastatic brain tumors preceding Gamma Knife radiosurgery

- Ommaya reservoir implantation is effective for volume reduction of the cystic brain tumor.
- The factors leading to failure in volume reduction have not been identified.
- This study clarified the tip of the reservoir tube should be placed at the center of the tumor cyst.

Introduction: Although Ommaya reservoir implantation is effective in reducing the target volume of cystic brain metastases preceding stereotactic radiosurgery, adequate volume reduction cannot be achieved in some cases, and the factors leading to failure in volume reduction have not been clearly identified. In this study, we investigated the factors leading to failure in volume reduction after use of the Ommaya reservoir. Materials and methods: Between December 2007 and February 2015, 38 consecutive patients with 40 cystic metastases underwent Ommaya reservoir implantation at our institution. The patient characteristics, treatment parameters, and all available clinical and neuroimaging follow-ups were analyzed retrospectively. Results: The rate of volume reduction was significantly related to the location of the tube tip inside the cyst. By placing the tip at or near the center, 58.7% reduction was achieved, whereas reduction of 42.6% and 7.7% occurred with deep and shallow tip placement, respectively (p = 0.011). Although there was no additional surgery in the center placement group, additional surgeries were performed in 5 out of the 23 deep and shallow cases due to inadequate volume reduction. No other factors were correlated with successful volume reduction. Conclusion: For adequate volume reduction using the Ommaya reservoir in the treatment of cystic brain metastases prior to stereotactic radiosurgery, the tip of the reservoir tube should be placed at the center of the cyst.