In Reply: Risk of Bone Wax Migration During Retrosigmoid Craniotomy for Microvascular Decompression: Case-Control Study

To the Editor: We sincerely appreciate the positive comments of the readers and the expansion of the discussion regarding our publication, "Risk of bone wax migration during retrosigmoid craniotomy for microvascular decompression: case-control study."1 We read their opinions with great interest. As they mentioned, the concept of "less is more" is important to avoid adverse events such as infections, granuloma formation, and foreign body reactions related to the usage of bone wax.2 In particular, the stress of histological findings showing the induction of inflammation cells around and into bone wax helps us to comprehend the complications of using bone wax. In the retrosigmoid approach, bone wax was used to control bleeding and prevent cerebrospinal fluid leakage. Open mastoid air cells are typically covered with bone wax to prevent cerebrospinal fluid leakage. This surgical technique was described in textbooks by Yasargil and by Tew JM.3,4 In this regard, we agree that a minimum amount of bone wax should be placed following the principle of "less is more." Since bleeding from the mastoid emissary canal (MEC) is often encountered during the retrosigmoid approach, bone wax is usually applied to sheathe it. Clinically, we have observed bone wax migration into the sigmoid sinus and sinus thrombosis related to the application of bone wax to MEC. Hence, our initial question was "What can be the risk factors of bone wax migration into the sigmoid sinus after the bone wax is applied to the MEC?" We reported that the large size of the MEC could contribute to complications after applying bone wax to the MEC in our paper.1 Large amounts of bone wax application as an intraoperative hemostatic agent can result in migration and sinus thrombosis. In our paper, we proposed an alternative surgical procedure to control bleeding from MEC without bone wax application.1 The authors proposed that we should use an alternative water-soluble hemostatic agent, which can be used instead of bone wax; however, we do not have experienced its use and its application in neurosurgery has not yet been standardized. As its name signifies, this water-soluble bone wax alternative is absorbed and dissolves within 24–48 hours. This feature seems favorable for preventing postoperative complications, infections, granuloma formation, and foreign body reactions and helps in intraoperative control of bleeding. However, whether this window of time is sufficient to avoid cerebrospinal fluid leakage through the mastoid air cells should be investigated. Ling et al5 described a surgical technique using bone wax to prevent cerebrospinal fluid leakage from the mastoid air cells. They sealed the mastoid air cell with bone wax and placed an autologous fat graft to fill the space between the dura and bone flap. Park et al6 also reported the application of bone wax and a muscle patch to seal an opened mastoid air cell. In addition, they mentioned that the dura should be water-tightly closed.5,6 In conclusion, to safely close the mastoid air cell using a water-soluble bone wax alternative, as described by Ling et al and Park et al, the incised dura should be tightly closed and the opened mastoid air cell should be sealed with a water-soluble bone wax alternative and patched with muscle tissue and/or fat graft.