Many studies have described several possible factors affecting postoperative CSF leakage following VS surgery, including sex, age, tumor size, tumor site, recurrence, PA pneumatization, and operation time (3–6). However, these factors were not associated with the occurrence of postoperative CSF leakage in our study, which showed that pneumatization of the posterior IAC wall cells increased the risk factor of CSF leak in retrosigmoid approach surgery.
Identifying IAC posterior wall pneumatization may help surgeons understand the risk profile of patients and also modify perioperative and interoperative management to reduce the risk of developing postoperative CSF leaks. Patients with highly pneumatized temporal bones are related to a high risk of CSF leakage (7). Stieglitz et al. observed that temporal bone pneumatization is a risk factor for CSF leakage. They considered air cell volume within the mastoid and the PA portion of the temporal bone (8). Temporal bones consist of several parts, including a petrous apex. Evidence suggests that compared to patients without PA pneumatization, patients with PA pneumatization showed higher rates of CSF leak (5). During the operation, it is also required to resection the tumor part in the internal auditory canal, which requires drilling open the posterior wall of the IAC. Therefore, not only the PA pneumatization but also IAC posterior wall pneumatization should be considered during the perioperative period. Few studies have focused on the possible relationship between the occurrence of a postoperative CSF leak and IAC posterior wall pneumatization following retrosigmoid approach resection. A study by Olivier Plainfossé et al. included 175 VS patients with retrosigmoid approach resections and found that IAC posterior wall pneumatization increased the risk of CSF leak. In addition, the distance of IAC posterior wall pneumatization was negatively correlated with CSF leakage (9). In contrast to these studies(5, 9), the surgical incision CSF leak was excluded in our inclusion criteria. Our study is unique since all 441 VS patients in our study exclusively underwent retrosigmoid approach resection, measures distance between the IAC posterior wall and the nearest air cell. Although, 246 patients had IAC posterior wall pneumatization, surprisingly, only ten patients exhibited CSF leakage.
However, the relationship between the IAC posterior wall pneumatization and postoperation CSF leak is not entirely clear. In our study, no patients showed CSF leak in the case of no petrous bone drilling (10). To completely remove VS, IAC posterior wall needs to be drilled open. Intraoperatively, the opened IAC posterior wall air cells may communicate with the subarachnoid space creating a track not only within the middle ear and mastoid air cell system but also in the eustachian tube (11, 12). The CSF is then led along the petrous cell opening through the Eustachian tube into the nose (10). Although IAC posterior wall pneumatization is a variable, identifying it as a risk factor for a postoperative CSF leak is important since it can allow surgeons to modify the risk. Before surgery, a CT scan of the mastoid can provide the surgeon with a complete understanding of its pneumatization extent. During surgery, when the internal auditory meatus is drilling open, immediately indiscrimination seal the ICA cells with bone wax and creating a continuous smooth surface. Simultaneously, the patient was informed pre- and postoperatively to avoid the Valsalva maneuver or blowing the nose for at least 1 week.
Failure to completely obliterate exposed mastoid and petrous air cells potentially increase the risk of postoperative CSF leakage. CSF rhinorrhea often occurs where the surgeon does not see it (8). The endoscope has the characteristics of a wide field of view, high definition, and multi-angle. An endoscope was used to visualize all exposed air cells directly, locating all air cells endoscopically, and they were blocked with bone wax. There was no CSF leakage after the operation (13). Finally endoscopic assist closure of the opened IAC posterior wall air cells may be an excellent method to prevent postoperative CSF leakage.
Many different materials have been applied for IAC reconstruction, including bone wax, muscle, bone cement, fascia, and fibrin glue (6, 14–17). Lisa Zhang et al. used bone cement for IAC reconstruction, where six of 117 patients developed postoperative rhinorrhea. Sealing the internal auditory canal with bone cement was a safe and low rate of postoperative CSF leakage (17). Moreover, Twenty-four patients underwent retrosigmoid approach to remove acoustic neuromas, used a fat graft-assisted internal auditory canal reconstruction did not exhibit any postoperative CSF leak (15). However, these methods also have drawbacks. For example, using bone cement for IAC reconstruction may cause a heavy economic burden (up to US$1,200 for 5 mL) (14), while the grafted fat leaves a surgical scar since it is removed from the abdomen. Bone wax was used to occlude petrosal air cells during acoustic neuroma resection through retrosigmoid approach, and the rate of CSF leak was 2.8% (18). Therefore, we used bone wax for internal auditory canal closure, which cost $6—$12 and exhibited a postoperative CSF leak of only 2.3%.