Vestibular schwannomas (VS) are benign tumors originating from Schwann cells, accounting for 7–9% of intracranial tumors they are the most common tumors in the cerebellopontine angle (1). Their incidence ranges between 3 and 5 cases per 100,000 people per year, and the median age of onset is 56–60 years (2, 3). The treatment strategy for VS varies, taking into consideration not only the benign nature of these tumors, but also the fact that their location and potential for further growth pose a significant danger to the patient. Current management options include active surveillance, microsurgical treatment, or radiotherapy. The most critical factor in choosing a treatment method is the size of the tumor. For large tumors causing brainstem compression, hydrocephalus, trigeminal neuralgia, or other neuropathies, surgery is the treatment of choice (4). One of the possible approaches to VS is the retrosigmoid approach. Its selection may be influenced by not only tumor size but also the patient’s hearing status, as it allows for the preservation of the inner ear structures and consequently hearing, unlike other techniques such as the translabyrinthine approach. The surgical risk is directly proportional to the size of the tumor. The most common complications include postoperative hearing loss, temporary or permanent facial nerve dysfunction, wound healing issues caused by cerebrospinal fluid (CSF) leakage, and aseptic meningitis. CSF leak after VS surgery can present in two forms: one is CSF rhinorrhea, where fluid leaks from the nose, and the other involves fluid accumulation under the wound, leading to poor wound healing and CSF discharge through the wound. CSF leak most commonly occur between the 2nd and 7th day after surgery (5). They are usually managed with external lumbar drainage, but in some cases, reoperation is necessary. Several studies in the literature point to factors predisposing to CSF leak, such as BMI, age, craniectomy, or reoperation (6–8). Shew et al. published a study in 2018, noting that pneumatization of the petrous apex (PA) may be associated with more frequent CSF leak through the nose and wound. Currently, there is a classification of temporal bone pneumatization types based on computed tomography, dividing the PA pneumatization into four groups, mastoid pneumatization into three groups, and infralabyrinthine pneumatization into three groups (9). The impact of these subtypes on CSF leak rates has never been evaluated, and the volumes of temporal bone pneumatization in these subtypes are unknown. As a result, the classification remains subjective; while it may suggest a more pneumatized bone type, without volumetric measurements of the pneumatized cells, there is no certainty.

The main objective of our study was to investigate whether the degree of temporal bone pneumatization affects the frequency of CSF leak from the nose or the wound. We hypothesize that an increase in the pneumatization of the temporal bone may be an independent risk factor for CSF leak. In order to validate our theory, we conducted a retrospective analysis of a group of patients who underwent vestibular schwannoma surgery, aiming to validate the temporal bone pneumatization classification by supplementing it with volumetric measurements for each pneumatization subtype.

The main aim of our study was to evaluate the pneumatization of the temporal bone and its potential association with the occurrence of cerebrospinal fluid (CSF) leak. The results of our study showed a statistically significant difference in the volume of temporal bone pneumatization between patients with and without CSF leak. Furthermore, the volumetric values of pneumatization assessed in our study are consistent with the average values reported in the literature (10). This indicates that, in the preoperative phase, the evaluation of temporal bone pneumatization could become a valuable tool—not only in terms of surgical access but also in enhancing the physician’s vigilance during the postoperative period. Importantly, to our knowledge, this is the first study that has morphometrically assessed the relationship between bone pneumatization and the frequency of CSF leak. We divided the classification into three parts, categorizing patients into groups of low, moderate, and significant bone pneumatization. This approach allowed us to assign absolute volume values to each group, enabling physicians to classify patients preoperatively not only through a classification system that could introduce subjective bias since it is based on radiological features but also to relate their own measurements to established literature values. Additionally, our analysis indicated that a higher degree of apex pneumatization was more frequently observed in the group of patients with CSF leak, supporting preliminary findings from the literature (8). However, it remains unclear whether infralabyrinthine pneumatization and mastoid pneumatization play any role in this aspect. To definitively confirm the findings of our study, a prospective study would be necessary to allow for causal inferences.

Currently, two classification systems exist in the literature: our study is based on the classification by Dexian et al., while the second classification by Han et al. evaluates pneumatization in relation to the sigmoid sinus, labyrinth, and carotid canal. Given that previous reports suggest that pneumatization of the petrous apex may influence the incidence of CSF leak, we chose to apply the first classification since it takes apex pneumatization into account. However, our observations indicate that using this classification may be problematic due to the subjective assessment of radiological features of the temporal bone. Moreover, our analysis highlighted that only the petrous apex has an impact on CSF leak. Therefore, relying solely on this classification without incorporating volumetric calculations may prove insufficient as a tool for preoperative evaluation.

While estimating the risk of CSF leak is crucial for the clinical vigilance of the surgeon and for potential intraoperative measures that may protect against postoperative CSF leak, it is important to emphasize that there is no definitive data in the literature indicating which interventions effectively prevent the leaks (11). Some studies have described the use of abdominal fat, wax, and the use of muscle fascia fragments to fill defects as effective measures; however, no prospective studies have been conducted comparing different surgical techniques aimed at preventing CSF leak (12). Based on our research, we did not observe a correlation between the type of surgical reconstruction used and the occurrence of CSF leak. Therefore, in addition to studies estimating the risk of CSF leak, it is also necessary to conduct research that identifies proven and effective prevention methods. Currently, preventive measures primarily rely on the actions taken by the surgeon based on their experience with specific techniques, highlighting the need for further evidence-based guidelines in this area.

We consider the meticulously collected clinical data of patients, along with the assessment of clinical findings, to be an additional asset of our study. This comprehensive approach will enhance the ability to estimate risk more effectively in discussions with patients. Our results are consistent with existing literature regarding transient deficits of the VII cranial nerve (acceptable damage on the House-Brackmann scale grades I-IV was found in 82.5% of our study, compared to 79% reported in the literature), preserving anatomical continuity of the VII nerve (91.26% in our study vs. 82–97% in other series), preoperative hydrocephalus (22.3% vs. 3.7–42% in other series), rates of reoperation, and length of hospitalization (13–15). The slightly higher mortality rate (2.9% vs. 1%) is due to the fact that it refers to a 30-day period, whereas in the literature, it is most often assessed during the perioperative period. However, the data is inconsistent; in some studies, the perioperative period is defined as 7 days, while in others, it extends to 30 days. Additionally, patients who present with significant vascular issues, burdened by multiple comorbidities and requiring urgent surgery, may constitute a larger proportion of our sample. In our group, at the preoperative stage, the group with total hearing loss accounted for 44.7%, patients with serviceable hearing represented 51.5%, and those with good hearing made up 3.8%. Considering only patients who retained hearing, postoperatively, hearing was preserved in 45.6% of them, with all achieving a serviceable level of hearing. According to the literature, the retrosigmoid approach allows hearing preservation in 40–60% of patients over a short observation period. However, it should be noted that hearing preservation is closely related to tumor size, and in our series, the tumors operated on were large, therefore the final percentage of patients with hearing impairment reached 72%. However, this statistics also includes patients who had significant hearing loss prior to surgery. Additionally, it should also be mentioned that the degree of hearing loss changes over time. After 5 years, hearing in the series of patients operated for VS using the retrosigmoid approach was reduced to 30–50% (16). These findings complement those in the literature and may serve as a valuable resource for future meta-analyses.

A significant advantage of our study is that the methods used are reproducible and are becoming available at nearly every neurosurgery department worldwide. Volumetric assessment has been successfully applied to numerous classifications and neurosurgical conditions (17–20). Our study indicated that bone pneumatization measured by volumetric methods is feasible, and the data do not differ from those in the literature. Moreover, it does not require specialized programs utilizing algorithms that are impractical in clinical practice. Consequently, we provide a tool that, although requiring prospective validation, can offer important clinical information.

The limitation of our study is its retrospective nature, which means we cannot draw conclusions about causal relationships. However, it indicates that the pneumatization of the temporal bone, particularly the pneumatization of the petrous apex, could be the focus of prospective analyses. Another significant limitation of the study is that it is single-center; however, it is important to note that there are no studies in the field of temporal bone pneumatization using reproducible and widely accessible tools.