Cerebellopontine angle meningiomas account for 6–15% of the tumors in the cerebellopontine angle region (1). They are characterized by the deep tumor location, narrow surgical field, and proximity to the brainstem, multiple pairs of (V–XI) cranial nerves (2). At present, surgical treatment is the first choice for large cerebellopontine angle meningiomas, while small cerebellopontine angle meningiomas are always treated by stereotactic radiotherapy, pharmacotherapy and experimental therapy (3). In recent years, many studies have found that stereotactic radiotherapy had the limitations of low tumor control rate, post-treatment brain edema, and tissue adhesion, which hindered the further treatments (4). Therefore, more and more small cerebellopontine angle meningioma patients are turning to surgical treatment.

The choice of surgery or stereotactic radiotherapy depends on the general situation of patients and the nature of tumors (7). Most of cerebellopontine angle meningiomas belong to benign tumors. The surgical effect of cerebellopontine angle meningiomas is always satisfied, and the rates of both post-operative symptom deterioration and tumor enlargement are lower than other nervous system tumors. However, the compression of the brain stem and cerebellum is a frequent occurrence of cerebellopontine angle meningiomas, especially in patients with large cerebellopontine angle meningiomas, the high intracranial pressure can lead to herniation and acute hydrocephalus. Either complete or partial resection can significantly reduce the risk of complications. Hence, surgery is the best choice for patients with large cerebellopontine angle meningiomas. For small cerebellopontine angle meningiomas, stereotactic radiotherapy, including Gamma Knife, cyber knife and other types of linear accelerator (8), is universally acknowledged as the first choice. With the development of medical treatment and the popularization of MRI, the early diagnosis of cerebellopontine angle meningioma in the small-volume or asymptomatic stage turns to possible. Early diagnosis and treatment greatly improve the prognosis of cerebellopontine angle meningioma, as well as bringing a confusion of choice between surgery and stereotactic radiotherapy for small cerebellopontine angle meningioma. In consideration of the edema and adhesion of brain tissue after stereotactic radiotherapy, which hindered the further surgery, more and more studies have supported early surgical treatments.

In terms of relieving pre-operative symptoms, the symptom deterioration rate in surgery group was similar to or even lower than the rate in radiotherapy group. Compared with stereotactic radiotherapy, surgical treatment can sometimes lead to better results in relieving pre-operative symptoms. Edema of peripheral brain tissue is a common side effect of stereotactic radiotherapy. Swelling of brain tissue will aggravate the tension and compression of nerves, which is the reason why the symptoms become worse after stereotactic radiotherapy. In order to reduce nerve injury and relieve symptom deterioration, operators need to carefully protect brain tissue, nerves, and blood vessels during the surgery. Compared with regular cerebellopontine angle meningiomas, surgical operation on small cerebellopontine angle meningiomas requires more protection for nerves and blood vessels, and neuroelectrophysiological monitoring during the whole surgery process is deemed essential, which contributes to the lower symptom deterioration rate in the surgery group. The most common clinical manifestation of small cerebellopontine angle meningiomas is functional defects of the facial and auditory nerves. Hence, protecting the facial and auditory nerves is a key point of surgery. Different types of cerebellopontine angle meningiomas will push the facial and auditory nerves to different positions (9). Thus, the first step of small cerebellopontine angle meningiomas surgery is locating the facial and auditory nerves. Anterior tumors generally push the facial and auditory nerves to the lateral or lateral inferior side. Posterior tumors generally push the facial and auditory nerves to the medial or medial inferior side. Middle tumors generally push the facial and auditory nerves vertically (Figure 2). Due to the compression of the tumor, the facial and auditory nerves are often elongated and become thin and discolored.

During the surgery, the operator needs to insist on sharp separation when separating the tumor from the facial and auditory nerves. The traction of the facial and auditory nerves and cerebellum should be minimized. The nutrient vessels around the facial and auditory nerves should be preserved as much as possible. Although the facial and auditory nerves are anatomically preserved after surgery, the loss of nerve function still exists in many patients, which may be result from the invasive growth of tumors, intraoperative traction, and heat conduction injury caused by electrocoagulation (10). Effective intraoperative neuroelectrophysiological monitoring can lessen the neuron injury by enabling the timely location of the facial and auditory nerves, thus increasing the rate of nerve function preservation.

In terms of inhibiting tumor progression, the tumor recurrence rate in the surgery group is similar to or even lower than the tumor enlargement rate in the radiotherapy group. Compared to stereotactic radiotherapy, surgical treatment can lead to the better results in inhibiting tumor progression. Stereotactic radiotherapy, mainly referring to Gamma Knife and cyber knife, suppresses tumor progression by killing tumor cells. The target of stereotactic radiotherapy is generally located in the center of tumors, and its dose decreases with the distance away from the center of tumors. Although peripheral dose enhancement technology has emerged in recent years, the problem of incomplete tumor boundary inactivation still exists, which also leads to the increase of the tumor enlargement rate in the radiotherapy group (11). For the surgical treatment of small cerebellopontine angle meningiomas, total resection of the tumor, dural attachment, and skull are key to preventing tumor recurrence. In the surgical principle, the operator needs to resect the dural attachment and skull after the tumor resection to achieve Simpson grade I. When the dural attachment and skull were resected incompletely, electrocoagulation is essential to reduce the possibility of tumor recurrence and achieve Simpson grade II. With the development of radiofrequency laser scalpels and other microinstruments, the surgical treatment of dural attachment and skull resection is becoming more and more standardized. The overall tumor resection rate of small cerebellopontine angle meningiomas is increasing, and the tumor recurrence rate is decreasing year by year.

Many radiotherapy studies have reported that the recurrence of small cerebellopontine angle meningiomas is connected with the pathology of the tumors. WHO grade II meningiomas are more likely to recur than WHO grade I meningiomas, which is related to the characteristic of high invasive growth. However, stereotactic radiotherapy cannot obtain the tumor tissue to examine the pathology of the tumor directly. Therefore, the grade of cerebellopontine angle meningiomas treated with radiotherapy is mostly inferred from imaging examination, which is uncertain. Contrary to stereotactic radiotherapy, surgery can directly obtain tumor tissue for pathological examination and guide further treatment through the exact pathological examination results. In the present study, WHO grade II and Simpson grade II were the risk factors of tumor recurrence after surgery. Therefore, patients with WHO grade II or Simpson grade II who undergo surgery need to receive further treatments at the early stage instead of waiting for the recurrence of tumors. This is also the reason why the recurrence rate in the surgery group was slightly lower than the tumor enlargement rate in the radiotherapy group.

In terms of further treatments, the further treatment rate in the surgery group was similar to or even lower than that reported in the radiotherapy group. Hence, compared with stereotactic radiotherapy, patients with surgical treatment might have a lower likelihood of further treatments. In Kyung et al.’s study, the subjects were asymptomatic patients with small cerebellopontine angle meningiomas. A lack of symptoms or relatively mild symptoms could significantly reduce the subjective desire of patients for treatment, which may be why the further treatment rate in Kyung et al. was lower than that reported in the surgery group. In the radiotherapy group, there was no significant difference between the number of patients who chose further radiotherapy and the number of patients who turned to surgery. In the surgery group, there was 1 patient (0.6%) who underwent a second resection, and 12 patients (7.4%) received stereotactic radiotherapy during follow-up. The reason for further radiotherapy for patients in the surgery group was the high invasiveness of the tumor and the incomplete treatment of the dural attachment and skull (12). Similar to other meningiomas, stereotactic radiotherapy of small cerebellopontine angle meningiomas is more likely to be an auxiliary treatment for inhibiting tumor progression after surgery.

The surgical complications mainly included dysfunction of the facial and auditory nerves, trigeminal nerve, and posterior cranial nerves as well as hydrocephalus. Facial paralysis, facial numbness, and hearing loss can seriously affect the quality of life of patients after surgery. The symptoms of posterior cranial nerve damage, such as hoarseness, dysarthria, and weakened cough reflex, significantly affect the prognosis of patients after surgery. Because of the small size of the tumor, complications, such as hydrocephalus and intracerebral hemorrhage, are rare in patients with small cerebellopontine angle meningiomas.

Compared with stereotactic radiotherapy, surgical treatment for small cerebellopontine angle meningiomas can sometimes lead to better results in relieving pre-operative symptoms and inhibiting tumor progression. In terms of further treatments, compared with the uncertainty of stereotactic radiotherapy, surgical treatment can obtain exact pathological examination results to guide the further treatment. Similar to large tumors, surgical treatment should be the first choice for small cerebellopontine angle meningiomas, while stereotactic radiotherapy, pharmacotherapy and experimental therapy are more suitable as supplement to surgical treatment.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and approved by the Institutional Review Board and Ethics Committee of the First Affiliated Hospital of Soochow University. The patients/participants provided their written informed consent to participate in this study.

JW and GC designed the study. JB, PP, HY, WG, YL, ZY, and ZW performed the experiments and analyzed the data. JB wrote the manuscript. All the authors read and approved the manuscript. JB, PJ, and HY have contributed equally to this work. All authors contributed to the article and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.