Malignant peripheral nerve sheath tumour transformation of histological benign vestibular schwannoma after stereotactic radiosurgery in patients without neurofibromatosis

Incidence of rare malignant transformation in vestibular schwannomas treated with stereotactic radiosurgery: a single-institution analysis of 1,061 cases

PURPOSE

This study assesses the incidence of malignant transformation (MT) in vestibular schwannomas (VSs) treated with stereotactic radiosurgery (SRS) over a 30-year period, with a median follow-up of 12 years.

METHODS

A retrospective analysis was performed on 1,051 individuals who underwent gamma knife surgery (GKS) for VS between May 1991 and March 2023. The cohort comprised 1,013 individuals with sporadic VSs and 38 with neurofibromatosis type 2-related schwannomatosis (NF2-SWN), totaling 1,061 treated VSs. The annual MT risk was calculated based on lesion-years at risk.

RESULTS

Among the 1,061 VSs treated with GKS, MT occurred in 2 cases (0.19%), both in individuals with sporadic VSs. Over 12,940 lesion-years from GKS to the latest follow-up, the annual MT risk was 0.016% for all VSs, with no cases observed within the first 5 years post-GKS. However, the risk increased to 0.025% beyond 5 years. No instances of MT were identified in individuals with NF2-SWN.

CONCLUSIONS

This study represents the most extensive investigation specifically examining the incidence of MT in VSs treated with SRS, leveraging the largest case series and longest observation period to date. The findings indicate that MT following SRS for VSs is exceedingly rare. Although the overall risk remains minimal, it may increase slightly with extended follow-up. These results support the continued use of SRS as a safe and effective treatment for VS while emphasizing the need for long-term monitoring.

Cerebrospinal fluid dissemination of an intracranial malignant peripheral nerve sheath tumor in the sellar region: illustrative case

BACKGROUND

Malignant peripheral nerve sheath tumors (MPNSTs) are uncommon types of soft tissue sarcomas. The occurrence of intracranial MPNSTs in the sellar region is exceedingly rare.

OBSERVATIONS

A 37-year-old female, who had undergone transnasal surgery for a pituitary adenoma followed by adjuvant stereotactic radiotherapy 10 years earlier, was diagnosed with an intracranial MPNST in the sellar region. A second transnasal procedure successfully removed the lesion and was followed by proton therapy. Three months postoperatively, spontaneous cerebrospinal fluid (CSF) rhinorrhea occurred and was repaired through a third transnasal surgery. A CSF test revealed the presence of suspicious tumor cells. Subsequently, acute hydrocephalus developed and was urgently managed with a ventriculoperitoneal shunt. About 2 months later, the patient died due to intraspinal metastasis.

LESSONS

Pathologically ambiguous lesions in the sellar region require meticulous observation, as MPNST can be erroneously diagnosed as a pituitary adenoma. Prompt surgical intervention provides the best opportunity for achieving complete resection, which remains the most effective treatment for MPNST. In addition to hematogenous metastasis, MPNST can also disseminate and implant via CSF, leading to recurrence. Acute hydrocephalus or intraspinal metastasis can significantly reduce overall survival. https://thejns.org/doi/10.3171/CASE24437.

Malignant transformation of vestibular schwannoma 29 years after Gamma Knife radiosurgery: illustrative case

BACKGROUND

Vestibular schwannomas are common posterior fossa tumors, often managed with stereotactic radiosurgery (SRS) due to its low invasiveness and high tumor control rates. However, malignant transformation of vestibular schwannoma (MTVS) is a rare but serious complication with a poor prognosis.

OBSERVATIONS

The authors present a case of MTVS occurring 29 years after initial SRS, the longest latency reported. A 68-year-old woman developed sudden facial nerve paralysis, with magnetic resonance imaging revealing tumor regrowth. Surgical removal and histopathological analysis confirmed malignant transformation, characterized by spindle-shaped atypical cells and significant p53 positivity. Despite multiple surgeries and radiation therapy, the tumor exhibited rapid regrowth and cerebrospinal dissemination, leading to a poor prognosis.

LESSONS

This case underscores the critical importance of long-term monitoring after SRS, as malignant transformation can occur decades later. Additionally, it highlights the potential necessity for early intervention during malignant transformation to improve patient outcomes, despite the challenges in identifying effective treatments for MTVS. https://thejns.org/doi/10.3171/CASE24526.

Malignant transformation of vestibular schwannoma after radiation therapy

Stereotactic radiosurgery (SRS) is an effective treatment for vestibular schwannomas, offering high rates of tumor control and low neurological risks. Long-term complications of SRS are not fully understood, with several cases of malignant transformation reported in the literature. We report the case of a 50-year-old female with no prior history of neurofibromatosis who presented in 2013 with MRI evidence of a benign vestibular schwannoma. Despite treatment with CyberKnife SRS, she presented 6 years later with new onset neurologic symptoms. Further investigation showed stable lesion size with increasing vasogenic edema and a new area of enhancement in the brainstem, suspicious for malignant transformation. Subsequent treatment with partial craniectomy and histopathologic analysis was consistent with a malignant peripheral nerve sheath tumor diagnosis. Our case adds to a series of 24 similar cases in the literature, details of which have been summarized in our study. Overall, findings support the need for lifelong surveillance following SRS treatment of benign vestibular schwannomas. Patients should be educated on the potential risk of this complication, and clinicians must maintain a high level of suspicion for potential radiation-induced malignancy during the patient's clinical course.

Malignant transformation of vestibular schwannoma following radiosurgery-a case report and review of the literature

Malignant transformation of vestibular schwannoma (VS) post-radiosurgery is an extremely rare but life-threatening complication. We present a patient who underwent two surgeries for a benign VS and received Gamma Knife radiosurgery for residual tumour. Five and a half years post-radiosurgery, the patient was reoperated for symptomatic recurrence of the tumour. Histopathology confirmed the diagnosis of a high-grade spindle cell sarcoma. Although near-total resection was uneventful, the patient deteriorated rapidly, and comfort care was chosen. This report is the 13th documented case of histopathologically confirmed malignant transformation of a benign VS that strictly meets the modified Cahan's criteria, suggesting the direct link to radiosurgery-induced malignancy.

Culture of attenuated Salmonella Typhimurium VNP20009 in animal-product-free media does not alter schwannoma growth control

Schwannomas are slow-growing benign peripheral nerve sheath tumors derived from Schwann-lineage cells that develop in association with NF2-related schwannomatosis (NF2) and schwannomatosis (NF3), as well as spontaneously. Individuals affected with NF2 and NF3 have multiple schwannomas with tumors arising throughout life. Surgical resection, the standard management, is limited in scope and efficacy and is itself associated with significant morbidity. We have previously shown that direct intratumoral injection of attenuated Salmonella Typhimurium (S. Typhimurium), strain VNP20009, showed a potent anti-tumor effect in preclinical NF-2 schwannoma models. The United States Federal Drug Administration (FDA) requires that bacterial products utilized in clinical trials be produced without exposure to animal-derived-products. In this context, we developed, characterized, and tested the antitumor efficacy of an attenuated S. Typhimurium serially passaged in animal-product-free media, naming it VNP20009-AF for "VNP20009-animal-product-free." Our in vitro data did not indicate any significant changes in the viability, motility, or morphology of VNP20009-AF, compared to its parental strain. In vivo efficacy data demonstrated that VNP20009-AF and VNP20009 controlled tumor growth to the same degree in both human NF2-schwannoma xenograft and murine-NF2 schwannoma allograft models. Together, these data support the use of VNP20009-AF for the translation of bacterial schwannoma therapy into clinical trials.

Stereotactic Radiosurgery for Vestibular Schwannoma in Neurofibromatosis Type 2: An International Multicenter Case Series of Response and Malignant Transformation Risk

BACKGROUND

Vestibular schwannomas (VSs) related to neurofibromatosis type 2 (NF2) are challenging tumors. The increasing use of stereotactic radiosurgery (SRS) necessitates further investigations of its role and safety.

OBJECTIVE

To evaluate tumor control, freedom from additional treatment (FFAT), serviceable hearing preservation, and radiation-related risks of patients with NF2 after SRS for VS.

METHODS

We performed a retrospective study of 267 patients with NF2 (328 VSs) who underwent single-session SRS at 12 centers participating in the International Radiosurgery Research Foundation. The median patient age was 31 years (IQR, 21-45 years), and 52% were male.

RESULTS

A total of 328 tumors underwent SRS during a median follow-up time of 59 months (IQR, 23-112 months). At 10 and 15 years, the tumor control rates were 77% (95% CI: 69%-84%) and 52% (95% CI: 40%-64%), respectively, and the FFAT rate were 85% (95% CI: 79%-90%) and 75% (95% CI: 65%-86%), respectively. At 5 and 10 years, the serviceable hearing preservation rates were 64% (95% CI: 55%-75%) and 35% (95% CI: 25%-54%), respectively. In the multivariate analysis, age (hazards ratio: 1.03 [95% CI: 1.01-1.05]; P = .02) and bilateral VSs (hazards ratio: 4.56 [95% CI: 1.05-19.78]; P = .04) were predictors for serviceable hearing loss. Neither radiation-induced tumors nor malignant transformation were encountered in this cohort.

CONCLUSION

Although the absolute volumetric tumor progression rate was 48% at 15 years, the rate of FFAT related to VS was 75% at 15 years after SRS. None of the patients with NF2-related VS developed a new radiation-related neoplasm or malignant transformation after SRS.

Vestibular Schwannoma Surgery with Endoscope-Assisted Retrolabyrinthine Approach under Modified Reinforced Continuous Intraoperative Monitoring for Hearing Preservation: Experience of 33 Cases in a Single Center

Surgery for vestibular schwannoma includes various techniques such as the middle cranial fossa, suboccipital, translabyrinthine, and retrolabyrinthine approaches. The retrolabyrinthine approach does not impair the labyrinth and allows postoperative hearing preservation. Previously, we reported an endoscope-assisted retrolabyrinthine approach under reinforced continuous intraoperative monitoring for preservation of hearing and facial nerve function. However, the hearing preservation rate was relatively low in patients with long-wave V latency in the auditory brainstem response or poor otoacoustic emission response under this approach. Thus, the hearing preservation rate in such patients remains to be improved. To overcome this limitation, we modified the previous approach. In 26 of the 33 consecutive cases (79%) over the last three years, preservation of hearing equivalent to that before surgery or improved hearing was achieved. Postoperative deafness was observed in only two of the 33 cases (6%). According to previous reports, the rate of hearing preservation using the retrolabyrinthine approach is approximately 30-50%. Therefore, we have achieved a higher hearing preservation rate than that previously reported using the endoscopy-assisted retrolabyrinthine approach under reinforced continuous intraoperative monitoring. These improvements in our department are considered to be helpful for hearing preservation.