Tufts Medical Center Experience With Long-Term Follow-Up of Vestibular Schwannoma Treated With Gamma Knife Stereotactic Radiosurgery: Novel Finding of Delayed Pseudoprogression

Association Between Pseudoprogression of Vestibular Schwannoma After Radiosurgery and Radiological Features of Solid and Cystic Components

BACKGROUND AND OBJECTIVES

The pathophysiology of vestibular schwannoma (VS) pseudoprogression after Gamma Knife radiosurgery (GKRS) remains unclear. Radiological features in pretreatment magnetic resonance images may help predict VS pseudoprogression. This study used VS radiological features quantified using an automated segmentation algorithm to predict pseudoprogression after GKRS treatment.

METHODS

This is a retrospective study comprising 330 patients with VS who received GKRS. After image preprocessing and T2W/contrast-enhanced T1-weighted image (CET1W) image generation, with fuzzy C-means clustering, VSs were segmented into solid and cystic components and classified as solid and cystic. Relevant radiological features were then extracted. The response to GKRS was classified into "nonpseudoprogression" and "pseudoprogression/fluctuation". The Z test for two proportions was used to compare solid and cystic VS for the likelihood of pseudoprogression/fluctuation. Logistic regression was used to assess the correlation between clinical variables and radiological features and response to GKRS.

RESULTS

The likelihood of pseudoprogression/fluctuation after GKRS was significantly higher for solid VS compared with cystic VS (55% vs 31%, P < .001). For the entire VS cohort, multivariable logistic regression revealed that a lower mean tumor signal intensity (SI) in T2W/CET1W images was associated with pseudoprogression/fluctuation after GKRS ( P = .001). For the solid VS subgroup, a lower mean tumor SI in T2W/CET1W images ( P = .035) was associated with pseudoprogression/fluctuation after GKRS. For the cystic VS subgroup, a lower mean SI of the cystic component in T2W/CET1W images ( P = .040) was associated with pseudoprogression/fluctuation after GKRS.

CONCLUSION

Pseudoprogression is more likely to occur in solid VS compared with cystic VS. Quantitative radiological features in pretreatment magnetic resonance images were associated with pseudoprogression after GKRS. In T2W/CET1W images, solid VS with a lower mean tumor SI and cystic VS with a lower mean SI of cystic component were more likely to have pseudoprogression after GKRS. These radiological features can help predict the likelihood of pseudoprogression after GKRS.

From the perspective of pseudo-progression rather than treatment failure, how long should we wait before considering treatment failure if large cystic enlargement occurs after Gamma Knife radiosurgery for vestibular schwannoma?: insight into pseudoprogression based on two case reports

Gamma knife radiosurgery (GKRS) has been accepted as a safe and effective treatment for vestibular schwannoma (VS). However, during follow-up, tumor expansion induced by irradiation can occur, and diagnosis of failure in radiosurgery for VS is still controversial. Tumor expansion with cystic enlargement causes some confusion regarding whether further treatment should be performed. We analyzed more than 10 years of clinical findings and imaging of patients with VS with cystic enlargement after GKRS. A 49-year-old male with hearing impairment was treated with GKRS (12 Gy; isodose, 50%) for a left VS with a preoperative tumor volume of 0.8 cc. The tumor size increased with cystic changes from the third year after GKRS, reaching a volume of 10.8 cc at 5 years after GKRS. At the 6th year of follow-up, the tumor volume started to decrease, up to 0.3 cc by the 14th year of follow-up. A 52-year-old female with hearing impairment and left facial numbness was treated with GKRS for a left VS (13 Gy; isodose, 50%). The preoperative tumor volume was 6.3 cc, which started to increase with cystic enlargement from the first year after GKRS, and reaching 18.2 cc by 5 years after GKRS. The tumor maintained a cystic pattern with slight changes in size, but no other neurologic symptoms developed during the follow-up period. After 6 years of GKRS, tumor regression was observed, eventually reaching a volume of 3.2 cc by the 13th year of follow-up. In both cases, persistent cystic enlargement in VS was observed at 5 years after GKRS, after which the tumors began to stabilize. After more than 10 years of GKRS, the tumor volume was less than that before GKRS. Enlargement with large cystic formation in the first 3-5 years after GKRS has been considered as treatment failure. However, our cases show that further treatment for cystic enlargement should be deferred for at least 10 years, especially in patients without neurological deterioration, as inadequate surgery can be prevented within that period.

Simultaneous Cochlear Implantation and Salvage Translabyrinthine Resection of Vestibular Schwannoma after Radiotherapy

OBJECTIVE

To report on the novel use of simultaneous cochlear implantation (CI) during salvage translabyrinthine resection of vestibular schwannoma (VS) after failed stereotactic radiosurgery (SRS).

PATIENT

A 52-year-old woman presented with a medium-sized right VS. She experienced continued tumor growth despite previous SRS, resulting in medial extension beyond the internal auditory canal into the cerebellopontine angle. Associated symptoms included asymmetrical right moderate to severe sensorineural hearing loss, poor word recognition, tinnitus, and dizziness.

INTERVENTION

Simultaneous CI with translabyrinthine VS resection.

MAIN OUTCOME MEASURE

CI-aided pure-tone averages.

RESULTS

After 4 months of device use, CI-aided speech audiometry revealed hearing thresholds in the normal range, with a four-tone pure-tone, average of 16.3 dB. Speech perception with consonant-nucleus-consonant testing in the CI-only condition was 46%, representing a 12% improvement compared with preoperatively. Tinnitus and dizziness burden were subjectively reduced.

CONCLUSIONS

Despite challenges inherent to second procedures after radiotherapy failure, successful CI outcomes can be achieved. The current study demonstrates the feasibility of simultaneous CI during salvage VS resection after SRS. A larger study should be undertaken to further substantiate these preliminary findings.

Long-term results of upfront, single-session Gamma Knife radiosurgery for large cystic vestibular schwannomas

Anecdotally, cystic vestibular schwannomas (cVSs) are regarded to have unpredictable biologic activity with poorer clinical results, and most studies showed a less favorable prognosis following surgery. While stereotactic radiosurgery (SRS) is a well-established therapeutic option for small- to medium-sized VSs, cVSs are often larger, thus making upfront SRS more complicated. The purpose of this retrospective study was to assess the efficacy and safety of upfront SRS for large cVSs. The authors reviewed the data of 54 patients who received upfront, single-session Gamma Knife radiosurgery (GKRS) with a diagnosis of large cVS (> 4 cm3). Patients with neurofibromatosis type 2, multiple VSs, or recurrent VSs and < 24 months of clinical and neuroimaging follow-up were excluded. Hearing loss (48.1%) was the primary presenting symptom. The majority of cVSs were Koos grade IV (66.7%), and the most prevalent cyst pattern was "mixed pattern of small and big cysts" (46.3%). The median time between diagnosis and GKRS was 12 months (range, 1-147 months). At GKRS, the median cVS volume was 6.95 cm3 (range, 4.1-22 cm3). The median marginal dose was 12 Gy (range, 10-12 Gy). The mean radiological and clinical follow-up periods were 62.2 ± 34.04 months (range, 24-169 months) and 94.9 ± 45.41 months (range, 24-175 months), respectively. At 2, 6, and 12 years, the tumor control rates were 100%, 95.7%, and 85.0%, respectively. Tumor shrinkage occurred in 92.6% of patients (n = 50), tumor volume remained stable in 5.6% of patients (n = 3), and tumor growth occurred in 1.9% of patients (n = 1). At a median follow-up of 53.5 months, the pre-GKRS tumor volume significantly decreased to 2.35 cm3 (p < 0.001). While Koos grade 3 patients had a greater possibility of attaining higher volume reduction, "multiple small thick-walled cyst pattern" and smaller tumor volumes decreased the likelihood of achieving higher volume reduction. Serviceable hearing (Gardner-Robertson Scale I-II) was present in 16.7% of patients prior to GKRS and it was preserved in all of these patients following GKRS. After GKRS, 1.9% of patients (n = 1) had new-onset trigeminal neuralgia. There was no new-onset facial palsy, hemifacial spasm, or hydrocephalus. Contrary to what was believed, our findings suggest that upfront GKRS seems to be a safe and effective treatment option for large cVSs.