Near-complete regression 19 years after Gamma Knife radiosurgery of vestibular schwannoma with massive pseudoprogression: case report

Lai-fung Li MRes(Med), FRCSEd(SN) 1 , Chung-ping Yu FRCS, FHKAM 2 , Anderson Chun-on Tsang MBBS, FRCSEd(SN) 1 , Benedict Beng-teck Taw MMedSc, FRCSEd(SN) 1 and Wai-man Lui FRCS, FHKAM 1
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  • 1 Division of Neurosurgery, Department of Surgery, Li Ka Shing Faculty of Medicine, The University of Hong Kong; and
  • 2 The Brain Center, Canossa Hospital, Hong Kong
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Gamma Knife radiosurgery (GKRS) is a frequent treatment choice for patients with small- to moderate-sized vestibular schwannoma (VS). However, pseudoprogression after GKRS is commonly observed, with a reported incidence ranging from 7% to 77%. The wide range of the reported incidence of pseudoprogression reflects the fact that there is no consensus on how it should be diagnosed.

The authors present the case of a 66-year-old woman who had a 2.5-cm right-sided VS treated with GKRS in 1997. The first posttreatment MRI obtained 5 months later showed that the tumor volume had increased to 9.7 cm3. The tumor volume increased further and reached its peak 24 months after treatment at 20.9 cm3, which was a 161% increase from pretreatment volume. Thereafter, the tumor shrank gradually and mass effect on the brainstem reduced over time. By 229 months after treatment, the tumor volume was 1.0 cm3, equaling 12.5% of pretreatment tumor volume, or 4.8% of peak tumor volume after treatment. This case demonstrates that if a patient remains asymptomatic despite a dramatic increase in tumor volume after GKRS, observation remains an option, because even a very sizable tumor can shrink with near-complete resolution. Patients undergoing GKRS for VS should be counseled regarding the possibility of pseudoprogression, and followed carefully over time while avoiding premature decisions for surgical removal after treatment.

ABBREVIATIONS GKRS = Gamma Knife radiosurgery; VS = vestibular schwannoma.

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Contributor Notes

Correspondence Lai-fung Li: The University of Hong Kong, Hong Kong. llfrandom@gmail.com.

INCLUDE WHEN CITING Published online May 8, 2020; DOI: 10.3171/2020.3.JNS20389.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

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