Delayed pseudoprogression of a vestibular schwannoma postradiosurgery

Radiosurgery (RS) can offer excellent local control in the management of both benign and malignant tumors measuring less than 3 cm in size. A known late complication of radiosurgery is radiation necrosis which generally occurs within 6-18 months following treatment and has an increased risk of occurrence with higher radiation doses. The lower dose used to treat vestibular schwannomas (VS) makes this complication less frequent. Tumors that do not respond to radiosurgery and continue to grow may require surgical intervention. We report a case of a young male who received radiosurgery (18 Gy in 3 fractions) in February 2016 for a recurrent VS following initial debulking surgery in 2008. Follow-up imaging revealed an interval decrease in size by May 2017; however, by April 2018, there was significant interval increase in the cisternal components of the tumor. By September 2018, the lesion had increased by >50% (to a size of 29 mm) compared to May 2017. The patient agreed to undergo repeat surgical debulking. Upon review of the preoperative MRI, the cisternal component of the tumor had substantially decreased in size. Although uncommon, this reflects delayed, pseudoprogression which, in our case, was self-limiting. This raises a question regarding when to proceed with surgical intervention of growing VS following radiosurgery given the potential for delayed resolution of radiation necrosis and demonstrates a gap in our current literature involving surgery of VS following radiosurgery.