How frequently do you observe transient enlargement of a vestibular schwannoma after SRS?
Transient enlargement of a vestibular schwannoma is not uncommon, and it's appropriate to reassure patients. I image these patients once every 6 months until radiographic stability, and then once yearly.
It is not uncommon to see transient enlargement of VS after SRS particularly for cystic tumors and data from Mayo Clinic showed that only 14% would need intervention due to continued enlargement:
If the patient is asymptomatic, I'd repeat an MRI in 6 months and would see the patient Q6months until the tumor shrinks back down or remains stable for 2 years. Then I'd image them annually.
If the patient is symptomatic, I'd consider steroids and repeat an MRI brain in 3-4 months till stabilization. Some patients do need surgical intervention if the symptoms are progressive or severe.
When post-radiosurgery enlargement occurs, I usually obtain MRI scans at least twice every 6 months to make sure it becomes stable or shrinks. Once stability is confirmed, I do imaging follow-up once a year.