Vestibular Schwannoma Gamma Knife radiosurgery complications
Patients treated with Stereotactic radiosurgery for vestibular schwannoma can have a similar complication profile to those treated with intracranial surgery. Vestibular Schwannoma Meta-analysis from early experience showed that 44% with serviceable hearing prior to treatment retained their ability after SRS, a statistically equivalent rate to the surgical data. This evidence also suggest that 37.9% of patients have other complications 1).
In the mid-1970s, early facial weakness occurred in 38% and facial numbness in 33%. This has gradually decreased to less than 2% in the 1990s. Preservation of hearing (unchanged or almost unchanged) is currently achieved in 65 to 70%. Tinnitus is rarely changed by the treatment. The risks of intracranial bleeding, infection, and CSF leak are avoided because of the non-invasive nature of the treatment. Hydrocephalus directly induced by the tumor occurred in 9.2% of patients. On the other hand, a treatment%related peritumoral reaction sufficient to block the CSF circulation and require shunt insertion was seen in only 1.4%. Based on experiences worldwide, the incidence of secondary neoplasia seems to be 0.1%. The effectiveness of GKR together with its low complication rate makes it a suitable treatment for anyone, regardless of age and general health 2).
Malignant transformation is possible 3). , and long-term post-SRS surveillance MRI is important 4).
Patients receiving > 13 Gy were significantly more likely to develop trigeminal neuropathy than those receiving < 13 Gy (p < 0.001) 5).
Case reports
Pollack et al. described an acute facial and acoustic neuropathy following gamma knife surgery (GKS) for vestibular schwannoma (VS). This 39-year-old woman presenting with tinnitus underwent GKS for a small right-sided intracanalicular VS, receiving a maximal dose of 26 Gy and a tumor margin dose of 13 Gy to the 50% isodose line. Thirty-six hours following treatment she presented with nausea, vomiting, vertigo, diminished hearing, and a House-Brackmann Grade III facial palsy. She was started on intravenous glucocorticosteroid agents, and over the course of 2 weeks her facial function returned to House-Brackmann Grade I. Unfortunately, her hearing loss persisted. A magnetic resonance (MR) image obtained at the time of initial deterioration demonstrated a significant decrease in tumor enhancement but no change in tumor size or peritumoral edema. Subsequently, the patient experienced severe hemifacial spasms, which persisted for a period of 3 weeks and then progressed to a House-Brackmann Grade V facial palsy. During the next 3 months, the patient was treated with steroids and in time her facial function and hearing returned to baseline levels. Results of MR imaging revealed transient enlargement (3 mm) of the tumor, which subsequently returned to its baseline size. This change corresponded to the tumor volume increase from 270 to 336 mm3. The patient remains radiologically and neurologically stable at 10 months posttreatment. This is the first detailed report of acute facial and vestibulocochlear neurotoxicity following GKS for VS that improved with time. In addition, MR imaging findings were indicative of early neurotoxic changes. A review of possible risk factors and explanations of causative mechanisms is provided 6).
Pseudoprogression
see Vestibular Schwannoma pseudoprogression.