Gamma Knife surgery in vestibular schwannomas: impact on the anterior and posterior labyrinth

Abstract

Object During the past decades, in small-to-medium size vestibular schwannomas, Gamma Knife surgery (GKS) has become a reliable therapeutic option because of either excellent local tumor control or minimal morbidity, with cranial neuropathy becoming increasingly rare. Although still insufficiently analyzed in larger cohorts of patients with long-term follow-ups, adequate chances of hearing preservation and vestibular sparing seem clinically guaranteed. However, deeper investigations are needed in this regard, expanding the number of cases and the follow-up period. Methods A small group of patients with vestibular schwannomas (74 patients, including 41 men and 33 women) treated between 2003 and 2009 using GKS at the authors' institution were analyzed—both before and after GKS—with computerized static stabilometry and electronystagmography for balance disorders, vertigo, and ataxia on 1 side and pure tone average, vocal speech discrimination score, auditory brainstem response, and so forth for hearing impairment and tinnitus on the other side. Eligibility criteria for this prospective study included previously untreated unilateral lesions and a Gardner-Robertson hearing class of I–III. Dosimetry plans had been programmed at the lower effective dosages for these tumors (median surface dose 12.4 Gy, range 10–13 Gy), carefully avoiding even minimal toxic dosages on the most vulnerable targets: the cochlea (never > 6 Gy) and the vestibular canals (< 7.5 Gy). Results To date, tumor growth control rates remain satisfactory; at a mean follow-up of 50 months, the rate was 96%. The overall level of hearing preservation was 72%, with 81% having Gardner-Robertson Class I hearing. Tinnitus decreased, from 52% to 28% of patients (p < 0.01). Significant improvements were also observed in vestibular symptoms, with computerized static stabilometry abnormalities decreasing from 62% to 32% (p < 0.001) and electronystagmography abnormalities reducing from 48% to 14% (p < 0.001). Conclusions Using appropriate radiodosimetry planning, GKS seems to guarantee not only adequate tumor growth control rates, but also better levels of hearing preservation, with a documented, long-lasting improvement in vestibular functions.

Fractionated Proton Beam Therapy for Acoustic Neuromas: Tumor Control and Hearing Preservation

“…This was not found to be statistically different from the local control rates of 95% to 97% seen in the higher-dose groups (P ¼ .80). The overall 5-year actuarial control rate is 95%, and the 10-year rates were 90%, which is consistent with 5-year local control rates published for stereotactic radiosurgery [4,[10][11][12][13][14][15][16].…”

“…The rates of hearing preservation in this study are comparable to photon stereotactic radiosurgery modalities ( Table 5). Hearing preservation rates of 59% to 75% are reported in the stereotactic radiosurgery literature with a reduced dose of 11-14 Gy and when using the same Gardner-Robertson Scale for assessment [10][11][12][13][14][15][16][17][18][19][20][21][22]. In support of these findings, Milligan also reported a 28% hearing preservation rate when large tumors (2.5 cm in diameter) were treated with modern SRS techniques [21].…”

The Use of Intratympanic Gentamicin in Patients With Vestibular Schwannoma and Disabling Vertigo

“…Vertigo is more frequently seen in small lesions where the tumor has not yet induced vestibular deafferentation. Resolution of episodic vertigo has been reported after surgical resection, whereas conflicting reports exist after stereotactic radiation (14). According to the literature, the cause of hearing loss, tinnitus, and vertigo may be due to an inner ear and not only to a retrocochlear dysfunction.…”

A meta-analysis of treatment of vestibular schwannoma using Gamma Knife radiosurgery

“…The works used different models of Gamma Knife, depending on the period of study and institutions. The latest model, PFX Leksell Gamma Knife, was used in studies at the University of Verona [34] and Marseille [42], and the 4-C model in the study at the University of Pittsburgh [12, 17, 25, 35], Nijmegen [31, 41], Philadelphia [43] and Maastricht [46, 47]. …”

“…The total number of patients meeting the criteria for the work selected in 28 articles was 3233 [7, 9, 12, 15–17, 22, 23, 25–27, 29, 30, 33, 34, 36–41, 43, 45, 47–50, 52]. The described groups of patients ranged from 21 to 444 in size depending on location and duration of the study [33, 36].…”