Gamma Knife radiosurgery in the treatment of abducens nerve schwannomas: a retrospective study

Abstract

OBJECTIVE Of the intracranial schwannomas, those arising from the vestibular nerves are the most common. Abducens nerve (AN) schwannomas are very rare, and there is limited literature on their optimal management. Therapeutic options include surgery and/or stereotactic radiosurgery. The aim of this study was to evaluate the role of Gamma Knife radiosurgery (GKRS) in these sixth cranial nerve (CN) schwannomas. METHODS The authors performed a retrospective analysis of patients who had undergone GKRS for intracranial tumors at their institute in the period from 2003 to 2010. Inclusion criteria were as follows: isolated AN paresis on presentation, a lesion along the course of the sixth CN, and imaging features characteristic of a schwannoma. Patients with other CN deficits and neurofibromatosis Type 2 were excluded. Symptomatic improvement was defined as the resolution of or an improvement in diplopia noted on a subjective basis or as an improvement in lateral eyeball excursion noted objectively on follow-up. A reduction in tumor volume by at least 20%, as noted by comparing the pre- and post-GKRS images, was deemed significant. RESULTS Six patients with a mean age of 37.1 years (range 17-55 years) underwent primary GKRS. There were 2 prepontine cistern, 3 cavernous sinus, and 1 cisterno-cavernous tumor. The mean duration of symptoms was 6.1 months (range 3-12 months). The mean tumor volume was 3.3 cm (range 1.5-4.8 cm). The mean tumor margin radiation dose was 12.5 Gy (range 12-14 Gy), while the median margin dose was 12 Gy (50% isodose line). The median number of isocenters used was 5 (range 4-8). The brainstem received an average 8.35-Gy radiation dosage (range 5.5-11 Gy). The mean follow-up duration was 44.3 months (range 24-78 months). Symptoms remained stable in 1 patient, improved in 3, and resolved in 2 (total improvement 83%). Magnetic resonance imaging at the last follow-up showed a stable tumor size in 3 patients (50%) and a reduction in the other 3. Thus, the tumor control rate achieved was 100%. No new CN deficits were noted. CONCLUSIONS Abducens nerve schwannomas are rare intracranial tumors. They can be cavernous, cisternal, or cisterno-cavernous in location. Excellent tumor control rates and symptomatic improvement can be achieved with GKRS, which appears to be a safe and effective, minimally invasive modality for the treatment of such lesions. Therefore, it is reasonable to consider GKRS as the initial treatment of choice for this rare pathology. Long-term follow-up will be essential for further recommendations.

Outcomes after stereotactic radiosurgery for schwannomas of the oculomotor, trochlear, and abducens nerves

“…In this study, we report actuarial tumor control rates of 96% at 1 year and 86% at 10 years, which are comparable with the 92%-100% control rates described in previous studies. 7,8,[10][11][12][13]15,17,18 These results also mirror some reports from prior studies pertaining to other cranial nerve schwannomas, most commonly those originating from the vestibular (10-year control of 92%), 3 trigeminal (10year control of 95%), 1 facial (5-year control of 90%), 6 and jugular foramen (10-year control of 82%) 5 nerves. This suggests that schwannoma radiosensitivity is an intrinsic characteristic of this tumor type and may be less related to the nerve of origin.…”

“…Nine studies published between 2002 and 2017 described a limited number of tumors managed by SRS, ranging from 1 to 6 cases per study. 7,8,[10][11][12][13]15,17,18 Eight of these studies reported long-term tumor control rates of 100%, while 1 study described a The rate of worsening symptoms was null in most studies, with one study describing 6% of neurological deterioration due to tumor expansion and another study identifying 3 instances of transient diplopia and 1 case of visual deterioration due to orbital tumor extension (Table 3).…”

“…In the current literature, clinical symptom control rates in oculomotor nerve schwannomas following SRS vary between 38% and 100%. 7,8,[11][12][13]15,16,18 Worsening of cranial nerve function is rare after radiosurgery, with only 2 studies each presenting a case of cranial nerve deterioration. 7,12 In the present study, we were able to confirm the safety of SRS for the management of oculomotor schwannomas.…”

“…7,8,[11][12][13]15,16,18 Worsening of cranial nerve function is rare after radiosurgery, with only 2 studies each presenting a case of cranial nerve deterioration. 7,12 In the present study, we were able to confirm the safety of SRS for the management of oculomotor schwannomas. Diplopia improved in 55% and remained stable in 30% of patients.…”

“…They are skull base neoplasms found close to the brainstem often involving the cavernous sinus, for which resection can cause significant morbidity. As for other schwannomas, SRS can be used to manage these tumors; however, only a handful of cases have been published so far, [7][8][9][10][11][12] often among reports of other uncommon schwannoma locations. [13][14][15][16][17][18] This paucity of current literature highlights the need to better evaluate the safety and efficacy of SRS for oculomotor cranial nerve schwannomas with regard to tumor control, clinical evolution, and the worsening or occurrence of new symptoms.…”