Lower Cranial Nerve Schwannomas: Microsurgical Outcomes in a Modern Cohort

Introduction: Schwannomas originating from the lower cranial nerves continue to pose a significant challenge for skull base surgeons. Surgical resection has been the mainstay of treatment, but often at the cost of significant morbidity. Sparse data exists on factors affecting surgical outcome. We report a series of 26 patients with pathologically confirmed lower cranial nerve schwannomas (LCNS), to better understand the natural history and outcome of this challenging entity.

Methods: A retrospective review was performed for pathologically proven lower cranial nerve schwannomas between 2003 and 2016 at a single institution. All cases were visually confirmed at the time of surgery to be originating from the 9th, 10th, 11th, and/or 12th cranial nerves. Various patient, tumor, and treatment characteristics were collected and analyzed to evaluate their impact on outcome.

Results: A total of 26 patients were included in the analysis. The median age was 47.5 years (range 17 – 71 years). There were 13 males and 13 females included in the study. Median duration of symptoms was 15.0 months, the most common of which included 50% with dysphagia, 23% with hoarseness or imbalance, and 15.4% with dysarthria, facial numbness, headache, or ocular muscle weakness. Median maximum tumor diameter found on pre-operative imaging was 4.4 cm. 36.4% of patients were found to have bony erosion on CT scan, 24% were found to have hydrocephalus on either CT or MRI, and 45.8% were found to have brainstem compression. Most lesions were found in the cerebellopontine angle/jugular foramen (17 patients, 65.4%), 5 lesions (19.2%) were isolated to the carotid space, and 4 lesions (15.4%) were found in the parapharyngeal space. A gross total resection was achieved in 14 patients (53.8%). Post-operatively, at a median follow-up of 132 days, 5 patients (19.2%) had dysphagia, 4 of which required placement of a PEG for nutrition. Utilizing a Pearson’s Correlation analysis, extension of tumor into the CPA was moderately correlated with erosion of bone (0.42) and subtotal resection (0.49), and was strongly correlated with hydrocephalus (0.68), mass effect on brainstem (0.74), and subtotal resection (0.49). Tumors greater than or equal to 4.5 cm in maximum diameter were twice as likely to have post-operative complications.

Conclusions: Surgical resection of lower cranial nerve schwannomas carries a significant risk, including major cranial nerve deficits. Our study found that growth into the CPA was associated with bony erosion, hydrocephalus, mass effect on the brainstem, and subtotal resection. This is pertinent as these lesions are most often found after significant growth. Although resection of these lesions pertain a high risk, aggressive surgical resection is possible with minimal complications.