Facial Nerve Function and Risk Factors in Resection of Large Cystic Vestibular Schwannomas

The incidence of cystic change in vestibular schwannomas (VS) ranges from 4 to 23%. Cystic VS tend to have different characteristics to solid VS namely larger initial volume, accelerated growth, atypical presentation, and a lobulated/adherent capsule. In general, cystic VS are more challenging, with worse surgical outcomes and higher rates of subtotal resection (STR).

From a total of 655 consecutive VS patients undergoing surgery in Cambridge between 2005 and 2019, 125 were cystic (19.1%). This retrospective study analyzed demographic, clinical, radiological, and intraoperative characteristics and postoperative outcomes, with particular reference to facial nerve outcome (House–Brackmann [HB] scale). Median age was 56 years (range, 17–85 years; 65 M, 60 F). The atypical presentation was common, including facial numbness (42%), headache (30%), diplopia (5%), facial palsy/hemifacial spasm (5.8%), and lower cranial nerve impairment (2.5%).

Median tumor volume was 9,048 mm³ (range: 715–48,950 mm³). Tumor growth was documented in 27.1%. In two, cyst formation occurred postradiotherapy. VS growth was caused by cyst enlargement in 73.5% and both the solid/cystic part in 14.7%. Cysts were peripheral/thin-walled in 74.4% and central in 34.6%. Seventy-nine percent of peripheral cysts were located on the brainstem surface. Translabyrinthine surgery was the preferred approach (97.6%). Gross total resection (GTR) was achieved in 78 (62.4%), near-total resection (NTR) with capsular remnant (<5%) in 43 (34.4%), and STR in 4 (3.2%). NTR/STR were significantly associated with tumor volume >4,000 mm³, high jugular bulb, intraoperative tumor adherence to the brainstem and/or facial nerve (p = 0,017; p = 0,012; p = 0,0006; p < 0.0001, respectively).

The facial nerve was preserved anatomically in all cases. Facial nerve outcome was available at 1 year in 100 cases; 76% were HB 1 to 2, 16% were HB 3 to 4, and 8% were HB 5 to 6. Worse outcomes (HB, 3–6) were associated with tumor volume >19,000 mm³, tumor cyst adjacent to the brainstem, inferior/posterior course of facial nerve, preoperative facial palsy (p = 0.039; p = 0.048; p = 0.3; p = 0.79).

Nonfacial morbidity included CSF leak (7.3%), meningitis (0.8%), facial numbness (6.5%), trigeminal neuralgia (1.6%), lower cranial nerve palsy (5.7%), VI nerve palsy (4.8%). There was no mortality. Tumor control was achieved in 99.1%. Regrowth was observed in one patient after STR, requiring radiotherapy. HB 1 to 2 rates when comparing solid VS operated in our unit were significantly higher than in cystic VS; 94 versus 76%, p = 0,03.

Our results compare favorably with the Thakur et al literature review of 428 cases from nine studies. Although our GTR rate was lower (62.4% vs. review rate of 81.2%), good facial function (HB, 1–2) was significantly higher in our cohort (76 vs. 39%; p = 0.0001), with comparable nonfacial morbidity (19.5 vs. 24.5%; p = 0.3).

Conclusion: Surgery for cystic VS has significantly worse outcome for facial nerve preservation compared with solid VS. This can be mitigated by performing less than total excision, with low risk of recurrence.

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