Background Facial nerve schwannomas generate a clinical dilemma because the morbidity of intervention
can be comparable to its natural course. The factors leading to morbidities associated
with this neoplasm are poorly understood.
Objective To establish predictors of facial paralysis and auditory morbidity secondary to facial
nerve schwannomas by assimilating patient-level patient data from the literature.
Methods A systematic review of the English literature was conducted for studies regarding
facial schwannomas. Studies were included only if they presented patient-level data
and reported House-Brackmann scores. Odds ratios were estimated using generalized
linear mixed models with case series as a random effect.
Results Data from 505 patients were collected from 32 studies. The mean age was 42.8 years
(SD = 16.0, N = 387), 46.7% were males (N = 351), and 50.6% were left-sided (N = 89) in studies where those factors were recorded. The most common presenting symptom
was facial palsy for intratemporal tumors and hearing loss for intradural tumors.
Patient age, sex, and tumor size were not associated with facial nerve or hearing
function. The odds of higher grades of facial weakness were greater for left-sided
tumors (OR = 3.05, p = 0.01), intratemporal involvement (OR = 5.52, p < 0.001), and a greater number of facial nerve segments involved (OR = 1.31, p < 0.001). Intradural (OR = 0.60, p = 0.01) and extracranial (OR = 0.53, p < 0.001) involvement was associated with lower odds of facial weakness. Positive
predictors of hearing loss were intradural involvement (OR = 2.97, p < 0.001) and number of facial nerve segments involved (OR = 1.37, p = 0.02). Extracranial involvement was a negative predictor of hearing loss (OR = 0.28,
p = 0.02), and intratemporal involvement had a protective effect (OR = 0.44, p < 0.05).
Discussion The most important factors associated with facial weakness and hearing loss are tumor
location and the number of facial nerve segments involved. Facial weakness is associated
with intratemporal location and hearing loss is associated with tumors more proximal
to the brainstem. An understanding of the factors that contribute most heavily to
the natural morbidity can help guide the appropriate timing and type of intervention
in future cases.
