Types of ANs
Tumor forms on one side spontaneously without any evidence of family history, accounts for 95% of acoustic neuromas.
Bilateral (both sides) is most likely caused by a genetic condition called Neurofibromatosis Type II (NF II) which is a rare disorder characterized by the growth of noncancerous tumors in the nervous system.
Virtually every patient with NF II at some point manifests bilateral acoustic neuromas. Patients with NF II also have a tendency to develop benign nerve tumors in other locations, which include, other nerves that arise from the brain stem, as well as, nerves arising from the spinal cord and located more peripherally in the extremities. (UTHSC, 2017).