Acoustic neuromas are benign tumors that grow on the covering of the acoustic nerve. They are more recently (and properly) known as vestibular schwanomas, since they actually grow on the covering (Schwann cells) of the vestibular (balance) nerve, but they usually damage the acoustic nerve, which runs together with the vestibular nerve.
They typically grow slowly and damage hearing and sometimes balance over time.
They can be removed surgically and they can be treated with radiation. Partial
hearing loss in the affected ear (usually a high frequency loss) is probable
and complete deafness in that ear is possible. The most common symptom is unilaterally
hearing loss, but other symptoms may include balance problems and unilateral
facial weakness or paralysis (similar to Bell's Palsy").
Although not malignant, acoustic neuromas can grow large enough to put pressure
on the brainstem and result in death.
Acoustic neuromas are normally unilateral, but can occur bilaterally in rare
circumstances. Unilateral acoustic neuromas are not hereditary, but if they
occur bilaterally, they are thought to be related to a completely different
condition called neurofibromatosis II (NF2),
which is hereditary.
Checkout the Acoustic Neuroma Association web page for more information.