The animated image, adapted from the website of the Acoustic Neuroma Association NSW (Australia), illustrates the growth of the tumor and the four stages.
Acoustic neuromas, ANs, usually originate on the Schwann-cell sheath of the vestibular nerve (hence the alternative name vestibular schwannoma), within the bony channel called the Internal Auditory Canal (IAC).
In stage I they slowly fill the IAC, compressing the auditory and balance nerves. At this point the first symptoms often appear: unilateral hearing loss and tinnitus.
In Stage II they protrude through the opening of the IAC on the brain side, into an area called the cerebellopontine angle (CPA), without touching the cerebellum nor the brain stem.
In Stage III the tumor has grown to come into contact with the cerebellum and/or the brainstem, without compressing these brain structures. At this point it may impact the trigeminal nerve resulting in loss of sensation on the cornea or the face. If it impacts the facial nerve it might produce unilateral facial paralysis to some extent. Other nerves can be affected resulting in paralysis of the soft palate, a hoarse voice and paralysis of the tongue.
Finally in Stage IV, if untreated the tumor will deform the cerebellum, possibly resulting in writing and gait problems, and/or the brainstem. It can block the flow of cerebrospinal fluid (CSF), causing hydrocephalus (pressure on the brain) and eventually lead to coma or even death.
To determine which stage your tumor is in, look at your MRI with the help of the radiologist. If you only know the largest dimension of the tumor (in millimeters - mm), here is a rough guide:
from 0 to 10 mm: stage I
from 10 to 20 mm: stage II
from 20 to 35 mm: stage III
more than 35mm: stage IV
No medical decision should be based solely on information provided here. See disclaimer.