The need for long-term monitoring of acoustic neuromas
Even after treatment, acoustic neuromas are routinely monitored with MRI tests initially after 6 months or maybe a year, and then, depending on the results, at longer and longer intervals. Hearing tests, balance tests, facial pain or paralysis tests may also be carried out. Any increase in symptoms will usually prompt an MRI test to discover the cause. In case of regrowth, a second treatment may become necessary.
Monitoring after surgery
The ideal outcome for surgery is complete removal of the tumor without damage to surrounding nerves and brain structures. In this case, regrowth is very unlikely, maybe of the order of 1 to 3%, except in the very rare case of patients with a genetic condition called NF2 which can lead to multiple tumors. An MRI test will be requested by the surgeon after 6 months or possibly one year. If everything seems perfect then the frequency of testing will probably be lengthened to 2 years, 5 years and then maybe none. The frequency of testing for each individual case will depend on the judgment of the surgeon and the circumstances of the patient.
There are cases where some of the tumor is not removed. This might be unintentional, but frequently the surgeon will purposely leave part of the tumor to avoid damage to the nerves or the brainstem. In these cases, depending on how much is left and the characteristics of each individual tumor, the risk of regrowth can be much higher, perhaps up to 25% or more. The frequency of monitoring will be consequently higher.
The extreme case of partial removal is called debulking. This can be done when the tumor is large. The intention is usually to kill the remaining portion of the tumor with subsequent radiation treatment.
Monitoring after radiation
Radiation treatment never removes the tumor. It remains in place but, ideally, starts to die and then to shrink, and causes no more problem. The best radiation centers boast of 98 to 100% success in controlling the tumor.
Swelling often occurs after radiation, usually between 6 months or one year following the treatment. Then, typically, the center of the tumor begins to darken on the MRI film due to necrosis, or death, of some of the tumor cells. MRI tests at 6 months are routinely prescribed after radiation.
Depending on the results of the first test, the frequency of testing may lengthen to one year, two years, five years, but the monitoring will continue more or less forever.
Monitoring for patients who have not had treatment
For "conservative management" patients (permanent wait & watch) periodic MRI tests are the norm. If no growth is observed after the first 6 months, and the symptoms do not increase, testing will be usually prescribed once a year for life.