Timothy C. Hain, MD
Meningiomas are the second most common tumor in the cerebellopontine angle (CPA), with acoustic neuroma's being the most commonly. They arise from the arachnoid villi of the venous sinuses. The usual sites are on the posterior surface of the petrous bone, tentorium, clivus, cerebellar convexity, foramen magnum, in order of decreasing frequency. According to Nager and Masica (1970), menigiomas originate in for places within the posterior petrous pyramid; the internal auditory meatus (where they might resemble an acoustic neuroma), the jugular foramen (where they might involve a variety of non-hearing related cranial nerves), the region of the geniculate (facial) ganglion, and the sulcus of the greater and lesser superficial petrous nerves.
Presenting symptoms commonly include hearing loss, imbalance, tinnitus, facial numbness and headaches. Less frequently patients may complain of trigeminal neuralgia, diplopia, nausea, facial paresis, otalgia, or loss of taste. These symptoms are very similar to those of acoustic neuromas.
Contemporary diagnosis, prior to surgery is presently based on neuroradiological tests.
Gadolinium enhanced MRI usually documents a broad dural base on the posterior petrous face with an enhancing tail. They are generally not centered aorund the internal auditory meatus and rarely cause erosion or penetration of the internal auditory canal. In addition they may present with signs of calcification and local hyperostosis.
In contrast, vestibular schwannomas (acoustic neuromas) tend to be round, often cystic masses that are centered around the internal auditory meatus causing erosion or extension into the internal auditory canal.
There are three distinct options:
Medical Management: Medical management consists of periodic monitoring of the patient's neurological status and periodic imaging studies. There is no medication known to have a substantial effect on the growth of mengiomas.
Gamma Knife: When the risk of surgery is high because of other medical problems, or where the patient simply refuses surgery, the "gamma knife" procedure may be used. This is a method of irradiating a tumor, invented by Lars Leksell in 1971. Although it avoids surgery with its attendant risks, this option is usually recommended only for high-risk surgical cases because of the possibilities of late radiation complications, hydrocephalus in about 10 percent of patients, and the need for ongoing MRI monitoring of the results of the procedure. However, as the operators of gamma knife become more proficient, these statistics are likely to improve substantially. Gamma knife does not generally make tumors go away . Patients are best followed with periodic MRI scans for the remainder of their lives.
Significant headache can occur following acoustic neuroma surgery and meningioma's require similar operative approaches.
Hearing preservation occurs in 30-90% of patients (Batra et al, 2002). The chance of hearing preservation is poorer in persons with tumors larger than 1.5 cm, but it is better than that reported for acoustic neuromas. Thus it is important to differentate between meningiomas and acoustics preoperatively whenever possible. This can be done using MRI. Normal post-operative facial nerve function can be conserved in about 65% of patients (Batra et al, 2002).