Magnetic resonance angiography (MRA):  A non-invasive study conducted in a magnetic resonance imager. The magnetic images are assembled by a computer to provide an image of the arteries in the head and neck. No contrast material is needed, but some patients may experience claustrophobia in the imager.
Magnetic resonance imaging (MRI):  Diagnostic test that produces three-dimensional images of body structures using powerful magnets and computer technology rather than x-rays.
Median nerve:  The nerve formed from the brachial plexus that supplies muscles in the anterior forearm and thumb as well as sensation of the hand. It may be compressed or trapped at the wrist in carpal tunnel syndrome.
Medulloblastoma:  A tumor composed of medulloblasts, which are cells that develop in the roof of the fourth ventricle (medullary velum).
Meninges:  The three membranes—the dura mater, arachnoid mater, and pia mater—covering the spinal cord and brain.
Meningioma:  A firm, often vascular tumor arising from the meninges of the brain or spinal cord. More about meningioma.
Meningitis:  An inflammation or infection of the meninges.
Meningocele:  A protrusion of the meninges of the spinal cord through a defect in the spinal column.
Meningoencephalitis:  An inflammation or infection of the brain and meninges.
Meningoencephalocele:  A protrusion of both the meninges and brain tissue through a skull defect.
Minimally invasive:  A surgical procedure where a small incision is made and instrumentation is used through this incision. More about our minimally invasive neurosurgery program.
MRI (magnetic resonance imaging):  A scanning technique for views of the brain or spinal cord. No radiation is involved, but rather pulsed magnetic waves are used to delineate the structures within the brain.
Myelogram:  An x-ray of the spinal canal following injection of a contrast material into the surrounding cerebrospinal fluid spaces.
Myelomeningocele:  A protrusion of the spinal cord and its coverings through a defect in the vertebral column.
Myelopathy:  Any functional or pathologic disturbance in the spinal cord.
Myopathy:  Any disease of muscle.

Weill Cornell Medicine Neurological Surgery 525 East 68 Street, Box 99 New York, NY 10065 Phone: 866-426-7787