Jugular veins:  The major veins on each side of the neck that drain blood from the head towards the heart.
Juvenile pilocytic astrocytoma:  A slow-growing brain tumor that develops—usually in children and adolescents—from cells called astrocytes.
Kyphoplasty:  An image-guided procedure in which a balloon is inserted into a fractured vertebra to create a cavity. A special bone cement is injected into the cavity to stabilize the bone and prevent worsening of the fracture. Kyphoplasty is often used to treat spinal compression fractures.
Lamina:  The portion of bone that extends from the pedicle and curves around to complete the vertebral arch on the right and left sides.
Laminectomy:  Removal of one or more entire lamina. Used when greater access is needed to perform a discectomy. Helps release pressure on the nerve when a disc bulges.
Laminotomy:  A surgical procedure where part of the lamina of a vertebra is removed for access to the disc.
Leptomeninges:  Two thin layers of fine tissue covering the brain and spinal cord (the pia mater and arachnoid).
Leptomeningitis:  Inflammation of the membranes covering the brain and spinal cord.
Lipoma:  A benign fatty tumor, usually composed of mature fat cells.
Lordosis:  Curvature of the spine with the convexity forward.
Lumbar drain:  A device (usually a long, thin flexible tube) inserted through the skin into the cerebrospinal fluid space of the lower back; provides a method of draining cerebrospinal fluid.
Lumbar puncture (spinal tap):  Diagnostic test in which a sample of cerebrospinal fluid is "tapped" from an area just below the end of the spinal cord through a thin needle inserted into the spinal canal. Used to detect blood in the cerebrospinal fluid.
Lumbar spine:  Lower spine, lower back. Usually consists of five vertebrae.
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.

Weill Cornell Medicine Brain & Spine Center 525 East 68 Street, Box 99 New York, NY 10065 Phone: 866-426-7787