Nystagmus:  Involuntary rapid movement of the eyes in the horizontal, vertical, or rotary planes of the eyeball.

The back part of the head.

Oligodendroglia:  Non-nerve cells (see glia) forming part of the supporting structure of the central nervous system.
Oligodendroglioma:  A growth of new cells derived from the oligodendroglia.
Orbital: Related to the bony eye socket and surrounding area.
Osteoma:  A benign tumor of bone.
Osteomyelitis:  Inflammation of bone due to infection, which may be localized or generalized.
Osteophytectomy:  Surgical removal of osteophytes (bony outgrowths). Osteophytes may develop on the upper and/or lower edges of the vertebral bodies, often causing pressure on the spinal cord.
Papilledema:  Swelling of the optic nerve head, can be seen in the back of the retina during eye examination.
Paraplegia:  Paralysis of the lower part of the body including the legs. More about spinal cord injury.
Paresthesia:  Numbness, tingling, or a "pins and needles" feeling.
Pars interarticularis:  The area between the upper and lower articulating (joining) facets of two vertebrae.
Pedicle:  One of the two short stems of bone that project outward from the body of each vertebra.
Peripheral nervous system:  The peripheral part of the nervous system external to the brain and spinal cord from their roots to their peripheral terminations.
Pituitary:  The gland at base of the brain that secretes hormones into the bloodstream. Those hormones then regulate other glands including the thyroid, adrenals, and gonads. The "master gland." More about our pituitary surgery program.
Polyneuritis:  Inflammation of two or more nerves simultaneously.
Posterior fossa:  A hollow depression in the back of the skull in which the cerebellum and several other structures are located.
Pre-ictal:  Preceding a seizure (see ictal).
Proprioception:  Sensation concerning movements of joints and position of the body in space.
Pseudarthrosis:  Failure of fusion to achieve proper union of vertebrae.

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