Diplopia:  Double vision, due usually to weakness or paralysis of one or more of the extra-ocular muscles.
Disc:  The intervertebral disc is a cartilaginous cushion found between the vertebrae of the spinal column. It may bulge beyond the vertebral body and compress the nearby nerve root, causing pain. The terms "slipped disc," "ruptured disc," and "herniated disc" are often used interchangeably, even though there are subtle differences. More about herniated discs.
Disc degeneration (also called degenerative disc disease):  A flattening or "wear and tear" of the disc.
Dome:  The round balloon-like portion of an aneurysm that usually forms above a smaller portion called the neck of the aneurysm.
Doppler:  A non-invasive study that uses sound waves to show the flow in a blood vessel and can be used to determine the degree of narrowing (percent stenosis) of the vessel. A wand is placed on the skin over the vessel to be imaged. This study has no risks and is not painful.
Dura mater:  A tough fibrous membrane that covers the brain and spinal cord but is separated from them by a small space.
Dysesthesia:  A condition in which a disagreeable sensation is produced by ordinary touch, temperature, or movement.
Dysphasia:  Difficulty in the use of language without mental impairment due to a brain lesion.
Dystonias:  A group of movement disorders that vary in their symptoms, causes, progression, and treatments. This group of neurological conditions is generally characterized by involuntary muscle contractions that force the body into abnormal, sometimes painful, movements and positions (postures). More about movement disorders.
Edema:  An excessive accumulation of fluid in cells, tissues, or body cavities.
Electroencephalography (EEG):  The study of the electrical currents set up by brain actions; the record made is called an electroencephalogram.
Electromyography (EMG):  A method of recording the electrical currents generated in a muscle during its contraction.
Encephalocele:  The herniation of brain meninges through a skull defect.
Endarterectomy:  The removal of fatty or cholesterol plaques and calcified deposits from the internal wall of an artery. More about carotid occlusive disease.
Endoscope:  A thin, telescope-like instrument. A video camera attached to the endoscope records images a surgeon can view on a monitor. Specially designed surgical tools enable a surgeon to operate through small incision(s). See illustration at right.
Endovascular:  Inside a blood vessel, especially a minimally invasive catheter-based approach for the treatment of central nervous system disorders (for example, a cerebral aneurysm).
Ependyma:  The membrane that lines the cerebral ventricles of the brain and central canal of the spinal cord.
Ependymoma:  A growth in the brain or spinal cord arising from ependymal tissue.
Epidural (extradural):  Immediately outside the dura mater.
Epidural hematoma:  A blood clot between the dura mater and the inside of the skull.

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