Glossary

The ampulla of the Aqueduct of Sylvius. The widening in the aqueduct’s lumen between the protuberances of the superior and inferior colliculi. Its length is typically 4.5 mm (3.5 to 6mm range)

Anti-nuclear antibody

Absolute Neutrophil Count – The number of neutrophils or polymorphonuclear white blood cells (AKA PMN’s, polys, granulocytes, segmented neutrophils or segs) present in the blood. These are a type of white blood cell that fights against infection.

A term used in ultrasound imaging meaning an area free from echo.

The process of blood vessel formation from existing blood vessels.

The picture of a blood vessel. In typical usage it refers to a radiographic image of a blood vessel that has been filled with a contrast element that is radiopague or radiodense on x-ray imaging.

Anterior-posterior.  This abbreviation typically is used to define a direction, such as a direction of a x-ray beam in an image (e.g., AP chest x-ray is an image where the patient stands facing a xray beam source with the film being placed behind them.

Atrial Septal Defect. A hole in the septum or wall that separates the right from left atria or upper chambers of the heart.

Acute ischemic stroke.  A stroke due to blockage of blood supply to an region of the body such as a part of the brain.

Atypical teratoid rhabdoid tumor – A rare, fast growing tumor arising in the central nervous system of young children. Roughly 50% will occur in the brainstem or cerebellum.