astigmatism A common form of visual impairment in which part of an image is blurred due to an irregularity in the dome-shaped curvature of the front surface of the eye, the cornea. With astigmatism, light rays entering the eye are not uniformly focused on the retina. The result is blurred vision at all distances. Significant…
astrocytoma A tumor that begins in the brain or spinal cord in small, star-shaped cells called astrocytes. The location of the tumor depends on the age of the person. In adults, astrocytomas most often arise in the cerebrum, whereas in children, they may arise in the brain stem, cerebrum, and cerebellum.
asymptomatic Without symptoms. For example, an asymptomatic infection is an infection with no symptoms.
asystole A dire form of cardiac arrest in which the heart stops beating and there is no electrical activity in the heart. As a result, the heart is at a total standstill.
ataxia Poor coordination and unsteadiness due to the brain’s failure to regulate the body’s posture and regulate the strength and direction of limb movements. Ataxia is usually due to disease in the cerebellum of the brain, which lies beneath the back part of the cerebrum.
ataxia-telangiectasia A progressive disease characterized by degeneration of the nervous system manifest by poor coordination and balance (cerebellar ataxia), red eyes due to widening of small blood vessels in the conjunctiva (ocular telangiectasia), and recurrent sinus and lung infections. Abbreviated AT. Patients with AT have a striking predisposition to leukemia and lymphoma and are extremely…
ATCC American Type Culture Collection.
atelectasis Failure of full expansion of the lung at birth, or lung collapse thereafter. Also known as collapsed lung.
atelectasis, primary Failure of full expansion of the lung at birth.
atelectasis, secondary Partial or complete collapse of a previously expanded lung. Secondary atelectasis may occur when full chest expansion is difficult, such as after chest surgery.
1. Definition Athelia is the congenital or acquired absence of one or both nipples. It is a rare condition often associated with genetic syndromes or developmental abnormalities. 2. Causes and Associations 3. Related Conditions 4. Diagnosis and Management
atherectomy A procedure to remove plaque (atheroma) from the inside of a blood vessel. Atherectomy is done most often in major arteries, such as the coronary, carotid, and vertebral arteries, that have experienced the occlusive effects of atherosclerosis. Atherectomy may be accomplished by various means, including angioplasty, laser surgery, conventional surgical incision, or use of…