schizophrenia One of several brain diseases whose symptoms may include loss of personality (flat affect), agitation, catatonia, confusion, psychosis, unusual behavior, and social withdrawal. The illness usually begins in early adulthood. The cause of schizophrenia is not known, but there appear to be both genetic (inherited) and environmental components to the disease. Schizophrenia is not…
schizophrenia, childhood The onset of schizophrenia before adulthood. This condition is very rare in young children, but it occurs with more frequency in the teenage years. Autism was once known as childhood schizophrenia, but it is a completely different disorder. See also autism; childhood disintegrative disorder; developmental disorder; schizophrenia.
schizotypal personality disorder A personality type that is characterized by unusual patterns of speech and behavior and by social withdrawal. See also Asperger syndrome.
Schmorl’s node An upward and downward protrusion (pushing into) of a spinal disk’s soft tissue into the bony tissue of the adjacent vertebrae. Schmorl’s nodes, which are common, especially with minor degeneration of the aging spine, are detectable via X-ray as spine abnormalities. Schmorl’s nodes are most common in the middle and lower spine. Schmorl’s…
Schwann cell An insulating cell found in the peripheral nervous system that surrounds nerve fibers (axons). Schwann cells form the myelin sheath that facilitates the conduction of impulses along the nerve. See also myelin; peripheral nervous system.
schwannoma A tumor that arises in the Schwann cells, or myelin sheath, of the peripheral nerves. Schwannomas are usually benign. Acoustic neuromas of the eighth cranial nerve are the most common schwannomas. Also known as neurilemmoma.
sciatic nerve The largest nerve in the body, which begins from nerve roots in the lumbar spinal cord in the low back (sacrum) and extends through the buttock area, sending nerve endings down through the legs and knees. See also sciatica.
sciatica Pain that results from irritation of the sciatic nerve and typically radiates from the buttock to the back of the thigh. Although sciatica can result from a herniated disc pressing directly on the nerve, any cause of irritation or inflammation of this nerve can reproduce the painful symptoms of sciatica. Diagnosis is made via…
scintigraphy A diagnostic test in which a twodimensional picture of a body radiation source is obtained through the use of radioisotopes. For example, scintigraphy of the biliary system (cholescintigraphy) is done to diagnose obstruction of the bile ducts by a gallstone, a tumor, or another problem; disease of the gallbladder; and bile leaks. For cholescintigraphy,…
scintimammography A scintigraphic imaging technique sometimes used as a supplemental test in the detection of breast cancer. Scintimammography can sometimes work better than standard mammography in situations where there is considerable uncertainty, as in women who have especially dense breast tissue. See also scintigraphy.
sclera The tough white outer coat that covers the surface of the eyeball. The sclera covers the back five-sixths of the eyeball. The sclera is continuous in the front of the eye with the cornea and in the back of the eye with the external sheath of the optic nerve. The plural is sclerae. See…
sclerencephaly Scarring and shrinkage of the substance of the brain. Sclerencephaly occurs because of chronic inflammation of the brain matter.