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.
scleritis Inflammation of the sclera. Scleritis causes local pain and can cause vision loss. Scleritis can occur with diseases such as rheumatoid arthritis, Wegener’s granulomatosis, and lupus. Treatment may include use of anti-inflammatory and cortisone medications taken by mouth, intravenously, or injected into the eye.
sclerodactyly Localized thickening and tightness of the skin of the fingers or toes. Sclerodactyly is commonly associated with atrophy of the underlying soft tissues. Sclerodactyly is a characteristic feature of scleroderma.
scleroderma A disease of connective tissue that causes scar tissue (fibrosis) to form in the skin and sometimes also in other organs of the body. Scleroderma is classified into diffuse and limited forms. Diffuse scleroderma affects many internal and external areas of the body, including the skin of the entire body, the bowels, and the…