Skip to Main Content


(mĕ-dŭl″ō-blas-tō′mă) [medulla + blast- + -oma] A malignant tumor of the roof of the fourth ventricle and cerebellum. The tumor is the most common malignant brain tumor in childhood. SYN: primitive neuroectodermal tumor.


(mĕ-dŭl″ō-ĕp″ĭ-thēl-ē-ō′mă) [″ + Gr. epi, upon, + thele, nipple, + oma, tumor] Tumor composed of retina epithelium and of neuroepithelium. SYN: glioma; neuroepithelioma.


(mĕd′wătch) A voluntary and confidential program of the Food and Drug Administration (FDA) for monitoring the safety of drugs, biologicals, medical devices, and nutritional products such as dietary supplements, medical foods, and infant formulas. The FDA provides forms for reporting adverse events associated with any of these products. Health professionals may obtain the form by calling 1-800-332-1088. Health professionals may obtain the form online by searching for Form FDA 3500A.

Mees lines

(mēz, mēs, mās) [R.A. Mees, 20th-cent. Dutch scientist] Transverse white lines that appear above the lunula of the fingernails about 5 weeks after exposure to arsenic.


[Gr. megas, large] 1. SEE: megalo-. 2. In the International System of Units (SI), a prefix meaning 1 million (106).


(meg′ă-kōd″) [mega- + code] A simulated cardiac arrest used for educational purposes by health care professionals during advanced cardiac life support training. It is intended to sharpen the technical and interpersonal skills needed during the cardiopulmonary resuscitation.


(mĕg′ă-kō″lŏn) [″ + kolon, colon] Massive dilation of the colon, which, if left untreated, may result in perforation and peritonitis.

aganglionic m. Hirschsprung disease.

toxic m. Marked enlargement of the colon, esp. the transverse colon. Clinically, tachycardia, fever, and leukocytosis occur. There may be abdominal tenderness, a palpable abdominal mass, confusion, cramping, and change in number of bowel movements per day. SYN: toxic dilatation of colon.

 ETIOLOGY: The most common causes of toxic megacolon in adults are ulcerative colitis, pseudomembranous colitis, Crohn's disease, drugs that slow intestinal motility (such as narcotics), and severe electrolyte disturbances. Megacolon in children may result from Hirschsprung disease.

 TREATMENT: Patients with toxic megacolon are treated by withholding oral intake, providing nasogastric suction, giving broad-spectrum antibiotics (and corticosteroids, in inflammatory bowel disease), and carefully resuscitating fluids and electrolytes. Surgery is required if the patient fails to improve or deteriorates.


(mĕg″ă-kū′rē) [″ + curie] ABBR: MCi. A unit of radioactivity equal to 106 curies.


(mĕg″ă-dŏn′shē-ă) [″ + odous, odont-, tooth] Macrodontia.


(mĕ′gă-dōs″) A dose of a nutrient, such as a ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.