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Medical Dictionary


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medulloblastoma (med′u-lo-blas-to′ma)
`A tumor consisting of neoplastic cells that resemble the undifferentiated cells of the primitive medullary tube; medulloblastomas are usually located in the vermis of the cerebellum, and may be implanted discretely or coalescently on the surfaces of the cerebellum, brainstem, and spinal cord; they comprise approximately 3% of all intracranial neoplasms, and occur most frequently in children; the neoplastic cells are compactly arranged, rounded or ovoid, with hyperchromatic nuclei and relatively scant cytoplasm, and lie in small and poorly defined groups, or, occasionally, in a pseudorosette pattern (Homer-Wright rosette). A type of primitive neuroectodermal tumor. desmoplastic m. subtype of m. with a biphasic pattern of compact sheets of undifferentiated cells alternating with islands of more loosely cohesive cells, generally occurs in adolescence and young adults and has a better prognosis than the usual m.. melanotic m. a rare variant of m. in which melanin-pigmented cells are present.

medullocell (med′u-lo-sel, med′oo-)
SYN: myelocyte (2) .

medulloepithelioma (me′du-lo-ep′i-the-le-o′ma)
A rare, primitive, rapidly growing intracranial neoplasm thought to originate from the cells of the embryonic medullary canal and hence included with ependymoblastomas by some neuropathologists; ganglion cells and astrocyte maturation have also been reported. Tumors that occur in the ciliary body are referred to as embryonal medulloepitheliomas. [medullo- + epithelium + -oma, tumor] adult m. SYN: malignant ciliary epithelioma. embryonal m. an epitheliomatous tumor of the nonpigmented layer of the ciliary epithelium. SYN: embryonal tumor of ciliary body.

medullomyoblastoma (med′u-lo-mi′o-blas-to′ma)
A rare histologic variant of medulloblastoma with scattered smooth and striated muscle cells incorporated into the neoplasm.

Meeh
K., 19th century German physiologist. See M. formula, M.-Dubois formula.

Mees
R.A., 20th century Dutch physician. See M. lines, under line, M. stripes, under stripe.

Meesman
A., German ophthalmologist, 1888–1969. See M. dystrophy.

mefenamic acid (me-fe-nam′ik)
An aspirinlike analgesic with antiinflammatory properties.

mefenorex hydrochloride (me-fen′o-reks)
A sympathomimetic drug with anorexic activity.

mefexamide (me-fek′a-mid)
An antidepressant.

mefloquine (mef′lo-kwin)
An antimalarial resembling quinine and chloroquine.

MEG
Abbreviation for magnetoencephalogram.

mega-
1. Combining form meaning large, oversize; opposite of micro-. SEE ALSO: macro-, megalo-. 2. (M) Prefix used in the SI and metric system to signify multiples of one million (106). [G. megas, big]

megabacterium (meg′a-bak-ter′e-um)
A bacterium of unusually large size. SYN: macrobacterium.

megacalycosis (meg′a-kal-i-ko-sis)
1. Congenital, nonobstructive enlargement of renal calices. 2. Excessively large number of calices. [mega- + G. kalyx, cup of a flower, + -osis, condition]

megacardia (meg-a-kar′de-a)
SYN: cardiomegaly.

megacaryoblast (meg-a-kar′e-o-blast)
SYN: megakaryoblast.

megacaryocyte (meg-a-kar′e-o-sit)
SYN: megakaryocyte.

megacephalia (meg-a-se-fa′le-a)
SYN: megacephaly.

megacephalic (meg′a-se-fal′ik)
Relating to or characterized by megacephaly. SYN: macrocephalic, macrocephalous, megacephalous.

megacephalous (meg-a-sef′a-lus)
SYN: megacephalic.

megacephaly (meg-a-sef′a-le)
A condition, either congenital or acquired, in which the head is abnormally large; usually applied to an adult skull with a capacity of over 1450 ml. SYN: leontiasis ossea, macrocephaly, macrocephalia, megacephalia, megalocephaly, megalocephalia, Virchow disease. [mega- + G. kephale, head]

megacins (meg′a-sinz)
Antibacterial proteins produced by strains of Bacillus megaterium.

megacoccus, pl .megacocci (meg′a-kok′us, -kok′si)
A coccus of unusually large size. SYN: macrococcus.

megacolon (meg′a-ko′lon)
A condition of extreme dilation of the colon. SYN: giant colon. acquired m. m. occurring on the basis of an acquired disease; occurs in inflammatory bowel disease (toxic m.) and Chagas disease (South American trypanosomiasis). congenital m., m. congenitum congenital dilation and hypertrophy of the colon due to absence (aganglionosis) or marked reduction (hypoganglionosis) in the number of ganglion cells of the myenteric plexus of the rectum and a varying but continuous length of gut above the rectum; also seen in dogs. SYN: Hirschsprung disease. idiopathic m. an acquired m., found in children and adults, without distal obstruction or absence of ganglion cells; the muscle of the dilated colon is thin. toxic m. acute nonobstructive dilation of the colon, seen in fulminating ulcerative colitis and Crohn disease.

megacycle (meg′a-si-kl)
One million cycles per second.

megacystis (meg′a-sis-tis)
Pathologically large bladder in children. SYN: megalocystis. [mega- + kystis, bladder]

megadactyly, megadactylia, megadactylism (meg-a-dak′ti-le, -dak-til′e-a -dak′til-izm)
Condition characterized by enlargement of one or more digits (fingers or toes). SYN: dactylomegaly, macrodactylia, macrodactylism, macrodactyly, megalodactylia, megalodactylism, megalodactyly. [mega- + G. daktylos, digit]

megadolichocolon (meg′a-dol′i-ko-ko′lon)
Excessive length and dilation of the colon. [mega- + G. dolichos, long, + kolon, colon]

megadont (meg′a-dont)
SYN: macrodont. [mega- + G. odous (odont-), tooth]

megadontism (meg-a-don′tizm)
SYN: macrodontia.

megadyne (meg′a-din)
One million dynes.

megaesophagus (meg′a-e-sof′a-gus, meg′a-e-sof′)
Great enlargement of the lower portion of the esophagus, as seen in patients with achalasia and Chagas disease.

megagamete (meg-a-gam′et)
SYN: macrogamete.

megagnathia (meg-a-na′the-a)
SYN: macrognathia.

megahertz (MHz) (meg′a-hertz)
One million hertz.

megakaryoblast (meg-a-kar′e-o-blast)
The precursor of a megakaryocyte. SYN: megacaryoblast.

megakaryocyte (meg-a-kar′e-o-sit)
A large cell (as much as 100 μm in diameter) with a polyploid nucleus that is usually multilobed; m.'s are normally present in bone marrow, not in the circulating blood, and give rise to blood platelets. SYN: megacaryocyte, megalokaryocyte, thromboblast. [mega- + G. karyon, nut (nucleus), + kytos, hollow vessel (cell)]

megal-
See megalo-.

megalecithal (meg-a-les′i-thal)
Denoting an egg rich in yolk, as in bony fishes, reptiles, and birds. [mega- + G. lekithos, yolk]

megalgia (meg-al′je-a)
Very severe pain. [mega- + G. algos, pain]

megalo-, megal-
Large; opposite of micro-. SEE ALSO: macro-, mega-. [G. megas (megal-)]

megaloblast (meg′a-lo-blast)
A large, nucleated, embryonic type of cell that is a precursor of erythrocytes in an abnormal erythropoietic process observed in pernicious anemia; a megaloblasts four stages of development are as follows: 1) promegaloblast, 2) basophilic m., 3) polychromatic m., 4) orthochromatic m.. SEE ALSO: erythroblast. [megalo- + G. blastos, + germ, sprout]

megalocardia (meg′a-lo-kar′de-a)
SYN: cardiomegaly. [megalo- + G. kardia, heart]

megalocephaly, megalocephalia (meg′a-lo-sef′a-le, -se-fa′le-a)
SYN: megacephaly.

megalocheiria, megalochiria (meg′a-lo-ki′re-a)
SYN: macrocheiria. [megalo- + G. cheir, hand]

megalocornea (meg′a-lo-kor′ne-a)
SYN: keratoglobus.

megalocystis (meg′a-lo-sis′tis)
SYN: megacystis. [megalo- + G. kystis, bladder]

megalocyte (meg′a-lo-sit)
A large (10–20 μm) nonnucleated red blood cell. [megalo- + G. kytos, cell]

megalocythemia (meg′a-lo-si-the′me-a)
SYN: macrocythemia.

megalocytosis (meg′a-lo-si-to′sis)
SYN: macrocythemia.

megalodactylia, megalodactylism, megalodactyly (meg′a-lo-dak-til′e-a, -dak′til-izm, -dak′ti-le)
SYN: megadactyly.

megalodont (meg′a-lo-dont)
SYN: macrodont.

megalodontia (meg′a-lo-don′she-a)
SYN: macrodontia.

megaloencephalic (meg′a-lo-en′se-fal′ik)
Denoting an abnormally large brain.

megaloencephalon (meg′a-lo-en-sef′a-lon)
An abnormally large brain. SYN: macroencephalon. [megalo- + G. enkephalos, brain]

megaloencephaly (meg′a-lo-en-sef′a-le)
Abnormal largeness of the brain. [megalo- + G. enkephalon, brain]

megaloenteron (meg′a-lo-en′ter-on)
Abnormal largeness of the intestine. SYN: enteromegaly, enteromegalia. [megalo- + G. enteron, intestine]

megalogastria (meg′a-lo-gas′tre-a)
Abnormally large size of the stomach. SYN: macrogastria. [megalo- + G. gaster, stomach]

megaloglossia (meg′a-lo-glos′se-a)
SYN: macroglossia. [megalo- + G. glossa, tongue]

megalographia (meg′a-lo-graf′e-a)
SYN: macrography.

megalokaryocyte (meg′a-lo-kar′e-o-sit)
SYN: megakaryocyte.

megalomania (meg′a-lo-ma′ne-a)
1. A type of delusion in which the individual considers himself or herself possessed of greatness. He/she believes him/herself to be Christ, God, Napoleon, etc., or everyone and everything, including a lawyer, physician, clergyman, merchant, prince, ace athlete in all divisions of sport, etc. 2. Morbid verbalized overevaluation of oneself or of some aspect of oneself. [megalo- + G. mania, frenzy]

megalomaniac (meg′a-lo-ma′ne-ak)
A person exhibiting megalomania.

megalomelia (meg′a-lo-me′le-a)
SYN: macromelia.

megalophthalmos (meg′a-lof-thal′mus)
Congenital large globe. SYN: macrophthalmia, megophthalmus. [megalo- + G. ophthalmos, eye] anterior m. SYN: keratoglobus.

megalopodia (meg′a-lo-po′de-a)
SYN: macropodia. [megalo- + G. pous, foot]

megalosplanchnic (meg′a-lo-splangk′nik)
Having abnormally large viscera. SYN: macrosplanchnic. [megalo- + G. splanchnon, viscus]

megalosplenia (meg′a-lo-sple′ne-a)
SYN: splenomegaly.

megalospore (meg′a-lo-spor)
SYN: macrospore.

megalosyndactyly, megalosyndactylia (meg′a-lo-sin-dak′ti-le, -dak-til′e-a)
Condition of webbed or fused fingers or toes of large size. [megalo- + G. syn, together, + daktylos, finger]

megaloureter (meg′a-lo-u-re′ter)
SYN: ureterectasia. SYN: megaureter.




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