Leukopenia - The antithesis of leukocytosis; any situation in which the total number of leukocytes in the circulating blood is less than normal, the lower limit of which is generally regarded as 4000-5000 per cu mm.
Lumbosacral - Relating to the lumbar vertebrae and the sacrum.
Lumen, pl. lumina - The space in the interior of a tubular structure, such as an artery or the intestine.
Lymphadenopathy - Any disease process affecting a lymph node or lymph nodes.
Lymphopenia - A reduction, relative or absolute, in the number of lymphocytes in the circulating blood.
Macula, pl. maculae - 1. A small spot, perceptibly different in color from the surrounding tissue. 2. A small, discolored patch or spot on the skin, neither elevated above nor depressed below the skin's surface.
Mediastinitis - Inflammation of the cellular tissue of the mediastinum.
Mediastinum - The median partition of the thoracic cavity, covered by the mediastinal pleura and containing all the thoracic viscera and structures except the lungs.
Megakaryocyte - A large cell with a polyploid nucleus that is usually multilobed; megakaryocytes are normally present in bone marrow, not in the circulating blood, and give rise to blood platelets.
Melena - Passage of dark-colored, tarry stools, due to the presence of blood altered by the intestinal juices.
Meningism - A condition in which the symptoms simulate a meningitis, but in which no actual inflammation of these membranes is present.
Meningococcemia - Presence of meningococci (N. meningitidis) in the circulating blood.
Meninges - Any membrane; specifically, one of the membranous coverings of the brain and spinal cord.
Microcyst - A tiny cyst, frequently of such dimensions that a magnifying lens or microscope is required for observation.
Microscopy - Investigation of minute objects by means of a microscope.
Moribund - Dying; at the point of death.