Pancytopenia: Deficiency of all three cell elements of the blood, erythrocytes, leukocytes and platelets.Anemia, Aplastic: A form of anemia in which the bone marrow fails to produce adequate numbers of peripheral blood elements.Lymphohistiocytosis, Hemophagocytic: A group of related disorders characterized by LYMPHOCYTOSIS; HISTIOCYTOSIS; and hemophagocytosis. The two major forms are familial and reactive.Hypersplenism: Condition characterized by splenomegaly, some reduction in the number of circulating blood cells in the presence of a normal or hyperactive bone marrow, and the potential for reversal by splenectomy.Bone Marrow: The soft tissue filling the cavities of bones. Bone marrow exists in two types, yellow and red. Yellow marrow is found in the large cavities of large bones and consists mostly of fat cells and a few primitive blood cells. Red marrow is a hematopoietic tissue and is the site of production of erythrocytes and granular leukocytes. Bone marrow is made up of a framework of connective tissue containing branching fibers with the frame being filled with marrow cells.Histiocytosis, Non-Langerhans-Cell: Group of disorders which feature accumulations of active HISTIOCYTES and LYMPHOCYTES, but where the histiocytes are not LANGERHANS CELLS. The group includes HEMOPHAGOCYTIC LYMPHOHISTIOCYTOSIS; SINUS HISTIOCYTOSIS; xanthogranuloma; reticulohistiocytoma; JUVENILE XANTHOGRANULOMA; xanthoma disseminatum; as well as the lipid storage diseases (SEA-BLUE HISTIOCYTE SYNDROME; and NIEMANN-PICK DISEASES).Bone Marrow DiseasesAnemia, Megaloblastic: A disorder characterized by the presence of ANEMIA, abnormally large red blood cells (megalocytes or macrocytes), and MEGALOBLASTS.Fatal Outcome: Death resulting from the presence of a disease in an individual, as shown by a single case report or a limited number of patients. This should be differentiated from DEATH, the physiological cessation of life and from MORTALITY, an epidemiological or statistical concept.Anemia, Macrocytic: Anemia characterized by larger than normal erythrocytes, increased mean corpuscular volume (MCV) and increased mean corpuscular hemoglobin (MCH).Lymphomatoid Granulomatosis: An angiocentric and angiodestructive lymphoproliferative disorder primarily involving the lungs. It is caused by an Epstein-Barr virus-induced transformation of the B-cells, in a T-cell rich environment. Clinically and pathologically it resembles EXTRANODAL NK-T-CELL LYMPHOMA.Myelodysplastic Syndromes: Clonal hematopoietic stem cell disorders characterized by dysplasia in one or more hematopoietic cell lineages. They predominantly affect patients over 60, are considered preleukemic conditions, and have high probability of transformation into ACUTE MYELOID LEUKEMIA.Bone Marrow Examination: Removal of bone marrow and evaluation of its histologic picture.Tuberculosis, Miliary: An acute form of TUBERCULOSIS in which minute tubercles are formed in a number of organs of the body due to dissemination of the bacilli through the blood stream.Hemoglobinuria, Paroxysmal: A condition characterized by the recurrence of HEMOGLOBINURIA caused by intravascular HEMOLYSIS. In cases occurring upon cold exposure (paroxysmal cold hemoglobinuria), usually after infections, there is a circulating antibody which is also a cold hemolysin. In cases occurring during or after sleep (paroxysmal nocturnal hemoglobinuria), the clonal hematopoietic stem cells exhibit a global deficiency of cell membrane proteins.Splenomegaly: Enlargement of the spleen.Tachycardia, Sinus: Simple rapid heartbeats caused by rapid discharge of impulses from the SINOATRIAL NODE, usually between 100 and 180 beats/min in adults. It is characterized by a gradual onset and termination. Sinus tachycardia is common in infants, young children, and adults during strenuous physical activities.Blood Cell Count: The number of LEUKOCYTES and ERYTHROCYTES per unit volume in a sample of venous BLOOD. A complete blood count (CBC) also includes measurement of the HEMOGLOBIN; HEMATOCRIT; and ERYTHROCYTE INDICES.