DISEASES OF THE SPLEEN AND THYMUS
Splenomegaly (splenic enlargement) can be caused by multiple things:
• Vascular congestion (portal hypertension)
• Reactive hyperplasia of white pulp (autoimmune disorder, infectious mono-nucleosis, malaria)
• Infiltrative disease (metastatic non-Hodgkin lymphoma, primary amyloidosis, leukemia)
• Accumulated macrophages in red pulp (Gaucher, Niemann-Pick disease)
• Extravascular hemolysis
• Extramedullary hematopoiesis in splenic sinusoids
Hypersplenism will result in thrombocytopenia.
Splenic dysfunction will result in a loss of ability to remove damaged red cells, which leads to Howell-Jolly bodies in peripheral red blood cells. Splenectomized, asplenic, and hyposplenic individuals are at risk for infection (sepsis, peritonitis), particularly due to Streptococcus, Haemophilus, and Salmonella.
Thymomas are low-grade tumors of the thymic epithelium with many histologic patterns. Recent large case series have shown that tumor behavior does not always correlate with histopathological features.
True thymic hyperplasia is enlargement of a histologically normal thymus; it can occur as a complication of chemotherapy.
Thymic lymphoid hyperplasia shows germinal center hyperplasia.