acts like the germinal center of the lymph node for T-cells. There is a lot of selection for T cells in the Thymus that properly rearrange receptors. Unlike B cells which finish rearrangement in the marrow, T cells complete their rearrangement in the Thymus then are selected on the thymic epithelium based on whether they have auto Ag or allo Ag. Then they emigrate to the periphery just like B cells
Two Cellular elements: T-lymphoblasts (dark staining), epithelial cells (pale staining) with Hassle’s corpuscles.
Normally involutes as one ages
Non-Neoplastic Thymic Disorders
HYPOPLASIA or APLASIA - DiGeorge’s syndrome (del of Ch22, assc with cardiac malformations and parathyroid hypolasia)
Pts don’t have T cells so they because they have no place to mature so they are immunodeficient.
HYPERPLASIA - Myasthenia gravis (patients tend to have lymphoid infiltrate, usually B cell, of thymus)
CYSTS: benign remnant of embryonic migration.
Thymomas
Malignancy of the thymic epithelium, clear nucleus, (not T cells) with intermixed benign thymocytes.
Unusual tumors that present as anterior mediastinal masses associated with auto immune disorders related to the distorted T cell function due to their prolipherative condition.
ASSOCIATED DISORDERS - Myasthenia Gravis (~40%) - Pure red cell aplasia (~10%) - Hypogammaglobulinemia (~10%) - Autoimmune disorders
Three types based on behavior (difficult to predict from histology, most important thing to not is are they infiltrating)