The Thymus

1 Introduction - Historical Background.- 2 Anatomy and Embryology of the Thymus.- 2.1 Embryology.- 2.2 Normal Anatomy.- 2.3 Involution.- References.- 3 Immunologic Function of the Thymus.- 3.1 Historical Overview.- 3.2 T Cell Molecules in Antigen Recognition.- 3.2.1 Accessory Molecules.- 3.3 Ontogeny of T Cells.- 3.3.1 Thymocyte Precursors.- 3.3.2 TCR Rearrangements.- 3.3.3 Maturation into Functional T Cells.- 3.3.4 Factors Governing T Cell Development Within the Thymus.- 3.4 Cellular Selection in the Thymus.- 3.5 Clinical Aspects.- 3.6 Summary.- References.- 4 Imaging Procedures for Visualization of the Thymus.- 4.1 Plain Film Diagnostics E.Walter and E.Willich.- 4.1.1 Chest Radiography in Two Planes.- 4.1.2 Fluoroscopy.- 4.2 Conventional Tomography.- 4.3 Ultrasonography.- 4.4 Computed Tomography.- 4.5 Magnetic Resonance Imaging W.R.Webb and G.deGeer.- 4.5.1 Principles of Magnetic Resonance Imaging.- 4.5.2 Image Production.- 4.5.3 Normal Appearances.- 4.5.4 Image Contrast and Interpretation.- 4.5.5 MRI Diagnosis of Mediastinal Masses.- 4.5.6 Image Acquisition and ECG Gating.- 4.5.7 Characterization of Mediastinal Masses.- 4.6 Nuclear Medicine E.Walter and E.Willich.- 4.6.1 67 Gallium Citrate.- 4.6.2 75 Selenium Methionine.- 4.6.3 99m Technetium Pertechnetate.- 4.7 Esophagography.- 4.8 Angiography.- 4.8.1 Arteriography.- 4.8.2 Angiocardiography.- 4.8.3 Phlebography and Superior Venacavography.- 4.9 Obsolete Methods.- 4.9.1 Kymography.- 4.9.2 Pneumomediastinography.- 4.10 Supplementary Procedures (Mediastinography, Bronchoscopy, Bronchography) E.Willich.- References.- 5 Diagnostic Imaging of the Normal Thymus.- 5.1 Conventional Diagnostics in Children E.Willich and E.Walter.- 5.1.1 Newborns and Infants.- 5.1.2 Preschool Age to Adolescence.- 5.1.3 Adults.- 5.2 Ultrasonography.- 5.2.1 Children.- 5.2.2 Adults.- 5.3 Computed Tomography E.Walter.- 5.4 Magnetic Resonance Imaging W.R.Webb and G.deGeer.- 5.4.1 Children.- 5.4.2 Adults.- 5.5 Invasive Procedures (Pneumomediastinography, Arteriography, Phlebography) E.Walter.- 5.6 Measurement of the Size of the Thymus E.Willich.- 5.6.1 Radiographic Method.- 5.6.2 Computed Tomography.- 5.6.3 Magnetic Resonance Imaging W.R.Webb and G.deGeer.- References.- 6 Acute and Stress-Induced Involution of the Thymus.- 6.1 Acute Endogenous Involution of the Thymus.- 6.2 Exogenous Involution of the Thymus: the Steroid Test.- 6.3 Transplacental Influence of Steroids on the Premature Infant's Thymus.- References.- 7 Developmental Abnormalities of the Thymus.- 7.1 Aplasia, Hypoplasia, and Dysplasia E.Willich and E.Walter.- 7.2 Dystopia.- 7.2.1 Cervical and Superior Mediastinum.- 7.2.2 Middle Mediastinum.- 7.2.3 Posterior Mediastinum.- 7.2.4 Miscellaneous.- References.- 7.3 Persistent Thymus E.Willich.- 7.3.1 Introduction.- 7.3.2 Pathophysiologic Causes.- 7.3.3 Clinical Features.- 7.3.4 Imaging Methods.- 7.3.5 Differential Diagnosis.- References.- 7.4 Hyperplasia.- 7.4.1 Introduction.- 7.4.2 Pathologic Features W.J.Hofmann and H.F. Otto.- 7.4.2.1 True Thymic Hyperplasia.- 7.4.2.2 Thymic Hyperplasia with Massive Enlargement of the Gland.- 7.4.2.3 Thymic Rebound in Childhood and Adolescence.- 7.4.2.4 True Thymic Hyperplasia in Association with Other Diseases.- 7.4.2.5 Lymphofollicular Hyperplasia of the Thymus.- 7.4.3 Clinical Features E.Willich.- 7.4.3.1 Asymptomatic Thymic Hyperplasia.- 7.4.3.2 Symptomatic Thymic Hyperplasia.- 7.4.4 Associated Diseases.- 7.4.5 Imaging Procedures and Findings.- 7.4.6 Regenerative Hyperplasia (Regrowth, Rebound Phenomenon).- 7.4.7 Differential Diagnosis.- 7.4.8 Therapy.- 7.4.9 Follow-up.- References.- 8 Tumors of the Thymus.- 8.1 Introduction E.Walter.- 8.2 Epithelial Tumors of the Thymus.- 8.2.1 Pathologic Features W.J.Hofmann and H.F. Otto.- 8.2.1.1 Macroscopic Appearance.- 8.2.1.2 Histologic Appearance.- 8.2.1.3 Classification.- 8.2.1.4 Immunohistology.- 8.2.1.5 Clinicopathologic Correlations.- References.- 8.2.2 Encapsulated and Invasive Thymomas E.Walter.- 8.2.2.1 Occurrence and Clinical Symptoms.- 8.2.2.2 Association of Thymoma with Other Syndromes and Diseases.- 8.2.2.3 Diagnosis with Imaging Procedures.- 8.2.2.4 Differential Diagnosis.- 8.2.2.5 Relative Value of the Imaging Procedures.- 8.2.2.6 Therapy and Prognosis.- References.- 8.2.3 Carcinoma of the Thymus.- 8.2.3.1 Occurrence and Clinical Symptoms.- 8.2.3.2 Diagnosis with Imaging Procedures.- 8.2.3.3 Differential Diagnosis.- 8.2.3.4 Relative Value of the Imaging Procedures.- 8.2.3.5 Therapy and Prognosis.- References.- 8.3 Carcinoid Tumors of the Thymus.- 8.3.1 Pathologic Features W.J.Hofmann and H.F. Otto.- 8.3.2 Occurrence and Clinical Symptoms E.Walter.- 8.3.2.1 Occurrence.- 8.3.2.2 Clinical Symptoms.- 8.3.3 Diagnosis with Imaging Procedures.- 8.3.4 Differential Diagnosis.- 8.3.5 Relative Value of the Imaging Procedures.- 8.3.6 Therapy and Prognosis.- References.- 8.4 Thymic Involvement in Malignant Lymphomas and Leukemia E.Willich and E.Walter.- 8.4.1 Pathologic Features W. J. Hofmann and H. F. Otto.- 8.4.2 Hodgkin's Disease E.Willich and E.Walter.- 8.4.2.1 Occurrence.- 8.4.2.2 Clinical Symptoms.- 8.4.2.3 Diagnosis with Imaging Procedures.- 8.4.2.4 Hodgkin's Disease of the Thymus Before and After Radiotherapy and Chemotherapy E.Walter and E.Willich.- 8.4.3 Non-Hodgkin's Lymphoma.- 8.4.4 Leukemia.- 8.4.5 Non-Hodgkin's Lymphoma and Leukemia with Thymic Involvement, During and After Radiotherapy and Chemotherapy.- 8.4.6 Differential Diagnosis E.Walter.- 8.4.7 Relative Value of the Imaging Procedures.- References.- 8.5 Mesenchymal Tumors (Thymolipoma) E.Walter.- 8.5.1 Pathologic Features W. J. Hofmann and H. F. Otto.- 8.5.2 Occurrence and Clinical Symptoms E.Walter.- 8.5.2.1 Occurrence.- 8.5.2.2 Clinical Symptoms.- 8.5.3 Diagnosis with Imaging Procedures.- 8.5.4 Differential Diagnosis.- 8.5.5 Relative Value of Imaging Procedures.- 8.5.6 Therapy and Prognosis.- References.- 8.6 Germ Cell Tumors and Teratomas E.Walter.- 8.6.1 Pathologic Anatomy W.J.Hofmann and H.F. Otto.- 8.6.2 Seminoma E.Walter.- 8.6.2.1 Occurrence and Clinical Symptoms.- 8.6.2.2 Diagnosis with Imaging Procedures.- 8.6.2.3 Differential Diagnosis and Relative Value of the Imaging Procedures.- 8.6.2.4 Therapy and Prognosis.- 8.6.3 Nonseminomatous, Pure or Mixed Germ Cell Tumors.- 8.6.3.1 Occurrence and Clinical Symptoms.- 8.6.3.2 Diagnosis with Imaging Procedures.- 8.6.3.3 Differential Diagnosis and Relative Value of the Imaging Procedures.- 8.6.3.4 Therapy and Prognosis.- References.- 8.7 Rare Tumors of the Thymus.- 8.7.1 Hemangioma of the Thymus.- 8.7.2 Choristoma of the Thymus.- References.- 8.8 Metastases to the Thymus.- Reference.- 9 Tumor-like (Nonneoplastic) Conditions of the Thymus and/or Mediastinum.- 9.1 Thymogenic Cysts.- 9.1.1 Pathologic Anatomy W.J.Hofmann and H.F. Otto.- 9.1.2 Occurrence and Clinical Symptoms E.Walter and E. Willich.- 9.1.3 Diagnosis with Imaging Procedures.- 9.1.4 Differential Diagnosis.- 9.1.5 Relative Value of the Imaging Procedures.- 9.1.6 Therapy and Prognosis.- 9.2 Hydatidosis of the Thymus.- 9.3 Tuberculoma of the Thymus.- 9.4 Histiocytosis X of the Thymus.- References.- 10 Trauma and Hemorrhage of the Thymus.- 10.1 Trauma.- 10.2 Hemorrhage.- References.- 11 Thymus and Myasthenia Gravis.- 11.1 Definition of Myasthenia Gravis H.Wlethölter.- 11.2 Clinical Manifestation.- 11.2.1 Symptoms and Signs.- 11.2.2 Classification.- 11.2.3 Clinical Examination.- 11.2.4 Prognosis.- 11.3 Associated Thymic Changes.- 11.3.1 Association of Thymic Changes with Other Diseases.- 11.4 Pathogenesis.- 11.5 Autoimmune Origin.- 11.6 Diagnosis.- 11.6.1 Radiological Diagnosis E.Willich and E.Walter.- 11.7 Treatment H.Wlethölter.- References.