All are true about thymus swelling except:
D i.e. Shift of trachea on X Ray Prominent but normal thymus is the most common pseudotumor of anterior mediastinum. On imaging anterior mediastinal tumors displace the trachea and oesophagus posteriorly and laterlly in a contradistinction to a normal enlarged thymus which does not displace adjacent structuresQ Thymic Tumors Normal Thymus Gland It is the commonest cause of mediastinal abnormality in infants and is usually seen as triangular soft tissue mass projecting to one side (usually right) of mediastinum. It may disappear during severe neonatal infections, or after major surgery coicosteroid treatmentQ, but may reappear following recovery from illness. Thymus gland is completely absent in Di-George's syndrome, an immune deficiency disease involving T lymphocyes. It is seen as a triangular arrow head or bibbed structure in children and young adult patients on CT but undergoes fatty involution in adults & elderly. Enlargement of thymus gland can be d/t thymoma, thymic hyperplasia, thymic carcinoma, lymphoma, thymo lipoma, carcinoids & germ cell tumors & thymic cysts. Thymic Hyperplasia Although uncommn & rare, it is the most common anterior mediastinal mass in paeditric age group. The most common association of thymic hyperplasia is mysthenia gravis (65%) and thyrotoxicosis (eg Grave's disease, treatment of hypothyroidism etc. Other associations include Addison's disease, acromegaly, SLE, RA, and after stress atrophy, where the thymus gland initially atrophies in patients on chemotherapy, or coicosteroid treament, irradiation, stress, severe illness (burns) or after treatment for Cushing's disorder and then becomes larger than its previous normal size (i.e. enlarges) once the treatment is stopped or stress is ended. The phenomenon is called rebound thymic hyperplasia. It is differentiated from recurrent malignant disease on the basis of a known reason for rebound and presence of normal shaped enlarged thymus Rarely cause visible enlargement, but when it does, both lobes are enlarged, usually uniformly with a diffuse symmetrical enlargment. Radiological signs include. Wave sign is a rippled thymic contour (border) d/t indentation by anterior rib ends. Notch sign is indentation at the junction of thymus with hea. Sail sign is a triangular density projection from superior mediastinum on one or both sides. Shape change with respiration & position Thymoma It is the most common tumor of thymus in adults and most common primary tumor of anterior mdidastinum in adultsQ. Most (90%) thymomas arise in upper anterior mediastinum usually anterior to ascending aoa, lying on the right ventricle outflow tract and pulmonary aery. It is rare under 20, extremely unusual below 15 and usually presents at 50 year age (earlier in those who present with mysthenia gravis) Thymoma is often asymptomatic 50% but can also present with mysthenia; red cell aplasia, hypogammaglobulinemia. About 10-25% mysthenics have thymoma and 25-50% of thymoma patients have mysthenia gravis. It may cause mediastinal wideningQ and displacement of hea and great vessels posteriorly (but not trachea)-in benign cases; and can invade mediastinal fat & pleura in invasive malignant variety. It may be undetectable on chest x-ray when small, indicating the need of CT (which is investigation of choice & most sensitive). Thymomas give rise to asymmetrical focal swelling which appear as well defined round or oval soft tissue mass projecting to one side of anterior mediastinum. It may contain punctate or curvilinear calcification and areas of low attenuation d/t cystic degenration. MRI is also useful for diagnosis. Thymic Carcinoid It presents with cushing's syndrome (d/t ACTH serection), hyperparathyroidism and inappropriate ADH secretion. Radiographic & CT features resemble thymoma Thymolipoma Can grow to a very large size before discovery and,being soft, mould themselves to the adjacent mediastinum and diaphragm, mimicing cardiomegaly or lobar collapse. Very large soft tissue mass with less radiographic density than expected for its size, which alters it shape on respiration indicates thymolipoma
Widening of mediastinum on X-Ray
Sharp border with shail like appearance
Steroid administration reduces size of swelling
Shift of trachea on X-ray