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Normal and abnormal thymus in childhood: MR imaging
M J Siegel1, H S Glazer, J I Wiener
1Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, MO 63110.
Insights
Magnetic resonance (MR) imaging helps differentiate normal from abnormal thymus in children. Key indicators include size, shape, margins, and signal intensity, aiding diagnosis of thymic diseases like lymphoma.
Area of Science:
- Pediatric Radiology
- Medical Imaging
- Thymus Gland
Background:
- The thymus plays a crucial role in immune system development.
- Accurate assessment of thymic morphology is essential for diagnosing pediatric diseases.
- Magnetic resonance (MR) imaging offers detailed anatomical visualization.
Purpose of the Study:
- To characterize the spectrum of MR imaging features of the normal thymus in children.
- To identify reliable MR imaging indicators for thymic abnormalities in pediatric patients.
- To compare MR findings with histopathological diagnoses of thymic diseases.
Main Methods:
- Retrospective analysis of MR imaging studies in 14 children with thymic abnormalities and 47 healthy children.
- Evaluation of thymic size, shape, margins, signal intensity, and homogeneity on T1- and T2-weighted images.
- Correlation of imaging findings with pathological diagnoses, including lymphoma, leukemia, and hyperplasia.
Main Results:
- Normal thymus morphology varies with age: quadrilateral and biconvex in younger children, triangular in older children.
- Homogeneous signal intensity, slightly greater than muscle on T1-weighted and near fat on T2-weighted images, characterizes the normal thymus.
- Abnormal thymic features include enlargement, multilobulation, inhomogeneity, and signs of degeneration, hemorrhage, or calcification.
Conclusions:
- Qualitative assessment of thymic morphology on MR imaging is generally sufficient to distinguish normal from abnormal thymus in children.
- Associated lymphadenopathy on MR imaging can be a helpful indicator of thymic lymphoma.
- MR imaging is a valuable tool for evaluating thymic abnormalities in pediatric patients, guiding diagnosis and management.
Abstract:
Magnetic resonance (MR) imaging studies of 47 children without thymic disease were compared with those of 14 children with proved thymic abnormalities (eg, lymphoma, leukemia, hyperplasia) to evaluate the spectrum of MR features of the normal and abnormal thymus and to determine the best indicators of thymic disease. In healthy children younger than 5 years of age, the thymus had a quadrilateral shape and biconvex lateral contours. Older children and adolescents had a triangular thymus with straight lateral margins. The thymus appeared homogeneous with a signal intensity slightly greater than that of muscle on T1-weighted images and close to that of fat on T2-weighted images. Qualitative evaluation of gross thymic morphology (size, shape, margins, and signal intensity) usually was sufficient for distinguishing between the normal and abnormal thymus. The abnormal thymus generally was enlarged, multilobular, or inhomogeneous because of the presence of cystic degeneration, hemorrhage, septations, fibrosis, or calcification on pathologic sections. In patients with lymphoma, the presence of associated lymphadenopathy also was helpful in distinguishing the normal from the abnormal thymus.