thymic shadow
Radiographic appearance of the thymus gland on chest X-ray, used to assess thymic presence and size in immunodeficiency evaluation.
Full Definition
The thymic shadow refers to the radiographic appearance of the thymus gland on chest X-ray, typically visible as a sail-shaped or triangular density in the anterior mediastinum of infants and young children. In pediatric immunology, assessment of the thymic shadow is an important part of evaluating suspected primary immunodeficiency, as absence or marked reduction of thymic tissue may indicate conditions affecting T-cell development such as DiGeorge syndrome or severe combined immunodeficiency. The thymus normally involutes with age, so interpretation must consider the patient's age. Advanced imaging with CT or MRI may be needed for detailed thymic assessment.
Usage
Usage note: Age-dependent finding; absence in young infants warrants immunologic evaluation.
In Context
- "The chest X-ray showed absence of thymic shadow in this infant with suspected immunodeficiency." — Radiology report
- "Normal thymic shadow was present, making severe T-cell immunodeficiency less likely." — Clinical assessment