Type:
Educational Exhibit
Keywords:
Normal variants, Ultrasound, Fluoroscopy, Paediatric, Anatomy, Tissue characterisation
Authors:
S. A. M. Ibrahim1, T. Salem Alyafei1, M. Sabawi1, N. M. Saloum2, M. M. H. Ahmed1; 1Doha/QA, 2Doha, Doha/QA
DOI:
10.26044/ecr2019/C-0975
Findings and procedure details
Conventional radiography:
The thymus is variable in size and position and The appearance of the thymus on frontal chest radiographs is variable and largely dependent on the age of the patient.
It may mimic cardiomegaly,
abnormally positioned vessels,
pericardial fluid,
or a mediastinal mass.
The normal thymus has a soft tissue density and smooth borders.
The thymus is prominent in size with a quadrilateral shape and convex margins during infancy.
After approximately the fifth year of life,
the
thymus becomes more triangular in shape with straight margins.
By the age of 15 years,
the margins of the thymus are either straight or concave.
Numerous radiological signs have been described to aid its differentiation from a mediastinal mass.
The “thymic sail sign” is seen as a triangular extension of the normal thymus laterally.
The right lobe of the thymus has a convex lateral margin and the straight inferior border gets demarcated by the minor fissure which gives the sail like appearance.
The anterior reflections of the ribs produce a wavy contour of the thymus known as the “thymus wave sign”.
It has no mass effect on vascular structures or airway.
The inferior margin of the thymus merges with the margin of the cardiac silhouette,
producing the “notch sign”
Ultrasound:
On ultrasound,
the thymus appears homogenous with echo texture similar to the liver but less than the muscle and shows multiple echogenic foci or strands.
These hyperchoic foci give a “starry sky” appearance and help to identify thymic tissue.
The characteristic ultrasound appearance is also helpful to identify normal anatomical variants like cervical or retrocaval extension of the thymus.
The shape of the thymus can be seen to vary with cardiac and respiratory movements on realtime ultrasound,
and this finding helps to differentiate it from solid tumors and infiltrative diseases.
What to do next if mediastinal mass is suspected?
Take the patient to US room and perform US to delineate the typical us appearance of the thymus tissue.
If the case suspicion lesion or atypical findings do cross sectional.
MRI is preferred over CT to decrease radiation exposure.