Sonographic appearances of intrathyroid thymus: emphasis on details

Maria Raissaki, Ioanna Tritou, Penelope Smirnaki

Abstract


Purpose: To thoroughly describe ultrasonographic findings of intrathyroid thymus including characteristics that have not been previously emphasised.

Material and Methods: Forty-six children aged 21 days-14 years (mean 5.8 years) underwent cervical ultrasonography. Diagnosis of intrathyroid thymus was based on comparison with visible mediastinal thymus and follow-up in all patients, MRI in 2 and needle biopsy in 1 child.

Results: Fifty-two lesions <0.9 cm were identified, 29 (55.8%) left-sided; fifty-one (98.1%) at the lower 2/3 of the respective lobe on sagittal images. No lesion was situated anteriorly on transverse scans. Forty-three (82.7%) lesions exhibited angulated borders at either axial and/or transverse images producing a geographic shape while 9 (17.3%) were round/ovoid at all images. Thirty-six (73%) lesions reached the thyroid’s capsule and 14 were peripheral, within 1-3 mm (mean 2.1 mm) from it. Eighteen (34.6%) lesions exhibited extrathyroid extension and 13 (25%) connecting tissue with mediastinal thymus. Echopattern was identical to the same patient’s thymus: hypo-or iso-echoic to the thyroid, containing bright scattered spots in all lesions. Forty-nine (94.2%) lesions exhibited a spared thin hypoechoic rim. Colour Doppler over 31 lesions showed no/sparce vascularity.

Conclusions: The starry-sky pattern with sparing of a thin peripheral rim, identical to the individual’s mediastinal thymus, was seen in 94.2% of intrathyroid thymus. Prevalent characteristics also included no/sparce vascularity, geographic elongated shape, angulated borders, as well as occasional extrathyroidal extension and connecting thymic tissue between the thyroidal and mediastinal thymus. These appearances, when seen in small posterior/caudal lesions, prompted conservative follow-up instead of invasive management.


Keywords


thyroid; ultrasonography; child; intrathyroid thymus; ectopic thymus

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References


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