Prevalence and sonographic features of ectopic thyroidal
thymus in children: A retrospective analysis
Adalet Elcin Yildiz MD
Atilla Halil Elhan
Suat Fitoz MD
Department of Pediatric Radiology, Faculty
of Medicine, Ankara University, Turkey
Department of Biostatistics, Ankara
University, Faculty of Medicine, Ankara,
Adalet Elcin Yildiz, G
Alper Sokak, No: 10/12, Çankaya/
Purpose: To assess the prevalence of ectopic thyroidal thymus tissue detected by sonography
(US) in children and to analyze the US features.
Methods: We retrospectively reviewed images of 216 children who had undergone a thyroid or
neck US examination from February 2015 to June 2015. Lesions within or adjacent to the thyroid
gland that showed echopatterns consistent with thymic tissue were diagnosed as ectopic thyroidal
thymus tissue. Lesions were reviewed according to their side, location, level, size, shape, echo pat-
tern, internal content, and vascularization.
Results: A total of 216 children (119 girls, 97 boys) with a mean 6 SD age of 8.6 6 5.2 years were
enrolled the study.Thirty children (13girls, 17 boys) (13.9%) had 35 lesions compatible with ectopic
thyroidal thymus tissue.Nine children had intrathyroidal (4.2%) and 21 children had extrathyroidal
(9.7%) ectopic thymus tissue.The mean 6 SD ages of the children with and without ectopic thyroi-
dal thymus tissue were 6.0 6 3.6 years and 9.1 6 5.2 years, respectively (P 5 .002). Twenty-five of
the lesions were extrathyroidal and 10 were intrathyroidal. All extrathyroidal and most (8/9) intra-
thyroidal ectopic thymuses had fusiform shape with well demarcated contours. Ectopic thymuses
were located either in the midportion (n 5 23) or lower portion of the neck (n 5 12). Both extra-
thyroidal and intrathyroidal ectopic thymuses showed typical hypoechoic (n 5 22/25, n 5 9/10,
respectively) or hyperechoic (n 5 3/25, n 5 1/10, respectively) echo patterns with internal linear
and punctate echoes.
Conclusions: Ectopic thyroidal thymic tissue is common in children. Radiologists should be vigilant
about the unique US features of ectopic thyroidal thymus, including a hypo- and hyper-echoic
echo pattern with multiple linear and punctate echoes, a fusiform shape, well-demarcated con-
tours, and middle or low-lying location to differentiate it from other neck or thyroid lesions.
children, ectopic thyroidal thymus, neck, thyroid, ultrasonography
The thymus first appears in the sixth week of gestation and originates
from the third and fourth pharyngeal pouches bilaterally. In the eighth
week of gestation, thymic primordials migrate into the anterior medias-
tinum in a inferomedial direction. When the thymic primordials reach
the anterior mediastinum, they fuse to form the thymus; this occurs by
the ninth week of gestation. A normal thymus resides in the anterior
mediastinum but may extend toward the lower pole of the thyroid, to
which it might be attached by the thyrothymic ligament. These cervical
components may mimic extrathyroidal ectopic thymus, but their conti-
nuity with the mediastinal thymus helps in distinguishing between the
two entities. During embryogenesis, migration arrest can lead to the
development of ectopic thymus along the pathway of descent.
ectopic thymic arrests are thyroidal in location and are detected inci-
dentally while the patient is being investigated for other reasons.
J Clin Ultrasound. 2018;46:375–379. wileyonlinelibrary.com/journal/jcu
2018 Wiley Periodicals, Inc.
Received: 10 September 2017
Revised: 5 January 2018
Accepted: 26 February 2018