Fax +41 61 306 12 34 E-Mail karger@karger.ch www.karger.com Original Paper Horm Res Paediatr 2011;75:258–263 DOI: 10.1159/000322441 Ectopic Intrathyroidal Thymus in Children: A Long-Term Follow-Up Study Maria Segni Raffaela di Nardo Ida Pucarelli Marco Biffoni Department of Pediatrics, Sapienza University, Rome, Italy embryologic anomaly that should be considered in the dif- ferential diagnosis of thyroid nodules in children and adoles- cents. Copyright © 2010 S. Karger AG, Basel Introduction Ectopic intrathyroidal thymus is thought to be a rare entity, often discovered incidentally, and is due to aberrant thymic migration during embryogenesis. When mistaken for a thyroid nodule, the finding of intrathyroidal ectopic thymic tissue may lead to surgery and/or invasive diagnos- tic procedures in children [1–7]. However, the thymus has a unique appearance on ultrasonography and ectopic thy- mus parenchyma can be easily identified [8–11]. Herein we report a series of 9 children with ectopic intrathyroidal thymic tissue in whom both diagnosis and follow-up were carried out non-invasively by thyroid ultrasound (US). Patients and Methods We studied 9 children (5 girls and 4 boys) with a mean age at first examination of 6.3 8 3.2 years (range 1.1–11.7). These 9 pa- tients were followed by thyroid US for 34 8 28 months (range Key Words Ectopic intrathyroidal thymus  Incidentalomas  Intrathyroidal thymus  Thyroid ultrasonography Abstract Background: Ectopic intrathyroidal thymus has recently been reported in children as a cause of surgery and/or inva- sive diagnostic procedures when mistaken for a thyroid nod- ule. Thymus has a unique appearance at ultrasound (US). Methods: We report a follow-up study (mean 34 months, range 6–84) performed by US on 9 children (5 females) with a mean age of 6.3 8 3.2 years with intrathyroidal thymic in- clusions diagnosed by US as ‘incidentalomas’. None has pal- pable nodules. Results: Intrathyroidal thymic inclusions ap- peared on US as a hypoechoic area, with regular linear or punctuate internal hyperechoic echoes. The 2 oldest pa- tients (13 and 17 years) showed a regression in both size and hypoechogenicity of thymic inclusions over time – reflecting the normal thymic involution with advancing age. Conclu- sions: Indeed, the lack of progression seen in our 9 patients over a mean time of 34 months confirmed the substantially benign and self-limited nature of this process. The increasing use of thyroid ultrasonography in children may result in an increased detection of intrathyroidal thymic inclusions – an Received: July 1, 2010 Accepted: October 26, 2010 Published online: December 22, 2010 HORMONE RESEARCH IN PÆDIATRICS Maria Segni, MD Sapienza University Via Giuseppe Vaccari 3, IT–00194 Rome (Italy) Tel. +39 06 4997 9212, Fax +39 06 4997 2580 E-Mail m.segni  @  mclink.it © 2010 S. Karger AG, Basel 1663–2818/11/0754–0258$38.00/0 Accessible online at: www.karger.com/hrp