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2011-06-02-17 Imaging of the thymus © Quiroga www.TheFetus.net

Imaging of the thymus

Hector Quiroga, MD.

Centro Médico Profesional Rosancar. Barquisimeto, Estado Lara, Venezuela.

Introduction

The thymus has been studied in fetuses with conotruncal anomalies as a marker of microdeletion 22q11. More recently, it has also been investigated in relation to its immune function in association with prolonged rupture of membranes and intrauterine growth restriction. The thymus can be identified on the three-vessel view of the upper mediastinum, but its visualization is not always straightforward.
Paladini [1] reported a simple way to locate the thymus, so called "Thymus-box". The internal mammary arteries course laterally to the thymus identifying its lateral borders, and by using color doppler ultrasonography with a low repetition frequency these vessels and, consequently, the thymic area, are readily displayed in the fetus from the first to the third trimester of pregnancy [1].

Case report

Here we present two uncomplicated pregnancies where we identified the normal looking thymus using the internal mammary arteries as landmarks. The third case is a case of thymic hypoplasia diagnosed at 23 weeks of gestation.

Case 1

Images 1-3: 23 weeks, Images are showing normal looking thymus which is located between the right and left mammary artery.

Video 1: 23 weeks, video of the normal looking thymus, mammary arteries form the lateral borders of the thymus.

Case 2

Images 4,5: 33 weeks, Images of the normal looking thymus.

Video 2: 33 weeks, thymus of normal size and appearance located between the right and left mammary artery.

Case 3

This is a case of an Aortic atresia associated with a hypoplasia of the thymus.

Image 6: 23 weeks, images of the hypoplastic thymus.

References:

1. Paladini D. How to identify the thymus in the fetus: the thy-box. Ultrasound Obstet Gynecol 2011;37:448-492.

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