thymus gland fetal ultrasound

 

THE THYMUS

located posterior to the sternum

at the level of the great vessels of the heart,

anterior to the aorta and pulmonary artery

hypoechoic structure

 

THE THYMUS

THE THYMUS

THE THYMUS

NORMAL THYMUS

 

The thymus appears as a homogeneous structure

in the upper mediastinum,

located between both lungs,

anterior to the pulmonary trunk,

aortic arch and superior vena cava 

 

Thymic tissue is characterized by tiny e

chogenic foci, which facilitate its differentiation from lung.

Its soft consistency allows it to

move with underlying vascular pulsations.

 

The thymus is composed of 2 distinct lobes

, each surrounded by a collagenous capsule

with septa extending into the corticomedullary junction

dividing the cortex further into lobules.

 

thymus gland fetal ultrasound

The thymus gland contains

3 major cell populations

—epithelial, hemopoietic, and accessory cells

(supports erythropoiesis and granulopoiesis).

 

 

Arterial supply to the thymus varies.

It could be derived from the internal mammary artery,

the inferior thyroid artery,

and from these 2 plus the superior thyroid artery.

A single vein frequently leaves each side of the medial lobe.

The veins join to form a short,

wide vein that drains into the left brachiocephalic vein.

A lateral vein drains from the right side of the gland

into the superior vena cava and

from the left side into the left brachiocephalic vein.

 

A hypothalamic-thymic neural pathway

has been suggested to explain the numerous neurological, social,

psychological, and environmental factors

that have been shown to influence the thymic hormones and the immune system.

thymus gland fetal ultrasound

thymus gland fetal ultrasound

thymus gland fetal ultrasound

thymus gland fetal ultrasound

ULTRASOUND

The best plane to visualize this structure

is the ventral cross-sectional plane of the 'three-vessel' view.

In a more cranial plane,

the gland can be demonstrated

anterior to the innominate vein at the confluence of the left and

the right jugular veins.

Use of a high-frequency transducer and

varying the gray scale can allow reliable delineation

of the thymus from neighboring lung.

There may be limitations in visualization

of the thymus, particularly where there is

abnormal intrathoracic anatomy;

e.g. cardiomegaly, diaphragmatic hernia, cystic lung lesions

, hydrothorax and pericardial effusion or

at an early (before 20 weeks) gestational age.

In such cases it is still unclear

whether the thymus is merely shifted from its place,

where its visualization is difficult,

or compressed by the distorted intrathoracic structures.

Observing the great vessels positioned directly posterior

to the sternum rather than centrally within the upper thorax is useful

to differentiate cases of absent or hypoplastic