Goubaa Mohamed MD Djerba Tunisia

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This is a 38-year-old female G4 P3, seen for her only prenatal visit, and referred at approximately 18 menstrual weeks for assessment of gestational age.
(To see the video : codec problem, sometimes, it is necessary to download and install these programs : Divx or Quicktime )
C'est une patiente de 38 ans, G4 P3, ne consultant qu'a cette date pour sa première visite prénatale, a été adressée approximativement à 18 semaines d'aménorrhée pour l'évaluation de l'âge gestational.
(Si la vidéo ne fonctionne pas, problème de codec, téléchargez et installez ces programmes : Divx or Quicktime)


video (full screen)

heart and cyst transversal(700K)

transversal scan of fetus(2,6M)

sagittal scan of fetus(2,3M)



fetus thymus cyst chest



ultrasonography fetus lung thymus cyst

échographie foetus poumon thorax kyste



Thoracic scans of infant 2 months after Birth (the thymic cyst disappeared)
Echographie thoracique du nouveau-née 2 mois après naissance (le kyste a disparu)

Click on the image below
Cliquez sur les images en bas


































































































The fetus was at 18 weeks gestational age. A 3-cm well-defined anechogenic cyst was noted within the right hemithorax of the fetus. Ultrasound revealed a relatively large echopoor cyst occupying the left side of the chest, displacing the mediastinum and the heart. The stomach was visualized below the hemidiaphragm.
The mass was believed to be a congenital cystic malformation. CT imaging was performed. CT images depicted bilocular thymic cyst.
The cyst became progressively smaller during the further pregnancy course. After delivery on term the thymic cyst disappeared. The infant has since developed without any abnormalfindings.

L'age fotal était de 18 semaines. Un kyste de 3 cm, anéchogène, bien limité a été noté dans le bon hémithorax du fotus. L'échographie a montré un kyste relativement grand de occupant le côté gauche du thorax, déplaçant le médiastin et le cour. L'estomac a été visualisé au-dessous du diaphragme.
On a pensé que la masse est une malformation kystique congénitale. Un scanner a été réalisée. Les images tomodensitométriques ont montré qu'il s'agissait de kyste thymique biloculaire. Par la suite et au fil de l'évolution de la grosse, le kyste est devenu progressivement de plus en plus petit. Après la naissance le kyste thymique a disparu. Le nourrisson, depuis lors, a grandi et n'a développé aucune anomalie.





Thoracic Fetal Thymic cyst
kyste thymique fœtal thoracique


Thoracic Fetal Thymic cyst

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Introduction :

The thymus is a soft organ comprising two asymmetric lobes joined by an isthmus and invested by a fibrous capsule. The thymus gland is embrylogically derived from the ventrolateral surfaces of the third pharyngeal pouch in the form of paired primordia during the sixth week of fetal life. The thymus occupies the anterior and superior mediastinum, located behind the sternum in the midline. the upper border of the thymus extends almost to the thyroid gland in the neck and the lower margin overlaps the upper part of the heart, occasionally extending as far as the diaphragm.
The thymus has its largest size relative to body weight at birth, weighing on average 10-15 g.
A normal thymus is the most frequent cause of a widened mediastinum in the newborn and infancy. The thymic lobes often differ significantly in size and this can give the impression of a mass related to one side of the mediastinum or the pulmonary hilum.
Thymic cysts are uncommon mediastinal lesions that account for only 1% to 2% of all tumors in the anterior mediastinum. It can be either congenital or acquired.

the thymus can be imaged in most fetuses. Prenatal ultrasonography is helpful in the discovery of a number of abnormalities in the fetal thorax, including thymic cysts.
Thymus can be thought of as a soft pancake-like structure draped over the mediastinal vessels.
Thymic cysts are rare lesions of the anterior mediastinum or neck along the path of the thymopharyngeal ducts from the level of the mandible to the chest.
Mediastinal thymic cysts account for about 1% of all mediastinal masses. the cysts are unilocular or multilocular and range in size from microscopic to as large diameter.

CT scan :
CT scan images can greatly assist in determining the exact location of the mediastinal cyst and in determining its relationship to adjacent structures.
Because the patient is not exposed to radiation, Magnetic resonance imaging may be preferred to CT scan by some physicians for the evaluation of a mediastinal cyst in a fetus.

Magnetic resonance imaging :
MRI is useful in both the initial diagnosis of a mediastinal mass and in follow-up evaluations. It provides superior vascular imaging and can help better delineate the relationship of an identified mediastinal mass to nearby intrathoracic structures.


Differential :
Prenatal ultrasound can be a sensitive method for the detection of pulmonary abnormalities, although thymic cyst can be difficult to differentiate from other cystic chest lesions :

* Congenital Diaphragmatic Hernia.
Congenital diaphragmatic hernias are unilateral in 97% and usually on the left. This hernia most commonly results from failure of the pleuroperitoneal canal to close completely. This should occur by week 10 of gestation (12). Failure of closure results in a herniation of abdominal viscera into the thorax, resulting in a mass effect that can prevent normal lung development.
Ultrasonography may reveal poly-hydramnios and visualization of abdominal viscera within the thorax. A unilateral pleural effusion may be present. Characteristically, a fluid-filled mass is seen behind the left atrium and ventricle, mediastinal shift is variable. Real-time sonography may reveal bowel peristalsis within the thorax.
Ways of attempting to exclude a congenital diaphragmatic hernias on prenatal ultrasound include visualization of an intact diaphragm and an appropriately located stomach, liver and gallbladder. Fetal breathing movements may assist in visualizing the bowel sliding up and down in the chest through the diaphragmatic defect in some cases of congenital diaphragmatic hernias.

* Cystic Adenomatoid Malformation :
this is a rare congenital malformation, which appears to result from an embryological anomaly occurring before the 7th week of gestation (4). Ultrasonographically, the cystic adenomatoid malformation may be multicystic with evidence of space occupation, or an echogenic mass lesion. Macrocystic lesions contain single or multiple cysts that are >5mm in diameter. Microcystic lesions are more solid, appear echogenic on ultrasound, and contain cysts measuring <5 mm in diameter.

* Bronchopulmonary Sequestration :
A portion of lung parenchyma does not communicate with the tracheobronchial tree, and usually receives its arterial supply from a systemic vessel. Cysts are occasionally seen with an intralobar sequestration, which may make differentiation from other cystic intrathoracic masses difficult.

* Teratoma :
Teratoma is a rare cause of cystic lung lesions. Anterior mediastinal teratomas are classified into mature and immature types. Mature teratomas present as large fetal lung tumors with cystic and solid components, polyhydramnios, hydrops fetalis, pleural effusions and hyperechoic spots with of calcifications. Immature teratomas form complex masses with multiloculate cystic components associated with polyhydramnios but may not have calcification or fetal hydrops.

* Dilated proximal pouch blind esophageal :
This is a large, purely cystic posterior mediastinal mass.

* Mediastinal meningomyelocele, meningocele :
This appears cystic with variable thickness of its wall, which may be associated with vertebral defect.

* Bronchogenic Cyst :
Bronchogenic cysts are a rare bronchopulmonary foregut malformation that result from an abnormal budding of the foregut. This may be unilocular or multilocular, closely related to the trachea or main bronchus and may communicate with the tracheobronchial tree.

* Simple lung cysts :
These appear as well defined cystic masses, unilocular, surrounded by normal lung.

* Enteric-neuroenteric :
cysts Diagnosis is suggested by the position of the cyst adjacent to the bowel and spine. They are often associated with vertebral abnormalities.

* Neuroblastoma :
occasionally, these may be visualized as purely cystic mediastinal masses

* Laryngeal Artesia :
Bronchial artesia results from a congenital obliteration of a proximal segment of bronchus. This results in a collection of mucus in the distal bronchi and the affected portion of lung appears large and echogenic on prenatal ultrasound due to the accumulation of fetal lung secretions.

* Congenital left ventricular aneurysm :
Congenital left ventricular aneurysm is a Midline cystic intrathoracic structure in close proximity to the heart, confirmed left ventrivle aneurysm by color Doppler.

* Pericardial cyst :
Pericardial cyst is usually attached to the pericardium overlying the right heart border, or rarely presents at the right costophrenic angle.

* Heterotopic Brain Tissue :
There is an isolated case report of heterotopic brain tissue causing an appearance consistent with macrocystic cyst postnatally. The neonate had several other abnormalities present.

* pleurisy :
pleurisy appear anechoic and normally conform to the thoracic - diaphragmatic contours

* Cystic hygroma :
Usually nuchal, but may rarely extend into the thorax.


Reference :
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