20 years old G1P0 woman, referred at 35 weeks of pregnancy for evaluation of a fetal thoracic lesion.

Findings:

The cystic mass in the chest has the following characteristics:

• the fluid is clear, and the low-level echoes that are seen on the posterior aspect have more the appearance of side-lobe artifacts then "debris".

• although this is a large cyst that is partially in several regions of the chest, the most important region for the differential diagnosis is that the cyst occupies the posterior mediastinum. If the cyst had been in the right lateral region, a pulmonary origin would have been almost the only likely differential diagnosis. Arising from the posterior mediastinum enlarges the diagnosis considerably.

• it displaces the heart.

Thoracic spine and posterior fossa demonstrated some irregularity of the thoracic spine.

The head (normal Doppler), was large (note the spacing of the dots along side the Doppler window, compared to the spacing of the dots on the image of the heart above). More important there was some soft-tissues edema at the level of the skull.

Differential diagnosis

The differential diagnosis is that of a single thoracic cystic mass that is partially in the posterior mediastinum. This excludes the other diagnosis like chylothorax and pleural effusions.

• Gastrointestinal duplication cysts
• Herniated stomach (diaphragmatic hernia, hiatal hernia)
• Bronchogenic cysts,
• Congenital lobar emphysema,
• Congenital cystic adenomatoid malformation
• Neurenteric cysts
• Anterior meningocele
• Pleuropulmonary blastoma (Type 1)[i]
• Neuroblastoma, although solid, can have few echoes and appear hypoechoic
• Intrathoracic solitary cyst of the liver[ii]

Although difficult to see there was some disorganization of the thoracic spine and mostly the cyst was in contact with the spine. Among the lesion previously mentioned, the pulmonary lesions are not typically that posterior, and neuroblastoma, the gastrointestinal anomalies and neurenteric cysts and anterior meningocele are the main entities that are expected in this compartment. Note on the Doppler images how the heart is displaced anteriorly more than laterally pointing to a posterior origin to the cyst.

Among the 3 categories of lesions the neuroblastoma can be eliminated since the lesion is frankly cystic, not simply hypoechoic.

Aside from the size of the cyst, the image is very compatible with that of a hiatal hernia. A herniated stomach (part of a diaphragmatic hernia) would be more lateral.

This leaves us with 2 rare conditions: anterior thoracic meningocele and neurenteric cyst. These might not be completely distinguishable, but a meningocele would be expected to cause intracranial findings (posterior fossa anomalies such as decrease of the cysterna magna, downward herniation of the cerebellum and ventriculomegaly). The most likely diagnosis thus was that of neurenteric cyst

Evolution

The baby was born at 37 weeks weighing 3250g with an APGAR score of 2 points at the first minute and O points at 5 minutes. He died of an acute respiratory failure due to lung hypoplasia. The enlargement of the head is well visible. No hydrocephaly though.

The pathology confirmed the diagnosis of neurenteric cyst of the posterior mediastinum (endodermic cyst).

The communication between the cyst and the central nervous system could be demonstrated by increasing the intracranial pression and demonstrating the increased turgescence of the cyst.

Section of the spine exquisitely demonstrated the communication. Note the opening in the vertebral body and the sac surrounding the spinal cord. There was also a hemivertebra.

At microscopy, the cyst had a wall lined by intestinal mucosa composed of different types of epithelia: cylindrical ciliated, planar stratified, small intestine glands and colonic glands. There were no cellular atypias.

References:

[i] Priest JR, McDermott MB, Bhatia S, Watterson J, Manivel JC, Dehner LP Pleuropulmonary blastoma: a clinicopathologic study of 50 cases. Cancer 1997 Jul 1;80(1):147-61

[ii] Kapouleas GP, Keramidas DC, Soutis M Bochdalek"s hernia combined with agenesis of the pericardium and intrathoracic solitary cyst of the liver. Z Kinderchir 1989 Dec;44(6):377-8