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Prenatal ultrasound, transverse slice at the level just below the liver: visualization of a hyperechogenic mass (white solid arrows) adjacent to a dilated digestive loop (white dotted arrows), surrounded by anechogenic ascites (asterisk [*]) in the right hemiabdomen.
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At 30 GW, fetal ultrasound (US) showed peritoneal ascites with septations and an echogenic mass adjacent to a right dilated bowel loop with an echogenic content ( Fig. 1 ).
Fetal MRI, coronal slices (T2-sequence on the left side, T1 on the right side): the abdominal mass (white arrows) appears as an intermediate hyperintense T2-lesion and a hypointense to isointense T1-lesion. Visualization of some adjacent dilated bowel loops with meconial content (tri-line arrow). The dotted arrows show the liver. MRI, magnetic resonance imaging.
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Antenatal magnetic resonance (MR) imaging at 33 GW confirmed the diagnosis ( Fig. 2 ) and demonstrated normal jejunal loops in the left flanck.
Intestinal fibrosarcoma (hematoxylin and eosin: original magnification x25 and x250 in inset), dense spindle cells proliferation occurring in the submucosa and extending to the whole intestinal wall.
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Moreover, inside the segment named "meconium cyst," there was a lumen which was full of meconium and bordered by an intestine mucosa infiltrated with tumor cells meaning that the "cyst" was a part of the tumor ( Fig. 3 ). 
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