Purpose or Case Report: To offer a complete overview of the diagnostic hypotheses of the various fluid-containing masses which can be found in the neonatal abdomen.
Methods & Materials: The abdominal fluid-containing masses of the newborn can be divided into newly-formed masses (ovarian cysts, gastroenteric duplication cysts, choledocal cysts, cystic teratomas and renal cysts) and dilation of pre-existing hollow structures, these latter being either normal viscera (stomach, renal pelvis, ureter, bladder, uterine cavity) dilated because of a downstream obstacle or persistent embryological remnants as observed in cloacal and urogenital sinus malformations.
Results: For each abnormality drawings, schemes (also illustrating embryological origin when needed), the radiological images (ultrasound, magnetic resonance, contrast enema and voiding cystourethrography) necessary to a full description and when useful surgical findings are provided.
Conclusions: The finding of a fluid-containing mass is not a rare event in the evaluation of the neonatal abdomen. General radiologists should be confident with the main imaging findings in order to choose the pathway leading to a correct diagnosis