Fetal Abdominal Cyst Differential Diagnosis

Step-by-step decision

Choose step by step as prompted; reaching an endpoint gives the management recommendation. You can go back a step or restart anytime.

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Full pathway

1. [Decision] Location + features + sex → characterize
   Location + features + sex → characterization? (Fetal MRI characterization of abdominal cystic lesions. Most common is a female ovarian cyst (third trimester). Judge by location/features/sex/relationship to organs. Mostly good prognosis, only a few (choledochal/atresia/tumor) need early surgery.)
   • Female, simple thin-walled round cyst (mostly ovarian), no daughter cysts/debris → Simple ovarian cyst · mostly regress
   • Complex cyst (daughter cyst/fluid-debris level/>5 cm) — suspect ovarian torsion/hemorrhage → Complex ovarian cyst · watch for torsion
   • Fixed near the liver, enlarging with gestation, gallbladder present (choledochal cyst) → Choledochal cyst · early surgery
   • Bowel-wall/migratory/multiloculated or with calcification-ascites (enteric duplication/mesenteric/meconium pseudocyst) → Enteric duplication/mesenteric/meconium pseudocyst
2. [End] Simple ovarian cyst · mostly regress
   Simple ovarian cyst (female, thin-walled, no daughter cysts/debris): mostly benign, appears in the third trimester, usually self-resolves within weeks postnatally; serial ultrasound monitoring of size/features; >5 cm or turning complex (hemorrhage/debris) raises torsion concern → aspiration/surgery; malignancy is very rare.
3. [End] Complex ovarian cyst · watch for torsion
   Complex ovarian cyst (daughter cyst/fluid-debris level/>5 cm): suggests torsion/hemorrhage risk; serial monitoring, turning complex or enlarging → assess (prenatal aspiration if needed); postnatal pediatric surgery assessment, often needs surgery or close follow-up; MRI helps characterize.
4. [End] Choledochal cyst · early surgery
   Choledochal cyst (fixed near the liver, enlarging with gestation, gallbladder present): differentiate from cystic biliary atresia (which is smaller, does not enlarge, small/absent gallbladder); MRI/MRCP to locate the biliary relationship; needs early postnatal surgery (to prevent cholestasis/cholangitis/malignant change) + follow-up.
5. [End] Enteric duplication/mesenteric/meconium pseudocyst
   Enteric duplication cyst (bowel wall, peristaltic/migratory, ultrasound detects only 20–30%)/mesenteric cyst (multiloculated lymphangioma, with Turner/Noonan/trisomy 18/21, mostly regress within 1 year)/meconium pseudocyst (perforation, extraluminal calcification 85% ± ascites/polyhydramnios, can self-heal): MRI characterization + check associated; proximal enteric duplication can cause polyhydramnios; postnatal assessment by type (enteric duplication/meconium peritonitis need surgical assessment).

Source guidelines & references

• Fetal abdominal cystic lesion MRI differentiation (Insights Imaging 2026; ovarian/choledochal/enteric duplication)

This pathway is our own synthesis of the decision logic in the guidelines above (not the guideline verbatim); thresholds and workflows change as guidelines update — in practice follow the latest guideline, your institution's protocol and the individual patient.

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