A 32-year-old woman with a history of previous caesarean section presents at 28 weeks with painless antepartum haemorrhage. Ultrasound confirms placenta praevia. Colour Doppler shows multiple intraplacental lacunae with turbulent flow and loss of the normal retroplacental hypoechoic zone. What is the most likely diagnosis and what additional MRI finding would confirm the most severe form?
- A Velamentous cord insertion causing vasa praevia
- B Placental abruption with retroplacental haematoma
- C Placenta accreta spectrum; MRI showing dark intraplacental bands and bladder wall invasion confirms placenta percreta ✓
- D Subchorionic haemorrhage in a circumvallate placenta
Explanation
Placenta accreta spectrum (PAS) occurs when the decidua basalis is deficient (commonly in the setting of previous uterine surgery) and trophoblast invades myometrium. Ultrasound features include placental lacunae with turbulent high-velocity flow, loss of the retroplacental hypoechoic zone, and myometrial thinning. MRI is the best adjunct for defining depth of invasion. Dark intraplacental T2 bands represent fibrin bands within lacunae. Bladder wall invasion (loss of fat plane between the bladder and uterus, irregular bladder wall signal) confirms the most severe form — placenta percreta. Early identification allows planned delivery at a specialist centre.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.