Lemon and banana sign

Case contributed by Dr Praveen Jha

Presentation

Antenatal imaging at 19 weeks pregnancy.

Patient Data

Age: 30
Gender: Female
ultrasound

Typical frontal 'pinching' of calvarium gives a 'lemon' appearance of the skull, and a 'banana' shaped cerebellum is seen due to a shallow posterior fossa. These are tell tale signs of a shallow posterior fossa anomalies or Chiari malformation.

Case Discussion

This case shows some easily recognizable features on regular axial projections in fetal imaging, to suggest a neural tube defect like Chiari malformation.

A physiological analog of Chiari malformation that could be thought for memorizing is, as if skull is trying to push the brain matter out of its opening (foramen magnum), by pinching from front, and compressing the fossa from behind, and pushing the tonsils or brainstem out of foramen magnum. This gives rise to 'lemon sign' and 'banana sign'.

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