Artifacts, Pitfalls & Normal Variants


"Lemon Sign" appearance of the frontal calvarium (arrows) Normal posterior fossa and cisterna magna (arrowhead)

Findings:

The image on the left demonstrates concave inward scalloping of the frontal bones in a second trimester fetus. Another image at a slightly more basal plane demonstrates the normal posterior fossa and cisterna magna. This fetus was normal at birth with no evidence of a neural tube abnormality.

Discussion:

The frontal scalloping which has come to be known as the "lemon sign" can be associated with neural tube defects ie myelomeningocele. It also may be seen in perfectly normal fetuses and is essentially a normal variant. While it is perfectly reasonable to do a more careful search of the fetus ie posterior fossa and spine, when this sign is seen, in the absence of other findings it should be declared a normal variant and the patient reassured. Please see the discussion of the Lemon Sign applied to neural tube defects.

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