lemon sign


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lemon sign

the ultrasound finding of frontal bone scalloping associated with Arnold-Chiari malformation.
An ultrasound finding seen when a major neural tube defect accompanies Arnold-Chiari malformation, with herniation of cerebellar tonsils and midbrain structures into the foramen magnum, causing ventriculomegaly due to compression of outflow from the 3rd and 4th ventricles; downward traction of the brain causes a reduction in the anterior calvarium, resulting in a triangular-shaped head in the biparietal diameter, fancifully likened to a lemon

lemon sign

Obstetrics An ultrasound finding seen when a major neural tube defect accompanies Arnold-Chiari malformation, with herniation of cerebellar tonsils and midbrain structures into the foramen magnum, causing ventriculomegaly due to compression of outflow from the 3rd and 4th ventricles; downward traction of the brain causes a reduction in the anterior calvarium, resulting in a triangular-shaped head in the biparietal diameter, fancifully likened to a lemon.

lem·on sign

(lĕm'ŏn sīn)
The ultrasound finding of frontal bone scalloping associated with Arnold-Chiari malformation