Distance between the calvaria and posterior skin line is called what?

• A. Nuchal thickness
• B. Proboscis
• C. Hypertelorism
• D. Keyhole sign

Answer: (A)

The distance from the occipital bone (calvaria) to the posterior skin line is called nuchal thickness. This measurement assesses the thickness of the soft tissue at the back of the fetal neck and is used in screening for chromosomal abnormalities and other conditions—the thicker the nuchal region, the higher the potential association with issues such as Down syndrome, though it is not diagnostic on its own. The other terms describe different findings: proboscis is a facial anomaly with a protruding nasal structure, hypertelorism means abnormally wide-set eyes, and the keyhole sign is a bladder ultrasound appearance associated with obstructive uropathy like posterior urethral valves.