A development defect of all CNS in which a sac containing spinal cord and meninges protrudes through a congenital cleft in the vertebral column is known as what?

• A. Myelomeningocele
• B. Nuchal thickness
• C. Proboscis
• D. Lemon sign

Answer: (A)

The described defect is an open neural tube defect where the spinal cord and meninges protrude through a vertebral defect, forming a sac. This is myelomeningocele, the most severe form of spina bifida. It happens when neural tube closure and the fusion of the vertebral arches fail early in embryonic development, usually in the lumbar–sacral region. The sac contains neural tissue and meninges, distinguishing it from conditions where only meninges herniate or where there is no protrusion. Nuchal thickness is a first-trimester marker for chromosomal abnormalities, not a spinal defect. A proboscis is a facial anomaly, not related to the spine. The lemon sign is an ultrasound finding associated with open neural tube defects but does not describe the defect itself. So the correct description is myelomeningocele.