USMLE Step 1 Question 290

Question:

A 32 year old woman gives birth to a baby boy. APGAR score was 10/10 both at 1 and 5 minutes after birth. Physical exam was normal except for a sac-like structure found on the sacrolumbar region of the baby’s back. Imagining studies reveals a fluid filled sac with the spinal cord positioned normally. What congenital defect is most likely present in this infant?

Correct Answer: D.  Spina bifida with meningocele

Spina bifida is a vertebral defect that occurs when the bony vertebral arches fail to properly form. Most commonly, the defect is located in the sacrolumbar region. Spina bifida with meningocele (choice D) occurs when the meninges protrude through the defect and form a CSF-filled sac with the spinal cord remaining in normal position. Besides the visible defect, these patients may present asymptomatically because the spinal cord is not compromised.

Spina bifida occulta (choice A) is marked by tufts of hair in the sacrolumbar region and is the least severe variation of spina bifida.

Spina bifida with meningomyelocele (choice B) occurs when both the meninges and spinal cord project through the defect to form a sac. These patients usually have neurologic dysfunction that parallels the section of cord that projects through the defect.

Spina bifida with rachischisis (choice C) occurs when the posterior neuropore fails to close, thus creating an open neural tube that lies on the surface of the back. This is the most severe form of spina bifida, and patients are usually paralyzed from the level of the defect caudally.

Encephalocele (choice E) occurs when the brain and the meninges project through a skull defect.