Embryologic Development and Defects · USMLE Step 1

A newborn with spina bifida occulta shows a tuft of hair over the lumbar spine. Which embryologic structure failed to close?

  1. Neural tube
  2. Somites
  3. Notochord
  4. Lateral body folds
Show answer and explanation

Correct answer: Neural tube

Spina bifida results from abnormal closure of the posterior neuropore. Occulta is the mildest form and is often associated with a skin marker like a hair tuft.

Difficulty: Medium Question 12 of 20

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