A 1-day-old infant was born with the vault of the skull undeveloped, leaving the malformed brain exposed. A diagnosis of exencephaly is made. What is the embryologic cause of this condition?
**Core Concept**
The underlying principle being tested is the understanding of **neurulation**, a process in embryonic development where the **neural tube** forms, eventually giving rise to the brain and spinal cord. This process is crucial for the proper formation of the central nervous system.
**Why the Correct Answer is Right**
Exencephaly is a rare congenital disorder where the **neural tube** fails to close, resulting in the brain developing outside of the skull. This condition is often related to defects in **neurulation**, specifically the failure of the **neural tube** to properly close during embryonic development.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it does not directly relate to the failure of neural tube closure.
**Option B:** Incorrect as it is more related to the formation of the heart.
**Option C:** Incorrect because, although it involves the nervous system, it is not directly related to the failure of neural tube closure.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that exencephaly is distinct from **anencephaly**, where a large portion of the brain and skull do not form. Understanding the difference between these conditions can be crucial for diagnosis and management.
**Correct Answer:** D. Failure of neural tube closure.