A congenital dermoid in Rhodesian ridgebacks is located on the back due to incomplete closure of which structure?

• A. Neural tube
• B. Spinal canal
• C. Notochord
• D. Epidermis

Answer: (A)

This question hinges on neurulation and how dorsal midline defects form. During early development, the neural tube must close properly and separate from the surface ectoderm. If closure is incomplete along the dorsal midline, ectodermal tissue can remain connected to neural tissue, creating a persistent tract from the skin on the back down toward the spinal canal. In Rhodesian ridgebacks, this results in a congenital dermoid sinus located along the dorsal midline. The other structures don’t explain this tract: the spinal canal is the bony passage behind the vertebrae, the notochord is the primitive axis that helps form the vertebral column, and epidermis alone wouldn’t create a channel to the spine.