Hydromyelia is defined as what abnormal process in the spinal cord?

• A. Abnormal widening of the central canal near the fourth ventricle with CSF accumulation
• B. Herniation of the spinal cord through the vertebral column
• C. Degeneration of myelin sheath only in the peripheral nerves
• D. Excessive flexion of the spine causing nerve root compression

Answer: (A)

Hydromyelia is the abnormal widening of the spinal cord’s central canal with accumulation of cerebrospinal fluid. The central canal is the CSF-filled channel that runs through the spinal cord and connects with the brain’s ventricular system, including the area near the fourth ventricle. When CSF dynamics cause this canal to dilate, CSF fills the expanded space, producing hydromyelia. This is distinct from syringomyelia, where a separate fluid-filled cavity forms within the cord tissue itself.

This isn't about a herniation of the spinal cord through the vertebral column, which would be a different condition, nor about peripheral nerve demyelination, nor about mechanical nerve root compression from spine flexion.