Which condition is most likely to present with upper extremity weakness due to CSF buildup in the spinal cord's central canal?

• A. Syringomyelia
• B. Hydromyelia
• C. Tethered cord
• D. Chiari II malformation

Answer: (A)

When CSF accumulates and forms a fluid-filled cavity within the spinal cord, the condition disrupts the gray matter and crossing sensory pathways most in the cervical region. This syrinx expansion injures the ventral horn cells that control distal upper-extremity muscles, leading to weakness (often with hand muscle weakness and atrophy) and can produce dissociated sensory loss in the cape-like distribution over the shoulders and arms as the fibers crossing at the anterior white commissure are affected.

This pattern is classic for syringomyelia, where a syrinx develops inside the spinal cord itself due to abnormal CSF dynamics. Hydromyelia describes dilation of the central canal and can present similarly, but the term syringomyelia is the more typical reference when a cavity within the spinal cord causes upper-extremity weakness from CSF buildup. Tethered cord and Chiari II malformation can have related neurologic effects, but they do not primarily present as weakness from a center-canal CSF buildup in the upper limbs.