If the anocutaneous reflex is absent, which neural region is most likely affected?

• A. Cauda equina
• B. Conus medullaris
• C. Corticospinal tract
• D. Posterior column

Answer: (A)

The anal (anocutaneous) reflex is a sacral spinal reflex that relies on the S2–S4 nerve roots. The afferent signal from the perianal skin travels via the pudendal nerve to the sacral cord, and the efferent signal returns via the pudendal nerve to the external anal sphincter. Damage to the nerve roots in the cauda equina disrupts both limbs of this reflex arc, leading to an absent anal wink. A corticospinal tract lesion affects upper motor neuron pathways and would not typically abolish this spinal reflex. A posterior column lesion impairs vibration and fine touch, not the reflex arc. A lesion at the conus medullaris can affect sacral functions as well, but involvement of the cauda equina nerve roots directly explains the loss of this reflex due to disruption of the sacral components of the reflex arc.