Testing S4/S5 Sensory Function
Test perianal sensation using light touch, pinprick, and temperature sensation in the perianal skin and anal canal, as these areas are innervated by the S2-S4 sacral nerve roots via the pudendal nerve. 1
Anatomical Basis
- The S4 and S5 sacral nerve roots provide sensory innervation to the perianal region, anal canal, and perineum 1
- Sensation from the anal canal travels via the inferior hemorrhoidal branches of the pudendal nerve to sacral roots S2, S3, and S4 1
- Rectal sensation (distension awareness) also travels with the parasympathetic system to S2, S3, and S4 1
Clinical Testing Methods
Anal Canal Sensation Testing
- Touch sensation: Test using light touch with a cotton swab or similar instrument in the anal canal 1
- Pinprick sensation: Apply pinprick stimuli to assess pain sensation in the perianal skin 1
- Temperature sensation: Apply warm or cold stimuli to the perianal region 1
Specialized Sensory Receptors Present
- The anal canal contains Meissner's corpuscles (touch), Krause end-bulbs (thermal stimuli), Golgi-Mazzoni bodies and pacinian corpuscles (tension/pressure), and genital corpuscles (friction) 1
- Large diameter free nerve endings exist within the epithelium 1
Quantitative Testing Options
- Electrical stimulation: Use a specialized constant current generator with bipolar electrode probe inserted in the anal canal for quantitative measurement of anal sensation 1
- This technique provides accurate and repeatable quantitative assessment of anal sensation 1
Clinical Context
- Testing S4/S5 sensation is particularly important when evaluating for cauda equina syndrome, sacral nerve root lesions, or when assessing surgical candidacy for sacral tumors 2
- For sacral chordomas, surgical decisions differ based on whether lesions arise from S4 and below versus above S3, given the neurological sequelae associated with resection 2