In axonotmesis, which statement is true?

• A. The axon and myelin are preserved
• B. Endoneurium is disrupted
• C. The epineurium and perineurium are disrupted
• D. The epineurium and perineurium remain intact

Answer: (D)

In axonotmesis the axon and its myelin are damaged and undergo Wallerian degeneration distally, but the surrounding connective tissue scaffolding remains intact. The preservation of the outer protective layers, particularly the epineurium and perineurium (and with endoneurial tubes still usable within the fascicles), provides a pathway for regenerating axons to grow toward their targets. That’s why the statement that the epineurium and perineurium remain intact is true.

If the axon and myelin were preserved, that would describe neurapraxia. If the endoneurium were disrupted, regeneration would be poorly guided. If the epineurium and perineurium were disrupted, that would reflect a more severe injury (neurotmesis/Sunderland grade V or IV).