Table 6.

Classification of facial nerve lesions and histological characteristics according to Sunderland.

Seddon	Sunderland	Characteristics
Normal	Normal	No changes
Neurapraxia	Grade 1	Axonal conduction block without damage to the neural structure There is complete recovery, without sequelae
Axonotmesis	Grade 2	Axonal injury leading to Wallerian degeneration with breakdown of the myelin sheath, but the nerve structure is not damaged. Full recovery is typically achieved.
Neurotmesis	Grade 3	Axonal and endoneurial injury: in addition to Wallerian degeneration, there is disruption within the endoneurium with the possibility of fibrosis, which leads to a worse recovery prognosis in relation to grades II and III
	Grade 4	Axonal + endoneurium + perineurium injury: with only the epineurium intact, there is great neural disruption, with loss of fascicle continuity. In addition to fibrosis that prevents the axon stumps from meeting, this also allows axonal growth toward neighboring fascicles, determining the appearance of synkinesis + Grade 4 lesions cause important sequelae, including synkinesis.
	Grade 5	Axonal + endoneurium + perineurium + epineurium injury: there is loss of nerve trunk continuity. In this case, there is no spontaneous recovery.