Table 1 Classification of nerve injury according to Seddon and Sunderland with corresponding findings on HRUS and MRI [10]

Neuropraxia

I

Conduction block

T2 hyperintensity

Decreased echogenicity of nerve (hypoechoic)

Axonotmesis

II

Discontinuity of axon with Wallerian degeneration

T2 hyperintensity with increased size.

Hyperintensity in muscles due to denervation.

Decreased echogenicity and increased calibre of the nerve

III

Scarring of the endoneurium

Endoneurium can-not be delineated with current MR technique.

T2 hyperintensity with increased size.

Hyperintensity in muscles due to denervation.

Focal decrease in echogenicity with increase in calibre with change in echotexture of the affected muscles.

IV

Neuroma in continuity with formation of scar which blocks nerve regeneration

T1 hypointense, T2 hyperintense focal enlargement with loss of fascicular pattern. Hyperintensity in muscles due to denervation.

Hypoechoic fusiform lesion in continuity with the nerve with loss of fascicular architecture with altered echogenicity of denervated muscles.

Neurotmesis

V

Rupture of the nerve

End neuroma formation at proximal end with denervation changes in muscle

Hypoechoic neuroma at proximal end with local soft tissue oedema and denervation changes in muscle.

Mackinnon and Dellon type VI

Mixed injury

Variable findings with nerve heterogeneity and muscle denervation changes

Hypoechoic enlarged with mixed findings of scarring, discontinuity or neuroma formation.