Peroneal nerve: Normal anatomy and pathologic findings on routine MRI of the knee

Insights into Imaging

Table 1 Differentiating features for peripheral nerve sheath tumours

Schwannoma-specific features	Neurofibroma-specific features	Non-specific features benign PNST	Malignant PNST
		Peripherally or centrally entering and exiting nerve	Size >5 cm
Fascicular appearance on T2-WI		Cystic areas On T2-WI	Heterogeneous appearance on T2-WI and T1-WI
Thin hyperintense rim on T2-WI	Target sign on T2-WI		Infiltrative margin
Diffuse enhancement on contrast-enhanced T1-WI	Central enhancement on contrast-enhanced T1-WI	Peripheral enhancement on fat-suppressed contrast-enhanced T1-WI	Heterogeneous enhancement on contrast-enhanced T1-WI

Fascicular appearance: multiple small ringlike structures (with peripheral higher signal intensity) on axial T2-WI or intermediate-WI
Thin hyperintense rim: rim is less than one quarter of the diameter of the lesion
Target sign: a central hypointense focus with a peripheral hyperintense rim on T2-WI, the central focus making up less than three quarters of the diameter of the lesion