Target sign (peripheral nerve sheath tumour)

Last revised by Ayla Al Kabbani on 30 Mar 2021

The target sign of peripheral nerve sheath tumour (PNST) is a lesional pattern of T2 signal on MRI consisting of a central area of low intensity surrounded by a T2 hyperintense rim. It is most commonly associated with localised neurofibroma, having been shown to correspond histopathologically with a dense central area of collagenous stroma surrounded by myxomatous tissue 5.

Unfortunately, the target sign is neither sensitive nor specific for either neurofibroma or for benign tumour:

  • one study including 22 benign PNSTs showed a target sign in only 21% 4
  • a similar "target sign" has also been observed in schwannoma, albeit less commonly. It is believed that the histopathologic correlate may be the alternating Antoni A and B zones, the latter of which consist of tumour cells surrounded by oedema-like fluid 1,2,5
  • a "target sign" has also been observed in malignant peripheral nerve sheath tumour 1,2,4

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