Target sign (peripheral nerve sheath tumor)

The target sign of peripheral nerve sheath tumor (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 localized neurofibroma, having been shown to correspond histopathologically with a dense central area of collagenous stroma surrounded by myxomatous tissue .

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

  • one study including 22 benign PNSTs showed a target sign in only 21%
  • 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 tumor cells surrounded by edema-like fluid
  • a "target sign" has also been observed in malignant peripheral nerve sheath tumor