Aggressive fibromatosis of the neck: MR findings.

We present a case of aggressive fibromatosis of the scalene and longus colli muscles with surgically proved secondary involvement of the brachial plexus and carotid sheath in a 29-year-old woman in whom MR imaging failed to show involvement of the carotid sheath. The well-defined lesion was isointense on T1-weighted images and hyperintense on T2-weighted images relative to adjacent normal muscle and enhanced brightly.