Figure 8a. Peroneal nerve neurilemoma in a 49-year-old woman. (a-c) Coronal T1-weighted (435/40) (a) and axial T2-weighted (2,000/80) (b) MR images and longitudinal US scan (c) (photographically spliced together to show both ends of the lesion) reveal a well-defined fusiform mass (M) with entering and exiting nerve (*). Nerve appears central and within the capsule (large black arrowheads) of the mass, making distinction of neurilemoma from neurofibroma nearly impossible. MR images also reveal the surrounding fat (split-fat sign) (white arrowheads) and fascicular sign (small arrowheads in b). (d-f) Intraoperative photographs of lesion resection initially (d) reveal the fusiform mass (M) with entering and exiting peroneal nerve (*). Subsequently (e, f), incision of the epineurium (arrowheads) shows the lesion (curved arrow in e) separable from the nerve and resected with peroneal nerve fascicles left intact (straight arrows in f).