Fig. 1.

MRI and fluorodeoxyglucose (FDG) PET evaluation of 2 distinct nodular lesions within a single large PN. (A, B) A 9-year-old boy with NF1 and newly diagnosed PN involving the right retroperitoneum, pelvis, and thigh. MRI evaluation at the NCI revealed 2 distinct nodular lesions, one in the right inguinal area (A; sample ANF14-2), and one in the right paraspinal area (B; sample ANF14-1). (C‒E) Volumetric MRI analysis demonstrated faster growth rates for the nodular lesions (black contour) compared with the PN (green contour). (F, G) FDG-PET demonstrated FDG avidity of the nodular lesions with minimal uptake in the surrounding PN (F and G, inguinal and paraspinal lesions, respectively). Core biopsy of the inguinal lesion showed ANF; core biopsy of the paraspinal lesion showed neurofibroma. The inguinal lesion was resected, and pathology confirmed atypical neurofibroma. Follow-up with MRI continues to demonstrate more rapid growth of the remaining paraspinal lesion compared with the PN (C, D).