Plexiform neurofibromas (PF) have a close association with and are virtually diagnostic of Neurofibromatosis 1. The lesions develop in early childhood. When involving nerve trunks in extremities, they can cause massive enlargement of the extremity, hypertrophy of long bones, and redundancy and hyperpigmentation of skin. Grossly, PF convert the involved nerve trunks into a thickened tortuous mass – an appearance that has been compared to “a bag of worms” as nicely captured in this image. Image courtesy of Dr. Jean-Christophe Fournet, Paris, France; humpath.com; Used with permission.