NF1 and plexiform neurofibroma: They represent the most common peripheral nerve sheath tumors and are usually diagnosed as apparently sporadic lesions; however, there is increasing evidence that a large number of histologically proven neurofibromas arise within the context of classical neurofibromatosis type 1 (NF1) or its alternative forms (Table 2), and that, when isolated, they may be caused by mosaic phenomena occurred in the NF1 gene at a somatic level, and it is currently accepted that virtually all individuals affected by NF1 develop neurofibromas (Figure 1 and Figure 2) [8].