Plexiform neurofibroma is an uncommon variant of neurofibroma, a benign tumour of peripheral nerves (WHO grade I), arising from a proliferation of all neural elements. Plexiform neurofibromas are essentially pathognomonic of neurofibromatosis type 1 (NF1). Unlike small sporadic localised neurofibromas and diffuse cutaneous neurofibromas (both discussed separately), these tumours are at a significant risk of eventual malignant transformation.
There is variable use and some confusion about the distinction between plexiform neurofibroma and diffuse cutaneous neurofibroma, with some sources not clearly distinguishing between the two. Generally, plexiform neurofibromas are deeper lesions affecting nerves and plexus. The two may, however, co-exist 5.
Importantly it appears that diffuse cutaneous neurofibromas may not be as closely associated with neurofibromatosis type 1 (NF1), nor have the same risk of malignant transformation 1-4. The distinction is thus important.
Plexiform neurofibromas are usually diagnosed in early childhood. They are found in approximately 30% of patients with NF1.
Clinically, it presents as a subcutaneous mass which feels like a "bag of worms". Most of the time, it is a superficial cutaneous/subcutaneous lesion, but it can occur almost anywhere in the body. Symptoms may be related to local mass effect.
Plexiform neurofibromas diffusely involve long nerve segments and its branches, often extending beyond the epineurium into the surrounding tissue.
Immunohistochemistry demonstrates findings in keeping with a neurogenic origin, including 6.
- S100: positive (fewer reactive cells than in schwannoma)
- SOX10: positive (fewer reactive cells than in schwannoma)
- neurofilament: only positive in entrapped axons
Non-specific infiltrative subcutaneous lesion.
Reported signal characteristics include:
- T1: hypointense
- T2: hyperintense +/- hypointense central focus (target sign)
- T1 C+: mild enhancement
Treatment and prognosis
Although generally benign tumours, there is a significant potential for malignant transformation, which occurs in 5-10% of larger tumours 5,6. If complete resection is possible, then a cure can be effected, however, due to the infiltrating nature of these tumours, such a resection is usually not possible.
History and etymology
The term plexiform comes from the infiltrative growth pattern that, histologically, looks like a plexus or a network. Plex- originates from the Latin verb plectere meaning "to plait" or "interweave".
It is typically associated with tumours of neural derivation. Plexiform neurofibromas are considered the prototype of the plexiform pattern 1.
On imaging consider:
- 1. Abbas O, Bhawan J. Cutaneous plexiform lesions. J. Cutan. Pathol. 2010;37 (6): 613-23. doi:10.1111/j.1600-0560.2010.01529.x - Pubmed citation
- 2. Prada CE, Rangwala FA, Martin LJ et-al. Pediatric plexiform neurofibromas: impact on morbidity and mortality in neurofibromatosis type 1. J. Pediatr. 2012;160 (3): 461-7. doi:10.1016/j.jpeds.2011.08.051 - Pubmed citation
- 3. Laffan EE, Ngan BY, Navarro OM. Pediatric soft-tissue tumors and pseudotumors: MR imaging features with pathologic correlation: part 2. Tumors of fibroblastic/myofibroblastic, so-called fibrohistiocytic, muscular, lymphomatous, neurogenic, hair matrix, and uncertain origin. Radiographics. 29 (4): e36. doi:10.1148/rg.e36 - Pubmed citation
- 4. Slam KD, Bohman SL, Sharma R et-al. Surgical considerations for the familial cancer syndrome, neurofibromatosis 1: a comprehensive review. Am Surg. 2009;75 (2): 120-8. Am Surg (link) - Pubmed citation
- 5. Cotran RS, Kumar V, Collins T et-al. Robbins pathologic basis of disease. W.B. Saunders Company. (1999) ISBN:072167335X. Read it at Google Books - Find it at Amazon
- 6. Louis DN, Ohgaki H, Wiestler OD, Cavenee WK "WHO Classification of Tumours of the Central Nervous System. 4th Edition Revised" ISBN: 9789283244929