Plexiform neurofibroma

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. 

 

Immunophenotype

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
CT

Non-specific infiltrative subcutaneous lesion.

MRI

Reported signal characteristics include:

  • T1: hypointense
  • T2: hyperintense +/- hypointense central focus (target sign)
  • T1 C+: mild enhancement

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. 

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:

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Article information

rID: 19088
Section: Pathology
Tag: cases
Synonyms or Alternate Spellings:
  • Plexiform neurofibromas
  • Plexiform neurofibromata

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Cases and figures

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    Case 1
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    Cor T2
    Case 2
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    Case 3
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    Case 4
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    Case 5: of infraorbital nerve
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    Case 6
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    Case 7: mesenteric plexiform neurofibroma
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    Case 8: abdominal and retroperitoneal
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