Updated: 6/22/2021

Neurofibroma

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  • summary
    • Neurofibromas are benign peripheral nerve sheath tumors most commonly associated with neurofibromatosis.
    • The condition usually presents in patients with neurofibromatosis with cutaneous lesions, as well as lesions near the brain, spinal cord and parotid glands. 
    • Diagnosis is made with clinical history, physical exam, and MRI with and without contrast.
    • Treatment is observation for asymptomatic lesions. Surgical excision is indicated for symptomatic lesions.  
  • Epidemiology
    • Demographics 
      • sporadic neurofibromas 
        • age 20-40 years
      • Neurofibromatosis (NF1)
        • age < 20 
    • Anatomic location
      • sporadic neurofibromas 
        • peripheral PNS tumors of the extremities
      • Neurofibromatosis (NF1)
        • tendency to be found near spinal cord/brain (CNS) and uncommon locations (parotid glands, tongue)
  • Etiology
    • Cell types
      • fibroblasts (predominant cell)
      • nonmyelinating Schwann cells
        • cell of origin, arises from this cell
      • perineural cells
      • differentiate from Schwannoma, which involves Schwann cell alone
    • Molecular biology
      • arise in nonmyelinating Schwann cells with biallelic inactivation of NF1 tumor-suppressor gene
      • loss of expression of protein neurofibromin
        • neurofibromin negatively regulates RAS-mediated pathway
        • loss of neurofibromin leads to increased RAS activity
        • affects RAS-dependent MAPK activity which is essential for osteoclast function and survival
      • rapid hyperplasia of nonmyelinating Schwann cells into neurofibromas after NF1 inactivation
        • recruits perineural cells, fibroblasts, mast cells, endothelial cells
  • Classification
    • Subtypes of neurofibroma
      Origin
      Description
      Associations
      Onset
      Malignancy
      Dermal
      Arise from single peripheral nerve
      Fusiform swelling of nerve
      90% sporadic, 10% arise in NF1
      At puberty
      Do not become malignant
      Plexiform
      Arise from multiple nerve bundles
      "Bag of worms" (tortuous enlargement of nerves)
      Pathognomic of NF1
      Early childhood
      10% become malignant (MPNST)
    • Types of Schwann cells
      Axons
      Disease process
      Myelinating
      Covers large-diameter PNS axons with myelin
      Nonmyelinating
      Covers small-diameter PNS axons with cytoplastic processes
      Responsible for neurofibromatosis
  • Presentation
    • Symptoms
      • asymptomatic
      • stinging, itching, pain, disfiguration
    • Physical exam
      • reduced sensation
      • cutaneous lesions
        • can "button hole" through skin defect using finger pressure
      • signs of neurofibromatosis (2 of 7) (NIH criteria)
        • 2 or more neurofibromas, or 1 plexiform neurofibroma
        • axillary or groin freckling (Crowe's sign)
        • 6 or more coast of California cafe-au-lait spots
          • 5mm diameter in prepubertal
          • >15mm diameter in postpubertal
        • sphenoid wing dysplasia or thinning of long bone cortex (anterolateral tibial bowing)
        • 2 or more Lisch nodules (iris hamartomas)
          • on slit lamp
        • optic glioma
        • 1st degree relative with NF1
      • associated with NF1
        • dystrophic kyphoscoliosis
        • rib penciling
        • intraspinal neurofibromas and dumbbell lesions
        • dural ectasia
        • meningiomas
  • Imaging
    • MRI with and without contrast
      • findings
        • differentiate Schwannoma from neurofibroma
          • Schwannoma are found ECCENTRIC to the nerve fibers
          • Solitary neurofibromas are found CENTRAL to the nerve fibers
      • nerve continuity sign
        • fusiform tumor in continuity with the neurovascular bundle
      • split fat sign
        • fusiform tumor surrounded by a thin margin of fat because the mass within the neurovascular bundle enlarges and displaces the adjacent intramuscular fat
      • target sign
        • lesion of high signal intensity peripherally and low signal centrally (on coronal STIR)
    • PET-CT
  • Histology
    • Characteristics
      • cells
        • hypocellular
        • predominantly fibroblasts
        • mixed Schwann cells, mast cells, lymphocytes
        • elongated, wavy nuclei
      • stroma
        • rich wire-like collagen fiber network
        • may be myxoid
      • distorted structures resembling Pacini or Meissner corpuscles
      • variable S100 staining
  • Differential
    • MPNST (malignant peripheral nerve sheath tumor or neurofibrosarcoma)
      • 5% of patients with NF, 10-25% lifetime risk
      • symptoms include painful, enlarging soft tissue mass
      • usually from plexiform neurofibroma
        • 10% of plexiform neurofibromas transform into MPNST
      • associated with loss of expression of CDKN2A or TP53 genes in non-myelinating Schwann cells (that also have biallelic inactivation of NF1)
      • poor prognosis
        • widespread metastasis
        • high rate of local recurrence
    • Schwannoma
    • Wilms tumor
    • Melanoma
    • Leukemia
    • Rhabdomyosarcoma
    • Pheochromocytoma
  • Treatment
    • Nonoperative
      • observe
        • if asymptomatic
    • Operative
      • surgical excision
        • if symptomatic
        • may require nerve grafting
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(OBQ13.269) A 40-year-old man presents with an 6-year history of a forearm mass and episodic, sharp forearm pain. MRI scans are seen in Figures A and B. What is the most likely diagnosis?

QID: 4904
FIGURES:
1

Soft tissue sarcoma

10%

(414/4066)

2

Soft tissue metastasis

1%

(24/4066)

3

Hematoma

1%

(44/4066)

4

Abscess

1%

(39/4066)

5

Nerve sheath tumor

87%

(3522/4066)

L 2 C

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