Neurofibroma is a benign peripheral nerve sheath tumour, typically affecting young adults, associated with neurofibromatosis type 1, characterised by a mixture of Schwann cells, fibroblasts, and perineurial cells, and manifests as a soft, encapsulated mass in cutaneous, subcutaneous, or plexiform forms.
Description
Neurofibroma is a benign tumour that originates from the peripheral nerve sheath, composed of a mixture of Schwann cells, fibroblasts, and perineurial cells. Neurofibromas can occur sporadically or as part of neurofibromatosis type 1 (NF1), an autosomal dominant disorder. These tumours are typically soft and encapsulated, occurring in the cutaneous, subcutaneous, or plexiform forms.
Pathogenesis
Neurofibromas develop from proliferation of Schwann cells, fibroblasts, perineurial cells, and endothelial cells. In NF1, mutations in the NF1 gene on chromosome 17 result in the loss of the tumour suppressor protein neurofibromin, leading to uncontrolled cell proliferation and tumour formation.
Subtypes
There are three main subtypes of neurofibromas:
- Cutaneous or Dermal Neurofibroma: These are the most common, typically arising in the skin.
- Subcutaneous Neurofibroma: These occur deeper in the skin, often attached to a nerve.
- Plexiform Neurofibroma: These involve multiple nerve bundles, are often larger, and are typically associated with NF1.
Epidemiology, Risk Factors & Associations
- Typically present in young adults, although they can occur at any age.
- Strong association with NF1 (Mutation in the NF1 gene on chromosome 17).
- No clear gender predominance.
Clinical Features
- Cutaneous neurofibromas present as small, skin-coloured nodules.
- Subcutaneous neurofibromas may cause localised pain.
- Plexiform neurofibromas can cause disfigurement and functional impairment due to their size and location.
Complications
- Malignant transformation is rare but is more common in plexiform neurofibromas (~10% lifetime risk).
- Plexiform neurofibromas can cause significant morbidity due to their size and location.
Pathological Features
Histopathology
- Macroscopic: Neurofibromas are typically soft, encapsulated tumours. Plexiform neurofibromas are larger and involve multiple nerve bundles.
- Microscopic: Characterised by a mixture of Schwann cells, fibroblasts, and perineurial cells, within a myxoid stroma.
Radiological Features
General Features
- Characteristically demonstrates fusiform swelling of the affected nerve, often referred to as the “bag of worms” appearance for plexiform neurofibromas.
CT
- Non-contrast: Usually appear as a well-defined, rounded mass, often iso- to slightly hypodense compared to the muscle.
- C+ Arterial/C+ Venous: They may show enhancement, especially the larger lesions.
MRI
- T1: Generally iso- to hypointense compared to muscle.
- T2: Characteristically hyperintense.
- T1 Gad+: Variable enhancement.
Grading and Staging
No specific grading and staging system exists for neurofibromas. The tumour size and location, along with any associated symptoms, guide treatment decisions.
Diagnosis
The diagnosis of neurofibroma is made by a combination of clinical findings, imaging, and confirmed by histopathological examination.
Differential Diagnosis
- Schwannoma: Unlike neurofibromas, schwannomas are encapsulated and displace the nerve, rather than intermingling with the nerve fibres.
- Malignant peripheral nerve sheath tumour: This is a potential complication of neurofibromas, particularly plexiform neurofibromas. It may demonstrate more aggressive growth and invasive features on imaging.
Prognosis
Neurofibromas generally have a good prognosis due to their benign nature. However, plexiform neurofibromas carry a risk of malignant transformation.
Management
Management depends on the size, location, and symptoms caused by the neurofibroma. Small, asymptomatic neurofibromas may be managed with observation. Symptomatic, large, or disfiguring neurofibromas often require surgical resection.