Fact-sheet: Neurofibromatosis
Updated on 09/17/2021 at 12:16 PM
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Definition
Neurofibromatosis type 1 is the most common autosomal dominant disease, with an incidence of approximately 1 in 3000 to 3500 births.
The disorder is a neurocristopathy characterized by the occurrence of neurofibromatous tumors in organs of ectodermal origin.
5% of affected patients develop malignant tumors.
Clinical features
Various clinical signs are noted:
- café-au-lait spots: often congenital, resulting from proliferation of nerve endings causing focal epidermal melanosis. During adulthood, these café-au-lait spots become less visible or even disappear.
- lentigines: these are macules 1 to 3 millimeters in diameter located in the axillary, inguinal, and inframammary folds.
- benign nerve tumors (Neurofibromas): cutaneous and mucosal tumor signs consist of the presence of Neurofibromas, sometimes associated with hypertrophy of underlying bony structures. Subcutaneous Neurofibromas are present in adulthood in approximately 20% of patients and appear before late childhood. They may be diffuse or nodular.
- Lisch nodules: these are small iris hamartomas that cause no visual impairment. Their size and number increase with age. They are nearly pathognomonic of the disease.
- optic pathway gliomas: this is the most common intracerebral tumor in Neurofibromatosis type 1. It mainly affects the optic nerve and chiasm and can extend along the optic pathways.
- skeletal involvement: this is associated with cutaneous and tumoral signs. Long bone dysplasias may be present, as well as sphenoid wing dysplasia, often congenital in origin and often accompanied by a plexiform orbital Neurofibroma, and vertebral dysplasias.
MRI
Optic pathway glioma Circumferential perineural infiltration extending into the subarachnoid space, manifesting either as tubular, tortuous enlargement of the nerve greater than 3 mm in size, or as a fusiform mass that is hypo- or isointense on T1, hyperintense on T2, with variable enhancement. Use FAT SAT++ sequences. Intra-axial tumors: appearance depends on histopathological type Low-grade gliomas Ependymomas Astrocytomas UBOs: Lesions: - Nodular - Less than 1.5 cm - Located in the basal ganglia, cerebellum, and supratentorial white matter - Iso on T1, hyperintense on T2 and FLAIR - No contrast enhancement and no perilesional edema Neurofibromas: Develop from nerve roots and plexuses. Relative hyposignal on T1 compared to muscle. T2 hyperintense Enhancement is variable: diffuse, central, target-like...
Management
The course is most often slow, with flare-ups during growth, puberty, or pregnancy. Sarcomatous transformation arising from mesenchymal elements of nerve structures (Fibrosarcomas, schwannomas, and malignant mesenchymomas) occurs rarely.
For benign tumors, treatment is surgical and depends on functional and cosmetic impairment.
Genetic counseling.
Patients' life expectancy is reduced by about ten years compared to the general population.
Differential diagnosis
Neurofibromatosis type 2, which most often manifests as bilateral vestibular schwannomas. It is much rarer than NF1 (1 in 33,000 to 40,000 births).