Investigations
1st investigations to order
MRI and/or CT scans
Test
Defines the presence, nature, and/or extent of lesion(s). May also show evidence of tumour growth.
Such tests are indicated whenever the presence of optic pathway gliomas, other brain tumours, hydrocephalus, paraspinal neurofibromas, or malignant peripheral nerve sheath tumours (MPNSTs) are suspected, whether at or after diagnosis.
The preferred imaging technique depends on the indications and the type of lesion being sought.
Result
may demonstrate findings compatible with optic pathway gliomas, other brain tumours, hydrocephalus, paraspinal neurofibromas, or MPNSTs
PET scan
Test
Defines the presence, nature, and/or extent of lesion(s). May also show evidence of tumour growth.
Imaging with PET, MRI, and/or CT is indicated whenever the presence of optic pathway gliomas, other brain tumours, hydrocephalus, paraspinal neurofibromas, or malignant peripheral nerve sheath tumours (MPNSTs) is suspected, whether at or after diagnosis.
PET can be especially useful for distinguishing MPNSTs from benign neurofibromas.[23] Abnormal test results may suggest surgery as a treatment approach. Normal results on a PET scan do not exclude malignant tumour behaviour. The significance of normal results when an optic pathway glioma is being sought depends on the age of the patient and indications for doing the study.
Result
may demonstrate features compatible with optic pathway gliomas, other brain tumours, hydrocephalus, paraspinal neurofibromas, or MPNSTs
biopsy
Test
May help to define the presence, nature, and/or extent of lesion(s) such as neurofibroma or malignant peripheral nerve sheath tumours (MPNSTs).
For young patients otherwise with only café au lait spots, histological identification of a neurofibroma may confirm the diagnosis of NF1. At other times, biopsy may be used to try to differentiate a benign neurofibroma from an MPNST. A biopsy is appropriate whenever indicated by the clinical findings, whether at or after diagnosis.
Failure to document a malignancy by biopsy does not exclude its presence.
Result
histological features of a neurofibroma or MPNST
genetic testing to confirm NF1 mutation
Test
The American Association of Cancer Research recommend RNA-based NF1 mutation testing to confirm the diagnosis. Diagnostic criteria for NF1 and Legius syndrome (NF1-like syndrome) also recommend genetic testing as a criterion and, in particular, to differentiate these from each other and from other disorders (e.g., congenital mismatch repair deficiency) in patients with multiple café au lait patches.[14][15] The increasing evidence for a genotype-phenotype correlation adds further to the utility of testing.
Identification of the NF1 mutation will confirm the diagnosis of NF1 (although it does not exclude other disorders from also being present).[24] If the purpose of the test is confirmation of the clinical diagnosis, negative results do not necessarily exclude NF1. Detection may be as high as 95%, but this is not true for all testing facilities. Such tests are indicated whenever the presence of such findings is suspected, whether at or after diagnosis.
Referral to an NF specialty clinic is warranted with positive, negative, or ambiguous results. Knowing the details of the NF1 mutation in an adult with NF1 will afford its use in antenatal diagnosis or in pre-implantation diagnosis protocols.
Result
identifiable mutation involving the NF1 locus
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