What is the likely diagnosis, and what is the underlying condition?
Extensive optic pathway glioma in a child who most likely has neurofibromatosis type 1.
When isolated to a shorter segment of optic nerve, what is the usual morphology?
The optic nerve is variably enlarged, and the mass may either be fusiform or exophytic in appearance. Additionally the nerve may be elongated with kinking or buckling.
What is the spectrum of behaviour of optic pathway gliomas in children with NF1.
In patients with NF1 it is not unusual for these tumours to be quiescent, with little progression demonstrated over a number of years. In others, the tumours are more aggressive with extension along the optic pathways (as is the case in this patient).
What is the genetic abnormality which results in NF1?
Mutations of the NF1 gene locus is on chromosome 17q11.2 are responsible for neurofibromatosis type 1. The gene product of NF1 is neurofibromin, a protein which acts as a tumour suppressor; inactivation of the gene thus predisposes to tumour development.
MRI of the brain demonstrates enlargement and enhancement of the optic apparatus, including the posterior optic nerves, optic chiasm, optic tracts and into the midbrain and basal ganglia.
The pituitary gland can be seen as separate to the mass which pushes down upon it.