Optic pathway gliomas represent 2 to 5% of all brain tumours in children,1 and are the most common central nervous system tumours in patients with neurofibromatosis type 1 (NF1).2 3 They can involve the nerve proper, chiasm, hypothalamus and optic tracts, and are classified as grade I pilocytic astrocytomas.

Previous reports have suggested perineural gliomatosis, defined as extraneural growth of glioma into the surrounding subarachnoid space, as a characteristic of NF1-associated optic nerve gliomas, whereas isolated optic nerve gliomas typically display intraneural growth.4^–8 We report three patients with non-NF optic nerve gliomas with perineural gliomatosis, which has not previously been reported in the context of combined MRI and clinicopathological evaluation.

Representative case report

A 2½-year-old girl was referred to the Orbit Service with gradual right proptosis over 3 months. Visual acuity in the right eye was light perception and 6/6 in the left eye. A right 1.9 afferent pupillary defect was noted, with 3 mm of proptosis and 3 mm of downward displacement. Ocular movements were normal. There was a congested right disc with venous dilatation. Cycloplegic refraction was +3.00 in the right …