In the normal healthy human brain, visual information is relayed from the lateral geniculate nucleus (LGN) to the primary visual cortex via the
optic radiations (for review, see Metzger et al.
- 5% supratentorially (typically in the
optic radiations).
Optic pathway gliomas can involve any portion of the visual pathway, including the hypothalamus, optic disc, nerve, chiasm, geniculate nucleus, and
optic radiations. Categorized as juvenile pilocytic astrocytomas, they account for 4-6% of all brain tumors in children, and the median age of diagnosis is 5-9 years [5, 53, 54].
Hemianopia due to the lesion in anterior optic tract is characteristically non congruous, while that due to pathology in posterior
optic radiations and occipital cortex are highly congruous1.
To quote Elisa Fazzi and her colleagues from Italy (2009): Cerebral visual impairment (CVI), a neurological disorder caused by damage to or malfunctioning of the retrogeniculate visual pathways (
optic radiations, occipital cortex, visual associative areas) in the absence of major ocular disease, (1) has been extensively studied in recent years.
For example, unilateral damage to VI, the optic tract (the section of the pathway that relays information from the optic chiasm to the LGN), or the LGN itself can lead to contralateral homonymous hemianopia (see Figure 2b), (9) while unilateral damage to Meyer's loop of the
optic radiations often results in homonymous quadrantanopia (see Figure 2c).
