Other less common causes of chiasmal syndrome are metabolic, toxic, traumatic or infectious in nature.
The supposed artifactual nature of Wilbrand's knee has implications for the degree of resection that can be obtained, namely by cutting the optic nerve immediately at the junction with the chiasm without fear of potentially resulting visual field deficits.
Ruben et al.[4] describe several compressive etiologies, which are important to understand if they are to be successfully managed.
Systemic hormonal aberrations such as Cushing's syndrome, galactorrhea and acromegaly usually predate the compressive signs.
The embryonic remnants of Rathke's pouch may undergo neoplastic change called a craniopharyngioma.
Tuberculum sellae and sphenoid planum meningiomas usually compress the optic chiasm from below.
At the chiasm, 53% of the axons from the nasal retina cross the midline to join the uncrossed temporal fibers.
The crossing of the nasal half of macular fibers of central vision occurs posteriorly in the chiasm.
Classical teaching was that, once crossed, the inferonasal fibers briefly loop back into the contralateral optic nerve sheath, before returning to the chiasm.
Andrew G. Lee has divided optic chiasmal syndromes into anterior, middle and posterior locations.
This will produce an ipsilateral optic neuropathy, often manifested as a central scotoma, and a defect involving the contralateral superotemporal field.
Lesions in the body of the chiasm most commonly disrupt the crossing nasal retinal fibers.
Posterior lesions may also involve the optic tract and cause a contralateral homonymous hemianopia.
This is due to loss of retinal ganglion cells nasal to the macula in the papillomacular bundle.
[1] If a mass is confirmed on MRI, an endocrine panel can help determine if a pituitary adenoma is involved.
Junctional scotomas classically show ipsilateral optic disc neuropathy with contralateral superotemporal defects.
Bitemporal hemianopia with or without central scotoma is present if the lesions have affected the body of the chiasm.
A posterior chiasm lesion should only produce defects on the temporal sides of the central visual field.