Visual Loss Due to Optic Chiasm and Retrochiasmal Visual Pathway Lesions (Neuro-Opthalmology 2014)

Educational Objectives

The goal of this program is to improve diagnosis and management of neuro-ophthalmologic conditions. After hearing and assimilating this program, the clinician will be better able to:

1. List lesions affecting vision at the level of the optic chiasm.

Summary

Lesions of chiasm: Classic presentation bitemporal hemianopsia; patient cannot perceive objects or motion in temporal fields; chiasmal lesions often progress insidiously; although patient may describe vague or nonspecific visual disturbances, VFT shows bilateral temporal loss of vision; most common cause pituitary adenoma.

Pituitary adenoma: Type of visual dysfunction depends on position of chiasm in relation to sella; in some individuals, chiasm not directly above pituitary, so lesion might compress anterior chiasm and cause unilateral deficit resembling central scotoma; if chiasm anterior to pituitary, adenoma can compress chiasm posteriorly, thus mimicking homonymous defect typical of cortical lesion.

Approach to patient: Check near and distant VA; color vision more sensitive indicator of dysfunction of optic nerve than VA (test with pseudoisochromatic plates); VFT most important evaluation (computerized VFT more specific and sensitive than bedside confrontation); assess structure of optic nerves (pallor or atrophy indicates progression).

Pituitary apoplexy (PA): Acute life-threatening hemorrhage or infarction of pituitary; presents as abrupt neurologic change, vision loss (can be bitemporal or total), severe headache or other localized neurologic symptoms; lateral extension into cavernous sinus can acutely disrupt cranial nerves III, IV, or VI; management — consider diagnosis of PA; many patients with PA have undiagnosed pituitary lesion; requires prompt laboratory evaluation, including complete blood count, electrolytes, coagulation parameters, renal and liver function tests, and pituitary hormone levels; MRI and acute neurosurgical consultation required and endocrinologic consultation useful.

Meningioma: Benign lesion that can involve sella and disrupt chiasm; resection sometimes incomplete or complicated by bleeding; tumors more vascular than pituitary adenomas.

Sellar and parasellar aneurysms: Circle of Willis close to optic chiasm; loss of vision caused by aneurysm of, eg, supraclinoid internal carotid arteries, junction between carotid and ophthalmic arteries or anterior communicating arteries; aneurysms can mimic bitemporal hemianopsia.

Sarcoidosis: Can cause loss of vision localized to optic chiasm; less common than other entities discussed; consideration of diagnosis mandates assessment for systemic manifestations.

Retrochiasmal lesions: Congruency refers to similarity of affected visual field in both eyes; right homonymous hemianopsia caused by lesion in left hemisphere considered congruent if right half of vision in both eyes affected; posterior retrochiasmal lesions closer to occipital lobes and usually more congruent than anterior lesions.

Macular sparing: Sometimes seen after strokes involving occipital cortex; when dense homonymous hemianopsia present, central vision sometimes spared; diagnosed by formal VFT; attributable to redundant blood supply to posterior pole of occipital lobe (ie, from posterior cerebral artery and from superior temporal occipital sylvian artery [branch of middle cerebral artery]).

Posterior reversible encephalopathy syndrome (PRES): Associated with hypertension, eclampsia, and exposure to immunosuppressive agents; typically presents with headache, altered mental status, and seizures; may cause bilateral total loss of vision; usually reversible with correction of underlying cause.

Cortical blindness: Total loss of vision, sometimes due to bilateral lesions of retrochiasmal visual pathways; cerebral blindness preferred terminology because cortical blindness implies disease limited to gray matter; characterized by complete loss of vision, including perception of light and contrast sensitivity; patients do not close eyelids in response to bright light or threatening gesture, but pupillary light reaction and near response intact (indicating lesion in cortex, not optic nerve or chiasm); Anton syndrome — some patients with cerebral blindness unaware of their inability to perceive visual stimuli; blindsight — refers to ability to see visual stimuli despite visual loss due to cortical blindness; not well understood.

Readings

Glisson, CC. Visual loss due to optic chiasm and retrochiasmal visual pathway lesions. Continuum (Minneap Minn) 2014;20(4).

Disclosures

For this program, the following was disclosed: Dr. Glisson has received personal compensation for consulting activities from Lundbeck and Questor Pharmaceuticals, Inc, and has received personal compensation for speaking engagements from Biogen Idec, Lundbeck, and Teva. Unlabeled Use of Products/Investigational Use Disclosure: Dr. Glisson reports nothing to disclose. To view disclosures of planning committee members with relevant financial relationships, visit: audiodigest.org/continuumaudio/committee. All other members of the planning committee report nothing to disclose.

Acknowledgements

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 0 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 0 CE contact hours.

Lecture ID:

CA031402

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.