Disorders Of The Chiasm

Question 1

Where does the chiasm sit

Answer 1

In a cerebrospinal fluid filled pace called the suprasellar cistern

Located at the anterior and inferior part of the third ventricle, immediately inferior to the hypothalamus

Question 2

Circle of Willis and chiasm

Answer 2

ACA and anterior communicating arteries lie superior (dorsal) to the optic nerves and chiasm, while the posterior communicating arteries lie inferior (ventral) to the chiasm and optic tracts

Question 3

Visual symptoms of chiasmal symptoms

Answer 3

Vision loss is usually insidious (compressive lesion)

Question 4

Patterns of visual field loss in chiasmal disroders

Answer 4

Temporal field defects respecting the vertical meridian, in one eye or both eyes, are the hallmarks of chiasmal dysfunction

Question 5

Bitemproal hemianopsia

Answer 5

Can have preservation of a small amount of temporal field in each eye inferiorly, reflecting the sparing of some fibers in the superior/posterior portion of the chiasm

Question 6

Incomplete asymmetric bitemproal hemianopsia

Answer 6

Sometimes it can be incomplete and asymmetric

Question 7

Inferior bitemporal hemianopsia

Answer 7

Doesn’t respect the vertical meridian. Usually they do, but sometimes they do not.

Question 8

Post fixation blindness associated with a complete bitemporal heminaopia

Answer 8

Post fixation blindness assoacited with a bitemproal heminaopia. The blind temporal fields overlap behind it. Objects directly behind the target are invisible

Everything behind the convergence point is gone

Question 9

Junctional scotoma

Answer 9

Due to pituitary adenoma afecrting the anterior chiasm.

• does not respect the vertical midline
• involves the WIlbrand knee
• usually arcuate defect in the right eye and a superior temporal defect superiority in the other eye

Question 10

Arcuate scotoma in chiasmal disorders

Answer 10

Arcuate scotomas ending abruptly at the vertical meridian due to chasmal compression, a pattern that may result from a disturbance of a the crossing optic nerve fibers anteriorly in the optic chiasm

Question 11

Tilted disc VF defect

Answer 11

Does not respect the vertical midline

Question 12

Binasal VF defect

Answer 12

If you have bilateral carotid artery compression on each side of the chiasm

Very rare
Usually first suspected as glaucoma

Question 13

Optic disc findings in chiasmal disorders

Answer 13

Papilledema due to third ventricular compression by a stellar mass

Transverse “band” optic atrophy

Question 14

Transverse band optic atrophy in chiasmal disorders

Answer 14

• in each eye, ganglion cells and their axons degenerate in the blind nasal hemirretina, leading to a nasal wedge of optic atrophy
• fibers from the blind nasal half of the macula are similarly affected, resulting in a temporal wedge of optic atrophy
• the nerve fibers coming from “seeing” temporal macula and retina, entering the disc superiority and inferiorly, are preserved

Question 15

Hemifield slide phenomena

Answer 15

Assocaited with complete bitemporal hemianopsia

Esotropia: uncrossed, nasal fibers, only see 1 and 3

Exo: crossed, temporal, see 1,2,2,3

Question 16

Chiasmal field loss accompanied by an ocular motor palsy

Answer 16

Implies cavernous sinus involvement

Question 17

See saw nystagmus and chiasmal dirsoders

Answer 17

Can be a sign of chiasmal process, and sellar masses and trauma are the usual culprits

• almost all pateitns with acquired see saw nystagmus have wither a bitemporal hemianopsia or bilateral invovlemt now of the interstitial nuclei of Cajal (inC) in the mesencephalon
• patients with see saw nystagmus and chiasmal truama usually have a bitemproal hemianopsia
• pateitn with see saw nystagmus and midbrain or hemorrhage have no visual field loss

Question 18

Hypothalamic syndromes

Answer 18

Russels diencephalic syndrome

Precocious puberty

Question 19

Russel deuncephalic syndrome

Answer 19

• skinny
• young kids
• hyper
• lid retraction

Question 20

Precocious puberty

Answer 20

• seen in boys more than girls
• affected kids are tall for age and exhibit early gonadal maturation
• lesions typically lie in the floor of the third ventricle, posterior hypothalamus, tuber cinereum or median eminence

Question 21

The most common cause of chiasmal dysfucntion in adults

Answer 21

Pituitary ademonas

-benign

Question 22

Pituitary adenoma neuro ophthalmic symptoms and signs

Answer 22

Chiasmal visual field loss
-insidious and slowly progressive. The crossing inferonasal fibers are usually the first to be disturbed by upward growing adenoma

Question 23

Pituitary adenoma prognosis

Answer 23

Is excellent following surgical or medical decompression

Question 24

Pituitary apoplexy

Answer 24

Sudden visual loss due to rapid expansion of a pituitary adenoma into the suprasellar space and cavernous sinuses

Third nerve palsies are more common than IV and VI nerve deficits

Question 25

Craniopharyngiomas

Answer 25

Any age 
Benign 
Cystic 
Bitemporal hemianopsias but asymmetric and incomplete defects 
See saw nystag us may also be a finding

Question 26

Meningioma of the skull base

Answer 26

Pinaless progressive visual loss is a feature of almost all symptomatic suprasellar meningioma, and often it is the only manifestation

Question 27

Aneurysms

Answer 27

Asymmetric bitemporal hemianopsia

Question 28

Chiasmal apoplexy

Answer 28

Vascular malformations

Describe sudden vision loss due to an intrachiasmal hematoma

Question 29

Chiasmal/hypothalamic gliomas prognosis

Answer 29

Posterior chiasmal glioma have a worse visual prognosis than those with anterior chiasmal glioma

Question 30

Optic chiasmal gliomas in adult

Answer 30

Malignant

Question 31

Germ cell tumors

Answer 31

The symptoms triad of diabetes insipidus, visual loss, and hypopituitarism
Pretty malignant

Question 32

Miscellaneous growths of chaismal disorders

Answer 32

Epidermoids or dermoids 
Chiasmal metastases
Granular and related tumors 
Chiasmal neuritis 
Inflammatory masses (sarcoidosis is the most common one)

Question 33

Infections of chiasm

Answer 33

Very rare
TB meningitis
Pitutary abscesses
Cysticercosis

Question 34

Common things with chiasmal disroders

Answer 34

• monocular or bitemproal hemianopsia
• vision loss of any type assocaited with endocrine dysfunction
• the most common etiologies are compressive sellar masses
• endicrinopathy is the result of pituitary stalk or hypothalamic dysfunctions
• ocular motility abnornalities can result from lateral extension and involvement of the cavernous sinus