Transcript optic tract syndrome

Disorders of chiasm and retrochiasm
1. Anatomy
2. Clinical features
3. Pituitary adenomas
3. Craniopharyngioma
4. Meningioma
• the visual system consists of ( in order) :
The eye, especially the retina
The optic nerve
The optic chiasma
The optic tract ( the retrochiasm)
The lateral geniculate body
The optic radiation
Visual cortex
Visual association cortex
• The optic chiasm is located at the bottom of
the brain immediately below the
hypothalamus.
• The optic nerves from both eyes meet and
cross at the optic chiasm
• Information from the right visual field
travels in the left optic tract. And vice versa.
Each optic tract terminates in the lateral
geniculate nucleus (LGN) in the thalamus
Anatomy of chiasm and pituitary gland
Upper nasal fibres
Macular fibres
III rd ventricle
Craniopharyngioma
Lower nasal fibres
Optic chiasm
Diaphragma sellae
Posterior clinoid
Anterior clinoid
Pituitary gland
Dorsum sellae
• The sella turcica is adeep saddle shaped
depression in the superior surface of the
body of the sphenoid in which the pituitary
• gland lies.The roof of the selle is formed by
afold of dura mater which strech from
anterior to posterior clinoids (diaphragma
sellae).The optic nerve and chiasm lie above
the diaphragma sellae posteiorly the chiasm
is continuous with the optic tract.
Normal anatomical variations
Central - 80%
Prefixed - 10%
Postfixed - 10%
The following anatomical variations in the location of the chiasm may be important
1- Central chiasm. Present in about 80% of normals , is located above the sellae so that
expanding pituitary tumours will involve the chiasm first.
2-Prefixed chiasm .Present in about 10% of normals,is located more anteriorly,over the
tuberculum sellae ,so that pituitary tumours involvethe optic tract first.
3-post fixed chiasm. Present in about 10% of normals,is located more posteriorly, over
the dorsum sellae, so that pituitary tumours involve optic nerve first.
Lower nasal fibers .traverse the chiasm low and anterioly . They are therefore most
vulnerable to damage from expanding pituitary lesions ,so the upper temporal quadrants
of the visual fields are involved first.
2. Upper nasal fiber.traverse the chiasm high and posteriorly and therefor are invoved
first by lesions coming from the chiasm e.g . Craniopharyngioma
If the lower temporel quardants of the visual field are affected more than the upper .
apituitary adenoma is unlikely.
3.Macular fibers deccusate throughout the chiasm.
• Approximately 25% of brain
tumors occur in chiasmal area ,
almost half of these with an initial
complaint of visual loss.
• Main symptoms of chiasmal lesions :
Visual loss
Headache
Diplopia
Endocrine dysfunction
• Main visual signs of chiasmal lesion:
Decreased visual acuity ipsilaterally
Incongruous homonymous hemianopsia
ipsilaterally.
RAPD conralateral to the lesion.
• Most lesions involving optic tract are usually large enough
to involve the chiasm and optic nerve , thus producing an
optic tract syndrome.
• Retrochiasmal lesions characteristically have field defects
that respect vertical
• midline and visual acuity is not affected.
• Retrochiasmal lesions results binocular fi eld defect
involving contralateral space so both eyes manifest partial
or loss total visual hemifield opposite the side of
retrochiasmal lesion.such ahemianopia involving the same
side of visual space in both eyes is homonymous,in
contrast to chiasmal lesion which produce bitemporal
hemianopia ,heteronymous in which opposite side of visual
• Field are affected in each eye.
Visual field defect in chiasmal and
retrochiasmal lesions
Incongruous homonymous hemianopsia.congruous
refers to how closely the extent pattern of field
loss in one eye matches that of the other.so
identical field defects in either eye are highly
congruous while mismatching field defects in both
eyes are incongruous.
The more posterior the lesions, the more congruous the
visual field
Because as the optic radiations pass posteriorly ,fiberes from
corresponding retinal pointslies progressively closer
together
Lesions of the optic radiations do not produce optic atrophy
these because t hese fiberes are third order neurones that
originate in the lateral geniculate body. But lesions of the
optic tract may result in optic atrophy because the fibres in
the optic tract are the axons of the retinal ganglion cells.
main ophthalmic test for diagnosing
retrochiasmal lesions is:
“Visual field testing”
Pituitary adenomas
Cushing syndrome
ACTH
Chromophobe
PROLACTIN
Growth hormone
Amenorrhoea
Infertility
Galactorrhoea
Acromegaly
Gigantism
Hypoglandism
Impotence
Infertility
Gynaecomastia
Galactorrhoea
Visual field defects in pituitary adenomas
LE
RE
HM
CF
Anteriorly
Decussating fibres
are most vunerable
• Pituitary adenoma is the most common
primary intracranial tumour to produce
neuro-ophthamological features.
• Typically presented in the middle age with
• 1.Headache.
• 2. Visual syptoms usually have avery
gradual onset and may not be noticed by
the patient until well established.
Craniopharyngioma
•
•
Presents
In children with endocrine dysfunction
In adults with visual field defects
LE
RE
CF
HM
The posteriorly crossing
fibres are most vunerable
Craniopharyngioma
Meningioma
Typically affect middle-aged women
LE
RE
Junctional scotoma
Tuberculum Sella
meningioma
Sphenoid ridge meningioma
Olfactory groove meningioma