|Neuro-ophthalmology: Case six|
This sixty five year old man was on timoptol 0.25% bd for bilateral low tension glaucoma. His recent visual field showed deterioration in both eyes. A MRI was requested and is shown as above.
a. What does the MRI scan show?The MRI scan which is T2 weighted shows enlargement of the pituitary gland with superior extension
b. What ocular signs and symptoms may be present?Ocular signs:
- visual field defect: this depends largely on the location of the optic chiasm. In the majority of patient (80%) the optic chiasm is situated directly above the pituitary gland and therefore upward extension results in bitemporal hemianopia with the superior field more involved than the inferior. In 15% of the population, the optic chiasm is prefixed (anterior to the pituitary gland) and compression causes incongruous homonymous hemianopia or quadrantinopia. In 5% of the population, the chiasm is post-fixed (posterior to the pituitary gland) and compression causes either monocular field loss or junctional scotoma (one blind eye and temporal field loss in the other)
- optic atrophy: bitemporal hemianopia causes classical bow-tie atrophy due to loss of nerve fibres nasal to the disc and in the papillomacular region.
- extra-ocular muscle palsy: lateral extension of the tumour can cause extra-ocular muscle palsy usually beginning with third nerve
- see-saw nystagmus: characterized by synchronous depression and extorsion of one eye and elevation and intorsion of the opposite eye
- papilloedema: rarely encountered
- decreased visual acuity: progressive loss of central visual acuity and temporal visual field
- abnormal depth perception with close work: convergence results in crossing of the blind temporal hemifields; and therefore image posterior to fixation will fall on the blind nasal retina. This causes difficulty with tasks like using precision tools or threading needle
- diplopia which may be vertical or horizontal: this results from hemifield slide phenomenon. This is caused by the loss of overlapping between the temporal field of one eye and the nasal field of the other. This overlap is important in maintaining ocular alignment and fusion of images.
c. What extra-ocular signs and symptoms may be present in this patient?These depend on the nature of the tumour:d. What treatment options are available?
1. Non-secreting tumour may produce no signs or causes hyposecretion of hormones resulting in hypopituitarism with impotence, tiredness, slow action and thought, hypotension, pallor and loss of body hair.
2. Secreting tumour produces signs and symptoms according to the hormone secreted and this may be:
- impotence and galactorrhea in prolactinoma (common)
- acromegaly with growth hormone secretion (common)
- Cushing's syndrome with ACTH secretion (rarely causes enlarged pituitary)
- hyperthyroidism with thyrotropic hormone secretion (rare and seldom causes enlarged pituitary)As the pituitary tumour causes compression of the optic chiasm, tumour reduction or removal is important to prevent progressive field loss. This can be achieved with:
- medical: bromocriptine is useful in treating and reduces the size of prolactinoma.
- surgery: which may be transphenoidal or transfrontal
- radiotherapy: using external beam or yttrium implantation
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