The pituitary gland is situated in the center of the brain, about 10 cm behind the nose, along a virtual line between the ears. In spite of its small size – about the size of a cherry-pit – it is very important. The pituitary gland is the superior ductless gland of the body and produces several different hormones which influence our growth, the functionality of our thyroid gland and our adrenal cortex.
A system in disorder
If a tumor develops from the cells of the pituitary gland, the tumor itself may start to produce hormones and unbalance the complete hormonal system. Not every pituitary tumor produces hormones, but it may exert pressure on the pituitary gland, thereby interfere with its normal hormone production and results in hormone deficiency.
If a tumor reaches a certain size and applies pressure to the neighboring brain, it may trigger severe headaches or blurry vision and visual field loss. These two symptoms together are a prompt for many physicians to order an MRI that would then show the tumor. A hormone check is also performed.
Vision impairments and visual field loss
Positioned directly above the pituitary gland is the “Chiasma opticum“, the cross point of the right and left optic nerves. All the nerve fibers that transport visual information from the right and the left eye to the visual cortex in the brain meet at this point. The two bundles of nerve fibers (coming from the right and the left eye) are divided in two halves; one half stays at the same side of the brain, one half crosses over to the other brain half. So one half of the nerve bundles of both eyes become part of the right visual pathway to the visual cortex and one half becomes part of the left visual pathway.
When a tumor applies pressure exactly to the Chiasma Opticum area this may result in heteronymous hemianopia. As opposed to a more frequent homonymous hemianopia with visual field loss either to the right side or the left side of EACH eye, heteronymous hemianopia affects either both outer peripheral halves of the visual field (bi-temporal hemianopia) or both inner halves of the visual field (bi-nasal hemianopia).
Left eye visual field Right eye visual field
Bi-temporal Hemianopia after damage at the chiasma opticum to the right nerve fiber bundle of the left optic tract (affecting the left eye’s vision to the far left) and the left nerve fiber bundle of the right optic tract (affecting the right eye’s vision to the far right).
Bi-nasal Hemianopia after damage at the chiasma opticum to the left nerve fiber bundle of the left optic tract (affecting the left eye’s vision to right, the nasal visual field) and the right nerve fiber bundle of the right optic tract (affecting the right eye’s vision to the left, also the nasal visual field). This can lead to blurry vision and to problems with spatial perception.
Intact visual field
Visual field defect to each eye’s periphery = bi-temporal Hemianopia
Bi-temporal Hemianopia is visual field loss of both temporal, peripheral parts of the visual field.
A pituitary tumor typically grows very slowly, which is why visual disorders also develop slowly and often take a long time to have an impact on daily life.
Activities of daily life that can be affected:
- Going out
- Reading
- Grooming
- Walking
- Watching TV
- Socializing
- Enjoying hobbies
For further information on pituitary tumors click the following link:
http://www.glandula-online.de/fileadmin/informationsmaterial_broschueren/hypophysentumoren.pdf
The symptoms often regress with successful tumor treatment.
However, if symptoms like heteronymous hemianopia remain even months after the treatment, Vision Restoration Therapy might be able to help.
Written By: Sigrid Kenkel
Resources:
www.hirntumorhilfe.de/projekte/oeffentlichkeitsarbeit/welthirntumortag/
http://www.glandula-online.de/fileadmin/informationsmaterial_broschueren/hypophysentumoren.pdf
http://flexikon.doccheck.com/de/Bitemporale_Hemianopsie
Neurochirurgie – eine Einführung von Michael Schirmer, Urban&Schwarzenberg Verlag, 7. Auflage
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