SECTION VII THE NERVOUS SYSTEM Acromegaly with Visual Field Defect A 35-yearold mn comes to his physician because of changes in his appearance. His hands and feet have been growing.and his brow and chin are also becoming larger. On exanination the patient did not see the fingers of the examiner when they were moved in either superior temporal visual field.Detailed visual field examination by an ophthalmologist revealed a visual field defect in both temporal fields,but the defect was more complete in the superior rather than in the inferior quadramts. The patient was referred to a neurosurgeon for treatment. 1.What is the most likely cause of the changes in the patient's appearance? 2.What bornone is being secreted in excess? 3.What type of visual field defect did the patient have? 4.What caused the visual field defect?why was the defect nore complete in the superior rather than in the inferior toaporal quadrants? ANSVER 1.The enlargement of the hands,feet,and facial prominences is typical of acronegaly.which is caused by hyperactivity of the acidophil cells of the anterior pituitary gland.Hypersecretion may be caused by the development of an acidophil turor.In younger individuals.whose norral bone growth has not been completed,a similar hyperactivity of the acidophils can produce pituitary gicantisn. 2.The bormone involved is the growth hormone. 3.The visual field defect is called a bitemporal hemianopsia:that is,the defect is in both terporal visual fields (bitemporal),and blindness occurs in half of the visual field (hemianopsia).This visual defect should be distinguished from binasal hemianopsia,a rare condition in which the visual field defect is in the
SECTION VII THE NERVOUS SYSTEM Acromegaly with Visual Field Defect A 35-year-old man comes to his physician because of changes in his appearance. His hands and feet have been growing, and his brow and chin are also becoming larger. On examination the patient did not see the fingers of the examiner when they were moved in either superior temporal visual field. Detailed visual field examination by an ophthalmologist revealed a visual field defect in both temporal fields, but the defect was more complete in the superior rather than in the inferior quadrants. The patient was referred to a neurosurgeon for treatment. 1. What is the most likely cause of the changes in the patient's appearance? 2. What hormone is being secreted in excess? 3. What type of visual field defect did the patient have? 4. What caused the visual field defect? Why was the defect more complete in the superior rather than in the inferior temporal quadrants? ANSWER 1. The enlargement of the hands, feet, and facial prominences is typical of acromegaly, which is caused by hyperactivity of the acidophil cells of the anterior pituitary gland. Hypersecretion may be caused by the development of an acidophil tumor. In younger individuals, whose normal bone growth has not been completed, a similar hyperactivity of the acidophils can produce pituitary gigantism. 2. The hormone involved is the growth hormone. 3. The visual field defect is called a bitemporal hemianopsia; that is, the defect is in both temporal visual fields (bitemporal), and blindness occurs in half of the visual field (hemianopsia). This visual defect should be distinguished from binasal hemianopsia, a rare condition in which the visual field defect is in the
nasal half of the visual fields of both eyes,and fron homonynous hemianopsia,a more common comdition in which the defect is in correspoeding halves of the visual fields of the two eyes (nasal visual field of oee eye and temporal visual field of the other eye）. 4.Visual field defects in both eyes can be produced by restricted lesions of the risual pathways:this occurs at pathway levels at which the nerve fibers that carry visual information from both eyes are close to each other.This level would be at the optic chiasm and more centrally.The axons of retinal ganglion cells in the nasal halves of the retinas project through the optic nerve and then cross in the optic chiasn to enter the contralateral optic tract.The axons of retinal gangl ion cells in the temporal halves of the retinas do not cross,but instead they course from the optic nerve along the lateral aspect of the optic chiasm to enter the ipsilateral optic tract.Retinal ganglion cells in the nasal halves of the retinas are responsible for vision in the temporal visual fields (because light from a teaporal visual field crosses through the leas and strikes the nasal half of the retina).Conversely.retinal ganglion cells in the terporal retinas signal inages in the nasal visual fields.Danage to the niddle of the optic chiasn,as can be produced by a pituitary tumor,can interrupt the crossing axons froa the two nasal hemiretinas,thereby producing a biteaporal hemianopsia.Furthernore,the axons on the undersurface of the optic chiass are from the lower retinas.Hence a pituitary tumor will disturb vision first in the superior temporal quadrants of the visual fields.Pressure on the lateral aspeets of the optic chiasm can produce a binasal hemianopsia (e.g.because of bilateral aneurysms of the internal carotid arteries). Homonynous hemianopsias are produced by lesfons of the optic tract,lateral geniculate nucleus,optic radiation.or visual cortex on one side. Because of the partial decussation of the visual pathway in the optic chiasm, the components of the visual pathsay on one side behind the optic chiasn are responsible for vision in the contralateral visual field.Therefore a lesion that completely interrupts the visual pathway at this level will cause a visual field
nasal half of the visual fields of both eyes, and from homonymous hemianopsia, a more common condition in which the defect is in corresponding halves of the visual fields of the two eyes (nasal visual field of one eye and temporal visual field of the other eye). 4. Visual field defects in both eyes can be produced by restricted lesions of the visual pathways; this occurs at pathway levels at which the nerve fibers that carry visual information from both eyes are close to each other. This level would be at the optic chiasm and more centrally. The axons of retinal ganglion cells in the nasal halves of the retinas project through the optic nerve and then cross in the optic chiasm to enter the contralateral optic tract. The axons of retinal ganglion cells in the temporal halves of the retinas do not cross, but instead they course from the optic nerve along the lateral aspect of the optic chiasm to enter the ipsilateral optic tract. Retinal ganglion cells in the nasal halves of the retinas are responsible for vision in the temporal visual fields (because light from a temporal visual field crosses through the lens and strikes the nasal half of the retina). Conversely, retinal ganglion cells in the temporal retinas signal images in the nasal visual fields. Damage to the middle of the optic chiasm, as can be produced by a pituitary tumor, can interrupt the crossing axons from the two nasal hemiretinas, thereby producing a bitemporal hemianopsia. Furthermore, the axons on the undersurface of the optic chiasm are from the lower retinas. Hence a pituitary tumor will disturb vision first in the superior temporal quadrants of the visual fields. Pressure on the lateral aspects of the optic chiasm can produce a binasal hemianopsia (e.g., because of bilateral aneurysms of the internal carotid arteries). Homonymous hemianopsias are produced by lesions of the optic tract, lateral geniculate nucleus, optic radiation, or visual cortex on one side. Because of the partial decussation of the visual pathway in the optic chiasm, the components of the visual pathway on one side behind the optic chiasm are responsible for vision in the contralateral visual field. Therefore a lesion that completely interrupts the visual pathway at this level will cause a visual field
loss on the opposite side:for example,a lesion that interrupts the visual pathway on the left side hehind the optic chiasms will cause a visual field loss in the nasal visual field of the left eye and of the temporal visual field of the right eye. Incomplete lesfons may cause quadrantal visual field defects.These vill also be homonymous (i.e.,occupy the corresponding parts of the visual fields of hoth eyes). For example,a lesion that interrupts Meyer's loop in the left temporal lobe (which carries signals fron the lower retinas)will result in a superior right homonynous quadrantanopsia
loss on the opposite side; for example, a lesion that interrupts the visual pathway on the left side behind the optic chiasms will cause a visual field loss in the nasal visual field of the left eye and of the temporal visual field of the right eye. Incomplete lesions may cause quadrantal visual field defects. These will also be homonymous (i.e., occupy the corresponding parts of the visual fields of both eyes). For example, a lesion that interrupts Meyer's loop in the left temporal lobe (which carries signals from the lower retinas) will result in a superior right homonymous quadrantanopsia