Optic chiasm

Review the available diagnostic data to determine pituitary tumor size and location. Determine if the patient has a coexisting prolactin-secreting tumor. Determine if the tumor extends toward the optic chiasm or if it is continuous on the optic tracts. 

Figure 12.3 Sections of rat brain at 0.2 mm anterior to bregma (B + 0.2), and 0.3 and 0.8 mm posterior (B - 0.3, B - 0.8), showing areas relevant to adenosine influences on sleep induction. HDB, horizontal diagonal band MCPO, magnocellular preoptic nucleus VLPO, ventrolateral preoptic nucleus ac, anterior commissure ox, optic chiasm.

The control of metabolism, growth, and reproduction is mediated by a combination of neural and endocrine systems located in the hypothalamus and pituitary gland. The pituitary weighs about 0.6 g and rests at the base of the brain in the bony sella turcica near the optic chiasm and the cavernous sinuses. The pituitary consists of an anterior lobe (adenohypophysis) and a posterior lobe (neurohypophysis) (Figure 37-1). It is connected to the overlying hypothalamus... 

In anticipatory response to these vital signals denoting energy and information availability to mammals, the brain has designed a clock for itself. Tinkered up from the biochemical rhythmicity of metabolic processes that change direction as temperature rises and falls, the mammalian circadian clock has come to be independent of temperature and it has been sequestered in two small nuclei sitting in the hypothalamus just above the optic chiasm. Unbeknownst to us, this clock controls the ebb... 

Figure 2.9 Path from the retina to the visual cortex. On its way to the lateral geniculate nucleus, some axons cross at the optic chiasm. Information from the right half of the visual field is processed inside the left hemisphere of the brain. Information from the left half of the visual field is processed inside the right hemisphere. (Reproduced from Semir Zeki. A Vision of the Brain. Blackwell Science, Oxford, 1993, by permission of Blackwell Science, UK.)...

Tissue cross-reactivity studies are required by FDA for monoclonal antibody products to determine if the product binds to target and/or nontarget tissues. They are also performed for nonmonoclonal biopharmaceuticals if warranted. For example, ARANESP was tested in a human tissue panel ex vivo to determine if it bound to nontarget tissues or cross-reacted with related cytokine receptors. These studies are also used to explore known or potential clinical adverse safety events (i.e., mechanism of toxicity). For example, one patient in a Raptiva study developed unilateral hearing loss. This finding was further evaluated by cross-reactivity studies with human optic chiasm, acoustic nerve, and inner ear tissues. 

Fig. 1. Location of dopaminergic perikarya (Au-A15) are depicted schematically on frontal sections (B-F) through the diencephalon of the rat. Section A is a sagittal view of the rat brain depicting the rostrocaudal location of frontal sections B-F. Abbreviations AH, anterior hypothalamus ARC, arcuate nucleus BST, bed nucleus of the stria terminalis f, fornix ic, internal capsule inf, infundibulum me, median eminence mt, mamillothalamic tract OC, optic chiasm ot, optic tract PH, posterior hypothalamus PIT, pituitary gland PeV, periventricular nucleus PVN, paraventricular nucleus RCH, retrochiasmatic area SON, supraoptic nucleus VMN, ventromedial nucleus ZI, zona incerta.

The posterior communicating artery is the next artery to arise from the internal carotid artery and passes back to join the first part of the posterior cerebral artery, so contributing to the circle of WiUis. Tiny branches supply the adjacent optic chiasm, optic tract, hypothalamus, thalamus and midbrain. 

The LGN and cortical areas exist in duplicate in the two halves of the brain. Each deals with one half of the visual world the optic nerves from the two eyes meet in a structure called the optic chiasm, where fibers from the tw o nasal retinas cross over to combine with those from the temporal retina of the fellow eye consequently each LGN and cortical hemisphere receive visual information from Cw o corresponding retinal halves on their own side, and thus from the contralateral half of the visual field. 

Berry, M., Carlile, J., Hunter, A., and Sievers, J., Optic nerve regeneration after intravitreal peripheral nerve implants. Behaviour of axons regrowing through the optic chiasm into the optic tracts, J. Neurocytol., 26, 1998, in press. 

The patient may complain of symptoms related to local effects of the prolactin-secreting tumor, such as headache and visual disturbances, that result from tumor compression of the optic chiasm. 

The optic nerve head is the portion of the optic nerve observed in the fundus formed by the meeting of all the retinal nerve fibers. The lamina cribrosa is a thin sieve-like membrane composed of neuroglia and connective tissue that bridges the posterior scleral foramen and is continuous with the choroid and the deepest third of the sclera. Fiber bundles of the optic nerve pass through the perforations of the lamina cribrosa toward the optic chiasm. Because glycosaminoglycans and... 

Clinical evidence, lesion, and stimulation studies all point toward the participation of vitally important neural sites in the control of saccades, including the cerebellum, superior colliculus (SC), thalamus, cortex, and other nuclei in the brain stem, and that saccades are driven by two parallel neural networks [Enderle, 1994, 2002]. From each eye, the axons of retinal ganglion cells exit and join other neurons to form the optic nerve. The optic nerves from each eye then join at the optic chiasm, where fibers from the nasal half of each retina cross to the opposite side. Axons in the optic tract synapse in the lateral geniculate nucleus (a thalamic relay), and continue to the visual cortex. This portion of the saccade neural network is concerned with the recognition of visual stimuli. Axons in the optic tract also synapse in the SC. This second portion of the saccade neural network is concerned with the location of visual targets and is primarily responsible for goal-directed saccades. 

Macroadenomas (>1 cm) occupy the pituitary fossa and may cause visual abnormalities when they put pressure on the optic chiasm. Macroadenomas also tend to invade the cavernous sinus and erode the bony floor. The extent of the tumor can be determined by means of contrast-enhanced MR imaging. 

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