Hypothalamus Nuclei

The extent of optic atrophy does not correlate with the extent of acuity loss. Even bilateral optic atrophy does not always rule out a possible recovery of both Snellen acuity and visual field. However, disc pallor does suggest that the recoverability of optic nerve and chiasmal function after surgical decompression is limited.

Development of papilledema caused by chiasmal/perichi-asmal disease is very uncommon but does occur when the mass compresses and obstructs the foramina of Monro. This can happen when a large mass compresses and invades the third ventricle from below. Suprasellar masses like the craniopharyngiomas (particularly in children) are more likely to cause papilledema before the atrophy sets in. Combined appearances of both edema and atrophy in the optic discs are a good indication that both acute and chronic disease processes are at play.

When a tumor is suspected in the chiasmal region, it helps to inquire about nonvisual symptoms that suggest damage to the hypophysis, e.g., diabetes insipidus via compression of the supraoptic and paraventricular nuclei of the diencephalon (■ Fig. 12.4). This alters the level of antidiuretic hormone (ADH), causing excretion of dilute urine in large volumes, and a persistent thirst with a marked increase in water consumption. Diabetes insipidus is particularly common in patients with craniopharyngiomas, glio-mas of the hypothalamus, and germinomas. Disturbances of pituitary function because of compression of the adeno-hypophysis are common and are more likely to be encountered in women than in men. A slowly developing insufficiency of the anterior lobe of the pituitary gland is usually associated with a drop in gonadotropic hormones, causing amenorrhea in women of childbearing age. This is often a presentation of chiasmal disease, although it is often first discovered by endocrinologists. A comparable hormonal syndrome occurs in men, with a loss of libido and erectile function, which is frequently assumed nonpathological. The tumors in men are on average larger than are those in women. This holds true for prolactinomas, which in women cause a galactorrhea and amenorrhea, and which in men usually cause a primary loss of libido and erectile function.

Hypothalamic Nuclei
Fig. 12.4. Diagrammatic view of the hypothalamic nuclei located superior to the chiasm (the supraoptic nucleus and the paraventricular nucleus), which are the first to be compressed by expanding tumors arising in the midline from beneath the chiasm (modified after Netter)

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  • mackenzie
    How is optic nerver decompressed?
    8 years ago
  • Kevin
    Where is the hypothalamus located?
    8 years ago

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