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A Sample Case: A child of 6 complained of headache and was vomiting. The mother described the child as constantly urinating. Neurologic examination showed mild papilledema and increased intracranial pressure but otherwise most of the neurologic examination, motor and sensory, was normal. Examination of the visual fields however revealed a bitemporal hemianopsia. X-ray studies revealed a midline, suprasellar, calcifying tumor.

Explanation -

Bitemporal hemianopsia is usually due to midline pressure on the optic chiasm. Headache, vomiting and papilledema are often due to increased intracranial pressure which may accompany space-taking lesions. Frequent urination may signal a decrease in antidiuretic hormone which is made in the supraoptic and paraventricular nuclei of the anterior hypothalamus. (It may also indicate a lesion of the posterior lobe of the pituitary.)

Craniopharyngiomas arise from the ectodermal remnants of Rathke's pouch. Most hypothalamic tumors occur in the midline and hence when they present with visual symptoms they impact the crossing fibers in the optic chiasm.