In humans, a regular feature of pineal pathology is the accumulation of calcareous deposits in structures termed acervuli (“brain sand”). These have a more complex composition than simply calcium; they are actually composed of carbonate-containing hydroxyapatite that is linked to calcium and other metals. A review of the mineralization of the pineal can be found in the text by Haymaker and Adams. These concretions are formed within vacuoles of pinealocytes and released into the extracellular space. The mineralization of the pineal body provides a convenient marker for its position in plain films and other neuroimaging studies.
It is of significance that pineal tumors do not secrete melatonin; in contrast, the loss of melatonin may be used as a marker for the completeness of surgical pinealectomy. Most interest in the past several years has centered on melatonin as a soporific agent and its potential to reset sleep rhythms. Its concentration in depressive illnesses, especially in the affected elderly, is also decreased. The subject of pineal tumors is discussed later and is contained in Chap. 31, with discussion of other brain tumors.
Hypothalamic syndromes may either be global, in which all or many hypothalamic functions are disordered, often in combination with signs of disease in contiguous structures, or they may be partial, in which there is selective loss of hypothalamic–hypophyseal function attributable to a discrete lesion of the hypothalamus and often resulting in a deficiency or overproduction of a single hormone.
A variety of lesions can involve and impair all or a large part of the hypothalamus. These include inflammatory disorders including sarcoidosis and neoplastic disorders. The hypothalamus is involved in approximately 5 percent of cases of sarcoidosis, often in combination with facial palsy and hilar lymphadenopathy but sometimes as the primary manifestation of the disease (see Fig. 31-2). Infundibuloneurohypophysitis is a cryptogenic inflammation of the neurohypophysis and pituitary stalk, with thickening of these parts by infiltrates of lymphocytes and plasma cells (Imura et al). Histiocytosis X is a group of diseases comprising Letterer-Siwe disease, Hand-Schüller-Christian disease, and eosinophilic granuloma that usually implicates multiple organs, especially the hypothalamus, neighboring structures, and the leptomeninges. Histopathologic analysis demonstrates proliferating histiocyte. The obscure infiltrative and inflammatory condition,
Erdheim-Chester disease, can also involve this region, and usually involves the orbit, sometimes with proptosis, but is primarily a bone disease.
Tumors that involve the hypothalamopituitary axis include metastatic carcinoma, lymphoma, craniopharyngioma, and a variety of germ-cell tumors. The last category (reviewed by Jennings et al) includes germinomas, teratomas, embryonal carcinoma, and choriocarcinoma. They develop during childhood, tend to invade the posterior hypothalamus, and are accompanied in some instances by an increase in serum alpha-fetoprotein or the beta subunit of chorionic gonadotropin. A unique syndrome of gelastic epilepsy is caused by a hamartoma of the hypothalamus (see Chap. 15). Irradiation for tumors in the hypothalamic region can also contribute to hypothalamic dysfunction (Mechanick).
Disorders of Sodium and Fluid Homeostasis