Pineal Gland

PINEAL GLAND, glandula pinealis (syn.: pineal body, corpus pineale, pineal gland, conarium, epiphysis, epiphysis cerebri), an unpaired organ, usually classified among the internal secretion organs, somewhat similar in shape to a compressed spruce cone (hence its name), reddish-brown in color, slightly nodular, located in the groove between the superior colliculi of the corpora quadrigemina under the thickened posterior end of the corpus callosum (tuber, s. splenium corporis callosi). In humans, its rounded apex faces backward, and its base, from which paired habenulae depart, passing into the striae medullares thalami optici, faces forward. The length of the pineal gland is up to 12 mm, width 8 mm, thickness 4 mm, and it weighs approx. 0.2 g. With age, on the surface of the gland, in the vascular plexuses, and in its depths, "brain sand" (acervulus cerebralis) is deposited in the form of yellowish granules of calcium carbonate and phosphate combined with an organic matrix; the gland is covered by a duplication of the pia mater, which easily detaches and penetrates into the fissure between the pallial and stem parts of the cerebrum (fissura cerebri transversa sup.). Due to the fact that the vascular roof of the third ventricle (tela chorioidea ventriculi III) is not attached to the free surface of the habenulae, invaginations (recessus supra- and infrapinealis) are formed above and below the pineal gland, and sometimes a remnant of the cavity (ventriculus pinealis) is preserved within it. In the developed state in humans, the connective tissue covering the pineal gland penetrates deep into the organ and divides it into lobules consisting of groups of polyhedral cells, neuroglia, blood vessels, nerve fibers, and cells containing brown pigment. Neither the specific granularity characteristic of glandular epithelium cells nor the arrangement of vessels peculiar to internal secretion organs is observed; subsequently, the entire tissue of the pineal gland turns into typical neuroglia rich in fibers. In a number of vertebrates, the pineal gland is a derivative of the rearmost of several folds appearing on the dorsal wall of the diencephalon, which transform in further development into peculiar vesicle-like protrusions on stalks, "epiphyses"; the anterior one gives rise to the not always constant paraphysis (paraphysis, Selenka) in the form of a wide pouch (whose epithelial walls give off rounded buds), developed, for example, in bird embryos amid the tent-like roof of the telencephalon. The so-called "parietal organ" (organon parietale) is present in reptiles and represents an elliptical vesicle, which constricts from the posteriorly located epiphysis; it is an initial eye-like organ having a retina and an optic nerve; a layer of connective tissue separates it from the epidermis. The pineal gland is absent in rays, crocodiles, armadillos, and some whales. Representatives of comparative anatomy are inclined to consider the pineal gland as a remnant of an epiphysial pair of eyes located behind the parietal pair, but this hypothesis is not sufficiently substantiated (Karpov). Only in mammals do epithelial cords develop from the embryonic epiphysis, breaking down into separate follicles, and the organ acquires the character of a gland with internal secretion (see Endocrine glands). The question of the development of the pineal gland in man has not yet been sufficiently studied. The greatest attention was paid to it by Krabbe (Krabbe, 1911) and Hoehstetter (Hoehstetter, 1923); a more recent study, performed on a larger amount of material, belongs to N. Turkevich, who, using the method of plastic reconstruction, produced 12 models from human embryos and fetuses. Turkevich notes the first traces of the appearance of the primordium in an embryo whose body length from crown to rump was 5.6 mm; in structure, it begins to resemble the pineal gland of an adult in a 350 mm fetus (i.e., approximately by the end of the 9th lunar month). On the completely flat surface of the roof of the diencephalon, a small, almost spherical bulge appears, into which a recess (“epiphysial”) invaginates from the side of the neural tube cavity; anterior and posterior lobes are formed from its epithelial wall; during further development, the constituent parts of the pineal gland fuse together; the lobes differ not only in the time of origin, but also in the course of development and structure. Thus, for example, the tissue of the posterior lobe around the time of the obliteration of the cavities previously existing in it resembles spongy tissue, which is not observed in the development of the anterior lobe. The difference in the development of the lobes indicates, in his opinion, a difference in their roots in phylogeny, their origin from various formations inherent in unknown distant ancestors of man, and the possibility of establishing homology between individual constituent parts of the human pineal gland and corresponding formations of vertebrates. In later stages of ontogenetic development, the pineal gland lengthens, its apex becomes rounded, the body changes its position, and deflects backward due to a change in the shape of the organ as well as the uneven growth of the surrounding brain parts. Physiological involution of the pineal gland occurs with the onset of puberty, but there are, however, assumptions that it is devoid of physiological significance and represents merely a rudimentary organ, a teratoid formation (see Apinealism).

By Kartooshyn. The physiology of the pineal gland, despite numerous studies, is still not sufficiently clarified. There is still no sufficiently clear idea whether the epiphysis is an internal secretion organ, or whether the metabolic and growth disorders observed in pathological or experimentally induced changes in the gland are caused by damage to nearby vegetative centers (see above). Removal of the epiphysis is a very difficult operation both due to the anatomical position of the gland and as a result of subsequent hemorrhage; yet in those cases where the removal of the gland was successful, the data on subsequent changes occurring in the experimental animal are contradictory among various authors (see Apinealism). In sexually mature animals, removal of the gland does not produce specific changes. Changes in females, even immature ones, are very indistinct. When the pineal gland is removed in immature males, they exhibit enhanced growth and enhanced development of both primary and secondary sexual characteristics. Significant hypertrophy of the gonads, both of the seminiferous tubules and of the interstitial tissue, is noted, but along with these clear data, a number of other experimenters (Lehmann and others) obtained no effect from pinealectomy or even obtained opposite data, namely, retardation in both somatic and sexual development (Demel on rams). The use of pineal gland extracts to induce phenomena of hyperpinealism has also failed to yield uniform, clear results. While a number of authors observed under the influence of subcutaneous and intravenous administration of aqueous extracts or feeding with dried epiphysis a delay in both somatic and sexual development (Del Priore, Pellizzi, Mac Cord and Allen), other authors either did not obtain any deviations or obtained acceleration of growth, and usually the gonads remained unchanged (Dana, Berkeley). However, it is possible that the acceleration of growth is due to the presence in the extracts of phosphoric acid, nitrogen, calcium, and other mineral substances that stimulate growth. Mac Cord, based on his experiments with feeding pineal glands to chickens, puppies, and guinea pigs, concluded that the syndrome of premature somatic and sexual development, usually attributed to insufficiency of the epiphysis, can arise as a result of hyperpinealism, and these phenomena appear particularly clearly if young animals are fed pineal glands taken from young animals themselves. Upon reaching a certain maximum of growth, further administration of the pineal gland ceases to produce an effect. Calvet, when transplanting the pineal gland subcutaneously (every other day for a month), obtained a significant delay in growth and puberty in rats. Consequently, if the pineal gland is considered an endocrine gland, it cannot yet be said with certainty on the basis of experiment whether the syndrome of early sexual and physical maturation is the result of hypofunction or hyperfunction of the epiphysis. The relationships between the pineal gland and other endocrine glands are likewise not fully clarified. After castration, premature atrophy of the epiphysis is sometimes observed. Removal of the thyroid gland causes both a decrease in weight and atrophy of the glandular tissue of the pineal gland and proliferation of neuroglia in animals and humans (Berblinger). These data are particularly interesting in connection with the involvement of the epiphysis in growth. A close connection between the adrenal glands and the epiphysis cannot be established despite the fact that the clinical picture of macrogenitosomia praecox is particularly close to that in hyperfunction of the adrenal glands. With atrophy of the thymus gland and pancreas, a decrease in the epiphysis is also observed. Pinealectomy leads to hypertrophy of the anterior lobe of the pituitary gland and an increase in the number of eosinophilic cells. Simultaneous transplantation of the anterior lobe of the pituitary gland and the epiphysis usually did not cause any consequences in young animals. Thus, a correlation seems to be outlined between the pineal gland, the pituitary gland, the gonads, and the thyroid gland. The correlation with the thymus and pancreas is significantly less clear. A number of authors believe that the regulatory connection between the pineal gland and the gonads is not direct, but is carried out through the pituitary gland (Calvet). It should also be noted that the substance of the epiphysis causes contraction of melanophores in tadpoles (Mac Cord, Allen) and milk secretion (Sharpey-Schafer).

By S. Zhulin. Pathological anatomy of the pineal gland. Studying the pathological morphology of the pineal gland, it is necessary to remember the physiological reorganizations of this organ in the form of age-related atrophy, deposition of calcareous concretions, nuclear excretion, and cyst formation; thus, not every cyst of the pineal gland is the result of a pathological process. Among the pathological processes developing against the background of general processes, one should dwell on vascular amyloidosis in general amyloidosis, their hyalinosis (admittedly, more often of a local nature), and arteriosclerosis. All these vascular changes occur in the presence of, but more often in the absence of, clinical manifestations. Banal degenerative processes are also observed in general infections, especially on the part of nerve cells. Circulatory disorders in the pineal gland are usually associated with some external conditions for it, sometimes in the form of cerebral circulation disorders associated with a growing tumor, and sometimes with circulation disorders throughout the organism. In both cases, venous stagnation takes place, often accompanied by enlargement of the organ. More severe changes in the form of hemorrhages usually develop in hemorrhagic diatheses, in typhoid fever, and the hemorrhages can cause significant destruction up to the formation of cysts from softening. Vascular thrombosis of the pineal gland usually develops in already altered vessels, most often in sclerosed ones. Inflammatory processes of the pineal gland usually do not develop in isolation. Of the non-specific ones, only purulent ones are known in purulent meningitis, often with the formation of abscesses (Birch-Hirschfeld). Tuberculosis of the pineal gland is known in general miliary tuberculosis, in tuberculous meningitis. Sometimes organ-type tuberculosis also takes place, as for example in the case of Schlagenhaufer, where Simmonds' cachexia syndrome was observed with isolated tuberculosis of the pituitary gland and epiphysis. Syphilis of the epiphysis occurred with multiple gummas of the brain; specific changes are described in congenital syphilis, as well as in the second period of acquired syphilis. Finally, accumulations of plasma cells and hemorrhages in the pineal gland in progressive paralysis are described (Josephy, Krabbe, Lavastine). Among other diseases involving the pineal gland, one must remember systemic sclerosis of the endocrine glands with sclerosis of the epiphysis as part of this system (Falta). Aplasia and hypoplasia of the epiphysis can occur, but their diagnosis requires a thorough examination of the brain. In particular, the pineal gland can be displaced and embedded in the thickness of the adjacent brain tissue without being aplastic. If the pineal gland is absent or reduced in internal hydrocephalus, it is not always easy to decide whether this is atrophy or hypoplasia or even complete aplasia. According to the opinion of Askanazy and Brock, one can speak of hypoplasia with complete certainty only when the pineal gland is sharply reduced, but has preserved all its inherent cellular elements. Aplasia and hypoplasia of the pineal gland can be isolated or coincide with microcephaly; however, with the latter, often no changes in the pineal gland are borne. Tumors of the pineal gland are much more often primary. Metastases in the pineal gland are described only a few times: in cancer of the mammary gland, pancreas, melanoma, and round-cell sarcoma (Foerster, Gierke, Askanazy, Walter). Primary tumors are incomparably more common in men—91.4%. Due to the variety of cellular forms making up the pineal gland, tumors of very different histological structure are found in it. Expressing an opinion on the nature of a pineal tumor by its macroscopic appearance is extremely difficult; a histological analysis is necessary, and besides, tumors of adjacent parts of the brain can simulate a tumor of the epiphysis. Among tumors, a tumor of the fibrous type is known as a great rarity. Hirtz described a myoma. Tumors with calcareous concretions of the psammoma type are more common. Sometimes sarcomas of the fibro-sarcoma, angiosarcoma, psammosarcoma type are observed. Lymphosarcomas have not been described. Primary melanoma of the epiphysis from its neuroepithelial part has been described twice. From the elements of nerve tissue embedded in the epiphysis, various types of gliomas develop. Adenomas (Berblinger's pinealomas), usually having an alveolar structure, arise from epithelial cells. Malignant adenomas and finally carcinomas with destructive growth are described. One of the frequent types of tumor of the pineal gland is teratomas, which is associated with the conditions of formation of the epiphysis, and both teratomas and teratoid tumors are spoken of. Berblinger cites 47 cases of teratomas, of which 25 are teratomas and 22 are teratoid tumors. Cases of dermoid tumors are known.

By N. Kraevsky. In clinical pathology, as well as in experimental research, the role of the pineal gland as an endocrine organ is far from clear. Among pathological processes in the clinic, either aplasia of the epiphysis or its tumor-like degenerations (sarcomas, teratomas, psammomas, etc.—see above) are known, and very often the disease of the pineal gland proceeds completely unnoticed and is an accidental finding at autopsy. Of the symptoms caused by a pineal tumor, a part is due to its localization and coincides with the symptoms of tumors of the corpora quadrigemina (see Brain, symptomatology of diseases), while another part consists of trophic disorders, which are possibly caused by damage to the epiphysis as an endocrine gland, and partly by the compression of the vegetative centers of the third ventricle. Most authors believe that in diseases of the pineal gland, endocrine disorders occur only at an early age and predominantly in boys. If the process has arisen after the onset of puberty, when the epiphysis regresses and transfers its role of regulating the sexual system to the hypophysis, the tumor-like disease proceeds already as a brain tumor with a definite localization. Endocrine disorders observed in lesions of the epiphysis are usually expressed in the syndrome of "macrogenitosomia" (Pellizzi) or praecoxitas psychosomogenitalis (Askanazy) (see Macrogenitosomia praecox). In a number of cases, with tumors of the epiphysis, marked obesity, glycosuria, and diabetes insipidus were noted. However, it must be thought that these symptoms are caused not by hyperfunction of the pineal gland, but rather by damage to the vegetative centers of the third ventricle. Bailey points out that pinealomas often proceed without any disturbances on the part of the sexual system, and considers the question of the role of the epiphysis in the occurrence of macrogenitosomia to be unclarified. The following clinical forms of pineal gland disease are distinguished: 1) a latent form, which is merely a finding at autopsy; 2) an acute form (pseudomeningitis according to Sezary), usually proceeding lightning-fast (from 24 hours to 2 weeks), with the meningeal symptoms being most marked; 3) a masked form, which can proceed (as, for example, in the case of Verger) as classic progressive paralysis; and 4) forms depending on sex and age: a) in newborns and infants, where along with a clearly expressed somatic picture of pineal disease, there are usually observed hydrocephalus, convulsions, drowsiness, hypothermia, and other symptoms of third ventricle involvement; b) in adult men and women, in whom the endocrine symptom complex is absent and there are only phenomena of a brain tumor; c) in girls before puberty; recent statistical data show that in such a case a fully developed Pellizzi symptom complex can be encountered; d) in boys, in whom the classic picture of macrogenitosomia was described. From the standpoint of therapy, it must be pointed out that as yet neither treatment with epiglandol, nor roentgenotherapy, nor surgical intervention has given encouraging results.

By S. Zhislin. At the present time, comparing data obtained in the clinic and in pathological-anatomical study, it must be recognized that morphologically different processes may underlie one and the same clinical manifestation of pineal gland disease. In particular, the most diverse tumors, teratomas, adenomas, dermoids, etc., in children and mainly in boys, can be accompanied by the same symptom complex of premature puberty and, conversely, sometimes the very same tumors, and also in children, do not give a specific clinical picture, but only the clinical picture of a brain tumor. Despite the existing indications by Askanazy and others on the possible role of specific products produced by the tumor itself in the development of a certain clinical picture, Kohn puts forward the thesis that any process accompanied by the destruction of the pineal tissue can give the same symptom complex of the loss of function of the pineal gland.