Pineal gland tumors

Focusing our attention on the serotonin branch of Figure 20.21, it is seen that the initial hydroxylation reaction requires tetrahydrobiopterin, which was introduced in Chapter 16 and is discussed further here. Serotonin per se is a neurotransmitter, and it can give rise to melatonin in the pineal gland. Melatonin is synthesized at night, and is believed to be associated with the phenomenon of circadian rhythms. Serotonin is metabolized to 5-hydroxyindoleacetic acid, which is excreted in the urine. Normal 5-hydroxyindoleacetic add excretion is about 7 mg/day, whereas in carcinoid tumor patients, this may be as high as 400 mg/day. Carcinoid is an intestinal tumor that may metastasize into the liver. 

Thymic regrowth and reactivation of thymic endocrine activity may occur in older animals by different endocrinological or nutritional manipulations than in young animals. Intrathymic transplantation of pineal gland or treatment with melatonin, implantation of a growth hormone (GH) secreting tumor cell line or treatment with exogenous... 

Tumors of the pineal gland include parenchymal neoplasms (pineocytomas, pineoblastoma, and pineal parenchymal tumor of intermediate differentiation). 

Most primary tumors of the pineal gland originate from pineocytes, which represent modified neurons similar to retinal photoreceptor cells.Pineocytomas are typically positive for NSE, synaptophysin, neurofilament proteins, tan protein, and microtubule-associated protein-2 (MAP2) (Fig. 10.5). GFAP and S-100 protein are present in 75% and 83% of cases, respectively. 

Perentes E, Rubinstein LJ, Herman MM, et al. S-antigen im-munoreactivity in human pineal glands and pineal parenchymal tumors A monoclonal antibody smdy. Acta Neuropathol (Berl). 1986 71 224-227. 

Pineoblastoma resembles medulloblastoma (Fig. 20.38 see Fig. 20.21) except for its origin in the pineal gland (see Table 20.8). Fibrillary rosettes may be evident and are more common than Flexner-Wintersteiner rosettes. Synaptophysin is most useful in identifying neuronal differentiation in these tumors (see Fig. 20.38A) because NF immunoreactivity is often negative (Box 20.3). Some tumors express retinal-S antigen. It would be interesting to know whether this sight-specific marker is more common in pineoblastomas than in other medulloblastomas. 

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