pineal

The pineal gland, also known as the epiphysis cerebri, is a small endocrine organ located deep in the brain. It sits in the epithalamus, between the two thalami, near the posterior aspect of the third ventricle and close to the habenular region. Despite its small size, it plays a distinctive role in neuroendocrine signaling.

Anatomically, the gland is composed mainly of pinealocytes, supportive glial cells, and a dense capillary network. It frequently develops calcifications with age, which are commonly visible on imaging studies. The pineal tissue is richly vascular and exhibits neuroendocrine properties rather than a conventional neural relay center.

The principal function of the pineal gland is the production and secretion of melatonin, a hormone that helps regulate circadian and seasonal rhythms. Melatonin synthesis rises in darkness and decreases with light. Light information is conveyed from the retina to the suprachiasmatic nucleus, which modulates sympathetic output to the pineal gland, thereby controlling melatonin levels.

Development and clinical relevance: The gland derives from the diencephalon during embryogenesis. Pineal-region lesions are uncommon but can have significant effects, including headaches, hydrocephalus, and Parinaud syndrome from dorsal midbrain compression. Pineal germ cell tumors can cause precocious puberty in children by secreting human chorionic gonadotropin. Benign pineal cysts are relatively common incidental findings.