ABSTRACT
Introduction The pineal gland (from the Latin for ‘pine’) is a pine-cone-shaped structure measuring about 8 4 mm in the adult and weighing about 200 mg. It is located in the midline of the brain, just above the tectum of the midbrain. It is tethered to the posterior portion of the 3rd ventricle by a neuroepithelial stalk that is partially ependymal-lined. The pineal gland is a neuroendocrine gland that is solid in childhood and has a tendency to calcify later in life. Sometimes cysts form; these are usually but not always asymptomatic.1 The pineal gland, often referred to as a third eye, recognizes light and darkness via the sympathetic nervous system. Retinal fibers project indirectly to the pineal gland; retinal photoreceptors project to the suprachiasmatic nucleus of the hypothalamus, and then via the median forebrain bundle to the brainstem, the spinal cord and the superior cervical ganglion. Sympathetic fibers from the superior cervical ganglion innervate the pineal gland. In amphibians, there are photoreceptors within the pineal gland, making it truly a ‘third eye’. The pineal gland produces the hormone melatonin, which appears to play an important role in the sleep-wake cycle.2 The pineal gland is enlarged in some patients with systemic cancer but the cause of that enlargement is not known.3
