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Pineal gland

Dr Frank Gaillard and Dr Jeremy Jones et al.

The pineal gland is a small, tiny pine cone shaped (hence its name) structure considered to be part of the epithalamus. It typically measures 7 x 6 x 3mm in size and is situated in a grove between the laterally placed thalamic bodies ^1-6. It is located above and behind the superior colliculi and behind and beneath and stria medularis.

Appearing to arise from the gland are two laminae. Above is the habenular commissure and below it is the posterior commissure.

Important vascular relations include the internal cerebral veins and vein of Galen located above the gland, above which is the splenium of the corpus callosum and the velum interpositum.

The pineal gland receives its blood supply from fine branches off the posterior choroidal arteries and drains superiorly by multiple branches eventually into the great cerebral vein of Galen ³.

Embryology

The pineal gland arises during the seventh week of gestation from a thickening of the ependyma at the posterior most aspect of the third ventricle ⁵.

Physiology

The pineal gland produces melatonin which affects the modulation of wake/sleep patterns and photoperiodic (seasonal) functions. Unlike much of the rest of the brain, it is not isolated from the body by the blood-brain barrier.

Radiographic appearances

Plain films

The pineal gland has a predilection for calcification which is invariably histologically present in adults but rarely seen below the age of 10 years ⁶. Calcification is visible on lateral skull x-rays in 50-70% of adults ⁶. The habenular commissure also calcifies and is visible as a small C-shaped (open part posteriorly) density above and infront of the pineal calcification.

CT

With CT's far higher contrast resolution calcification is almost always visible in the adult pineal gland, sometimes visible as specs embedded in a small soft tissue nodule similar in density to grey matter. In children under the age of 5 years no calcification is present, but prevalence increases rapidly with age, reaching a plateau at about 30 years of age ⁵.

MRI

MRI is the modality of choice for evaluating the pineal region although its sensitivity to calcification on conventional sequences is poor (note: susceptibility weighted imaging (SWI) has sensitivity to calcification similar to CT).

The gland appears as a small nodule of tissue with similar intensity to grey matter. It enhances vividly during contrast administration as it is outside the blood brain barrier.

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The pineal region is anatomically complex and plays host to a number of unique masses and tumours as well as potentially affected by many entities seen more frequently elsewhere in the brain.