[pinea, Latin = pine cone]

= PINEAL BODY = EPIPHYSIS CEREBRI = “Third eye”

Development: diverticulum lined by ependyma at the most caudal portion of diencephalic roof of 3^rd ventricle → area of ependymal thickening → evaginates into pinecone-shaped mass during 7^th week GA

Function: secretion of melanin

1. Regulation of long-term biologic rhythm (eg, onset of puberty)
2. Regulation of short-term biologic rhythm (eg, diurnal / circadian) due to photoperiodic clues via accessory optic pathway

Histo:

1. lobules of pineocytes with dendritic processes (= specialized neuronal cells related to retinal rods and cones) make up 95% of population
2. astrocytes as neuroglial supporting cells = 5% of population
3. fibrovascular stroma
4. corpora arenacea = concentric calcifications appear in adolescence (in 40% of patients 17–29 years old)
   [arenacea, Latin = sandy]

Location: midline

suspended from pineal stalk that is attached to upper aspect of posterior border of 3^rd ventricle

1. inferior to splenium + vein of Galen
2. superior to tentorium + superior colliculi
3. posterior to cistern of velum interpositum (= cistern of transverse fissure)
4. surrounded by CSF of quadrigeminal cistern

Size: 10–14 mm

• enhancement with contrast ← absence of blood-brain barrier