The normal thyroid gland weighs 20–25 g. The functioning unit is the lobule supplied by a single arteriole and consists of 24–40 follicles lined with cuboidal epithelium. The follicle contains colloid in which thyroglobulin is stored (Figure 50.2). The arterial supply is rich, and extensive anastomoses occur between the main thyroid arteries and branches of the tracheal and oesophageal arteries (Figure 50.3). There is an extensive lymphatic network within and around the gland. Although some lymph channels pass directly to the deep cervical nodes, the subcapsular plexus drains principally to the central com- partment juxtathyroid – ‘Delphian’ and paratracheal nodes