In iodine-sufficient regions, the most common cause of hypothyroidism is the autoimmune disorder Hashimoto's thyroiditis. The presence of the thyroid and its various diseases have been noted and treated for thousands of years, although the gland itself has only been described and named since the Renaissance. Knowledge of the thyroid, its biochemistry, and its disorders developed throughout the late nineteenth and twentieth centuries. Many modern treatments and investigative modalities evolved throughout the mid-twentieth century, including refinement of surgical techniques for thyroid removal (thyroidectomy) for the treatment of goitre; the use of radioactive iodine and thiouracil for the treatment of Graves' disease; and fine needle aspiration for diagnosis of thyroid nodules. The thyroid gland is a butterfly-shaped organ composed of two lobes, left and right, connected by a narrow isthmus. It weighs 25 grams in adults, with each lobe being about 5 cm long, 3 cm wide, and 2 cm thick, and the isthmus about 1.25 cm in height and width. The gland is usually larger in women than in men, and increases in size during pregnancy. The thyroid is near the front of the neck, lying against and around the front of the larynx and trachea. The thyroid cartilage and cricoid cartilage lie just above the gland, below the Adam's apple. The isthmus extends from the second to third rings of the trachea, with the uppermost part of the lobes extending to the thyroid cartilage and the lowermost around the fourth to sixth tracheal rings. The infrahyoid muscles lie in front of the gland and the sternocleidomastoid muscle to the side. Behind the outer wings of the thyroid lie the two carotid arteries. The trachea, larynx, lower pharynx and esophagus all lie behind the thyroid. In this region, the recurrent laryngeal nerve and the inferior thyroid artery pass next to or in the ligament. Typically, four parathyroid glands, two on each side, lie on each side between the two layers of the thyroid capsule, at the back of the thyroid lobes. The thyroid gland is covered by a thin fibrous capsule, which has an inner and an outer layer. The inner layer extrudes into the gland and forms the septae that divides the thyroid tissue into microscopic lobules. The outer layer is continuous with the pretracheal fascia, attaching the gland to the cricoid and thyroid cartilages via a thickening of the fascia to form the posterior suspensory ligament of thyroid gland, also known as Berry's ligament.