{"id":4422338,"date":"2025-01-11T14:15:28","date_gmt":"2025-01-11T20:15:28","guid":{"rendered":"https:\/\/myendoconsult.com\/learn\/topics\/anatomy-of-the-thyroid-gland\/"},"modified":"2025-01-13T06:17:24","modified_gmt":"2025-01-13T12:17:24","slug":"anatomy-of-the-thyroid-gland","status":"publish","type":"oen_topic","link":"https:\/\/myendoconsult.com\/learn\/topics\/anatomy-of-the-thyroid-gland\/","title":{"rendered":"Anatomy of the Thyroid Gland"},"content":{"rendered":"\n<h2 class=\"wp-block-heading\">ANATOMY OF THE THYROID AND PARATHYROID GLANDS<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Location and Dimensions<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Thyroid Gland<\/strong>\n<ul class=\"wp-block-list\">\n<li>Situated between the <strong>larynx<\/strong> and <strong>trachea<\/strong> medially, and the <strong>carotid sheath<\/strong> and <strong>sternocleidomastoid<\/strong> muscles laterally.<\/li>\n\n\n\n<li>Weighs approximately <strong>15\u201325 g<\/strong>.<\/li>\n\n\n\n<li><strong>Lateral Lobes<\/strong>: ~3\u20134 cm long and 1.5\u20132 cm wide.<\/li>\n\n\n\n<li><strong>Isthmus<\/strong>: ~1.2\u20132 cm long, ~2 cm wide, crossing the trachea between the first and second rings.<\/li>\n\n\n\n<li>Typically <strong>asymmetric<\/strong> (right lobe often larger or extends higher).<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"3450\" height=\"2100\" src=\"https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroid-gland-hist-and-anatomy.png\" alt=\"\" class=\"wp-image-4422850\" srcset=\"https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroid-gland-hist-and-anatomy.png 3450w, https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroid-gland-hist-and-anatomy-300x183.png 300w, https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroid-gland-hist-and-anatomy-768x467.png 768w, https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroid-gland-hist-and-anatomy-1536x935.png 1536w, https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroid-gland-hist-and-anatomy-2048x1247.png 2048w\" sizes=\"auto, (max-width: 3450px) 100vw, 3450px\" \/><figcaption class=\"wp-element-caption\">Gross Anatomy of the Thyroid Gland<\/figcaption><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Surgical Exposure of the Neck Structures<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Superficial Layer<\/strong>\n<ul class=\"wp-block-list\">\n<li>Skin, subcutaneous fat, and <strong>platysma<\/strong> muscle can be reflected as flaps for wide exposures.<\/li>\n\n\n\n<li><strong>External<\/strong> and <strong>anterior jugular veins<\/strong> and <strong>transverse cervical nerves<\/strong> run within this superficial layer.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Deeper Exposure<\/strong>\n<ul class=\"wp-block-list\">\n<li>The <strong>sternocleidomastoid<\/strong> muscle, <strong>omohyoid<\/strong> muscle, <strong>sternohyoid<\/strong>, and <strong>sternothyroid<\/strong> muscles lie beneath.<\/li>\n\n\n\n<li><strong>Ansa hypoglossal nerve<\/strong> (motor to infrahyoid muscles) courses near the carotid sheath. Preserving it helps maintain swallowing function.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Anterior Jugular Veins<\/strong>\n<ul class=\"wp-block-list\">\n<li>Supplement venous return from pharynx\/upper neck.<\/li>\n\n\n\n<li>Important to <strong>retract<\/strong> (rather than divide) these vessels during thyroid\/parathyroid exposure to reduce postoperative edema of the neck\/larynx.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Facial Nerve Branches (Lower Divisions)<\/strong>\n<ul class=\"wp-block-list\">\n<li>Injury to the <strong>marginal mandibular branch<\/strong> can cause drooping of the lower lip on that side (no spontaneous regeneration).<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Midline Lymph Node<\/strong>\n<ul class=\"wp-block-list\">\n<li>A solitary node can be found just in front of the thyroid isthmus, between pretracheal muscles.<\/li>\n\n\n\n<li>Enlarged in pharyngitis or laryngitis, but not typically in thyroiditis or tracheitis.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"1148\" height=\"709\" src=\"https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroidusgfig2.jpg\" alt=\"\" class=\"wp-image-440339\" srcset=\"https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroidusgfig2.jpg 1148w, https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroidusgfig2-300x185.jpg 300w, https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroidusgfig2-768x474.jpg 768w, https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroidusgfig2-624x385.jpg 624w, https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroidusgfig2-50x31.jpg 50w, https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroidusgfig2-100x62.jpg 100w\" sizes=\"auto, (max-width: 1148px) 100vw, 1148px\" \/><figcaption class=\"wp-element-caption\">Anatomic relations (Thyroid Gland)<\/figcaption><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Relation to the Esophagus<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The esophagus often lies slightly to the <strong>right of midline<\/strong>, adjacent to the typically larger <strong>right thyroid lobe<\/strong>.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Exposure of Thyroid, Parathyroid, and Thymus<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Achieved by <strong>retracting<\/strong> or <strong>transecting<\/strong> pretracheal (infrahyoid) muscles.<\/li>\n\n\n\n<li><strong>Maximum exposure<\/strong> sometimes requires a transverse cut of these muscles to reflect them superiorly and inferiorly.<\/li>\n<\/ul>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"694\" height=\"541\" src=\"https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroidusgfig1.jpg\" alt=\"\" class=\"wp-image-440329\" srcset=\"https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroidusgfig1.jpg 694w, https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroidusgfig1-300x234.jpg 300w, https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroidusgfig1-624x486.jpg 624w, https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroidusgfig1-50x39.jpg 50w, https:\/\/myendoconsult.com\/learn\/wp-content\/uploads\/thyroidusgfig1-100x78.jpg 100w\" sizes=\"auto, (max-width: 694px) 100vw, 694px\" \/><figcaption class=\"wp-element-caption\">Anatomical position of the Thyroid Gland<\/figcaption><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">THYROID GLAND: ADDITIONAL DETAILS AND ANOMALIES<\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Shape and Position<\/strong>\n<ul class=\"wp-block-list\">\n<li>Usually shaped like a horseshoe (\u201cU\u201d or \u201cH\u201d) with two lateral lobes connected by an isthmus.<\/li>\n\n\n\n<li><strong>Right lobe<\/strong> often larger; in dextrocardia, the left lobe may be larger.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Common Developmental Variations<\/strong>\n<ul class=\"wp-block-list\">\n<li><strong>Pyramidal Lobe<\/strong> (~15% of people): Extends upward from the isthmus; may enlarge with <a href=\"https:\/\/myendoconsult.com\/learn\/goiter\/\" data-wpil-monitor-id=\"99\">goiter<\/a> or be a site of neoplasia.<\/li>\n\n\n\n<li><strong>Accessory Thyroid Tissue<\/strong> (\u22655%): Small nodules separate from main thyroid; can mimic a tumor on exam.<\/li>\n\n\n\n<li><strong>Isthmus Agenesis<\/strong> (&lt;1%): Medial aspects of lobes may feel like separate nodules.<\/li>\n\n\n\n<li><strong>Partial Lobe Absence<\/strong> (rare): Often involves lower half of a lobe.<\/li>\n\n\n\n<li><strong>Ectopic Thyroid<\/strong> (lingual thyroid, substernal thyroid).<\/li>\n\n\n\n<li><strong>Complete Agenesis<\/strong>: Extremely rare; usually discovered postnatally when congenital hypothyroidism develops.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">PARATHYROID GLANDS<\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Number and Typical Location<\/strong>\n<ul class=\"wp-block-list\">\n<li>Usually <strong>four<\/strong> (two upper, two lower), located on the <strong>posterior surface<\/strong> of the thyroid lobes.<\/li>\n\n\n\n<li>Each parathyroid has its <strong>own capsule<\/strong> but is attached to the <strong>back of the thyroid\u2019s proper capsule<\/strong>.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Upper Parathyroid Glands<\/strong>\n<ul class=\"wp-block-list\">\n<li>More constant in position, often slightly larger.<\/li>\n\n\n\n<li>Lie near the <strong>upper thyroid pole<\/strong> to the region of the <strong>inferior thyroid artery<\/strong>.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Lower Parathyroid Glands<\/strong>\n<ul class=\"wp-block-list\">\n<li>More variable in location (can be found from upper thyroid region to <strong>anterior mediastinum<\/strong>).<\/li>\n\n\n\n<li>Embryologically associated with the thymus descent.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Surgical Relevance<\/strong>\n<ul class=\"wp-block-list\">\n<li>A <strong>fifth<\/strong> parathyroid gland may exist, especially important if searching for hyperparathyroidism sources (e.g., adenoma or hyperplasia).<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">LYMPHATIC DRAINAGE OF THE THYROID REGION<\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Anterior Midline Nodes<\/strong>\n<ul class=\"wp-block-list\">\n<li><strong>Delphian Node<\/strong>: Above the thyroid isthmus, in front of the cricoid cartilage; may be palpable if enlarged (e.g., thyroid cancer, <a href=\"https:\/\/myendoconsult.com\/learn\/histology-of-hashimotos-thyroiditis\/\" data-wpil-monitor-id=\"98\">Hashimoto thyroiditis<\/a>).<\/li>\n\n\n\n<li><strong>Pretracheal Nodes<\/strong>: Below the thyroid isthmus, variable position.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Lateral and Deep Cervical Nodes<\/strong>\n<ul class=\"wp-block-list\">\n<li>Along the <strong>lateral thyroid veins<\/strong>, near the <strong>recurrent laryngeal nerve<\/strong>, at the <strong>carotid sheath<\/strong> (jugular chain), and the <strong>supraclavicular fossa<\/strong>.<\/li>\n\n\n\n<li>\u201cSentinel\u201d or <strong>Virchow Nodes<\/strong> are the low jugular nodes near the thoracic duct inlet.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">LARYNGEAL MOTOR NERVES<\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>External Branch of the Superior Laryngeal Nerve<\/strong>\n<ul class=\"wp-block-list\">\n<li>Supplies the <strong>cricothyroid muscle<\/strong> (tenses vocal cords).<\/li>\n\n\n\n<li>Injury can lead to subtle voice changes or \u201cfuzziness,\u201d more pronounced if bilateral.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Recurrent (Inferior) Laryngeal Nerves<\/strong>\n<ul class=\"wp-block-list\">\n<li><strong>Right Recurrent Nerve<\/strong>: Hooks under the subclavian artery, then ascends diagonally.<\/li>\n\n\n\n<li><strong>Left Recurrent Nerve<\/strong>: Hooks under the aortic arch, often ascending in the <strong>tracheoesophageal groove<\/strong>.<\/li>\n\n\n\n<li>Important to identify and preserve during thyroid\/parathyroid surgery to avoid vocal cord paralysis.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">DEVELOPMENT OF THE THYROID AND PARATHYROID GLANDS<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Overview of Pharyngeal Development<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>During early embryonic life (~second month), the <strong>pharynx<\/strong> forms from the foregut, with <strong>four pairs<\/strong> of <strong>pharyngeal pouches<\/strong> protruding laterally.<\/li>\n\n\n\n<li><strong>Branchial Clefts<\/strong> align externally; anomalies may lead to fistulas or cysts along the neck.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Thyroid Gland Embryology<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Thyroid Diverticulum<\/strong>\n<ul class=\"wp-block-list\">\n<li>Appears in the <strong>midline floor of the primitive pharynx<\/strong> (~end of fourth week).<\/li>\n\n\n\n<li>Rapidly becomes bilobed; initially attached to the pharynx by the <strong>thyroglossal duct<\/strong>.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Descent to Neck<\/strong>\n<ul class=\"wp-block-list\">\n<li>By ~seventh week, the thyroid primordium descends to the <strong>tracheal level<\/strong>.<\/li>\n\n\n\n<li><strong>Thyroglossal Duct<\/strong> usually obliterates; a remnant at the tongue base is the <strong>foramen cecum<\/strong>.<\/li>\n\n\n\n<li>Residual duct segments can form <strong>thyroglossal duct cysts<\/strong> or ectopic thyroid tissue.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Thyroid Follicles<\/strong>\n<ul class=\"wp-block-list\">\n<li>Start forming around the <strong>eighth week<\/strong>; contain colloid by the <strong>third month<\/strong>.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Congenital Anomalies<\/strong>\n<ul class=\"wp-block-list\">\n<li><strong>Lingual Thyroid<\/strong>: Gland remains at tongue base.<\/li>\n\n\n\n<li><strong>Pyramidal Lobe<\/strong>: Retention of the distal thyroglossal duct.<\/li>\n\n\n\n<li><strong>Absent or Hypoplastic Gland<\/strong>: Can result in congenital hypothyroidism if untreated after birth.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n\n\n\n<h3 class=\"wp-block-heading\">Parathyroid and Thymus Embryology<\/h3>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Parathyroid Glands<\/strong>\n<ul class=\"wp-block-list\">\n<li><strong>Third and Fourth Pharyngeal Pouches<\/strong>: Dorsal portions form parathyroid primordia.<\/li>\n\n\n\n<li><strong>\u201cInferior\u201d Parathyroids<\/strong>: Usually from third pouch, migrating caudally with the thymus.<\/li>\n\n\n\n<li><strong>\u201cSuperior\u201d Parathyroids<\/strong>: From fourth pouch, remain more cranial.<\/li>\n\n\n\n<li>Variable locations possible (e.g., mediastinal, near thymus).<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>Thymus Gland<\/strong>\n<ul class=\"wp-block-list\">\n<li><strong>Ventral parts of the third (and sometimes fourth) pouches<\/strong>.<\/li>\n\n\n\n<li>Descends into the <strong>superior mediastinum<\/strong>, merging into a bilobed structure.<\/li>\n\n\n\n<li>Undergoes <strong>involution<\/strong> after puberty, replaced largely by adipose tissue in adults.<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"<p>ANATOMY OF THE THYROID AND PARATHYROID GLANDS Location and Dimensions Surgical Exposure of the Neck Structures Relation to the Esophagus Exposure of Thyroid, Parathyroid, and Thymus THYROID GLAND: ADDITIONAL DETAILS AND ANOMALIES PARATHYROID GLANDS LYMPHATIC DRAINAGE OF THE THYROID REGION LARYNGEAL MOTOR NERVES DEVELOPMENT OF THE THYROID AND PARATHYROID GLANDS Overview of Pharyngeal Development Thyroid [&hellip;]<\/p>\n","protected":false},"featured_media":0,"template":"","oen_topic_chapter":[683],"class_list":["post-4422338","oen_topic","type-oen_topic","status-publish","hentry","oen_topic_chapter-thyroid-gland","post-wrapper","thrv_wrapper"],"_links":{"self":[{"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/oen_topic\/4422338","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/oen_topic"}],"about":[{"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/types\/oen_topic"}],"version-history":[{"count":5,"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/oen_topic\/4422338\/revisions"}],"predecessor-version":[{"id":4422864,"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/oen_topic\/4422338\/revisions\/4422864"}],"wp:attachment":[{"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/media?parent=4422338"}],"wp:term":[{"taxonomy":"oen_topic_chapter","embeddable":true,"href":"https:\/\/myendoconsult.com\/learn\/wp-json\/wp\/v2\/oen_topic_chapter?post=4422338"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}