anatomy OF THYROID GLAND

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THYROID GLAND , ANATOMY , VARIATIONS, DEVELOPMENT RELATIONS

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anatomy OF THYROID GLAND

  1. 1. ANATOMY OF THYROID GLAND AHAMMED KABEER M A 55TH BATCH GOV MED COLLEGE CALICUT
  2. 2. INTRODUCTION DEVELOPMENT GROSS ANATOMY BLOOD SUPPLY NERVE SUPPLY LYMPHATIC DRAINAGE HISTOLOGY SURFACE ANATOMY APPLIED ANATOMY
  3. 3. • Largest endocrine gland • Thyroid hormones (T3 , T4 )- BMR • Thyrocalcitonin – antagonize PTH (i.e decrease serum Ca) • Highly vascular*
  4. 4. DEVELOPMENT OF THYROID GLAND • Median endodermal thyroid diverticulum • Thyroglossal duct • Tuberculum impar • Foramen caecum • Lateral thyroid (4th pouch n ultimobranchial body) – parafollicular cells
  5. 5. SITUATION C5 T1 / 4th or 5th tracheal ring 2nd 4th Tracheal rings
  6. 6. DIMENSIONS AND WEIGHT • Butterfly/H shaped • Lobes 5*3*2cm • Isthmus 1.2*1.2cm • Weight 25g • Larger in females • Enlarges in pregnancy & menstrution
  7. 7. CAPSULES • True capsule (fibrous) – condensation of CT of gland • Septae & lobules • Arteries and plexus of veins deep to it • False capsule – pretracheal fascia • Moves during deglutition and speech • Suspensory ligament of Berry*
  8. 8. Deep cervical fascia
  9. 9. RELATIONSs 1. Lobes • Conical • Apex, base • 3 surfaces – L, M, PL • 2 borders – A, P • Apex – oblique line of thyroid cartilage* • Base – 4th/5th tracheal ring
  10. 10. • Apex is sandwitched b/w inf constrictor and sternothyroid I.e upward extension is restricted
  11. 11. • Lateral surface – convex, • Covered with sternohyoid, SCM, superior belly of omohyoid, sternothyroid
  12. 12. Deep cervical fascia
  13. 13. • Medial surface- 2 tubes(larynx-trachea) and (pharynx-oesophagus) - 2 muscles cricothyroid, inferior constrictor - 2 nerves external and recurrent laryngeal N • PL surface – carotid sheath
  14. 14. • Ant border – anterior branch of STA
  15. 15. • P border - ITA - anastomosis b/w STA & ITA - parathyroid glands - thoracic duct on left
  16. 16. 2. Isthmus • 2 surfaces A & P • 2 borders Sup & Inf • A surface – skin & fascia - anterior jugular veins - R & L sternohyoid & sternothyroid • P surface- 2nd – 4th tracheal rings • Sup border – anastomosis b/w R&L STA • Inf border - ITV leave
  17. 17. Pyramidal lobe • Extend superiorly from isthmus/left lobe • Attached to body of hyoid bone by fibromuscular band • Levator glandulae thyroidae( LGT) • U/L or B/L • LGT represent detached part of infrahyoid muscles • May be innervated by ansa cervicalis • Remnant of thyroglossal duct
  18. 18. BLOOD SUPPLY – Arterial supply 1. Superior thyroid artery (STA) • 1st ant br of ECA • External laryngeal N * • Ligature * • Pierce pretracheal fascia at apex • Divide into A & P branches • A branch- ? • P branch?
  19. 19. 2. Inferior thyroid artery (ITA) • Largest branch of thyrocervical trunk (SCA) • Pass behind carotid sheath, MCG and in front of vertebral A • Terminate near lower pole • Recurrent laryngeal N* • Ligation* • Ascending br*? • Glandular br?
  20. 20. 3. Thyroidea ima artery*( lowest thyroid artery) 3% • from arch of aorta/brachiocephalic trunk/right common carotid/right subclavian/ internal thoracic A • Enter lower border of isthmus • Tracheostomy* 4. Accessory thyroid arteries
  21. 21. VENOUS DRAINAGE 1. Superior thyroid vein (STV) • Accompany STA • Drain to IJV/ facial v
  22. 22. 2. Middle thyroid vein • Very short • From middle of lobe • Drain to IJV
  23. 23. 3.Inferior thyroid vein* • Plexus on trachea • Drain to left brachiocephalic vein • R – passes ant to innominate a  R BCV or ant trachea  L BCV • L – drainage  L BCV • **occ – both inf veins form a common trunk “thyroid ima vein”  empties into L BCV • Thyroid vein of Kocher* emerge from lower pole drain to IJV profuse bleeding 4. kocher’s thyroid vein*
  24. 24. LYMPHATIC DRAINAGE • Extensive, multidirectional flow • periglandular  prelaryngeal (Delphian)  pretracheal  paratracheal (along RLN)  brachiocephalic (sup mediastinum)  deep cervical  thoracic duct • Upper part via prelaryngeal LN to upper deep CLN • Lower part via pretracheal and paratracheal LN to lower deep CLN • Brachiocephalic LN and thoracic duct • regional metastasis of thyroid carcinoma are superior and lateral, along IJV ie: invasion of the pretracheal and paratracheal LNs and obstruction of normal lymph flow
  25. 25. INNERVATION • Vasoconstrictor sympathetic innervation • Mainly from MCG • Partly from SCG and ICG • Cardiac and laryngeal branches of vagus(parasympathetic) • Enter along wuth blood vessels • Never secretomotor (secretion regulated by TSH)
  26. 26. HISTOLOGY • Septae from fibrous capsule • Lobules • Follicles filled with colloid • Follicular cells- T3 ,T4 ( level of activity) • Parafollicular cells( Clear cells, pale cells)- thyrocalcitonin (ultimobranchial body), an APUD cell • Colloid – iodothyroglobulin
  27. 27. SURFACE ANATOMY • Anterior triangles in the lower neck on either side of the air way and digestive tract inferior to the position of the oblique line of the thyroid cartilage . • sternothyroid muscles- oblique line of thyroid cartilage ,prevent the lobes from moving upwards • Palpated by finding the thyroid prominence and arch of the cricoid cartilage and then feeling posterolateral to the larynx. • Isthmus crosses anterior to the upper end of the trachea and can be easily palpated in the midline inferior to the arch of the cricoid. • Presence of isthmus makes palpating the tracheal cartilages difficult and difficult tracheostomy.
  28. 28. • Isthmus marked by – • Lobes extend – apex to middle of thyroid crtilage - base to clavicle - laterally overlapped by ant border of SCM Arch of cricoid 1.2cm 1.2cm 1.2cm
  29. 29. APPLIED ANATOMY • Presence of thyroidae ima A- chance of profuse bleeding procedures in neck below isthmus • Thyroglossal duct cysts – remnants of thyroglossal ducts at any point in the way of descent,(midline near hyoid) • Pyramidal lobe and presence of levator glandulae thyroidae • Ectopic thyroid glands – lingual/higher placed • Accessory thyroid glands – in thymus/ on thyrohyoid muscle • Non neoplastic, noninflammatory enlargement – goiter
  30. 30. • pressure symptoms and nerve involvments are common in goiter and carcinoma • Compression of trachea, carotid sheath, and venous engorgement
  31. 31. • Endemic goiter - I2 deficient soil/water • Subtotal thyroidectomy often preferred in hyperthyroidism – -to preserve external and recurrent laryngeal N - to spare parathyroid glands - to prevent post operative myxoedema • Injury to recurrent laryngeal N – horsness of sound -temporary aphonia/ dysphonation - laryngeal spasm • Recurrent laryngeal N- supply all laryngeal muscles except *cricothyroid • Nonrecurrent laryngeal N* • Injury to external laryngeal N – monotonous voice(paralysis of cricothyroid) • Inadvert removal of parathyroid gland – tetany (fatal)
  32. 32. - relationship between RLN and ITA highly variable Examples: • Deep to ITA (40%) • superficial (20%) • b/w branches of the artery (35%)
  33. 33. Anomalies of development • Anomalies of shape • Anomalies of position • Ectopic thyroid glands • Remnants of thyroglossal duct
  34. 34. In agenisis of ishthmus and lobes presence of ectopic thyroid tissue must be looked for
  35. 35. Thyroglossal fistula Thyroglossal cyst
  36. 36. Thyroid Neoplasm Benign Malignant PrimaryFollicular Papillary Follicular Cells Parafollicular Cells Lymphoid Cells LymphomaMedullary Differentiated Undifferentiated AnaplasticFollicular Papillary Hurthle Cell Secondary

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