Thyroid

High Yield Anatomy Figure 1: Thyroid Anatomy (Thyroid in Grey) Vascular supply:

• Superior thyroid artery: branch from External carotid artery
• Inferior thyroid artery: branch off of thyrocervical artery
• Ima artery off of innominate directly to the isthmus
• Superior thyroid vein drains into IJV, inferior drains into innominate vein Nerves:
• Superior laryngeal nerve: motor to cricothyroid muscle; loss of projection and fatigue

• Recurrent laryngeal nerve: Right travels with vagus and loops around Right innominate artery

• Left travels with vagus and loops around aorta
• Preoperative laryngoscopy to visualize cords, bilateral damage can obstruct airway Thyroglobulin: stores T3 (more active) and T4 Thyroid Embryology: 4th Endodermal pouch → Bilobed solid organ—follicular cells, colloid and parafollicular cells (produces calcitonin) Pyramidal lobe extension can cause thyroglossal duct cyst; resect this as it has the potential to get infected or malignant transformation High-Yield Pathophysiology/Treatment
• Thyroid storm:
• Seen in Grave’s disease
• Treatment with beta blockers, Lugol’s solution, cooling blankets
• Thyroid Nodule:

• Ultrasound (Look for hypoechogenecity, microcalcification, irregular margins, unorganized vascular patterns, lymphatic invasion) followed by FNA - Indeterminant - Repeat FNA - Benign - Repeat US in 6-12 months - AUS/FLUS - Repeat FNA - Follicular neoplasm - Lobectomy - Suspicious malignancy - Lobectomy - Malignancy - Total thyroidectomy Table 1: Bethesda Criteria *AUS - Atypia of undetermined significance **FLUS - Follicular lesion of undetermined significance

• Hyperthyroidism:
• Low TSH, elevated T3, T4
• Treatment with PTU (side effects of aplastic anemia or agranulocytosis) or methimazole (cretinism, aplastic anemia and agranulocytosis)
• PTU OK during Pregnancy as it does not cross placenta
• Graves’ disease:
• Diffuse uptake of radioactive iodine (RAI), antibodies against TSH receptors
• RAI worsens ophthalmopathy
• Multi-nodular goiter:
• Total or subtotal thyroidectomy
• Thyroiditis:
• Hashimoto’s: caused by antithyroid antibodies; treatment with thyroid replacement
• Subacute granulomatous: viral etiology, treatment with NSAIDs, steroids
• Papillary thyroid cancer:
• MC thyroid malignancy; in women; spread lymphatically
• Biopsy pathology shows psammoma bodies, orphan Annie nucleus
• Tx with total thyroidectomy with Level VI involvement
• Do total - so can follow up thyroglobulin for surveillance, postoperative radioiodine treatment, remove potential multifocal disease
• Follicular Thyroid Cancer:
• FNA is not reliable so do diagnostic/therapeutic lobectomy
• Hematogenous spread

• Treatment with total thyroidectomy, MRND for + nodes and postoperative Radioactive iodine ablation

• Medullary Thyroid Cancer:
• Cancer from parafollicular C cells producing Calcitonin
• 20% associated with germline mutations in RET oncogene
• Tx with total thyroidectomy with Central dissection, modified radical dissection if lymph nodes involved
• Surveillance with CEA, Calcitonin Table 2: MEN and Medullary Thyroid Cancer Quick Hits
• Radioactive Iodine ablation does not work for MTC
• Avoid injuring the Superior Laryngeal Nerve by ligation close to the superior pole of the thyroid
• MC symptom of elevated calcitonin is diarrhea

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