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Thyroid and Parathyroid glands
Terms in this set (35)
Develops as a ventral diverticulum from the endoderm of the first and second pharyngeal pouches at the foramen cecum.
Diverticulum forms at the 4th week and descends from the base of tongue to the pretracheal position.
The Parafollicular C cells arise from neural crest cells of the 4th pharyngeal pouch.
If migration arrests, end up with a lingual thyroid.
Ligament of berry
The thyroid is attached to the larynx/trachea through anterior and posterior suspensory ligaments. The thyroid elevates with swallowing because of this.
The posterior suspensory ligament is Berry's ligament. Condensation of the thyroid capsule.
The RLN can penetrate the thyroid gland within the ligament of Berry in some patients.
Superior laryngeal nerve
Internal branch supplies sensation to the lower pharynx, supraglottis, and base of tongue.
External branch innervates cricothyroid muscle and inferior constrictor.
Recurrent laryngeal nerve
Motor innervation to all intrinsic laryngeal muscles except cricothyroid.
Also supplies sensation to the larynx, upper esophagus, and trachea.
Right: Enters the neck base at the thoracic inlet more laterally than the left. Ascends in the neck traveling lateral to medial crossing the inferior thyroid artery.
Left: Enters the thoracic inlet in a more paratracheal position and runs more medially in the tracheoesophageal groove and crosses the distal branches of the inferior thyroid artery.
Arterial supply to the thyroid
Superior thyroid branches from the ECA and inferior thyroid branches from the thyrocervical trunk.
Thyroid ima artery is a separate unpaired vessel that may come from the innominate, carotid, or aortic arch and is present in 1.5 - 12%
Venous drainage of the thyroid
Superior, middle, and inferior thyroid veins.
Superior is a branch of IJ and travels with the superior thyroid artery.
Middle doesn't have an artery counterpart and drains into the IJ.
Inferior travels alone from the lower part of IJ or the brachiocephalic
More potent than T4, but only 10% of thyroid hormone produced.
80% of circulating T3 is made from T4.
Exogenous T3 is liothyronine.
Strongly correlated with TSH and is likely predominent in TSH negative feedback.
Exogenous T4 is levothyroxine
Synthesis of thyroid hormone
Iodine is actively transported into follicular cells and is oxidized to thyroglobulin-bound tyrosine residues.
4 iodination sites are available. If all 4 are active, makes T4. If 3, T3.
Stored bound to thyroglobulin in colloid. Upon release, it is taken up from colloid, cleaved off thyroglobulin, and released.
T3 resin uptake test
Test that allows for correction of total T4 level for fluctuation in TBG. T3 resin uptake measures the binding capacity of existing TBG.
The more available binding sites on native TBG, the less resin uptake of radiotagged T3.
60% of clinical hyperthyroidism.
Autoimmune. Ig autoantibodies bind to TSH receptor and act like TSH.
Diffusely enlarged thyroid. Can get thyroid bruits from increased vascularity.
Can have infiltrative ophthalmopathy with exophthalmos.
I-123 scanning shows diffusely increased uptake.
Toxic multinodular goiter
Develops from pre-existing nontoxic nodular goiter.
Occurs more often in iodine-deficient regions.
Patients can develop overt hyperthyroidism after exogenous iodine administration (CT scan). Called Jod-Basedow phenomenon.
Uninodular toxic goiter
Hyperthyroidism doesn't occur until the nodule is 3cm or larger.
Nodules produce more T3 than T4.
Low rate of spontaneous remission and antithyroid hormones don't work well. Treatment is RAI or surgery
I131 vs I123
I123 is used in scans to assess fo rhot nodules.
I131 is used in RAI
PTU and methimazole
Block iodine organification and thyroid hormone synthesis. PTU also blocks peripheral conversion of T4 to T3.
Takes 6-8 weeks to get euthyroid.
PTU has recently been linked with liver failure especially in kids. Methimazole is first line.
Iodides for treatment of hyperthyroidism
Potassium iodide and Lugol solution.
Inhibit organification and prevent TH release.
Given preoperatively to decrease thyroid gland vascularity.
Antithyroid effect is transient (Wolff-Chaikoff effect) with escape occuring within 2 weeks.
Beta blockers for hyperthyroidism
Block peripheral TH effects (Do NOT alter production).
Useful in symptomatic control while other therapies are being initiated.
Definitive treatment of hyperthyroidism.
Conception must be delayed for 6 months after treatment.
Up to 80% with Graves and 50% with toxic nodules become hypothyroid.
Potential for long-term second malignancies.
Surgical treatment of Graves and toxic nodules
For Graves, usually do total thyroidectomy. Can do lobectomy and subtotal lobectomy on the other side, but risk of developing hyperthyroidism again is 6%.
For nodule, resect involved nodule. Best to get scintillography and ultrasound because sometimes problem areas are not in the area of other nodules.
Autoimmune. Increased thyroid peroxidase antibodies in 70-90%.
Patients are usually euthyroid at presentation. Hypothyroidism progresses with time from loss of follicular cells.
Histologically, lymphocytic infiltration with germinal center formation, follicular cell atrophy, Hurthle metaplasia, and fibrosis.
Surgery only if goiter is large, symptomatic, and refractive to thyroid hormone.
Rare complication is thyroid lymphoma. Any mass or nodule should be biopsied.
Subacute granulomatous thyroiditis
AKA deQuervain thyroidism.
Viral in etiology. Enlarged, painful thyroid.
50% present with hyperthyroidism, elevated TH, and sed rate.
Pain resolves in 3-6 weeks.
50% enter a hypothyroid phase lasting several months.
Large, nontender goiter with woody consisty fixed to surrounding structures.
Extensive fibrosis extends into surrounding neck structures.
Bethesda system for reporting thyroid cytopathology from FNA and risk of malignancy
Nondiagnostic or unsatisfactory: 1-4% risk of malignancy. Should get repeat FNA.
Benign: 0-3% risk of malignancy. Follow cinically.
Atypia of undetermined significance or follicular lesion of undetermined significance: 5-15% risk of malignancy. Should get repeat FNA.
Follicular neoplasm: 15-30% risk. Lobectomy.
Suspicious for malignancy: 60-75% risk. Thyroidectomy.
Malignant: 97-99%. Thyroidectomy
Algorithm for evaluation of thyroid nodule
1. H&P, TSH.
2. If low TSH, I123 or technetium scan. If nodule is hot, treat hyperthyroidism.
3. Normal or high TSH, get ultrasound.
4. No nodule, treat hypothyroidism. If normal TSH, done.
5. If nodule greater than 1-1.5cm or greater than 50% cystic, get FNA.
6. FNA results:
Inadequate: Repeat FNA in 3 months
Indeterminate: Can get I123 scan. If hot, follow. Cold, surgery
Benign: monitor clinically if palpable or repeat u/s if not.
Papillary thyroid cancer
Histopathology: Papillae with unique nuclear features. Orphan annie nuclei, nuclear grooves. Diffuse sclerosing, tall cell, and columnar cell variants are worse.
Strongly lymphotrophic with very early nodal spread.
Multiple foci are often seen in the gland.
30% have positive nodes at diagnosis. Likely no significant prognostic implications.
Low dose radiation exposure may plan an inductive role.
MAPK pathway is central to metastatic transformation.
Ras, RET, BRAF are parts of this pathway. BRAF mutation encodes a constitutively active kinase B-Raf. This mutation is found in 50% of PTC. The presence of BRAF mutation is a negative prognosticator.
Histopathology: Well-differentiated malignancy. Significant overlap with follicular adenoma but with capsular invasion. This is the only way to diagnose it. Not possible to diagnose follicular carcinoma on FNA because you have to look at the whole capsule.
Less likely to spread to cervical nodes than PTC, but more present with distant mets. Typically unifocal and limited to one lobe.
Hurthle cell carcinoma
Variant of follicular carcinoma. More aggressive, especially with regard to distant mets.
Prognostic factors in well-differentiated thyroid cancer
Mortality in the low risk group is 1-2%. High risk is 40-50%.
Females below age 50 and males below 40yo have better prognosis.
Increased invasiveness and mets increase mortality.
Males have a poorer prognosis than females.
Greater than 5cm lesions are worse. Less than 1.5cm is better.
Guidelines for operative management in well-differentiated thyroid cancer
Total is indicated for patients with cancer diagnosed on FNA that are greater than 1cm.
Majority of patients with cancer should have a total.
Level 6 ND for advanced stage PTC.
If biopsy-proven mets to cervical lymph nodes, should do a lateral ND.
Medullary thyroid cancer
Pathology: Arises from parafollicular C cells. Calcitonin is elevated. Also good for postoperative monitoring.
RET oncogene missense mutations have been identified in inherited forms of MTC.
No therapy available aside from surgery. CANNOT do RAI because C cells don't take up iodine. Should do total thyroid and central neck dissection. All patients with palpable medullary ca should also have an ipsilateral level II-V ND with consideration for bilateral.
May metastasize hematogenously to lung, liver, bone.
5-10% of thyroid cancer. All hereditary forms are autosomal dominant and preceded by multifocal C-cell hyperplasia.
Highly curable if diagnosed early. Treatment is based on the subtype. CRT. Surgery is restricted to biopsy.
Presents as a rapidly enlarging firm, painless mass. 30-40% have a history of hypothyroidism.
Believed to occur from terminal dedifferentiation of a previously undiagnosed longstanding cancer.
Rapidly growing neck mass with adherence of larynx, trachea, RLN, frequently distant mets.
Surgical treatment is limited to debulking or for biopsy often combined with trach.
Treatment = hyperfractionated radiation with chemo.
<5% of thyroid cancer and occurs in older patients. One of the most lethal malignancies with average survival of 6 months. Does not concentrate iodine.
Benign familial hypocalciuric hypercalcemia
High calcium and high PTH levels.
Autosomal dominant. Excess renal calcium reabsorption. No surgery needed.
Indications for surgery for hyperparathyroidism
Significantly elevated calcium (>1mg/dL above normal), patients <50 because of increased risk for symptoms or sequelae, life-threatening episode of hypercalcemia, significant bone or renal dysfunction.
Creatinine decreased by 30% for age without other cause, urine calcium > 400, bone density less than 2 standard deviations for age and gender matched normal.
Parathyroid surgical anatomy
Superiors typically occur at the level of the cricothyroid articulation approximately 1cm above the intersection of the RLN and inferior thyroid artery. Located at a plane deeper to the plane of the RLN and can be retrolaryngeal or retroesophageal.
Inferiors have a more variable location. Closely associated with the inferior pole of the thyroid often on the posterolateral aspect of the capsule of the inferior pole. Generally located ventral to the plane of the RLN
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