The #ProjectSmackdown team understands how difficult things are now with #Coronavirus. We've been working from home for weeks and it's just not easy.
To help out and thank you all for your support, the team has decided to release our Thyroid review section along with an audio version so that you can get some review done while you're out, working, or on the road.
We've previously released our Colorectal section.
Take a look at the audio version (above), video lecture, and written section. If you like the review, the whole course (with review book included) is available here on our site.
Thanks for everything you're doing, and remember:
The Project Smackdown Team
Anatomy and Physiology:
Thyroid originates from endoderm. It descends from foramen cecum to just above cricoid at 3rd week of gestation. Embryologically derived from 1st and 2nd pharyngeal arches
Ultimobrachial bodies (derived from neurectoderm at 4th pharyngeal pouch) give rise to C cells that produce calcitonin. Calcitonin antagonizes PTH. Calcitonin shifts calcium into bones: “Calcitonin puts the bone in”.
Arterial supply from the inferior thyroid artery (branch of thyrocervical trunk) & superior thyroid artery (first branch of external carotid)
Venous drainage is via the superior, middle, and inferior thyroid veins. Inferior drains into the innominate or brachiocephalic vein.. Superior and middle drain into the internal jugular.
Lymphatic drainage occurs via delphian lymph nodes.
Recurrent Laryngeal Nerves (RLNs)
- RLNs from the vagus innervate all intrinsic laryngeal muscles except cricothyroid.
- Ligament of Berry is suspensory ligament located posteriorly near RLN.
- Left RLN branch loops around the aorta at ligamentum arteriosum & ultimately sits in tracheoesophageal groove
- Right RLN loops around the right subclavian artery.
- RLNs are associated with inferior thyroid arteries. Ligate close to thyroid to avoid damage to the RLN.
- In 1-2% of people, RLN is not recurrent. This is more likely to occur on right side.
- Injury gives hoarseness. Bilateral injury may cause airway obstruction and need for tracheostomy.
- Superior laryngeal nerve arises from Vagus and gives rise to internal and external branches. This is the most commonly injured nerve with thyroidectomy. Injury results in inability to project voice and early voice fatigue. This is especially problematic for singers.
- Internal branch provides sensation to the larynx
- External branch gives motor function to cricothyroid muscle.
T4 is the major hormone produced in the thyroid (80–85% total hormone production). T3 is synthesized within the thyroid and also via peripheral conversion of T4. T3 is the more active form and has a shorter half-life.
TSH and Free T4 are used for surveillance and to monitor hyper vs hypothyroid status.
Thyroid Releasing Hormone (TRH) from hypothalamus acts on the anterior pituitary to cause release of thyroid stimulating hormone (TSH)
TSH acts on thyroid to cause release of T4 and T3.
A thyroid mass is evaluated by FNA. If the mass is not palpable or near vascular structures, US guided biopsy indicated
Abnormal Thyroid Descent:
Pyramidal lobe: occurs in 10% population. Extending from isthmus towards thymus
- Persistent thyroid tissue at foramen cecum (base of tongue)
- Pt presents with dysphonia, dysphagia, dyspnea
- risk of malignancy 2%
- Most likely to be pt only source of thyroid tissue ~70%
- Tx: Thyroxine suppression, I131
Thyroglossal duct cyst:
- Mass located at midline: between hyoid bone and isthmus of thyroid.
- Upwards movement with swallowing
- may be premalignant
- susceptible to infection
- Tx: Resection using Sistrunk procedure. Must resect mid portion of hyoid bone with cyst
- Symptoms include increased HR, fever, numbness, high output cardiac failure (most frequent cause of death)
- Typically seen in patients with undiagnosed Graves’ disease who undergo surgical procedures.
- Wolff-Chaikoff effect: patients given Lugol’s solution (high dose iodine)leads to inhibition of TSH action on thyroid and coupling of iodine, therefore less T4 and T3
- Tx: beta blockers, steroids, iodine and propylthiouracil (PTU)
- Indications for thyroidectomy:
- tracheal compression
- Radioiodine contraindicated in pregnancy. Tx with PTU.
- Increased free T4, low TSH
- Grave’s disease is MC cause:Diffuse uptake seen on scintigraphy. >90% positive for Anti-TSAb. May also have ophthalmopathy on physical exam (exopthalmos, proptosis, peri-orbital swelling)
- MC affecting women 20-40y
- HLA B8 and DR3 are associated with Grave’s
- Symptoms:Moist skin, atrial fibrillation, tachycardia, goiter, pretibial myxedema, ophthalmic issues
- In addition to free T4 elevation and decreased TSH, will see thyroid receptor autoantibodies
- Initial therapy is medical:
- PTU/Methimazole associated with aplastic anemia, agranulocytosis
- If patient fails medical treatment, has large goiter, or is pregnant, surgical intervention is indicated. Surgical intervention during 2nd trimester.
Toxic Multinodular Goiter:
- Low TSH, high FT3, FT4
- MC in older individuals >50y, W >M
- Hyperthyroidism precipitated by iodine also known as Jod-Basedow phenomenon; seen with contrast and supplementation of iodide
- Extra-thyroidal manifestations uncommon
- Radioactive iodine uptake increased with multiple nodules and suppression of remaining gland.
- Tx: Sub-total vs Total thyroidectomy. I131 trial if patients are poor surgical candidates
- In general, salicylates are given to different types of thyroiditis for symptomatic relief.
- Suppurative is due to bacterial infection. May result from bacterial URI (staph/strep). WBC elevation. Treatment is antibiotics and I&D of abscesses.
- DeQuervain’s is due to viral infection. May be preceded by viral URI,. ASA, NSAIDS, steroids are treatment options and typically this resolves in 4-6 months. Typical changes of hyperthyroidism on labs: increased free T4 and TSH low. However ESR is elevated.
- Postpartum thyoiditis is an autoimmune condition. Occurs in postpartum period. Treat symptoms. Looks like DeQuervain’s except ESR is normal.
- Hashimoto’s is an autoimmune condition. Painless inflammation of gland. Initially hyperthyroidism (with labs consistent) then later hypothyroidism. Anti-thyroid antibody positive, antithyroperoxidase antibody positive. May treat hypothyroid phase with thyroid hormone replacement. Thyroid cancer can develop in a patient with Hashimoto’s thyroiditis, so maintain a high index of suspicion for conditions like thyroid lymphoma / nodules.
- Riedel’s fibrous struma is painless “woody” inflammation of gland. Lymphocytic infiltrate of gland seen. Pts present with hypothyroidism and compressive symptomatology. Resect thyroid stromal tissue (isthmectomy or tracheostomy) to relieve compressive symptoms. Treat with thyroxine and steroids.
- Common causes include thyroid resection, I-131 ablation, thyroiditis, medications (eg lithium and amiodarone)
- Symptoms include weight gain, constipation, thinning hair, cold intolerance, pretibial myxedema
- Cretinism is congenital hypothyroidism
- Treat with levothyroxine
- Myxedema coma is associated with a high mortality rate. Secure airway, achieve normothermia, and treat with IV T4 (thyroxine)
- 5H’s of myxedema coma: hypotension, hypothermia, hypoventilation, hyponatremia, hypoglycemia
- most frequent endocrine malignancy (in US)
- Age is the most important prognostic factor with older age having the worst prognosis.
- Fine Needle Aspiration:
- nodules > 1 cm with suspicious features (hypoechoic, microcalcifications, increased vascularity)
- Nodules >1.5 cm without suspicious features
- 5-10% chance of malignancy if follicular cells seen on FNA
- cold nodules, male patient, age > 50 all worrisome for cancer
- Papillary cancer
- 80% of CA. MC in women 20-40 Y. Associated with exposure to radiation
- Spreads via lymphatics
- MAJORITY of these present with metastasis, but that is NOT prognostic of outcome
- Remember “lateral ectopic thyroid” or node biopsy that says normal thyroid tissue is actually metastatic papillary cancer.
- SO…if you biopsy a lymph node in the neck and pathology comes back “ectopic thyroid tissue” or “benign thyroid tissue” it’s NOT benign thyroid tissue…it’s papillary thyroid cancer.
- Psammoma bodies and orphan annie cells seen on pathology
- If < 1cm, lobectomy and isthmusectomy is standard. Some argue though that total thyroidectomy is justified because papillary cancer is multicentric and diffuse
- If > 1cm, high risk, or bilateral do total thyroidectomy
- If positive central node at neck, do central node dissection
- If lateral node positive at neck, do modified radical neck dissection (MRND)
- Give iodine 131 postop if lesion > 1.5cm (unless pregnant)
- Follow thyroglobulin levels post op because will help indicate tumor recurrence
- Approximately 95% five year survival. In the 5% who do die, death is from local disease.
- AMES and TNM system may be used to determine mortality risk
- Age is the biggest prognostic factor for thyroid cancer.
- Follicular cancer
- Most common type in women > 50 YOA
- Represents about 10% of thyroid cancer cases
- Cannot be distinguished from follicular adenoma on FNA. Must perform ipsilateral lobectomy and send to pathology for biopsy
- Hurthle cell variant is more likely to be both multifocal and bilateral
- Hurthle cells are eosinophilic cells that increase the rate of lymphatic spread
- However, in general, follicular CA demonstrates hematogenous spread.
- FNA demonstrates microfollicles.
- Treatment is lobectomy or total thyroidectomy
- If cancer persists or recurs after lobectomy, perform completion thyroidectomy and treat with postop iodine 131. Follow thyroglobulin levels.
- Five year survival approximately 70% except Hurthle cell does give increased mortality rate.
- Post op Iodine 131:
- Consider I 131 6 weeks after surgery, when TSH is at maximum. This allows maximal response.
- Tumor > 1cm
- extra-thyroidal disease
- Need total thyroidectomy for I 131 to be effective
- Choice of surgical procedure for Papillary and Follicular
- Lobectomy if does not meet total thyroidectomy indications beneath
- Total thyroidectomy if
- Lesion > 1cm
- Extrathyroidal Disease: beyond capsule, nodes or metastasis
- Multifocal or bilateral disease
- Previous radiation therapy to neck
- Anaplastic cancer
- Most common type in women over 65 YOA, but represents approx. 3% of cancers overall.
- Most aggressive form of thyroid CA
- Often shows up with metastatic disease at time of diagnosis. Poorly differentiated or undifferentiated.
- Any resection is for improvement of airway issues only
- TWO year survival is approximately 10%. Most commonly patients only survive approximately 4 months.
- Hurthle cell carcinoma:
- More commonly benign
- If malignant, more likely to metastasize to bone and lung
- Ashkenazi cells seen on pathology
- Tx: lobectomy as diagnosis cannot be made with biopsy alone. MRND for clinically positive nodes
- 5% of all thyroid cancers. M=W.
- ¼ of patients have MEN-2 (see bilateral disease more often and multicentric disease more often). RET mutation causes MEN.
- This cancer arises from C cells. Hyperplastic C-Cells result in increased calcitonin (flushing, diarrhea) and are considered premalignant.
- Spreads lymphatically: early metastasis seen to lung, liver and bone
- increased CEA secreted from tumors
- Amyloid seen on biopsy that gives “apple green birefringence” Then that’s medullary carcinoma of the thyroid and may be associated with MEN. Remember to look for the adrenal lesion that may be associated perform adrenalectomy first.
- Perform total thyroidectomy and central node dissection
- If nodes positive, approximately 40% survival at ten years.
- Palpable thyroid mass: MRND
- If nodes negative, approximately 80% survival at 10 years
- I 131 ineffective and therefore not routinely given.
- 1% of thyroid CA cases. More common in women
- seen with Hashimoto’s thyroiditis.
- Non-Hodgkin’s, B-cell type
- May need airway intervention if expands quickly
- 50% five year survival
- drops to 35% if extrathyroidal disease is present
- Treatment: RCHOP
- Both MEN 2A and MEN 2B are due to autosomal dominant mutation in RET on chromosome 10.
- Both MEN 2A and MEN 2B include medullary carcinoma of the thyroid and pheochromocytoma.
- When you find a family with MEN 2 remember that the children will inherit the disease from biologic parents. So if you find yourself discovering a medullary carcinoma of the thyroid in an adult, recall that 25% are MEN 2 related, test chromosome 10 and find RET mutation…remember that any biologic children will have the gene as well. So follow the recommendations beneath regarding thyroidectomy for them.
- MEN 2A (Sipple syndrome)
- In addition to above, includes hyperparathyroidism
- Test for RET
- Prophylactic thyroidectomy by 5 years of age
- MEN 2B
- As above with marfanoid body habitus and mucosal neuromas, but NO hyperparathyroidism.
- Also, prophylactic thyroidectomy should be performed before 2y