Thyroid Gland Flashcards
What is the arterial blood supply to the thyroid?
- Superior thyroid artery (first branch of the external carotid artery)
- Inferior thyroid artery (branch of the thyrocervical trunk)
What is the venous drainage of the thyroid?
- Superior thyroid vein
- Middle thyroid vein
- Inferior thyroid vein
What is the thyroid lobe appendage coursing toward the hyoid bone from around the thyroid isthmus?
Pyramidal lobe
What percentage of patients have a pyramidal thyroid lobe?
50%
What veins do you first see after opening the platysma muscle when performing a thyroidectomy?
Anterior jugular veins
What is the lymph node group around the pyramidal thyroid lobe?
Delphian lymph node group
What is the thyroid isthmus?
Midline tissue border between the left and right thyroid lobes
Which ligament connects the thyroid to the trachea?
Ligament of Berry
What is the IMA artery?
Small inferior artery to the thyroid from the aorta or innominate artery
What percentage of patients have an IMA artery?
3%
What is the most posterior extension of the lateral thyroid lobes?
Tubercle of Zuckerkandl
Which paired nerves must be carefully identified during a thyroidectomy?
Recurrent laryngeal nerves, which are found in the tracheoesophageal grooves and dive behind the cricothyroid muscle.
Damage to these nerves paralyzes laryngeal abductors and causes hoarseness if unilateral, and airway obstruction if bilateral
What nerve (other than the recurrent laryngeal nerves) is at risk during a thyroidectomy and what are the symptoms?
Superior laryngeal nerve.
If damaged, patient will have a deeper and quieter voice.
What is TRH?
Thyrotropin-Releasing Hormone
Released from the hypothalamus; causes release of TSH
What is TSH?
Thyroid-Stimulating Hormone
Released by the anterior pituitary; causes release of thyroid hormone from the thyroid
What are the thyroid hormones?
T3 and T4
What is the most active form of thyroid hormone?
T3
What is the thyroid negative feedback loop?
T3 and T4 feed back negatively on the anterior pituitary, causing decreased release of TSH in response to TRH
What is the most common site of conversion of T4 to T3?
Peripheral (e.g. liver)
What is Synthroid (levothyroxine): T3 or T4?
T4
What is the half-life of Synthroid (levothyroxine)?
7 days
What do parafollicular cells secrete?
Calcitonin
What percentage of people have a thyroid nodule?
5%
What is the differential diagnosis of a thyroid nodule?
Multinodular goiter, adenoma, hyperfunctioning adenoma, cyst, thyroiditis, carcinoma, lymphoma, parathyroid carcinoma
What are 3 types of non-thyroidal neck masses?
- Inflammatory lesions (e.g. abscess, lymphadenitis)
- Congenital lesions (e.g. thryoglossal duct, branchial cleft cyst)
- Malignant lesions (e.g. lymphoma, metastases, squamous cell carcinoma)
What studies can be used to evaluate a thyroid nodule?
U/S (solid or cystic); FNA (cytology); I scintiscan (hot or cold)
What is the diagnostic test of choice for a thyroid nodule?
FNA
What is the percentage of false negative results on FNA for thyroid nodule?
5%
What is meant by a hot vs. cold nodule?
Nodule uptake of IV I-123 or mT-99:
Hot: increased I-123 uptake = functioning or hyperfunctioning nodule
Cold: decreased I-123 uptake = nonfunctioning nodule
What are the indications for a I-123 scintiscan?
- Nodule with multiple non-diagnostic FNAs with low TSH
2. Nodule with thyrotoxicosis and low TSH
What is the role of thyroid suppression of a thyroid nodule?
Diagnostic and therapeutic (administration of thyroid hormone suppresses TSH secretion, and up to half of the benign thyroid nodules will disappear)
In evaluating a thyroid nodule, which history findings suggest thyroid carcinoma?
- Neck radiation
- Family history (thyroid cancer, MEN-II)
- Young age (especially children)
- M > F
In evaluating a thyroid nodule, which signs suggest thyroid carcinoma?
- Single nodule
- Cold nodule
- Increased calcitonin levels
- LAD
- Hard, immobile nodule
In evaluating a thyroid nodule, which symptoms suggest thyroid carcinoma?
- Voice change
- Dysphagia
- Discomfort (in neck)
- Rapid enlargement
What is the most common cause of thyroid enlargement?
Multinodular goiter
What are indications for surgery with multinodular goiter?
Cosmetic deformity, compressive symptoms, cannot rule out cancer
What is Plummer’s disease?
Toxic multinodular goiter
What percentage of cold thyroid nodules are malignant?
25% in adults
What percentage of multinodular masses are malignant?
1%
What is the treatment of a patient with a history of radiation exposure, thyroid nodule, and negative FNA?
Most experts would remove the nodule surgically
What should be done with thyroid cyst aspirate?
Send to cytopathology
What are the 5 main types of thyroid carcinoma?
- Papillary carcinoma (80%)
- Follicular carcinoma (10%)
- Medullary carcinoma (5%)
- Hurthle cell carcinoma (4%)
- Anaplastic carcinoma (1-2%)
What are the signs and symptoms of thyroid carcinoma?
Mass or nodule, LAD (most euthyroid)
What comprises the workup of thyroid carcinoma?
FNA, thyroid U/S, TSH, Ca level, CXR, +/- I-123 scintiscan
What oncogenes are associated with thyroid cancers?
Ras gene family and RET proto-oncogene
What is the most common thyroid cancer?
Papillary carcinoma
What is the environmental risk factor for papillary carcinoma?
Radiation exposure
What is the average age for papillary thyroid carcinoma?
30-40 years
What is the sex distribution for papillary thyroid carcinoma?
M:F = 1:2
What are the associated histologic findings with papillary thyroid carcinoma?
Psammoma bodies
What is the route and rate of spread of papillary thyroid carcinoma?
Most spread slowly via lymphatics (cervical adenopathy)
What is the I-131 uptake by papillary thyroid carcinoma?
Good uptake
What is the 10-year survival rate for papillary thyroid carcinoma?
95%
What is the treatment for a papillary thyroid tumor < 1.5 cm with no history of neck radiation exposure?
Options:
- Thyroid lobectomy and isthmectomy
- Near-total thyroidectomy
- Total thyroidectomy
What is the treatment for a papillary thyroid tumor > 1.5 cm, bilateral, positive cervical node metastasis, or a history of radiation exposure?
Total thyroidectomy
What is the treatment for lateral palpable cervical lymph nodes in papillary thyroid carcinoma?
Modified neck dissection (ipsilateral)