Oral Exam - Thyroid and Parathyroid Flashcards
Grave’s findings
○ Homogeneously enlarged thyroid with markedly
increased radiotracer uptake
○ Decreased uptake in salivary glands
○ Superimposed nodules occur in 5-10%
– Consider Marine-Lenhart syndrome
• RAI: Usually > 50%, often 80-90%
Thyroid scan protocol
– Radiopharmaceutical:
I-123 (200-400μCi PO
Tc-99m pertechnetate (2-10 mCi)
Thyroid uptake dose
Radiopharmaceutical
□ I-131: 5-10μCi(0.2-0.4MBq) I-131 for uptake if planning Tc-99m pertechnetate scan
□ I-123: can do uptake and scan with same dose (200-400 uCi)
○ Uptake acquisition
– 24 hr most common, may add 4hr uptake to evaluate for rapid turnover
○ NormalRAIUvalues(varybyinstitution)
– 4hr:~5-15%
– 24hr:~10-35%
Differential Graves
Subacute thyroiditis - low RAIU (<5%)
MNG - heterogeneous, RAIU not as high
Toxic adenoma - nodule, RAIU not as high
Autoimmune thyroiditis - Hashimoto’s with hashitoxicosis (anti-TPO, anti-thyroglobulin); Silent/post-partum
Medication/contrast -
Graves treatment
PTU/Tapazol - Rare agranulocytosis and hepatic dysfunction
RAI
Empiric - SEE NEW NOTES
Calculated - SEE NEW NOTES
MNG findings
○ Heterogeneous uptake in enlarged thyroid gland with multiple variable-intensity nodules
○ Dominant cold nodule in MNG: 5% chance of malignancy
○ May extend substernally
○ Evaluate for dominant cold nodule (large, cold nodule
when compared with other nodules)
RAIU in nodular thyroid disease
– Can be low, normal, or mildly elevated (often<50%)
in thyroid nodular disease
– Obtained in patients with hyperthyroidism
– Used for diagnosis and radioactive iodine therapy
planning
DDx cold or warm nodule
Cyst/hemorrhage/abscess
Adenoma - non-functioning
Carcinoma - thyroid, lymphoma, metastases
Parathyroid adenoma
Ddx hot nodule
Functioning adenoma
Focal thyroiditis
Discordant nodule on Tc99m pertechnetate (traps, does not organify)
Toxic multinodular goiter
Dual phase Sestamibi protocol
– 20-30 mCi Tc-99m sestamibi/tetrofosmin
○ Early images
– 10-20 min post injection
– Activity in thyroid and parathyroid adenoma
○ Delayed images
– 90 min post injection
– Activity in thyroid washes out, activity in adenoma
persists
□ ~60% of adenomas retain radiotracer longer than
thyroid
○ SPECT/CT
– SPECT/CT at 90 min (after thyroid washes out)
– Better to localize activity posterior to thyroid, in
tracheoesophageal groove, or to ectopic site
• Dual radiotracer protocol
Sestamibi + 10-20 mCi Tc-99m pertechnetate
○ Tc-99m sestamibi parathyroid scintigraphy to localize thyroid and parathyroid adenoma
○ Thyroid-only radiotracer to distinguish borders of thyroid gland:Tc-99m pertechnetate or I-123
○ Often used when Tc-99m sestamibi parathyroid scintigraphy indeterminate
Ddx parathyroid adenoma
Parathyroid hyperplasia
Parathyroid carcinoma
Other malignancy
Thyroid adenoma
Location of Parathyroid glands
○ Posterioror inferior to thyroid (mostcommon)
○ Intrathyroidal(2%): Withinthyroidparenchyma
• Ectopic (5-10%)
• Supranumerary
○ 25% may have 5 or more glands
• Multiple adenomas
○ 4-5% have multiple adenomas
○ Consider parathyroid hyperplasia
RAI treatment dose Graves
10-15 mCi
RAI treatment dose MNG
10-20 mCi
Post-op - pre-therapy thyroid scan
Used if post-op stage not adequately assessed
I123 preferred
Should be done within 72 hours of therapy
Thyroid CA risk stratification
Low risk:
- No local/distant mets
- No tumour invasion
- Non-agressive histology (not tall cell)
- Clinical N0 or <= 5 micromets on path
Low risk RAI
If total thyroidectomy - RAI not routinely recommened
- if so, 30 mCi
If subtotal thyroidectomy - RAI not recommended
Moderate risk
Consider RAI
High risk
Routinely recommend RAI
Benefits RAI
Reduces risk of local recurrence
Prolongs survival in patients with lung and/or bone metastases
Eliminates sources of Tg to facilitate follow-up
Helps complete staging
RAI dosing recommendations
For RAI remnant ablation
Dose of 30 mCi recommended
For treatment of suspected microscopic residual disease
Dose up to 150 mCi can be considered
Lung mets
100-200 mCi (Max 150 if > 70)
Bone mets
100-200 mCi
Mediastinal uptake on Thyroid scan
Substernal uptake in an enlarged gland
Physiologic thymic uptake
Grave’s bloodwork
Anti-TSH antibodies
Anti-thyrotropin receptor antibodies
If inferior activity, ask to swallow water
Sestamibi
Non-specific malignancy/inflammatory agent
Rising thyroglobin with negative I131 post-op scan
Do F18-FDG PET for de-differentiated thyroid CA
Follow-up for hot nodule on Tc99m-pertechnetate study
Consider I123 scan to exclude a discordant nodule
Subacute thyroiditis differential on thyroid scan (low uptake, clinically thyrotoxic)
Subacute thyroiditis (granulomatous, post-partum, silent) Exogeneous thyroid use Amiodarone Iodine load Struma ovarii
Ddx lingual thyroid
Hyperfunctioning thyroid adenoma
Ectopic thyroid
Hashimoto’s
Early hashimoto’s can be associated with an increased RAIU, mimicking Grave’s
Thyroid hormon production is inefficient and TSH should be increased (hypothyroid)
Same pattern in early phase of subacute thyroiditis
Ddx Poorly visualized thyroid gland and clinical hypothyroid
After I131 ablation, surgery, radiation
Hashimoto’s
Amyloid
Ddx Poorly visualized thyroid gland and clinical euthyroid
Iodine load
IV contrast
Amiodorone
Antithyroid medications
Ddx Poorly visualized thyroid gland and clinical hyperthyroid
Subacute, silent, or post-partum thyroiditis
Facticious
Amiodorone
Ectopic thyroid tissue - mets or struma ovarii
