L16 - Radiology and Radioactive iodine therapy Flashcards
List the imaging techniques to confirm enlargement of thyroid gland?
Ultrasound
CT
List the imaging technique for thyroid function?
Radionucleotide scan
List the imaging techniques to characterize nodules and masses?
Ultrasound
Radionucleotide
List imaging techniques for evaluating thyroid carcinoma?
Evaluate local disease: US, CT, MRI
Detect recurrence after thyroidectomy / treatment: US, CT, MRI, radionuclide scan
Limitation of CXR for imaging thyroid?
Cannot evaluate soft tissue structure, evaluate extent of local invasion/ compression, characterize thyroid lesion
Advantages of using ultrasound for thyroid imaging?
No radiation
High frequency probe good for superficial structure evaluation: characterize nodule, vascularity
Excellent spatial resolution, sensitive to tiny nodules
List 5 physical features pf thyroid nodules that may be identified by ultrasound imaging?
- Solid vs. cystic (internal necrosis)
- Vascularity (colour doppler)
- Calcification
- size and number of nodules
- Margin of nodules
Solid vs cystic thyroid nodule: which is more likely malignant?
Purely cystic: very rarely malignant
Purely solid: 23% malignant
Mixed solid & cystic: 14% malignant
Thyroid Ultrasound shows Rung-down artifacts: bright dots with comet tails. What is indicated?
inspissated colloid calcifications (colloid aggregates)
= benign cyst
Unlike microcalcification which indicated malignancy
How does vascularity of thyroid lesion indicate malignancy?
Complete avascular= unlikely malignant
Intrinsic/intranodular vascularity: 69-74% malignant (e.g. papillary carcinoma)
Perinodular vascularity: 22% malignant
Is thyroid nodule calcification a sign of malignancy?
Nonspecific – both in benign and malignant conditions
Define 3 types of thyroid nodule calcification and their asso. neoplasm?
Microcalcifications (punctate calcification, psammoma bodies)
Common in papillary carcinoma (also in follicular, anaplastic carcinomas)
Benign: follicular adenoma, Hashimoto thyroiditis
Coarse calcifications: common in medullary carcinoma
Dystrophic calcifications: multinodular goiter
How does the margin of thyroid nodules indicate malignancy?
Irregular margin = likely malignant
e.g. anaplastic carcinoma»_space; local invasion beyond capsuleinto surrounding tissues (e.g. to vertebral muscle, vertebral body, displace carotid artery)
Well-defined = follicular adenoma
How does the size of thyroid nodule indicate malignancy?
> 4cm = likely malignant
How does the number of thyroid nodules indicate malignancy?
Non-specific, cant use to indicate malignancy
Define the echogenic nature and vascularity of thyroid nodules in Grave’s?
Diffuse enlargement of thyroid=homogenously hypoechoic (very dark)
Increase vascularity (thyroid inferno)
List 3 clinical uses for ultrasound related to thyroid pathologies?
- Characterize nodule
- Assess neck for lymph node metastasis in thyroid cancer
- Guides fine needle aspiration (FNA)/biopsy for cytology
Major limitation of Fine needle aspiration cytology in thyroid cancer ddx?
Cannot distinguish between:
Follicular adenoma and Follicular carcinoma
Requires histology: Rely on capsular or venous invasion
What is the most sensitive and specific imaging for ddx benign vs malignant thyroid nodules?
Ultrasound + FNAC (fine needle aspiration cytology)
Indication for CT and MRI in thyroid diseases?
CANCER
Cross-sectional anatomy: intrathoracic extension of goiter
- Post-surgery or radiology: surverillance*** for recurrence of cancer
- Evaluate local, regional and distant metastasis***
Compare the function of 99m-Tc pertechetate vs Iodide scan for thyroid?
99m-Tc pertechnetate: Trapped by thyroid tissue but not incorporated into thyroglobulin for organification = NO FUNCTION CHECK
Iodide = Trapped and organified = FUNCTION CHECK
Which iodide isotopes are used for thyroid scans?
I-123, I-124
I-131 = more for treatment, notoriously high false-negative rate
What is indicated by “hot” and “cold” nodules seen on radionucleotide scans of thyroid??
Hot = increase uptake, Cold = no uptake
Shows ectopic thyroid gland + evaluate function
Hot: Hyperthyroidism, Iodine deficiency, functional adenoma: EXCLUDE CANCER
Cold: Hypothyroid/ adenomas/thyroiditis: COLD= CANCER, mostly benign, 20% malignant
Radionucleotide scans are sufficient for dx of thyroid cancer. T or F?
Always require needle biopsy/aspiration
Multinodular goiter produces “hot nodules” T or F?
False
Mixture of hot and cold
3 clinical uses for radionucleotide scans for thyroid diseases?
- Assess metabolic function: Hot or Cold
- Shows position of ectopic thyroid glands
- Surveillance after treatment with whole-body I-131 scan
Increased thyroglobulin always shows up on 131-I scans. T or F?
False
High rate of false negative on 131-I
Need to use 99mTc-MIBI or 18F-FDG PET/CT scans for higher specificity and sensitivity
List the iodine isotopes for thyroid treatment
I-131
List the iodine isotopes for prostate cancer imaging and treatment
I-125
List the iodine isotopes for thyroid imaging
I-123 I-124
Describe the radiation emitted by I-131 and how it’s used for thyroid diseases?
I-131 trapped inside follicles
destructive beta- particles = destroy parenchymal cells w/o damage to surrounding tissue
Gamma-radiation detected externally for thyroid function monitoring
Which thyroid diseases are treated by I-131?
- benign thyroid disease/ hyperthyroidism: GRAVE’S ***
- Toxic multinodular goiter ***and thyroiditis
- well-differentiated thyroid cancer (e.g. papillary and follicular)
- Iodine-induced hyperthyroidism (amiodarone)
- Ectopic/ metastatic thyroid cancer
Admin of I-131?
orally, sodium iodide, capsule
Limitation of I-131 in identifying metastasis? think about which tissue take up
Uptake by Salivary gland, esophagus, thymus, breast, Liver, stomach, colon, bladder
> > easily misinterpret as metastasis
C/O of I-131 therapy for hyperthyroidism?
- Absolute contraindication: pregnancy and lactation
- Relative contraindication: children and adolescents
Worsening Grave’s ophthalmopathy
Indications for using I-131 to treat hyperthyroidism?
Poor compliance, ADR and recurrence after anti-thyroid drugs
Patients with CVS diseases : Cardiac arrhythmias, heart failure
thyrotoxic periodic paralysis
ADR and long-term safety of I-131/ Radioactive iodine?
1) Mild, well-tolerated: Neck swelling, painful swallowing
2) Nausea, GI discomfort
3) High risk of HYPOthyroidism after one year
4) Rare: radiation cystitis, gastritis, fibrosis
5) Very rare: Bone marrow suppression, anaplastic anaemia, leukemia
No long-term effect on fertility, cancer, congential malformations
Treatment for hypothyroidism caused by I-131?
regular serum thyroid function test and thyroxine replacement
List advantages of I-131 therapy for thyroid diseases?
- Cost effective
- Few adverse effects
- Out-patient therapy
- Reduction in goiter size
List disadvantages of I-131 therapy for thyroid diseases?
- Radiation exposure
- Risk of exacerbation of ophthalmopathy
- Need to delay pregnancy and avoid breastfeeding
- Radiation thyroiditis: 10%
Treatment of Differentiated Thyroid Cancer ?
Total thyrodectomy/ lobectomy +/- radioactive iodine
I-131:
- for eradication of residual cells
- reduce risk of metastasis
- increase sensitivity of serum thyroglobulin and I-131 WBS for surveillance
Anti-thyroid medication can be taken concurrently with I-131 therapy. T or F?
False
Stop anti-thyroid medications 4-14 days before RAI (hyperthyroidism)
Precautions and preparations before starting I-131 therapy?
- No breastfeeding and practice contraception for 4 weeks before (female)
- Low iodine diet for 2 weeks: cut seafood, dairy, soy
- Stop all T4/T3 therapy or switch to recombinant human TSH: increase radioactive iodine uptake by tumour cells
Which patients need recombinant human TSH before I-131 therapy?
- Hypopituitarism
- Severe ischemic heart disease
- psychiatric disturbance
- Functional metastasis causing TSH suppression
Precautions after I-131 therapy?
- Distant/ social isolation (radioactive)
- No pregnancy, breastfeeding, fathering for a year
- No iodine food, meds
Indication for I-131 whole body scan?
- Screen for residual thyroid uptake or distant metastasis
Summarize all the long-term follow-ups after I-131 therapy?
Regular monitoring with serum thyroglobulin
131I-whole body scan 6-12 months after:detect any relapse/metastasis
thyroxine (TSH suppression therapy) to keep TSH below the lower limit
