Thyroid Radiology

Question 1

Anatomy

Answer 1

a. Thyroid gland is made up of two lobes located along either side of trachea and connected across the midline by the isthmus.
b. 10 – 40% of normal patient have small pyramidal lobe arising sup. from the isthmus, lying in front of thyroid cartilage.
c. Variable size.

Question 2

Imaging Modalities

Answer 2

a. Anatomic imaging- Ultrasound, CT and MRI.
i. Indicated to detect or characterize palpable or incidentally found thyroid nodule on other modalities.
ii. Ultra Sound is the best modality.

b. Functional Imaging- Iodine ( I123 or I131) scan.
i. To evaluate for function of the thyroid gland or nodule in patient with abnormal thyroid function.
ii. Evaluate for distant metastatic disease.

c. PET/CT scan- Staging and restaging of thyroid cancer.

d. Radiograph
i. Not useful to detect thyroid disease
ii. May incidentally suggest a thyroid enlargement or mass by noting mass effect on the soft tissues (often more obvious clinically) or on tracheal air column

Question 3

Imaging and Radiograph

Answer 3

Radiograph

a. Not useful to detect thyroid disease
b. May incidentally suggest a thyroid enlargement or mass by noting mass effect on the soft tissues (often more obvious clinically) or on tracheal air column

Question 4

Incidental Thyroid Mass

Answer 4

Chest radiograph

shows incidental mass effect on the trachea

Question 5

Imaging Modalities

Ultrasound

Answer 5

Ultrasound –
1) No radiation, real time, Doppler capability

2) The best modality to detect and characterize thyroid nodule.
3) Best modality to detect lymph node metastasis in post-op patient of thyroid cancer.

Real-time guidance for FNA biopsy (tissue diagnosis)

Question 6

Thyroid nodule

Answer 6

a. A thyroid nodule on Ultrasound is a discrete lesion within the thyroid gland that is radiologically distinct from the surrounding thyroid parenchyma.
b. Nonpalpable nodules detected on US or other anatomic imaging studies are termed incidentally discovered nodules or “incidentalomas.”

Question 7

Lymph Node Assessment

Answer 7

a. Essential in the setting of thyroid cancer.
b. Detection of lymph nodes.
c. Characterization- Normal vs. Abnormal
d. Mapping of lymph nodes: Lymph node mapping will alter the surgery in 40% of the patients, as it may find abnormal nodes in different compartment of the neck.

Question 8

CT Neck

Normal Thyroid

Answer 8

a. Hyperdense on Noncontrast
b. Hypervascular with IV contrast.
c. Radiation
d. Need IV contrast to detect local invasion.

Question 9

Neck CT

Answer 9

CT
a. Useful to define local extension of cancer in adjacent structures.

b. Detect abnormal lymph nodes specifically in the areas not visualized by ultrasound.
c. Distant metastasis.

Question 10

Imaging Modalities

Answer 10

MR

a. Useful in identifying infiltrative disease particularly in post-therapy neck where anatomy is distorted
b. Detection of invasion of adjacent structures and deep nodal disease.

Question 11

Neck MRI

Answer 11

a. Thyroid is slightly hyperintense on T2.
b. Can’t differentiate solid vs. cystic nodule.
c. Can’t visualize micro-calcification.
d. Expensive

Question 12

PET/CT Scan

Answer 12

Hypermetabolic adenopathy- met from thyroid cancer

Question 13

PET positive nodule

Answer 13

a. 58 year old female with metastatic melanoma.
b. PET positive thyroid nodule- Approximately 30% risk for malignancy.
c. FNA thyroid nodule

Question 14

Iodine scan

Answer 14

a. Thyroid imaging with radioiodine demonstrates the distribution of functioning thyroid tissue, including ectopic tissue, since thyroid tissue is the only tissue that concentrates large amounts of iodine.
b. Must discontinue iodine containing preparation and medications that could potentially affect the ability of thyroid tissue to accumulate iodide.

Question 15

Iodine Scane

I-123 vs I-131

Answer 15

a. I-123 scan- To evaluate function of the thyroid gland and thyroid nodule in patient with abnormal thyroid function.
i. Half life of I-123 is 13 hrs.

b. I-131 scan- Diagnostic and therapeutic role.
i. Half life of I-131 is 8 days.
ii. Detect local and distant thyroid cancer metastasis.
iii. Treatment of hyperthyroidism as well as for well differentiated thyroid cancer.

Question 16

Gamma Camera

Answer 16

a. 0.5 mCi (500 micro curie) I-123 as sodium iodide capsule (oral suspension).
b. Image thyroid gland after 6 hours with gamma camera

Question 17

Thyroid Probe

Answer 17

a. 5 mins ANT, 5 mins RAO and LAO and additional 5 mins ANT image if palpable nodule.
b. Calculate uptake with thyroid probe.

Question 18

I-123 thyroid scan

Answer 18

a. Normal gland takes up iodine

b. I-123 scan- To evaluate function of the thyroid gland and thyroid nodule in patient with abnormal thyroid function.
i. Half life of I-123 is 13 hrs.

c. Hot large thyroid gland
Graves disease

Question 19

I-123 scan

Cold Nodule

Answer 19

Cold Nodule:

What Next?
i. Ultrasound- Solid Vs. cyst.

ii. If solid- 15-25% cancer risk
U/S guided FNA.
Cyst- Benign

Question 20

Hot Nodule found from I-123 scan

Answer 20

Hot Nodule
i. Malignancy is unlikely in functioning nodule
(< 1%).

ii. 5-10% of nonfunctioning nodules (cold nodules) are thyroid cancer.

Question 21

I-131 Scan

Answer 21

Diagnosis and treatment:
1. Hot lymph nodes

2. Hot lungs
3. Normal low-level salivary gland activity

Question 22

Telling benign and malignant thyroid disease apart

Answer 22

a. No imaging modality can reliably differentiate between benign and malignant thyroid disease.
b. Tissue diagnosis by FNA should be obtained on suspicious lesions.

Question 23

Thyroid nodule and size

Answer 23

a. Nonpalpable nodules have the same risk of malignancy as palpable nodules with the same size.
b. Generally, only nodules >1 cm should be evaluated, since they have a greater potential to be clinically significant cancers.
c. Occasionally, there may be nodules <1 cm that require evaluation because of suspicious US findings, associated lymphadenopathy, a history of head and neck irradiation, or a history of thyroid cancer in one or more first-degree relatives.

Question 24

The imaging test of choice to evaluate a thyroid lesion size, location, and simple cyst vs not simple cyst is:

a. A lateral skull X-ray
b. A CT (computed tomography) scan without contrast
c. An MRI (magnetic resonance imaging) with contrast
d. A PET (Positron emission tomography) scan
e. Ultrasound

Answer 24

e. Ultrasound

Ultrasound –
1) No radiation, real time, Doppler capability

2) The best modality to detect and characterize thyroid nodule.
3) Best modality to detect lymph node metastasis in post-op patient of thyroid cancer.

Real-time guidance for FNA biopsy (tissue diagnosis)

Question 25

What is the imaging testof choice to evaluate a patient with hyperthyroidism?

a. Iodine scan
b. Ultrasound
c. CT (computed tomography) scan
d. MRI (magnetic resonance imaging)

Answer 25

a. Iodine scan
1. Thyroid imaging with radioiodine demonstrates the distribution of functioning thyroid tissue, including ectopic tissue, since thyroid tissue is the only tissue that concentrates large amounts of iodine.
2. Must discontinue iodine containing preparation and medications that could potentially affect the ability of thyroid tissue to accumulate iodide.