Imaging Assessment of the Thyroid Gland

Question 1

What are the different imaging modalities?

Answer 1

• PLAIN RADIOGRAPHY (X-RAYS)
• ULTRASOUND
• COMPUTED TOMOGRPAHY (CT)
• MAGNETIC RESONANCE IMAGING (MRI)
• RADIONUCLIDE IMAGING (RNI including PET/CT), thyroid specific radio tracer

Question 2

What is the best initial imaging modality?

Answer 2

Ultrasound

Neck is superficial structure and not ionising

Question 3

Describe ultrasound for imaging

Answer 3

• High frequency linear array probe
• Excellent soft tissue resolution
• Real time assessment
• Does not use ionising radiation

Disadvantages:

• Operator dependent
• Not all patients are suitable ultrasound subjects (obesity)

Question 4

Can ultrasound characterise the clinically palpable nodule?

Answer 4

-Benign versus malignant

-B mode assessment (black/white image)
=structure, border, size, placement
-Colour flow Doppler
=vascularity
-Elastography
=stiffness

Question 5

How do we classify thyroid nodules?

Answer 5

• BTA (2014) classification of thyroid nodules
• Ultrasound ‘U’ grade 1 - 5

=U1: normal
=U2: benign
=U3: indeterminate
=U4: suspicious
=U5: malignant

Question 6

Describe U1

Answer 6

Normal

(a) smooth outline
(b) homogenous echogenic parenchyma

Question 7

Describe U2

Answer 7

Benign

(a) halo, hyper- / iso-echoic (to background thyroid tissue)
(b) cystic change +/- ring down sign (white flecks) (colloid)= black, no internal tissue, well-defined border
(c) micro- cystic / spongiform
(d) peripheral egg shell calcification
(e) peripheral vascularity

Hyperplastic nodules= well-defined margin, hypoechoic halo, spongiform

Question 8

Describe U3

Answer 8

Indeterminate

(a) homogenous, isoechoic/hyperechoic, solid, halo (follicular lesion)
(b) hypo-echoic, equivocal echogenic foci, cystic change
(c) mixed/central vascularity

=Irregular lower margin

Question 9

Describe U4

Answer 9

Suspicious

(a) solid, hypo-echoic (cf thyroid)
(b) solid, very hypo-echoic (cf strap muscle)
(c) disrupted peripheral calcification, hypo-echoic
(d) lobulated outline

=Less defined, dark areas, hypoechoic, echogenic foci
=Mixed colour flow pattern

Question 10

Describe U5

Answer 10

Malignant

(a) solid, hypo-echoic, lobulated/irregular outline, micro-calcification (papillary carcinoma)
(b) solid, hypo-echoic, lobulated/irregular outline, globular calcification (medullary carcinoma)
(c) intra-nodular vascularity
(d) shape (taller >wide)- invade normal structures
(e) characteristic associated lymphadenopathy

=Marked internal vascularity in colour
=Hard

Question 11

When do we use fine needle aspiration?

Answer 11

U3: indeterminate
U4: suspicious
U5: malignant

Question 12

Describe ultrasound-guided fine needle aspiration

Answer 12

• 25G spinal needle
• Non suction capillary technique (as very vascular)
• Three passes (multiple samples)
• Slides (two fixed, two air dried) + needle rinse in Cytolytic solution

Question 13

What are the risks of fine needle aspiration?

Answer 13

• Bleeding
• Infection
• Iatrogenic injury to surrounding structures
• Inadequate sampling requiring repeat FNA/biopsy

Question 14

Describe core biopsy

Answer 14

• Core biopsy established technique, usually for lymph nodes, for pathologists
• Data mixed
• Probably more useful than repeat FNA in previous non-diagnostic samples
• Generally well tolerated (anaesthetic)
• Probably no excess of complications compared to FNA

Question 15

Describe Radionucleotide imaging

Answer 15

• (99mTc) Technicium Pertechnetate= good half life, not radioactive for days
• (I-123) Iodine (imaging)= emits gamma rays
• (I-131) Iodine (treatment)= higher strength
• Typically used to assess the functionality of a thyroid nodule (context of hyperthyroidism).
• Assessment of the cause for hyperthyroidism when the aetiology is not clear.

Question 16

How is RNI used in a solitary thyroid nodule?

Answer 16

• 99mTc Pertechnetate scan
• Increased uptake/functionality – “hot” nodule
• No uptake/non-functioning – “cold” nodule (16% malignant)
• Malignancy is extremely rare in “hot” nodules on RNI imaging in this setting
• However, 16% of “cold” nodules are malignant

Question 17

How does RNI vary in different pathologies?

Answer 17

-Graves
=Homogenously increased isotope uptake throughout thyroid gland
-Solitary toxic nodule
=solitary area of increased uptake with reduction in uptake elsewhere in the gland
-Cold nodule
=Focal area of reduced uptake cold nodule

Question 18

What are the different isotopes of radioactive iodine used for?

Answer 18

-I-123: imaging of active thyroid tissue
=harmless to thyroid
=determine activity of thyroid
=ectopic thyroid tissue

-I-131: treatment of thyroid disorders
=destroys thyroid cells
=hyperthyroidism
=thyroid cancer. micro metastasis

Question 19

Describe I-131 radioiodine treatment

Answer 19

• Whole body planar imaging 10 days post treatment for thyroid cancer.
• Uptake of radioiodine in lymph nodes and distant metastases is associated with a favourable prognosis (undifferentiated bad)
• Demonstration of disease is essential to ensure optimum follow up and management

Question 20

Describe cross-sectional imaging

Answer 20

-Role of CT/MRI

• Staging of patients with suspected metastatic thyroid cancer
• Assessment of patients with metastatic thyroid cancer following treatment or on surveillance
• Assessment of patients with suspected recurrence where ultrasound is negative

Question 21

Describe PET scans

Answer 21

• Positron emission tomography
• FDG – Fludeoxyglucose
• Glucose metabolism scan
• Used in staging of a number of cancers (looking for involved lymph nodes + distant disease).
• Role in thyroid cancer: useful in patient with known thyroid cancer with suspected recurrence not demonstrated on US/CT/MR.