THYROID IMAGING

MODERATOR: DR NASEER AHMAD CHOHSR RESIDENT INCHARGE: DR TEHLEEL ALTAF

PRESENTER: DR SHARIQ AHMAD SHAH

OVERVIEW

• Anatomy and embryology• Imaging modalities• Diffuse thyroid disease• Evaluation of a thyroid nodule• Recent developments

ANATOMY OF THYROID

SIZE: NEWBORN: 18-20 mm long 8-9 mm AP ADULTS: 4-6 cm long 13- 18 mm AP isthmus :4-6 mm VOLUME: 19.6 ml males 18.6 ml females

EMBRYOLOGY

• Develops from median and lateral anlages.

• Median anlage: arises in the middle of oropharynx at 4th

to 5th gestation age , gives rise to follicular tissue.

• Lateral anlage: arise from ultimobrachial bodies

(derivatives of fourth and fifth branchial pouches), gives

rise to parafollicular c cells.

• Fusion occurs by tenth week forming bilobed gland

IMAGING MODALITIES

• X RAY• USG• RADIONUCLIDE IMAGING• CT / MRI

X ray

• Enlargement• Tracheal shift or narrowing• calcifications• Retrosternal extension• Bone destruction• Pulmonary metastasis

Nuclear scintigraphy

• Agents used are I-123, I-131, TC-99• Done with a gamma scintillation camera• Normal gland shows homogenous

radionuclide uptake and distribution

INDICATIONS

• Assessment of anatomy

• Assessment of function

• Post operative assessment

• Detection of nodule – hot or cold or warm

• Detection of functional metastatic tissue in known case

of thyroid ca.

• Detection of retrosternal goitre.

CONTRAINDICATIONS

• Pregnancy

• Hypersensitivity to iodine

• Discard breast milk for 26 hrs after injection

PREPARATION

• Stop antithyroid drugs 2 days before.

• Stop thyroid hormones 1 week before.

• Avoid iodinated contrast 4 weeks before.

• Stop iodine rich foods ( fish , cauliflower) a week

before.

• Done after 4 hr fasting.

Normal thyroid scan

Diffuse toxic goitre

DIFFERENTIAL DIAGNOSIS

COLD NODULE(8-25% chances of malignancy)

• Thyroiditis• Cyst• Fibrosis• Non functioning

adenoma• Multinodular goitre• Malignancy

HOT NODULE (Malignancy rare)

• Functioning adenoma

• Thyroiditis

USG

• First choice of evaluation• Acessible, inexpensive and non invasive• High spatial resolution- 0.5 to 1 mm• Size and volume measurements.• Doppler USG ( PSV of major thyroid A = 20-

40cm /s and intraparenchymal arteries= 15-30cm/s)

Congenital anomalies• Hypoplasia/aplasia• Ectopia• Thyroglossal cyst

Diffuse thyroid disease• Thyroiditis Acute suppurative Sub acute granulomatous (De Quervans) Chronic lymphocytic ( Hashimoto) Invasive fibrous throiditis (Riedels)

• Graves disease

Sub acute thyroiditis

Hashimoto - micronodularity

Hasimoto- coarse septation

Graves disease

Invasive fibrous ( Riedel’s thyroiditis)

EVALUATION OF THYROID NODULE

• NODULE: a discrete lesion that is radiologically distinct from sorrounding parenchyma.

• Some Palpable lesions may not be radiologically distinct….not considered as nodule

• Non-palpable nodules detected on imaging studies --- incidentalomas

• Prevalence

• Incidence of malignancy : 9-13 %

• Generally only nodules > 1 cm should be

evaluated.

• Long term studies showed no difference in

outcome between patients with biopsy proven

carcinoma < 1 cm undergoing thyroidectomy

and those with no surgical intervention.

( Ito et al, world j surg 2010;34;28-35)

Serum TSH

• Serum TSH should be measured during initial evaluation

• If serum TSH is subnormal, a radionuclide scan should be

performed.

• If serum TSH is normal or elevated, a radionuclide scan

should not be performed as the initial imaging modality.

Serum thyroglobulin measurement

• Routine measurement of serum Tg is not recommended. ( revised ATA 2015)

TSH and Radionuclide scan• A higher TSH level , even within upper part of

refrence range is associated with increased risk of

malignancy in a thyroid nodule

• If TSH is low, risk of malignancy depends on tracer

uptake in scan

Hot nodule : rarely harbours malignancy, no

need for cytology.

Cold nodule: non functioning

USG

SUSPICIOUS NODULE

1. Taller than wide shape

2. Spiculated or irregular margins .

3. Markedly hypoechoic nodule.

4. Predominant solid composition.

5. Microcalcification in a predominantly solid nodule (3 fold risk).

6. Macrocalcification in a solid nodule ( 2 fold risk)

7. Absence of halo.

8. Intranodular vascularity.

AMERICAN THYROID ASSOCIATION NODULE GUIDELINES , JANUARY

2016.

•

HIGH HIGH

INTDD LOW

VERY LOW

Thyroid nodule evaluation and management algorithm

Recommendations for initial follow up of nodules with BENIGN FNAC

1. Nodules with high suspicion US pattern: repeat US and USG guided FNAC within

12 months.

2.Nodules with low to intermediate suspicion US pattern:

repeat US at 12 months

rapid growth or development of new suspicious features repeat FNAC

3. Nodules with very low suspicion: utility of surveillance not known

4. If a nodule has undergone repeat FNAC with a second benign cytology

no need to follow up with US

Follow up for nodules that do not meet FNAC criteria

high suspicion us pattern repeat us in 6-12 months

low or intermediate suspicion us pattern

repeat us at 12- 24 months

>1 cm nodules with very low suspicion pattern

repeat us at > 24 months

< 1 cm nodules with very low suspicion us pattern

no need of follow up

CROSS SECTIONAL IMAGING

• Important adjunctive anatomic information.

• Better delineation of lesion within thyroid.

• Detection of lymph node metastasis.

• Extension of disease to adjacent tissues of neck.

• Assess paraspinal muscle, esophageal, tracheal,

jugular vein invasion.

CT SCAN• On NCCT thyroid appears as two wedge

shaped structures of homogenous attenuation with density of 80- 100 HU because of iodine content

• Enhances homogenously on iv contrast.• Contrast interferes with radionuclide scan. so

scan should be performed either before CT or 6 weeks after it.

NCCT CECT

GOITRE

MRI

• Dedicated surface coils centered over thyroid.

• T1 : thyroid shows homogenous signal intensity slightly

greater than that of neck muscles.

• T2: gland is hyperintense relative to neck muscles

• Gadolinium contrast can be administered.

• Gadolinium does not interfere with iodine uptake and

organification, so can be used in conjunction with

scintigraphy.

T1W T2W

RECENT DEVELOPMENTS

PERFUSION CT • Measures temporal changes in tissue density after

iv contrast.

• Quantifies abnormal vasculature within tumours,

thus allowing assessment of tumour agressiveness.

• Benign tumours have been found to show low BF

and MTT compared to malignant tissue.

DIFFUSION WEIGHTED MRI:• Performed with the aim of differentiating

malignant from benign lesions.

• This technique evaluates rate of microscopic

water diffusion in tissues.

• All benign nodules have higher mean ADC value

than malignant nodules.

CONTRAST ENHANCED ULTRASOUND• Enhancement pattern is recognised.

• Ring enhancement correlates with benign

lesions while heterogenous enhancement

correlates with malignant lesions.

COLLOID

CYSTIC PAPILLARY CA

ELASTOGRAPHY• Obtains information about tissue stiffness non invasively.

• Elastography score (ES) is assigned based on colour

pattern of lesion relative to sorrounding tissue.

• Red ( soft tissue), green ( intermediate degree of

stiffness), blue ( anelastic tissue).

• An ES of 4-5 is highly predictive of malignancy

(sensitivity 94%).

ELASTOGRAM PATTERNS

• PATTERN 1: Whole nodule elastic

• PATTERN 2: Most part elastic, inconsistent

inelastic areas

• PATTERN 3: Constant portions of anelastic areas

• PATTERN 4: Uniformly anelastic

BENIGN NOD HYPERPLASIA

PAPILLARY CA

PET SCAN• Used in follow up of patients with thyroid cancer due

to incresed glucose metabolism by malignant tumours

• May be useful in tumours which don’t concentrate

iodine.

• In patients with raised thyroglobulin levels after

thyroidectomy, whole body scans are obtained to

identify regions of FDG uptake.

MAGNETIC RESONANCE SPECTROSCOPY

OPTICAL COHERENCE TOMOGRAPHY

Thyriod ultrasound reporting lexicon-- TIRADS

Refrences1. Carol rumack, diagnostic ultrasound 4e

2. David sutton,text book or radiology & imaging

3. Journal am coll radiol 2015;12:1272-1279

4. Open journal of radiology,2013,3 103-107

5. Radiology;vol 260:number 3-september 2011

6. Radiographics 2014;34:276-293

THANKS