imaging of the thyroid
TRANSCRIPT
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