Role of imaging in management of thyroid nodules Abstract ID – IRIA - 1240

Investigations Ultrasound – Best modality USG guided FNAC CT MRI Technetium-99m pertechnetate or 131/123I scintigraphy Ga68 DOTA scintigraphy PET-CT

USG descriptors of thyroid nodules Echogenicity Hyperechoic (> thyroid), Isoechoic (= thyroid), Hypoechoic (< strap muscles) Taller > wide Shape Microcalcification = / < 1mm Calcifications Margin Circumscribed, Microlobulated, Irregular Vascularity Central or peripheral Composition Solid, Cystic, Mixed Radiology. 2011 Sep;260(3):892-9

US features of benign nodules Uniform halo around nodule Enlarged thyroid with multiple nodules Predominantly cystic Avascular Peri-nodular or spoke-and-wheel like appearance of vessels Radiographics. 2007 May-Jun;27(3):847-60

Less specific features US features of malignant nodules Specific features Less specific features Microcalcifications Markedly hypoechoic Taller than wide in transverse plane Extension beyond thyroid margin Cervical lymph node metastasis No halo around nodule Ill-defined or irregular margin Solid Increased central vascularity Radiographics. 2007 May-Jun;27(3):847-60

1. Calcifications Microcalcifications Psammoma bodies Common in papillary carcinoma Specificity 86%–95% Positive Predictive Value: 42 – 94 % Inspissated colloid calcifications May mimic microcalcifications Distinguished by ring down/reverberation artefact Coarse calcifications MC in medullary carcinomas May coexist with microcalcifications in papillary cancers Peripheral calcification Most common in MNG Break in peripheral calcification – malignant change in an underlying multinodular goitre Radiographics. 2007 May-Jun;27(3):847-60

2. Margins, contour and shape Hypoechoic halo highly suggestive of benignity pseudocapsule of fibrous connective tissue or compressed thyroid parenchyma specificity 95% Ill-defined margins > 50% of its border is not clearly demarcated indicate infiltration of adjacent parenchyma sensitivity: 53%– 89% and specificity 7%–97% Hence frank invasion beyond the capsule has to be demonstrated on HPE Shape taller than wide 93% specificity for malignancy Contour Smooth and rounded Irregular/jagged edges Radiographics. 2007 May-Jun;27(3):847-60

3. Echogenicity of the nodule 4. Vascularity Marked intrinsic hypervascularity Flow in the central part of tumour > surrounding thyroid parenchyma Benign nodules Perinodular vascularity – 25% of circumference Complete avascularity is a more useful sign These features are more useful in selecting a nodule for FNAC in multinodular goitre Malignant nodules are solid and hypoechoic Sensitivity 87% but low specificity 15-27% Marked hypoechogenicity Darker than strap muscle Specificity 94% Radiographics. 2007 May-Jun;27(3):847-60

5. Local invasion and lymph node metastasis Features of nodal involvement Rounded bulging shape Increased size Replaced fatty hilum Irregular margins Heterogeneous echotexture Calcifications / Cystic areas Vascularity throughout the lymph node instead of normal central hilar vessels

TIRADS - Thyroid image reporting and data system TIRADS 1 - normal thyroid gland TIRADS 2 - benign lesions TIRADS 3 - probably benign lesions  TIRADS 4 - suspicious lesions (4a, 4b, and 4c with increasing risk of malignancy) TIRADS 5 - probably malignant lesions (> 80% risk of malignancy) TIRADS 6 - biopsy proven malignancy J Clin Endocrinol Metab. 2009 May;94(5):1748-51

TIRADS 2 – Colloid nodules - 0% risk of malignancy Avascular anechoic lesion with echogenic specks (colloid type I) Vascular heteroechoic non-expansile, non-encapsulated nodules with peripheral halo (colloid type II) Isoechoic or heteroechoic, non-encapsulated, expansile vascular nodules (colloid type III) Hyperechoic, iso-echoic or hypoechoic nodules, with partially formed capsule and peripheral vascularity <5% risk of malignancy TIRADS 3 J Clin Endocrinol Metab. 2009 May;94(5):1748-51

TIRADS 4 & 5 Based on five features: solid component markedly hypoechoic nodule microlobulations or irregular margins microcalcifications taller-than-wider shape TIRADS 4a - one suspicious feature TIRADS 4b - two suspicious features TIRADS 4c - 3-4 suspicious features TIRADS 5 - all five suspicious features 4a - 5-10% risk of malignancy 4b & 4c - 10-80% risk of malignancy 5 - >80% risk of malignancy J Clin Endocrinol Metab. 2009 May;94(5):1748-51

Pitfalls on USG - 1. Cystic variant of papillary carcinoma Cystic component occurs in 13-26% Predominant cystic appearance is rare Can mimic benign cystic hyperplastic nodule Look for Solid components with vascularity Solid excrescences protruding into the cyst Angle of contact by the solid component with the cyst wall Acute – malignancy Obtuse – degenerating cyst (colloid) Microcalcifications RadioGraphics 2007; 27:847–865

2. Diffusely infiltrative hypervascular tumour This variant can be seen in papillary, follicular carcinomas and lymphoma Mimics autoimmune conditions Ex. Graves / thyroiditis De Quervain’s thyroiditis – hypoechoic nodule, may be taller than wide / may have microcalcification Short duration of history of pain Soft on Elastography Look for Echogenicity – markedly hypoechoic History Microcalcifications Case of thyroid lymphoma – markedly hypoechoic and diffusely enlarged thyroid gland in a 62 year old man

ELASTOGRAPHY VTI – Virtual Touch Imaging Objective evaluation of tissue stiffness to differentiate between benign and malignant nodules Sensitivity – 96.3 %; Specificity – 96.2% VTI – Virtual Touch Imaging Reflects the elasticity of tissue with gray-scale image in the field of view (FOV) Dark indicates hard tissue whereas the bright indicates soft tissue VTQ – Virtual Touch Quantification Range for shear wave velocity is 0–9 m/s (beyond this range displayed as “x.xxm/s”)  The mean shear wave velocity of VTQ malignant nodules – 3.88 ± 2.24 m/s Benign nodules - 2.57 ± 0.79 m/s Ultrasonography 2014; 33(2): 75-82

FNAC CT & MRI CT protocol Any palpable thyroid nodule if its not TIRADS 2 – FNAC should be done CT & MRI CT protocol Non-contrast Thin slice thickness – 0.7-0.8mm Axial, coronal & sagittal planes Neck & thorax (MC & AC – include liver) Inferior to ultrasound in diagnosing thyroid cancer Main role is in staging Intravenous iodinated contrast agents interfere with the 131/123I uptake for at least 1–3 months Advantage of MRI avoids the use of iodinated contrast agents Very specific in showing tracheal, oesophageal and recurrent laryngeal nerve invasion

CT preferred Calcification Retrosternal region Extent Metastasis Mediastinal nodes

Ga68 DOTA PET/CT Thyroid scintigraphy Somatostatin analogs labelled with Ga 68 High affinity for Somatostatin receptors SSTR expressed – neurons & endocrine cells Thyroid – medullary carcinoma To localize an inconclusive nodule Staging Recurrence Treatment response Medullary carcinoma Thyroid scintigraphy Indications whole body scan for distant metastases estimation of local residual thyroid post thyroidectomy follow-up for tumour recurrence Cold – 85% of nodules are cold, hence not used to diagnose malignancy

Imaging for post-op, pre-radiotherapy planning and surveillance FDG-PET Imaging in distant metastases 131I – treatment of functioning thyroid cancer & imaging of functioning metastases Ga68 DOTA PET/CT Bone scan / scintigraphy – bone metastases CT / MRI – if needed High negative predictive value Incidental focal uptake in thyroid  Specific USG features  80 % malignant Imaging for post-op, pre-radiotherapy planning and surveillance To look for residual / recurrence of primary tumour & nodal involvement Routinely done with ultrasound; CT / MRI – no significant role Yearly ultrasound of the neck +/− FNA for surveillance of disease-free patients PC/FC - normal thyroglobulin (Tg > 50 ng/mL – functioning metastases after complete ablation of thyroid tissue) Cancer imaging.2008;8(1):57-59

Conclusion Ultrasound plays a major role differentiating benign & malignant nodules Specific features: markedly reduced echogenicity microcalcifications taller than wide local invasion lymph node metastases Histopathological examination – confirmatory Recent advances – Elastography increases the positive predictive value when combined with conventional ultrasound