1. Imaging of Thyroid Gland
Bengi Gürses, M.D.
Yeditepe University, Medical Faculty
Department of Radiology

2. Anatomy
Located in the anteroinferior part of the neck, outlined by muscle, trachea, esophagus, carotid arteries and jugular veins
Two lobes located along either side of the trachea, connected in the midline by the isthmus
Size and shape can vary among individuals
In adults the mean length is 40-60mm, mean AP diameter is 13-18mm.
Mean thickness of the isthmus 4-6 mm

3. Imaging Modalities Ultrasound Computed Tomography
Magnetic Resonance Imaging

4. Ultrasound Primary radiological imaging modality
US is an accurate method to calculate thyroid volume
Normal thyroid parenchyma has homogeneous medium-high level echogenicity
In color Doppler studies, the gland is seen hypervascular

5. Ultrasound A signal generator is combined with a transducer.
Piezoelectric crystals in the signal generator convert electricity into high-frequency sound waves, which are sent into tissues.
The tissues scatter, reflect, and absorb the sound waves to various degrees.
The sound waves that are reflected back (echoes) are converted into electric signals.
A computer analyzes the signals and displays the information on a screen.
Ultrasonography is portable, widely available, and safe. No radiation is used.

6. Doppler US Doppler US is used to assess blood flow.
Doppler ultrasonography uses the Doppler effect (alteration of sound frequency by reflection off a moving object). The moving objects are RBCs in blood.
Direction and velocity of blood flow can be determined by analyzing changes in the frequency of sound waves.
Changes in frequency of the reflected sound waves are converted into images showing blood flow direction and velocity.

7. Disadvantages Quality of images depends on the skills of the operator.
Obtaining clear images of the target structures can be technically difficult in overweight patients.
Ultrasonography cannot be used to image through bone or gas, so certain images may be difficult to obtain.

10. Thyroid Diseases Congenital Anomalies Nodular Thyroid Diseases
Diffuse Thyroid Diseases

11. Congenital Anomalies Agenesis of one lobe or the whole gland
Hypoplasia
Ectopia (lingual, suprahyoid,pelvic)

12. Ectopia

13. Pyramidal lobe

14. Thyroid Diseases Congenital Anomalies Nodular Thyroid Diseases
Benign nodule(s)
Malignant nodule(s) Carcinoma
Papillary, Follicular, Medullary, Anaplastic
Diffuse Thyroid Diseases

15. Nodular Thyroid Disease
Thyroid nodule  Discrete lesion within the thyroid gland that is sonographically distinguishable from the adjacent parenchyma
Thyroid nodules are very common
Observed at 50% of the population
< 7% of thyroid nodules are malignant
The imaging modality of choice for the investigation of thyroid nodules is US.

17. Thyroid Malignancy

18. Thyroid Malignancy
Papillary Thyroid Carcinoma  Excellent prognosis, 20ys 90-95%
Follicular Thyroid Carcinoma  Excellent prognosis, 20ys 70%
Medullary Thyroid Carcinoma  More aggressive, 10ys 42-90%. May be familial or as a part of MENII syndrome
Anaplastic Thyroid Carcinoma  Poor prognosis, 5ys 5%

19. US Features Suggestive of Malignancy
Suspicious margins, contour and shape
Hypoechoic Solid Nodule
Calcifications
Vascularity
Local invasion and lymph node metastases

20. Margins, Contour and Shape
Complete uniform halo around a nodule  Suggestive of benignity (spec 95%)
Halo / Hypoechoic rim  Pseudocapsule of fibrous connective tissue, compressed thyroid parenchyma and chronic inflammatory infiltrates
HOWEVER!!!
A halo is absent in more than half of all benign nodules
10-24 % of papillary carcinomas have complete / incomplete halo

22. Margins, Contour and Shape
Ill-defined nodule  >50% of the border is not clearly demarcated!!
Suggests malignant infiltration of the parenchyma
No pseudocapsule formation
Sens 7-97%
Some papillary carcinomas may have well-demarcated margin
THEREFORE!!
Unless frank invasion is demonstrated US appearance of the nodule margins alone is unreliable for determining malignancy or benignity!!

24. Margins, Contour and Shape
Shape; Not well-described in the literature
Oval shape  benign
Solid thyroid nodule taller than wide  93% specificity for malignancy
Thought to be due to centrifugal tendency in growth

25. Hypoechoic Solid Nodule
Malignant nodules (carcinoma, lymphoma) typically appear solid and hypoechoic
When compared with thyroid parenchyma
Sens 87%, spec 16-27%
Present in also 55% of benign nodules!!
When compared with strap muscles (very hypoechoic)
Sens 12%, spec 94%
Marked hypoechogenicity is very suggestive of malignancy!!

26. Calcification 2 types Specificity for malignancy 85.8% - 95%
Microcalcification
Coarse calcification
Specificity for malignancy 85.8% - 95%
Found in 29%-59% of all thyroid carcinomas, most commonly in papillary type.
May be seen in benign conditions such as follicular adenoma, Hashimoto thyroiditis

30. Calcification Coarse calcification Secondary to tissue necrosis
Malignancy rate 75%
Cause posterior acoustic shadowing
Inspissated colloid calcifications cause reverberation artifact  Benign!!
Peripheral calcification in MNG >> malignancy

32. COMPLETELY AVASCULAR NODULE IS UNLIKELY TO BE MALIGNANT!!!
Vascularity
Detected with color / power Doppler US
Intrinsic hypervascularity  flow in the central part of the tm greater than the surrounding parenchyma
69-72% of all thyroid malignancies
However; >50% of hypervascular solid thyroid lesions were benign!!
COMPLETELY AVASCULAR NODULE IS UNLIKELY TO BE MALIGNANT!!!

34. Local invasion and lymph node metastases
Highly specific for thyroid malignancy!!
Clinically; dyspnea, hoarseness, dysphagia
Aggressive local invasion  anaplastic thyroid carcinoma, lymphoma, sarcoma.

36. Local invasion and lymph node metastases
Metastases to regional cervical lymph nodes 19,4% in all thyroid malignancies
Most common in papillary type (40-90%)
Medullary type (50%)
Follicular type – very rare!!
Should be a routine part of US evaluation!!

37. Metastatic lymph nodes
Rounded bulging shape
Increased size
Replaced fatty hilum
Irregular margins
Heterogeneous echotexture
Vascularity throughout the lymph node (instead of normal central hilar vessels)

39. Nonspecific US features
Size of nodule
Nodules > 4 cm – more likely to be malignant
Benign nodules may be very large in size!!
Number of nodules
Interval growth of a nodule
Poor indicator of malignancy
The exception; rapid interval growth!!

40. US Criteria (Benign vs Malignant)
Hyper-isoechoic
Halo/Hypoechoic rim
Peripheric (eggshell) calcification
Peripheral vascularity
Oval shape
LAP Ø
Malignant
Marked hypoechoic
Irregular border /microlobulation
Intranodular microcalcification
Internal vascularity
Taller than wide
LAP 

41. FNAB of Incidental Thyroid Nodules
Controversial!!
High prevalence of benign nodules X
Low incidence of thyroid carcinoma
Low rate of mortality of small thyroid carcinomas
Three sets of guidelines for FNAB (fine-needle aspiration biopsy) of thyroid nodules
Kim criteria
American Association of Clinical Endocrinologists
Society of Radiologists in Ultrasound

42. FNAB of Incidental Thyroid Nodules
Kim Criteria
A nodule should have at least one of the following findings
Marked hypoechogenicity, irregular or microlobulated margins, microcalcifications, length greater than width.
American Association of Clinical Endocrinologists
A hypoechoic nodule with at least one additional feature should be biopsied
Irregular margins, length greater than width, microcalcifications.
Society of Radiologists in Ultrasound
FNAB should be performed
Microcalcifications within a nodule (>1 cm)
Coarse calcification within a nodule / Solid nodule (> 1,5 cm)
Mixed cystic and solid nodule (> 2 cm)
Abnormal lymph node
Substantial growth

43. FNAB of Incidental Thyroid Nodules
In a recent study by Ahn et al. (AJR2010;194:31-37)
Kim Criteria and American Association of Clinical Endocrinologists are more accurate!!
Kim Criteria  higher sensitivity!!
AACE  higher specificity!!

45. Thyroid Diseases Congenital Anomalies Nodular Thyroid Diseases
Diffuse Thyroid Diseases
Acute suppurative thyroiditis
Subacute granulomatous thyroiditis
Hashimoto’s (chronic lymphocytic) thyroiditis
Painless (silent) thyroiditis
Graves’ disease

46. Thyroiditis
Acute suppurative thyroiditis  Rare inflammatory disease, caused by bacterial infection, usually affects children. On US; frank thyroid abscess.
Subacute granulomatous (DeQuervain) thyroiditis  Self-limiting viral disease. Fever, enlargement of gland, pain on palpation.
Hashimoto’s (chronic lymphocytic) thyroiditis  Most common type. Autoimmune disease. Young or middle-aged woman. Painless, diffuse enlargement of the gland
Painless (silent) thyroiditis  Lymphocytic infiltration in thyroid. Variant form of Hashimoto. No tenderness. May be seen in the postpartum period.
Graves’ disease  Extensive lymphocytic infiltration of the gland. Usually characterized by thyrotoxicosis.

47. US Features in Thyroiditis
Diffuse glandular enlargement
More hypoechoic than normal parenchyma
Coarsened parenchymal echotexture
Multiple discrete hypoechoic micronodules from 1 to 6 mm in diameter (pseudonodular appearance).
Fibrotic septations – pseudolobulated appearance
Vascularity   Subacute granulomatous (DeQuervain) thyroiditis
Vascularity   Graves’ disease