Table of Contents
Definition / general | Essential features | Terminology | Diagrams / tables | Clinical features | Radiology images | Additional referencesCite this page: Jug R, Jiang X. Ultrasound. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/thyroidultrasound.html. Accessed January 18th, 2021.
Definition / general
- See also Cytopathology chapter
- Basic physics principles
- Ultrasound probe both emits and receives sound waves
- Medical ultrasound: 2 - 20 MHz
- Lower frequencies: better penetration, lower resolution
- Higher frequencies: lower penetration, higher resolution
- B-Mode (Brightness Mode):
- 2D black and white image in < 1mm "slice"
- Emitted waves are reflected back from the target material relative to the degree of the material's acoustic impedance, which is dependent on density
- Higher density materials generally "reflect" more and look brighter
- For example, bone is more "reflective" than soft tissue; thus bony structures appear brighter on ultrasound images in contrast to darker surrounding tissue
- Doppler mode:
- Measures direction and speed of tissue / blood motion
- M-Mode (Motion mode):
- Pulses are emitted in quick succession and each time, an image is taken; over time, this is analogous to recording a video in ultrasound (used for heart valves)
- References: Arch Pathol Lab Med 2010;134:1541 and Radiol Clin North Am 2011;49:417
Essential features
- Sonographic features of benign thyroid nodules
- Small size (< 1 cm)
- Fluid filled
- Honeycomb morphology
- Hyperechoic (colloid nodule or focal nodular Hashimoto thyroiditis)
- Large nodules if they are predominantly cystic (cystic change accounting for > 50% of nodule)
- Sonographic features of thyroid nodules suspicious for malignancy (Diagn Cytopathol 2008;36:390, Eur J Endocrinol 2009;161:103)
- Solid oval nodules (anterior-posterior dimension: transverse dimension ratio is > 1)
- Presence of discrete coarse echogenic foci and/or microcalcifications
- Hypoechoic (medullary and papillary thyroid cancers)
- Thin capsules or irregular borders (suggestive of extracapsular spread)
- Intranodular vascularity
- Nodal metastases
- Sonographic features of benign lymph nodes
- Oval shape (short axis: long axis ratio ≤ 0.5)
- Hypoechoic cortex and echoic hilum (due to adipose tissue)
- Clearly demarcated margin from surrounding tissue
- Central vascularization
- Sonographic features of lymph nodes suspicious for malignancy (Eur J Endocrinol 2009;161:103)
- Round shape (short axis: long axis ratio > 0.5)
- Echogenic heterogeneity of cortex and absent fatty hilum
- Irregular margin with surrounding tissue
- Increased or abnormally located vascularity
- Features suggestive of metastatic thyroid cancer: cystic appearance, hyperechoic punctations / calcifications
- Strongly recommend ultrasonic examination of thyroid and cervical lymph nodes if thyroid nodules; recommend FNA for sampling if > 1 cm in greatest dimension and high suspicion sonographic pattern (estimates a 70% - 90% risk of malignancy), including:
- Solid hypoechoic nodule or nodule that is partially solid and hypoechoic and partially cystic with one or more of the following features:
- Irregular margins (infiltrative, microlobulated)
- Microcalcifications
- Oval (taller than wide) shape
- Rim calcifications with an extrusive soft tissue component
- Evidence of extrathyroidal extension (Thyroid 2016;26:1)
- Solid hypoechoic nodule or nodule that is partially solid and hypoechoic and partially cystic with one or more of the following features:
Terminology
- Anechoic: black (e.g. blood, cystic fluid)
- Azimuthal plane: midsagittal plane of transducer, "beam" used to guide needle in UGFNA
- Hyperechoic: brighter than surrounding tissue (e.g. bone)
- Hypoechoic: darker than surrounding tissue (e.g. soft tissue vs. bone)
- Isoechoic: same intensity as surrounding tissue
- Ultrasound artifacts:
- Posterior (acoustic) shadowing: strong reflectors (air) or absorbers (stones, bones) block visualization of structures beyond them in relation to the beam
- Posterior (acoustic) enhancement: anechoic structures (cysts) show brighter signals from areas beyond them in relation to the beam
- Eggshell calcification: nodules surrounded by a layer of calcium have bright anterior and posterior walls due to a reflection from the surface, but posteriorly there is acoustic shadowing; this phenomenon also leads to edge artifact in which parallel dark lines extend posteriorly from the sides of nodules
- Reverberation artifact: sound waves reflect off a very reflective surface and are re-reflected from the skin, resulting in phantom images behind the target image
- Comet tail artifact: reverberation artifact from front and back of a very strong reflector / absorber (air bubble, metal fragment) - can also happen with dense colloid
- Bayonet sign:
- Due to speed propagation artifact - machines use average speed of sound to calculate depth
- If sound actually travels faster in the tissue (anechoic or hypoechoic structures), a reflector will appear closer to the transducer than its actual depth and vice versa
- A needle with its tip in a cyst or nodule with differing echogenicity from surrounding tissue will appear to have its tip bent due to this artifact, looking like a bayonet
- See Arch Pathol Lab Med 2010;134:1541 and Radiol Clin North Am 2011;49:417
Diagrams / tables
Contributed by Rachel Jug, M.B.B.Ch.
Images hosted on other servers:
Typical appearances of diffuse thyroid diseases:
Thyroid disorder | Grayscale ultrasound | Color doppler | Key features |
---|---|---|---|
Graves thyroiditis | Enlarged, mildly hypoechoic, heterogeneous | Markedly ↑ | Markedly hyperemic; proptosis; hyperthyroid; + antithyroid antibodies |
Hashimoto thyroiditis | Enlarged, heterogeneous with lobular margins; hypoechoic and micronodular, septal lines | Highly variable: both ↑ and ↓ flow possible | + Antithyroid antibodies, hypothyroidism; cervical adenopathy |
Subacute lymphocytic thyroiditis (painless) | Hypoechoic | Insufficient data | + Antithyroid antibodies; postpartum; transient |
De Quervain thyroiditis (subacute granulomatous) | Painful patchy areas of hypoechogenicity | ↓ in the hypoechoic patch | Thyroid pain over area of hypoechogenicity; ↑ ESR |
Acute suppurative thyroiditis | Abscess or infected linear tract in the thyroid | Normal background; no flow within an abscess | Acute presentation with signs of infection and pain; ↑ ESR; possible pyriform sinus fistula |
Riedel thyroiditis | Large hypoechoic thyroid with coarse parenchyma | Insufficient data | Large, rock hard gland; encases adjacent structures |
Medication induced (i.e. amiodarone) (AIT) | Type 1: abnormal thyroid; Type 2: normal thyroid | Type 1: ↑; Type 2: absent | History of current or recent amiodarone use; hyperthyroid |
Atrophic thyroiditis | Small, hypoechoic thyroid | ↓ | + Antithyroid antibodies; usually hypothyroid |
Radiation thyroiditis | Small, hypoechoic thyroid | Variable | Known external beam or I131 administration |
Thyroid lymphoma | Large, ill defined, markedly hypoechoic nodules or masses with ↑ through transmission on background of Hashimoto's thyroiditis | ↓ in the hypoechoic mass | Rapidly enlarging neck mass in patient with history of Hashimoto, ± adenopathy |
Multinodular goiter | Closely opposed or interspersed, similar appearing nodules replace parenchyma, coarse calcifications, variable cystic changes in nodules | Variable | Confluent nodules in a normal or enlarged thyroid; ± abnormal thyroid function tests |
Abbreviations: AIT, amiodarone induced thyrotoxicosis; ESR, erythrocyte sedimentation rate
See: Radiol Clin North Am 2011;49:391
Clinical features
- Indications for Ultrasound Guided Fine Needle Aspiration (UGFNA)
- Nonpalpable or difficult to palpate nodules, most commonly of thyroid
- Targeting specific areas in complex and cystic nodules, such as solid areas
- For repeat FNA, when a prior palpation guided FNA sample was insufficient (Diagn Cytopathol 2008;36:390)
- Followup for patients post partial or total thyroidectomy for malignancy, such as to sample thyroid bed (J Ultrasound Med 2013;32:1319)
- Benefits of UGFNA compared to conventional FNA alone
- Higher rates of successful biopsy (J Clin Ultrasound 1994;22:535, Thyroid 1998;8:15, Thyroid 1998;8:283)
- Potentially lowers risk of damage to surrounding structures, which can be visualized
- Varying reports on cost effectiveness (BMC Endocr Disord 2009;9:14, Thyroid 2006;16:555)
- Efficacy of UGFNA is improved by the presence of a cytopathologist onsite, decreasing the overall inadequacy rate from 9.3% to 6% (Br J Radiol 2014;87:20130571)
- Complications and contraindications: Same as conventional FNA
- Overview of procedure - Focused thyroid U / S and biopsy
- Image each thyroid lobe in the transverse and longitudinal planes to determine the overall appearance and locate nodules
- After completing ultrasonic assessment of the thyroid, relocate the position and measure size of suspicious nodules
- Approaches to UGFNA relative to the transducer beam (azimuthal plane)
- For each approach, orient the needle with the bevel tip up to create the greatest reflection
- Parallel approach "in beam"
- Point the needle down along the plane of the beam towards the nodule
- Maintain needle and transducer in the same plane, parallel to the plane of the transducer and advance the needle into the nodule
- Advantage: entire length of needle seen
- Perpendicular approach "out of beam"
- Point the needle towards the midpoint of the transducer's side (long axis)
- The perpendicular approach will result in visualization of the needle as it transversely crosses the plane of the beam at 90 degrees
- The nodule and needle point will be centered in the midpoint of the transducer's long axis
- Advantage: desirable due to anatomy in some locations
- Disadvantage: entire length of needle not visualized
- Needle based sample collection techniques
- With aspiration / suction
- 27 or 25G needle attached to a 10 cc syringe (with or without extension tubing) withdrawn so that 1 - 2 cc of negative pressure induces aspiration
- Without aspiration / nonsuction
- 27 or 25G needle (with or without stylet, may attach open syringe) is introduced into nodule and capillary action causes uptake of cellular material into the needle
- With aspiration / suction
- Sample preparation: same as for palpation guided FNA
Radiology images
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