Thyroid gland
General
Ultrasound

Author: Rachel Jug, M.D. and Xiaoyin "Sara" Jiang, M.D. (see Authors page)

Revised: 15 February 2017, last major update June 2016

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Ultrasound [title] thyroid gland

Cite this page: Ultrasound. PathologyOutlines.com website. http://pathologyoutlines.com/topic/thyroidultrasound.html. Accessed December 16th, 2017.
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

2015 American Thyroid Association (ATA) Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer:
  • 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)
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

Images hosted on other servers:

Figure 1: ATA algorithm for evalu-
ation and management of patients
with thyroid nodules based on
US pattern and FNA cytology

Figure 2: ATA association between
nodule sonographic patterns and
corresponding risk of malignancy

Table 6: Risk of thyroid cancer based on
appearance of thyroid gland and
characteristics of any nodules identified

Ultrasound FNA techniques



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 course 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, course 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
  • 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

  • Sample preparation: same as for palpation guided FNA
Radiology images

Images hosted on other servers:

Calcified nodule

Complex cystic thyroid nodule

Ultrasound physics
and instrumentation
for pathologists

Multinodular goiter


17 year old girl with Graves disease

35 year old
woman with
diffuse Hashimoto
thyroiditis

50 year old woman with
colloid multinodular goiter


Hypoechoic nodule:
a sonographic appearance
concerning for medullary
or papillary thyroid cancer

Microcalcifications in a thyroid
nodule: a sonographic appearance
concerning for thyroid cancer


Intranodular vascularity within
a thyroid nodule: a sonographic
appearance concerning
for thyroid cancer

Oval shaped thyroid nodule: a sonographic
appearance concerning for thyroid cancer,
particularly when the anterior-posterior
dimension: transverse dimension ratio is > 1