20 hours ago Thyroid Ultrasound Reports: Will the Thyroid Imaging, Reporting, and Data System Improve Natural Language Processing Capture of Critical Thyroid Nodule Features? J Surg Res. 2020 Dec;256:557-563. doi: 10.1016/j.jss.2020.07.015. Epub 2020 Aug 13. Authors Kallie J Chen 1 ... >> Go To The Portal
8 806 patients underwent 11 618 thyroid ultrasounds during the study period including 105 diagnosed with thyroid cancer (incidence 0.9 cancers per 100 ultrasound examinations). The cancers were diagnosed 1 day to 6.1 years following ultrasound imaging, and among control patients, there was a mean follow up of 4.2 years (range 2.0 – 10.9).
Recent advances in thyroid ultrasound have further improved the diagnostic accuracy. It is the imaging modality of choice for evaluating thyroid masses in children and pregnant females. Real time USG also helps to guide the diagnostic and therapeutic interventional procedures in various thyroid diseases.
The ultrasound diagnosis rests on the finding of multiple nodules within a diffusely enlarged gland. A diffusely enlarged thyroid gland with multiple nodules of similar US appearance and with no normal intervening parenchyma is highly suggestive of benignity, thereby making FNA biopsy unnecessary.[10]
Objective: Thyroid ultrasound plays a major role in the clinical management of patients with thyroid nodules. Comprehensive reporting enables malignant risk stratification and biopsy decisions.
All patients are examined in supine position with hyperextended neck, using a high frequency linear-array transducer (7-15 MHz) that provides adequate penetration and high resolution image. Scanning is done both in transverse and longitudinal planes. Real time imaging of thyroid lesions is performed using both gray-scale and color Doppler techniques. The imaging characteristics of a mass (viz. location, size, shape, margins, echogenicity, contents and vascular pattern) should be identified. Fine needle aspiration (FNA) biopsy should be suggested to the referring physician if required.[4,5]
High-resolution ultrasonography (USG) is the most sensitive imaging modality available for examination of the thyroid gland and associated abnormalities. Ultrasound scanning is non-invasive, widely available, less expensive, and does not use any ionizing radiation. Further, real time ultrasound imaging helps to guide diagnostic and therapeutic interventional procedures in cases of thyroid disease. The major limitation of ultrasound in thyroid imaging is that it cannot determine thyroid function, i.e., whether the thyroid gland is underactive, overactive or normal in function; for which a blood test or radioactive isotope uptake test is generally required.[1,2]
Hence, in these conditions, ultrasound findings should be viewed in relation to clinical and biochemical status of the patient. Multinodular goitre (MNG) is the commonest cause of diffuse asymmetric enlargement of the thyroid gland. Females between 35-50 years of age are most commonly affected.
The common conditions that present as diffuse enlargement of the thyroid gland include multinodular goitre, Hashimoto's (lymphocytic) thyroiditis, de-Quervain's subacute thyroiditis and Graves’ disease. The sonographic features of these processes may be similar but they have different biochemical profile and clinical presentations. Hence, in these conditions, ultrasound findings should be viewed in relation to clinical and biochemical status of the patient.
The most common cause of benign thyroid nodule is nodular hyperplasia. Thyroid adenomas are other common benign neoplasms of thyroid that are mostly solitary but may also develop as a part of multinodular masses. Iso-or hyper-echogenicity of the thyroid nodule in conjunction with a spongiform appearance is the most reliable criterion for benignity of the nodule on gray-scale ultrasound [Figures [Figures33and and4].4]. Other features like nodule size >1 cm, width < length, presence of hypoechoic halo around the nodule (fibrous capsule or compressed thyroid tissue) and coarse/curvilinear calcification are less specific but may be useful ancillary signs.[1,5] “Ring down” or “comet-tail” artifact or sign is typical of benign cystic colloid nodule [Figure 5].[11] Perinodular flow or spoke-and-wheel-like appearance of vessels on color Doppler examination is characteristic of a benign thyroid nodule [Figures [Figures33and and4].4]. However, this flow pattern may also be seen in thyroid malignancy. A complete avascular nodule is very unlikely to be malignant.[1,10]
Color and power Doppler ultrasound (US) are useful to evaluate vascularity of the thyroid gland and focal masses. Thyroid gland is a highly vascular structure supplied by superior and inferior thyroid arteries. The thyroid arteries can be visualized on color Doppler examination [Figure 1b], while the flow parameters from these vessels can be measured by spectral Doppler examination. Normally, a low resistance flow with high peak systolic velocity (PSV) is detected in these vessels on spectral Doppler analysis [Figure 1c]. The normal PSV in intra thyroid arteries ranges between 15-30 cm/second, but it can rise in certain pathologies (like Graves’ disease) to over 100 cm/sec.[6]
To detect post-operative residual or recurrent tumor in thyroid bed or metastases to neck lymph nodes.
A standardized US report should always document position, extracapsular relationships, number, and the following characteristics of each thyroid lesion: shape, internal content, echogenicity, echotexture, presence of calcifications, margins, vascularity, and size. Combining the previous US features, each thyroid nodule can be tentatively classified as: malignant, suspicious for malignancy, borderline, probably benign, and benign.
Vascularity of a thyroid lesion can be evaluated with CD and/or PD imaging. Based upon the Doppler effect, CD is a measure of the directional component of the velocity of blood moving through the sample volume. It provides information regarding both direction and velocity of blood flow within the nodule, but its shortcomings include the interference by noise and angle dependence. PD analysis, instead, indicates the total amount of flow present, without information about velocity. PD is more sensitive for detection of flow in small vessels that would not be detected by CD. Furthermore, PD imaging is relatively independent of the angle of the probe and has less noise interference than CD. Therefore, PD should be the preferred imaging technique for assessing the vascularity of thyroid nodules [37]. CD and PD are frequently used to differentiate between solid thyroid nodules and avascular structures such as a blood clots or debris [10].
The internal content of thyroid nodules can be classified following terminology based on the ratio of the cystic portion to the solid portion of the lesion: solid(liquid portion ≤10% of the nodule volume) (fig. (fig.1.7),1.7), mixed predominantly solid(liquid portion >10% but ≤50% of the nodule volume) (fig. (fig.1.8),1.8), mixed predominantly cystic(liquid portion >50% but ≤90% of the nodule volume) (fig. (fig.1.9),1.9), cystic(liquid portion >90% of the nodule volume) (fig. (fig.1.10),1.10), and spongiform(more than half of the nodule volume characterized by aggregation of multiple microcystic areas (<5 mm) separated by thin septations that are interspersed within solid tissue) (fig. (fig.1.11)1.11) [20].
The shape of a nodule has gained diagnostic importance for the differentiation of benign and malignant nodules only recently [15]. Based on their shape, thyroid nodules can be classified as: ovoid(when the anteroposterior diameter of a nodule is less than its transverse diameter on a transverse or longitudinal plane) (fig. (fig.1.1),1.1), round(when the anteroposterior diameter of a nodule is equal to its transverse diameter on a transverse or longitudinal plane) (fig. (fig.1.4),1.4), taller-than-wide(when the anteroposterior diameter of a nodule is longer than its transverse diameter on a transverse or longitudinal plane) (fig. (fig.1.5)1.5) or irregular(when a nodule is neither ovoid/round nor taller-than-wide) (fig. (fig.11.6).
Schematically, each thyroid lobe can be virtually divided into three portions: one third superior, one third medium, one third inferiorand each portion can be further subdivided into two sub-portions: anteriorand posterior. Isthmus can be divided into: right parahistmic, left parahistmicand central part. Any thyroid lesion can be described as approximately located in one of these sections. Seldom, thyroid nodules are located in the pyramidal lobe and more rarely they can be ectopic. Careful attention should be placed on nodules placed near the thyroid capsule. In this case, description of possible deformation or infiltration of the hyperechoic thyroid capsule and of invasion of adjacent structures is always recommended (see Extracapsular Relationships). Nodules localized in the posterior part of the two thirds inferior of thyroid lobes, close to the thyroid capsule, should be differentiated from parathyroid adenomas.
Both ovoid shape and round shape are reported in benign lesions but they do not obviously exclude malignancy. Instead, a taller-than-wide shape, although in which plane the ratio should be calculated is still a matter of debate, is reported to be associated with thyroid malignancy [15,16,17]. These findings reflect that malignant nodules grow across the normal tissue plane in a centrifugal and antigravitational way, in contrast to benign nodules usually growing along the tissue plane in a parallel fashion [15,18,19]. A nodule with irregular shape may be a malignant lesion, but irregular shape can also be noticed in benign conditions, such as focal thyroiditis [20].
The echotexture of the normal thyroid is usually homogeneous and bright. A thyroid nodule is defined as a discrete lesion within the thyroid gland that is ultrasonographically distinct from the surrounding thyroid parenchyma [12]. A nodule usually differs from a pseudonodule for being always clearly distinguishable in both transverse and longitudinal planes.
Thyroid ultrasound could be used to identify patients who have a low risk of cancer for whom biopsy could be deferred. Based on these results, these findings should be validated in a large prospective cohort.
Ultrasound has replaced nuclear medicine as the most frequently used imaging test of the thyroid.1The growth in the use of thyroid ultrasound by radiologists, endocrinologists and head and neck surgeons has led to the discovery of large numbers of asymptomatic thyroid nodules, which may occur in 50% or more of adults.2,3as well as a rapid rise in the diagnosis of thyroid cancer. 4In contrast, clinically apparent thyroid cancer is rare, affecting 1/10,000 people annually, and fewer than 1% of individuals over the course of their lives.4–6Because of the high prevalence of nodules, and the rarity of symptomatic cancer, only a minority of thyroid nodules is malignant. Uncertainty about which nodules may harbor cancer and lack of evidence-based management guidelines has resulted in a myriad of conflicting recommendations regarding which nodules warrant biopsy, 6–17,18,19–21frequent thyroid biopsies, and the over-diagnosis of thyroid cancers that would otherwise likely have remained asymptomatic in the absence of detection.4,22,23
1Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA