Can the ultrasound echogenicity of normal parotid and submandibular glands be used as a reference standard for normal thyroid echogenicity?

Abstract

Purpose: This study aimed to determine whether the normal parotid gland (PG) and submandibular gland (SMG) can be used as reference standards for normal thyroid echogenicity.Methods: In total, 1,302 consecutive patients with normal salivary glands were included in this study. The echogenicity of the SMG and PG was assessed during real-time ultrasound examinations, and the glands were categorized as hyperechogenic, isoechogenic, and hypoechogenic relative to the thyroid parenchyma in patients without diffuse thyroid disease (group 1, n=1,106) and with diffuse thyroid disease (group 2, n=196). The frequency of the echogenicity categories of the normal PG and SMG was assessed according to patients’ age.Results: In group 1, the normal PG showed isoechogenicity in 94.0% and hypoechogenicity or hyperechogenicity in 6.0%, and the normal SMG showed isoechogenicity in 73.6% and hypoechogenicity in 26.4% of patients (P<0.001). There was no significant association of the frequency of isoechoic PG with age (P=0.834); however, there was a trend for an increasing frequency of isoechoic SMG with aging (22.9%-81.4%) (P<0.001). Similar findings were found in group 2 patients without decreased thyroid echogenicity.Conclusion: The normal PG was mostly isoechoic to the normal thyroid parenchyma, whereas the normal SMG showed hypoechogenicity at various frequencies according to age. The echogenicity of the normal PG can be used as an alternative reference standard for normal thyroid echogenicity; however, the normal SMG is not suitable for a reference standard when assessing thyroid nodule echogenicity in patients who have diffuse thyroid disease with decreased parenchymal echogenicity.

Principles and features of ultrasound hypoechogenicity in diffuse thyroid pathology

“…Furthermore, it can be assumed that not all researchers distinguish between isoechogenicity and slight hypoechogenicity, thereby affecting their findings and conclusions. This assumption is based on the attempts of specialists to compare thyroid echogenicity with the frequent slight hypoechogenicity of salivary glands ( 20 ), as well as their insufficient experience in visually evaluating a grey scale.…”

“…Therefore, sonologists can visually differentiate between lower and higher hypoechogenicity at the same basic settings of the device. Furthermore, they can assess the echogenicity of the thyroid gland not only from memory and personal perception but also by comparing it with that of the parotid gland, if necessary ( 20 ). During US examination, human vision can distinguish isoechogenicity ( Figure 1A ) and the three variants of hypoechogenicity as follows: slight, moderate (average) and significant ( Figure 1B-1D ).…”

Quantification of Thyroid Viscosity in Healthy Subjects Using Ultrasound Shear Wave Dispersion (Viscosity PLUS)

“…Interestingly, thyroid viscosity found by our study and submandibular gland viscosity values found by the above-mentioned study are highly similar. The echogenicity of the SMG and PG has previously been considered as reference for the echogenicity of normal thyroid tissue [ 27 ], but elasticity or viscosity values were not yet compared.…”

Multiparametric ultrasound-based assessment of overt hyperthyroid diffuse thyroid disease

“…- Initially in B-mode US, the thyroid volume and echogenicity were evaluated. The thyroid volume was calculated in each case by measuring for each lobe the anteroposterior, transverse, and longitudinal diameter and calculated by the machine using the ellipsoid volume formula; the echogenicity was qualitatively assessed by the US operator as isoechoic (0), mildly (1) or intensely hypoechoic (2) (compared to salivary gland aspect) ( 40 );…”