Impact of adipocytes on ultrasound evaluation of parathyroid adenomas

Abstract

Purpose: Parathyroid lipoadenomas are difficult to recognize preoperatively; hence, they may remain undetected. Difficulty in recognition is thought to be due to the adipocytes present in the tumor. This study aimed to clarify the impact of adipocytes as a component of parathyroid adenomas on ultrasound evaluation.

Methods: Eighteen parathyroid adenoma cases, in which the adipose tissue accounted for more than 10% of the tumors, were included in this study. Of these, five were consistent with lipoadenomas. Twenty-five consecutive patients with parathyroid adenoma without adipocytes were used as controls.

Results: Ultrasonography revealed a lipoadenoma detection rate of 20.0%. This increased to 80.0% at re-examinations performed after obtaining information from other imaging modalities. Compared with parathyroid adenoma cases with no adipocytes or few adipocytes, the frequencies of ill-defined margins, iso- and/or hyperechogenicity, heterogeneous consistency with a two-tone pattern, poor vascular flow, no polar artery, and no hyperechoic line were significantly higher in parathyroid lipoadenoma cases. The hyperechoic and isoechoic areas in tumors with a two-tone pattern correspond to adipocyte- and parathyroid cell-rich areas, respectively. The lipoadenoma tumor sizes measured using ultrasound tended to be smaller than the actual sizes.

Conclusions: The characteristic ultrasound findings of lipoadenomas were clearly different from those of parathyroid adenomas with or without adipocytes. We believe that our findings may contribute to an increased detection rate of lipoadenomas and allow us to consider them in the differential diagnosis.

Keywords: Lipoadenoma; Parathyroid adenoma; Two-tone pattern; Ultrasound.

Fig. 1

a (Group 1): The tumor is well-defined, hypoechoic, and shows a hyperechoic line at its border with the thyroid. b (Group 4): The tumor is ill-defined, heterogeneous, and hyperechoic. The triangular arrows indicate the margins of the tumor (B-mode)

Fig. 2

a: A parathyroid adenoma showing a two-tone pattern (Group 2) (B-mode). b: The hypoechoic and isoechoic areas correspond to adipocyte- and parathyroid cell-rich areas, respectively (hematoxylin and eosin-stained preparation)

Fig. 3

a (Group 1): A blood flow signal is present within the nodule. Note the polar artery. b (Group 4): A minimal blood flow signal is seen (power Doppler)

Fig. 4

Differences in tumor size measured using ultrasound compared with the actual tumor size

Fig. 5

A parathyroid adenoma with heterogeneous echogenicity (Group 2). Triangular arrows indicate the margins of the tumor. On ultrasound examination, only a hypoechoic area was recognized as a tumor