Abstract Disclosure: A. Żyłka: None. K. Dobruch-Sobczak: None. H. Piotrzkowska-Wróblewska: None. P. Góralski: None. J. Gałczyński: None. E. Bakuła-Zalewska: None. M. Dedecjus: None. Objectives: Preoperative localization of parathyroid gland adenomas in patients diagnosed with primary hyperparathyroidism (pHPT) is challenging process. The aim of the study was to assessed the usefulness of contrast-enhanced ultrasound (CEUS) as complimentary diagnostic modality to conventional ultrasonography for detection of hyperfunctioning parathyroid gland lesions. Methods: Between the years 2021 and 2022, 36 adult patients (33 women and 3 men, aged 37-76) diagnosed with pHPT, underwent high-resolution ultrasound (US) and CEUS of parathyroid gland adenomas, suspected after fine-needle aspiration biopsy with positive parathormone (PTH) wash-out results and/or avid in 99mTechnetium -sestamibi scintigraphy. During CEUS examination 1.5 ml of SonoVue contrast has been injected and followed by analysing of qualitative CEUS enhancement features. All patients were qualified to surgical treatment according to clinical symptoms, laboratory and imaging findings and underwent parathyroidectomy with histopathologic results confirming parathyroid gland adenomas. Analysis of the B-mode features and visual CEUS enhancement patterns was performed retrospectively. Ten CEUS qualitative parameters of lesions were assessed including: homo- or heterogenous enhancement; hyper- or hypoenhancement; distribution of contrast in wash-in phase as: centripetal, centrifugal or combined and in wash-out phase as: centrally, peripherally or combined. Then the model was extended using the results based on US B-mode imaging which involved size, echogenicity, calcifications, cystic components and vascularity patterns assessed in Color Doppler (CD) and superb microvascular imaging (SMI). Results: Histopathologic results included 36 parathyroid adenomas (in 33 women and 3 men), the medium size 18.8mm (±11.1) and volume 3.7mm3 (±8.2). In B-mode US examination the majority of lesions were assessed as hypoechoic (n=36; 100%) with dominant inhomogenous echostructure (n=20; 55.5%), mixed vascularity (n=24; 66.6%) and polar vessel observed in 14 lesions (38.8%). There were no adenomas with calcifications, cystic components were observed only in 4 nodules (11.1%). In the CEUS study, dominated qualitative features were homogenous (n=22; 61,1%) and hyperenhancement (n=27; 75%), with centripetal distribution of contrast in wash-in phase (n=24; 66,6%) and dominant centrally wash-out of the contrast (n=20; 55,5%). Conclusions: Preliminary results indicate ultrasonographic patterns characteristic for parathyroid gland adenomas in multiparametric ultrasound involved CEUS examination, which seemed to be valuable tool for localization hyperfunctional parathyroid glands. Further multicenter studies should be performed to standardize qualitative CEUS features in order to diagnose primary hyperparathyroidism preoperatively. Presentation: 6/1/2024