Diagnostic performance of contrast-enhanced ultrasound (CEUS) in testicular pathologies: Single-center results

2.1 Study cohort

This retrospective study was approved by the local institutional ethical committee (EA4/148/18) and authors followed the ethical guidelines for publication in Clinical Hemorheology and Microcirculation [20]. Oral and written informed consent of all patients was obtained before examination. All study data were collected in compliance with the principles expressed in the Declaration of Helsinki 2002.

A total of 47 patients between 2012 and 2018 with unclear testicular pathology received an ultrasound examination of both testis using B-mode, CCDS, CEUS. Two patients were excluded due to missing follow up data (e.g. histopathological report and clinical follow up). Therefore, 45 patients with complete follow up data were included in the final analysis.

2.2 B-mode and CCDS

For gray-scale B-mode, both testicles were examined using a 14–24 MHz linear array transducer looking for lesion size, echogenicity and homogeneity of the lesions using high-end ultrasound systems (Aplio500/Aplio i900; Canon Medical Systems Corporation, Tochigi, Japan; Acuson Sequoia, Siemens Healthineers). In very large tumors, a 1–6 MHz convex probe was used additionally to determine the full size of the tumor. Color-coded and power Doppler ultrasound were employed to determine vascularization of the masses.

2.3 CEUS examination protocol

CEUS examinations were performed during clinical routine using high-end ultrasound systems with up-to-date CEUS specific protocols available at the time of the examination. All patients included were examined with a 5 or 4 cm linear broadband transducer. The examinations were performed at 4 to 18 Megahertz (MHz), depending on size and lesion depth, using 14L5 (Canon, Otawara, Japan), linear broadband transducer, 4–14 MHz, MI 0.07, 10 fps and i18LX5 (Canon, Otawara, Japan), matrix broadband transducer, 4–18 MHz, MI 0.06, 10 fps. Ultrasound B-mode images were optimized using spatial compounding, frequency-based compounding, ApliPure™ level 5, differential Tissue Harmonic Imaging (dTHI)©, and Precision Imaging^© with level 4 Speckle Reduction (SR). CEUS images were performed at 4 to 5 MHz, 10fps. Each ultrasound system was configured with a very low MI (0.06 to 0.07) to avoid early microbubble-destruction. A bolus of 2.4 ml of ultrasound contrast agent (SonoVue^®, Bracco Imaging, Milan, Italy) was repeatedly injected up to three times until satisfying cine loops were acquired. Baseline B-mode US, CCDS and CEUS (e.g. qualitative assessment of contrast enhancement pattern) were performed and interpreted by a single high-experienced radiologist with more than ten years’ experience in CEUS (EFSUMB level 3).

2.4 Reference standard

All testicular lesions (n = 19) underwent surgical exploration with the respective histopathologic results serving as reference standard. All other pathologies underwent sonographic follow-up in combination with clinical surveillance served as reference standard. A follow-up was performed with CEUS up to six months. Negative tumor markers with stable or diminishing lesion size or the disappearance of the lesion after six months was considered to indicate a benign nature of the lesion.

2.5 Statistical analysis

Continuous variables were tested for normal distribution using the Kolmogorov-Smirnov-test; variables not following a normal distribution are reported as median and interquartile range (IQR) and were compared using the Mann-Whitney U-Test. Categorical variables were compared using student’s t-test or chi² test, as appropriate. The obtained CEUS results and matched histopathological reports from each patient were analyzed retrospectively for diagnostic accuracy by testing sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV). Correlation of tumor size in ultrasound compared to histopathological report was tested using Pearson correlation. Interpretation of correlation between size in US and in histopathological report was defined by Cicchetti [21]: Less than 0.40 – poor, 0.40 to 0.59 – fair, 0.60 to 0.74 – good and 0.75 to 1.00 as excellent.

A two-sided significance level of α 0.05 was defined appropriate to indicate statistical significance. All statistical analyses were performed using the SPSS software (IBM Corp. Released 2016. IBM SPSS Statistics for Windows, Version 25.0. Armonk, NY: IBM Corp.).

4.1 Inflammatory and traumatic pathologies

B-mode US and CCDS can demonstrate morphologic and hemodynamic changes in epididymitis and orchitis. Inflammatory disease is usually associated with acute swelling, fever, acute pain, increased blood flow to the epididymis and testis in real time CEUS is examination is a well-established criterion for the diagnosis of epididymo-orchitis. [22] CEUS does not seem to add to the diagnostic accuracy in acute or chronic inflammation but may play a role in the investigation of possible complications occurring as a consequence of epididymitis and orchitis, showing perilesional rim enhancement in abscesses or infarction with the ability to quantify avascular testicular parenchyma [13]. Therefore real time contrast enhancement pattern on CEUS may provide further diagnostic information if B-Mode ultrasound appearances are uncertain [22, 23]. CEUS is a feasible tool during follow-up showing a change in the size or shape of the infarction [23, 24]. Changes in lesion features during follow-up confirm the differential diagnosis from other testicular lesions and allow conservative management in these patients.

4.2 Evaluation of unclear testicular lesions

CEUS has advantages over contrast-enhanced magnetic resonance imaging (MRI) including unmatched temporal resolution due to continuous real-time imaging [22, 25]. Multiparametric scrotal MRI has been proposed as a valuable supplemental imaging technique in the investigation of testicular pathology as a problem-solving tool when sonographic findings are equivocal. [26–28] According to the recommendations by the Scrotal and Penile Imaging Working Group (SPI-WG) MRI can be clinically applied for lesion characterization and differentiation between germ-cell and non-germ-cell neoplasms, and for local staging of TGCTs, when organ-sparing surgery is planned and US findings are indeterminate. [29] Finally, MR imaging is superior to US in differentiation between an undescended testis and testicular agenesis and can demonstrate an intraabdominal undescended testis, which can be difficult to detect with US. [26] Nevertheless compared to CEUS, MRI is more time consuming especially in the diagnostic workup of acute alterations and may not be widespread available in smaller non-university hospitals.

Real time imaging CEUS allows visualization of testicular microvascularization and may thus aid in the preoperative assessment of testicular lesions with hypervascularization as an important feature in the diagnosis of malignancy [30, 31]. Similar to Auer et al. (33%), CCDS was not able to demonstrate complete vascularization in form of contrast enhancement in 4/14 lesions (28%), which were positive for cancer at CEUS [32]. CEUS outperformed CCDS in the visualization of complete contrast enhancement in all testicular lesions (60% vs 42%) as well as neoplastic lesions (79% vs 53%) and especially malignant lesions (92% vs 69%). One burn-out seminoma showed only areas of relevant contrast enhancement in CEUS and hypervascularization in CCDS due to intralesional Leydig cell hyperplasia.

Lock et al. demonstrated that hyperenhancement of a testicular lesion had a positive predictive value of 97% (95% CI, 85–100) for a neoplasia. Nevertheless, differentiation between benign and malignant lesions due to contrast enhancement in CEUS is currently not possible [16,33–35, 16,33–35]. Representative cases of contrast enhancement pattern in benign and malignant lesions are demonstrated in (Figs. 2 and 3). CEUS may be valuable in the assessment of small intratesticular masses (<5 mm) where CCDS comes to its limits because small testicular tumours may appear avascular. In this study, all benign tumour lesion were smaller than 9 mm (IQR, 8–12.5 mm) while malignant lesions presented a median tumour size of 29 mm (IQR, 13.5–51.5 mm).

Benign lesions appeared as isolated hypoechoic, mostly infracentimetric masses, with a clear demarcation from the surrounding tissue. They presented intrinsic and peripheral rim hypervascularization [30, 36]. While especially small situated hypoechoic tumors appears with short filling time or circumferential vessel with a rapid centripetal filling on CEUS, the visualization of specific contrast enhancement pattern in small lesion is limited [6]. CEUS therefore allows detection of contrast enhancement in small lesions and a differentiation of a small tumors lesions from focal scars. The use of time intensity curve (TIC) measurements with could be helpful to differentiate burned-out tumours from vascularised testicular tumours but also failed to differentiate benign and malignant lesions [34, 37]. While Drudi demonstrated higher wash-in in Leydig cell tumors to seminomas [37], Luzurier et al. noted no difference of perfusion kinetics in benign (mostly Leydic cell tumors) and malignant (mostly seminomas) tumor lesions [34]. The vessel structure of Leydig cell tumors due to more regular neovascularization, seminoma presents large areas of necrosis due to irregular neovascularization, which may explain the different perfusion kinetics. Perfusion analyses with different phases of wash-in and wash-out kinetics can further be evaluated with color-coded images and. Using pseudo-colors, an increased microcirculation and low tissue perfusion can be displayed in shades of different colors represented by different values of AUC and Peak. [38]

While malignant lesions represented greater median tumor size in this study (p = 0.005) and hyperenhancement on CEUS (p = 0.003), differentiation of benign and malignant lesion may be based on a combination of echogenicity, homogeneity and contrast enhancement. While testicular abscess and focal tumors shows typical enhancement pattern, the differentiation of concomitant diseases like tuberculosis or primary testicular lymphoma might aggravate the exact detection of benign versus malignant alterations [8, 39]. While both lymphoma and leukaemia can be represented by focal or multifocal hypoechoic lesions and may be indistinguishable from germ cell tumors, correlation to relevant clinical history would be required in reaching the correct diagnosis. To date, there are only a few case reports describing contrast enhancement patterns on CEUS in the evaluation of tuberculous orchitis or testicular lymphoma, providing only small amount of data on it’s typical contrast enhancement [22, 39]. The use of multiparametric US including shear wave elastography, microflow imaging and CEUS may represent a promising tool in the diagnosis of testicular alterations in the future [16, 41].