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Context: Experimental studies on Klinefelter syndrome (KS) reported increased intratesticular testosterone (T) levels coexisting with reduced circulating levels. Abnormalities in testicular microcirculation have been claimed; however, no studies investigated in vivo testicular blood flow dynamics in humans with KS. Objective: To analyze the testicular microcirculation in KS by contrast-enhanced ultrasonography (CEUS) and correlate vascular parameters with endocrine function. Design and Setting: Prospective study. University setting. Patients: Sixty-eight testicular scans, 34 testes from 19 T-naïve subjects with KS and 34 testes from age-matched eugonadal men (control) who underwent CEUS for incidental nonpalpable testicular lesions. Main Outcomes: CEUS kinetic parameters. Results: CEUS revealed slower testicular perfusion kinetics in subjects with KS than in age-matched controls. Specifically, the wash-in time (P=0.018), mean transit time (P=0.035), time to peak (P<0.001), and wash-out time (P=0.004) were all prolonged. Faster testicular blood flow was associated with higher total T levels. Principal component analysis and multiple linear regression analyses confirmed the findings and supported a role for reduced venous blood flow as independent predictor of total T levels. Conclusions: Testicular venous blood flow is altered in KS and independently predicts T peripheral release.

Original publication




Journal article


Journal of Clinical Endocrinology and Metabolism

Publication Date





E236 - E245