To determine the prevalence of testicular microlithiasis (TM) seen by testicular ultrasonography (US) in Japanese adult men referred for andrologic symptoms and evaluate associations of TM with pathologic conditions.

For 7 years, US was performed in 969 patients (mean age 40.9 years) at one institution. The patients were divided into groups with infertility (n = 550), unilateral testicular tumor (n = 46), or other andrologic conditions (n = 373). TM was identified as multiple small hyperechogenic foci. In the tumor group, only images of the tumor-free testis were reviewed. Patients with TM accompanying tumor or infertility completed follow-up questionnaires and US examinations.

TM was diagnosed in 46 patients (mean age 38.5 years, range 23 to 75). The prevalence of TM was 17.4% in the tumor group, 5.6% in the infertility group, and 1.9% in the other-conditions group. TM was associated with testicular tumor and infertility, but not with other conditions. In patients with unilateral testicular germ cell tumor, the prevalence of carcinoma in situ in the contralateral testis was greater when TM was present in that testis (2 of 8 patients) than when TM was absent (0 of 32, P = 0.0037). No new testicular tumor developed subsequently. In the infertility group, the 31 patients with TM showed no subsequent testicular tumor development, and neither patient undergoing testicular biopsy had carcinoma in situ.

TM, as demonstrated by US, was associated with infertility, as well as testicular tumor. TM in a testis contralateral to a unilateral testicular germ cell tumor may increase the risk of carcinoma in situ.