Testicular microcystic stromal tumor: a case report with MRI findings and literature review.

Microcystic stromal tumor (MST) is an extremely rare subtype of sex cord-stromal neoplasm, with the majority of published literature consisting of isolated case reports or small case series, underscoring its scarcity. Most documented cases involve ovarian MST, whereas only two prior instances of testicular MST have been reported. The histological features of testicular MST are analogous to those of ovarian MST, and its diagnostic criteria are extrapolated from the well-established guidelines for ovarian MST. However, the clinical and imaging characteristics of testicular MST remain poorly understood, leading to frequent underdiagnosis or misdiagnosis. Herein, we present a rare case of MST arising in the right testis of a 54-year-old Chinese male. Histopathologically, the tumor exhibited characteristic microcystic and stromal architectures, with immunohistochemical positivity for vimentin, CD10, cyclin D1, WT-1, and CD56, and a low Ki-67 proliferation index. Scrotal ultrasonography revealed a heterogeneous hypoechoic intratesticular mass containing both solid and cystic components. Magnetic resonance imaging (MRI) demonstrated a complex cystic lesion in the right testis, which showed slightly heterogeneous hyperintensity on T2-weighted images and hypointensity on T1-weighted images. This represents the first reported case of testicular MST with MRI findings, and its distinctive imaging features correlate with the tumor's unique histological structure. In this study, we comprehensively analyzed the clinical, radiological, histological, and immunohistochemical characteristics of this case and compared them with previously documented features in the literature, aiming to enhance the understanding of this rare entity and facilitate accurate diagnosis.