MRI findings of ovarian microcystic stromal tumor with pathologic correlation: a case report and literature review.

Ovarian microcystic stromal tumor (MCST) is a rare benign sex cord-stromal tumor that commonly occurs in women of reproductive age, associated with aberrant Wnt/β-catenin signaling pathway. We report a case of a 49-year-old woman with a right ovarian MCST presenting as a cystic mass with an irregularly thickened cyst wall corresponding to the solid component, and differentiation from malignancy was challenging. MRI revealed a hemorrhagic cystic mass with an irregularly thickened, T2-hyperintense wall, lobulated by thin hypointense septa. It showed inhomogeneous, rapid, intense contrast-enhancement but heterogeneous apparent diffusion coefficients (ADC) without marked diffusion restriction. Histopathology demonstrated lobulated proliferation of stromal cell nests with fibrous septa exhibiting microcystic and hemorrhagic changes. Immunohistochemistry showed nuclear and cytoplasmic β-catenin positivity, confirming MCST. While the hemorrhagic changes may suggest malignancy, these features and the heterogeneous ADC actually reflect varying degrees of intercellular loosening and microcyst formation resulting from decreased cell-cell adhesion due to loss of E-cadherin expression. Characteristic findings of this rare tumor include T2-hypointense thin septations reflecting fibrous stroma interposed between lobulated proliferative foci, a capsule-like compressed cortex reflecting slow tumor growth, and cystic changes (often hemorrhagic) resulting from tumor cell dissociation. This is the first paper to conduct a detailed comparative analysis of MRI and pathological findings in MCST and to examine findings considered characteristic. Recognition of these imaging features is crucial for correct diagnosis to avoid extensive surgery for preserving ovarian function.