Segmental Atrophy of the Liver: An Increasingly Recognized Pseudotumor With Distinct Clinicopathologic and Imaging Features.

Segmental atrophy of the liver (SAL) is a recently described vascular-related pseudotumor. We report a series of 26 SAL cases in cancer patients, highlighting clinical, pathologic, and imaging features, with insights into pathogenesis. Cases were prospectively collected between 2017 and 2023 at the Montpellier Cancer Institute. Lesion staging, vascular lesions, and extralesional changes were systematically assessed, with immunohistochemical analysis. All patients (mean age 68 y; female-to-male ratio 1.7) were under oncologic follow-up; 46% had cardiovascular disease and/or diabetes. The median lesion size was 14 mm. Obliterative thrombosis was identified in 14 of 16 evaluable surgical specimens (88%), involving arteries, veins, or both, with intralesional and/or perilesional distribution. Arteriolar hyperplasia was present in 50% of cases, predominantly in advanced lesions, and showed a nonsignificant trend toward higher prevalence in bevacizumab-treated patients. Sinusoidal obstruction syndrome was observed in 31% of cases. Local contributing factors included prior liver-directed therapy (12% of patients) and concurrent tumor involvement (37% of patients), occasionally suggesting tumor-related vascular compression. We identified SMA-positive stromal cells clustered around small- and medium-sized vessels, supporting a perivascular origin and implicating thrombotic vascular injury in fibroelastotic remodeling. These findings highlight the contribution of both local and systemic factors to vascular injury underlying SAL. Recognition of this pseudotumor is essential to avoid misinterpretation and inappropriate clinical management.