Focal Sinusoidal Obstruction Syndrome Caused by Oxaliplatin-Induced Chemotherapy: A Case Report

INTRODUCTION Sinusoidal obstruction syndrome (SOS) is a severe adverse event of long-term chemotherapy in patients with colorectal cancer. It usually develops as liver congestion due to diffuse microscopic obstruction in liver parenchyma. In contrast, it sometimes appears as a liver mass occurring with local parenchymal hemorrhaging, and is often misdiagnosed as liver metastasis. CASE PRESENTATION A 40-year-old woman with rectal cancer underwent high anterior resection and partial liver resection of segment 7 due to synchronous liver metastasis. She received oxaliplatin-based chemotherapy (mFOLFOX6) as adjuvant chemotherapy for 6 months. A 13-mm irregular low-echoic mass was detected by CT in segment 3 of the liver 12 months after the operation. The mass was again resected as a liver metastasis because it had increased in size. The pathological diagnosis was focal SOS, which showed sinusoidal dilation and congestion by hepatocyte trabeculae in the liver parenchyma. CONCLUSIONS Atypical irregular tumors should be considered as SOS when the patient has received oxaliplatin-based chemotherapy. A qualitative imaging modality diagnosis, such as with diffusion-weighted MRI, is superior to a morphological diagnosis in focal SOS. This imaging modality can prevent unnecessary operations.