BackgroundIntrahepatic cholangiocarcinoma (ICC) is an aggressive cancer with high frequency of extrahepatic metastasis at diagnosis. However, there have been very few reports of direct invasion to transverse mesocolon with lymph node metastasis in the regional mesocolon.Case presentationA 71-year-old man presented to our hospital with anorexia and weight loss. Abdominal computed tomography (CT) revealed enlarged gallbladder wall with intrahepatic tumor extended from the gallbladder. The transverse colon was located adjacent to the gallbladder and its wall was thickened, indicating tumor invasion. Some enlarged lymph nodes were observed in the transverse mesocolon, suggesting metastatic or inflammatory lymph node swelling. Percutaneous liver biopsy detected poorly differentiated adenocarcinoma. After confirming the absence of remote metastasis and peritoneal dissemination, surgical resection including right hepatectomy and right hemicolectomy was performed. The pathological diagnosis was adenosquamous carcinoma of the liver and lymph node metastasis in the transverse mesocolon. The surgical margins were negative and R0 resection was achieved. Although adjuvant chemotherapy was administered, follow-up CT detected multiple metastases to the lung 4 months after surgery. The patient died 12 months after the operation.ConclusionsDirect colon invasion from ICC may cause lymph node metastasis in the regional mesocolon. Careful assessment is necessary for the diagnosis of enlarged lymph nodes in ICC with direct colon invasion.