A 70-year-old woman presented to our hospital with a positive fecal occult blood test and a 3-year history of taking a herbal medicine (shiniseihaito) for chronic sinusitis. A Computed tomography scan showed no mesenteric vein calcification and a colonoscopy revealed a dark bronze-colored mucosa from the ileocecal region to the ascending colon. Histopathological examination showed fibrous thickening of the vein wall in the lamina propria and submucosal layer, diagnosing mesenteric phlebosclerosis. The patient stopped taking shiniseihaito, and endoscopic evaluations a year later showed an improvement in the color tone from the ileocecal region to the ascending colon. Furthermore, if endoscopic findings exhibit a peculiar dark bronze-colored mucosa, even without mesenteric vein calcification, it may be necessary to perform an aggressive mucosal biopsy. It is important to consider the patient's history of taking herbal medicine containing gardenia fruit when diagnosing.
