Diffuse granulomatous mesenteric disease caused by intravesical bacillus Calmette-Guérin instillation masquerading as peritoneal carcinomatosis.

Intravesical instillation with bacillus Calmette-Guérin is the most common therapy used for nonmuscle invasive bladder cancer in North America. Although local side effects are common, systemic side effects are rare when it is administered correctly. We present a case of diffuse mesenteric granulomatous disease resulting from inappropriate instillation of this agent. This patient was thought to have peritoneal carcinomatosis. One must be cognizant of the possibility when evaluating patients with similar findings and images after bacillus Calmette-Guérin therapy.