|| The patient was a 35-year-old Japanese man diagnosed with appendicitis with abscess formation. An appendectomy was performed, but a refractory surgical wound infection developed, and eventually a cutaneous-rectovesical fistula was detected. In a review of the first-time CT scan, a small high-density construction resembling a bone from a fish was detected in the ileum. The histopathological examination revealed granules of actinomyces. These findings suggested that abdominal actinomycosis due to intestinal mucosal breakage by the fish bone caused the secondary appendicitis, and that after the appendectomy, residual actinomyces caused the cutaneous-rectovesical fistula.
After the diagnosis, total parenteral nutrition and a long-term administration of antibiotics improved the patient's clinical symptoms, and the fistula closed within a month. Antibiotics were administered for 6 months, and there has been no recurrence for 6-1/2 years. Because actinomycosis is difficult to diagnose based on the typical clinical features, a direct identification of the infecting organism from a tissue sample or from sulfur granules is required for the definitive diagnosis. Actinomyces is also known to cause fistula formation, and intestinal penetration caused by a fish bone may indicate abdominal actinomycosis. A rectovesical fistula requires surgical intervention in most cases, but in cases caused by abdominal actinomycosis, such a fistula may be cured by conservative therapy, as in our patient's case. It is important to consider the possibility of actinomycosis when a refractory rectovesical fistula is observed.