Actinomycosis, a rare and unsuspected cause of anal fistulous abscess: report of three cases and review of the literature.

Primary perianal actinomycosis is rare. Sporadic cases, with lesions varying in extent have been reported. The infection is caused by the bacterium Actinomyces, which often is a saprophyte. Male gender and diabetes are risk factors, but the exact pathogenic mechanism remains speculative. The diagnosis is a challenge and often delayed, with a protracted history of masses and sinuses extending into the gluteal and genital region. The treatment, a combination of surgery and antibiotics, is poorly standardized. We report three cases and compare their characteristics to those of published cases, found by a computerized literature search (1968-2002). The lesions, a simple fistula-in-ano or a mass, were diagnosed in an early stage in all three patients. The infection always spread into the scrotum. There were no risk factors other than gender, except in one patient. The diagnosis was suspected by the observation of draining sulfur granules and promptly confirmed by histology in the three cases. All patients healed with antibiotics in addition to simple surgical procedures. Treatment consisted of amoxicillin for two weeks in two cases and more extended antimicrobial treatment in the third. These findings are contrasting with the classic picture of perianal actinomycosis. It is concluded that perianal actinomycosis can occur in the absence of risk factors and that early diagnosis requires a high degree of suspicion. An infection with Actinomyces should be suspected in the presence of lesions containing watery purulent material with sulfur granules. The indication for extended antibiotherapy combined with sphincter damaging surgery may need to be revised in the presence of early detection.