[Actinomycosis of the buttock]

Cutaneous actinomycosis of the buttocks is a rare granulomatous bacterial infection that usually starts in the perianal area. We present an exceptional case in the form of a pseudo-tumor.

A 69 year-old woman, in general good health, developed an indurate mass on the supra-external quadrant of the right buttock. The tumor was centered by an ulcerated nodule with a diameter of around 10 centimeters. Imaging showed invasion of the soft tissue of the skin in the internal psoas muscle, the adipose tonality of which was compatible with a liposarcoma. The skin biopsy revealed characteristic bacterial grain in the center of a cholesterol granuloma. Subsequent culture in aerobic milieu identified Actinomyces gerencseriae. Cure was obtained following complete exeresis of the fibrous tissue and 8 months of antibiotic amoxicillin-clavulanic acid therapy.

Other than the most unusual clinical aspect, the originality of this case of actinomycosis of the buttocks is based on its potential appendix origin, 4 years after acute appendicitis, with slow posterior fistulation. Other cases of actinomycosis of appendix origin have been reported and its delayed onset following the intervention has been documented. The pseudo-sarcomatous aspect was responsible for diagnostic wandering. The histological image and, subsequently, the results of the bacteriological culture confirmed the diagnosis.