Colocutaneous Fistula Presenting as a Lateral Thigh Mass With Secondary Prosthetic Hip Infection.

An 83-year-old woman presented with progressive right lateral hip pain and a gradually enlarging lateral thigh mass in the setting of prior abdominal surgery and right total hip arthroplasty. No definitive bowel communication was identified, although evaluation was limited by artifact from the prosthesis. Given these findings, it was presumed to be an abscess. However, the proximity of the bowel to the mass raised concern for a possible hernia or fistulous process. The patient underwent incision and drainage of the right lateral thigh, and unexpectedly, a feculent material was found within the cavity, raising concern for a colocutaneous fistula with the involvement of the prosthetic joint. This case highlights the diagnostic challenge of enteric fistulas presenting in atypical extraperitoneal locations, such as the lateral thigh, and emphasizes the importance of considering enteric sources in deep soft tissue infections containing gas, even when imaging may be unclear.