Abdominal Actinomycosis Abscess Presenting as an Isolated Gastrointestinal Pseudotumor

Abstract

Actinomyces is a gram-positive anaerobic bacterium that is ubiquitous in nature. It typically presents as respiratory, cervicofacial, or abdominopelvic abscesses. We present a 66-year-old man with a progressive enlarging abdominal wall nodule concerning for malignancy. The patient had a negative workup, including an ultrasound-guided fine-needle aspiration and colonoscopy, with biopsy for a possible extension to the colonic wall. Diagnosis of an Actinomyces abscess was obtained through surgical resection with right hemicolectomy. He was successfully treated with a prolonged course of intravenous antibiotics. This is a rare case of an isolated abdominal wall Actinomyces abscess mimicking a gastrointestinal malignancy.

Figure 1.

Initial abdominal and pelvic computed tomography with contrast showing an ill-defined round density mass (white arrow) measuring 2.5 cm in greatest diameter adherent to or arising from the posterior margin of the abdominal wall.

Figure 2.

Abdominal and pelvic computed tomography with contrast 6 months after initial presentation showing increased size of soft-tissue density with surrounding fat stranding within the right medial rectus measuring 6.2 × 2.2 cm (white arrow).

Figure 3.

Diagnostic colonoscopy showing multiple views of localized erythematous, nodular, scarred mucosa in the transverse colon with proximally placed tattoo spot ink (black arrow).