Actinomycosis of the omentum with invasion of the abdominal wall, small bowel and transverse colon mimicking malignancy

Abstract

We report the case of a 59-year-old Russian man who presented with a painless, slow-growing, epigastric mass. CT revealed a large heterogeneous mass within the omentum infiltrating into adjacent tissues. During diagnostic laparoscopy, the omental mass was noted to be firm, raising the suspicion of malignancy. Surgical en-bloc resection of the mass, including the posterior rectus sheath, transverse colon and small bowel, was performed with primary anastomoses at laparotomy. Histological examination was inconsistent with malignancy and revealed the mass to be actinomycosis, confirmed by microscopy and gram staining. Surgical resection was followed by an 8-week course of penicillin and doxycycline antibiotic therapy. This treatment resulted in full clinical and radiological recovery with no complications. Although the clinical and radiological findings, in this case, were highly suspicious of malignancy, abdominal actinomycosis should be considered a differential diagnosis in patients with infiltrative abdominal masses and mild constitutional symptoms.

Keywords: colon cancer; gastrointestinal surgery; infectious diseases.

Figure 1

CT scan in the portal venous phase of the abdomen in coronal section showing a 6.1 cm×3.2 cm×4.4c m heterogeneous mass within the omentum of the left upper quadrant with extensive inflammatory changes in surrounding fat tracking to the mesenteric border of the transverse colon, anterior abdominal wall and intimately related to adjacent small bowel loops.

Figure 2

Mesenteric abscess associated with filamentous organisms (H&E ×4).

Figure 3

Positive Gram stain (×20).