Teaching Case

67-year-old woman with history of abdominal surgical procedures (umbilical hernia, cystocele, and cholecystectomy) presents with abdominal pain localized to the left lower quadrant, starting last month and worsening in the past few days. Blood analyses reveal only a slight elevation of acute-phase reactants.

A contrast-enhanced abdomen and pelvis CT was obtained (Figure 1), and a 7 cm nodular heterogeneous lesion was found in the left lower quadrant. The mass was located in the greater omental fat, contacting the anterior abdominal wall but without direct contact with the intestinal loops. The initial consideration was an omental infarction and the patient received symptomatic treatment with analgesics.

A follow-up spectral CT scan (Figure 2) was performed 6 months later. The nodular lesion in the greater omentum is now smaller, measuring 3 versus 7 cm, but appears more solid and enhancing. Moreover, clear extension to the adjacent abdominal wall is now present. The possibility of abdominal wall actinomycosis was raised, and a fine needle aspiration biopsy confirmed the diagnosis.

After 3 months of treatment with amoxicillin, a follow-up CT (Figure 3) showed a reduction in the size of the lesion and less involvement of the abdominal wall.

Background

Actinomycosis is a bacterial infection caused by gram-positive, anaerobic or microaerophilic, non-sporulating bacilli, primarily belonging to the Actinomyces genus. It predominantly affects the cervicofacial area (50-60%), followed by thoracic (15-30%), and abdominal regions (20%) [1,2].

Although abdominal actinomycosis can manifest as lesions in the abdominal wall, these cases are mostly secondary to direct spread from other intra-abdominal locations. Isolated actinomycosis of the abdominal wall is exceptionally rare [2-4].

Clinical perspective

Abdominal wall actinomycosis is more prevalent in women, particularly over the age of 60. Predisposing factors include diabetes, appendicitis, diverticulitis, perforated gastric ulcers, previous bowel surgery, cholecystectomy, pancreatitis, endoscopic manipulation, trauma, immunosuppression, prolonged use of intrauterine devices, and loss of gallstones after laparoscopic cholecystectomy [3,5].

The most common presentation is the detection of a tender mass in the abdominal wall, commonly found in the periumbilical region, hypogastrium or left iliac fossa. Anorexia and weight loss may also be present. Fever and signs of inflammation occur in only a minority of patients. Laboratory analysis typically reveals signs of anaemia, leukocytosis, and elevated inflammatory markers [5-7].

The onset of symptoms usually occurs within a few days to a few weeks, which is shorter compared to other abdominal sites [3].

Imaging Perspective

Computed tomography (CT) is the preferred imaging technique for studying abdominal inflammatory processes. Actinomyces abscesses typically appear as solid, infiltrative masses with areas of decreased attenuation. Although these characteristics are non-specific, CT enables accurate localization of abscesses and facilitates guide for percutaneous access for diagnostic and therapeutic purposes. The rectus muscles are the most frequently involved structures of the abdominal wall. Magnetic resonance imaging (MRI) may reveal areas of low signal intensity on T2-weighted sequences, further raising suspicion of actinomycosis [1,2].

Definitive diagnosis of actinomycosis is based on visualizing typical "sulfur granules" in histological studies or isolating Actinomyces spp through anaerobic culture media [8].

Outcome

Penicillin is the first-line antibiotic for treating actinomycosis, and tetracyclines for cases of allergy. The duration of treatment, although not standardized, should be prolonged and guided by the patient's clinical and radiological response. In our case, oral amoxicillin was used to facilitate prolonged outpatient treatment [2,9].

In cases of poor clinical or radiological evolution, surgery may be considered as an adjunctive treatment alongside antibiotic therapy [9].

Overall, the prognosis for actinomycosis is generally favourable [2,9].

Written informed patient consent for publication has been obtained.