Actinomycosis is an infection caused by gram-positive anaerobic bacteria Actinomyces spp., a commensal microorganism of our respiratory and gastrointestinal tract. Abdominal actinomycosis is one of the main subtypes, involving either the intestines or the genitourinary system. Previous mucosal injury is almost a prerequisite for this infection to occur. The diagnosis can be made after a thorough clinical, laboratory, and imaging workup, but conventional microbiological studies are of limited efficacy.
Abdominal actinomycosis is one of the clinical subtypes of Actinomyces spp. infection, a commensal microorganism of our gastrointestinal, respiratory, but also genitourinary tracts  . Actinomyces (principally A. israelii) seems to cause an infection in the gastrointestinal tract only after a significant injury to the intestinal mucosa, as seen in diverticulitis, appendicitis, abdominal trauma, and following gastrointestinal surgery    . Despite the fact that a large number of cases is now being associated with the use of intrauterine devices (IUDs), the infection is encountered almost three times more frequently in males than females    . In the abdomen, Actinomyces can cause an infection of the gastrointestinal, biliary, and genitourinary tracts, whereas pelvic actinomycosis might also be encountered, often as a complication of abdominal infection   . In the GI tract, the appendix, the cecum, and the large intestine are the predominant sites of infection, and abdominal pain accompanied by a firm and or even hard palpable mass is the main presenting feature   . Other reported complaints are fever, right lower or right upper quadrant pain (in colonic or hepatic actinomycosis, respectively), and alterations in bowel habits   . Similar to the GI tract, the infection of the genitourinary tract will manifest as a palpable mass as well, with fever and other organ-related complaints .
The indolent course of the infection, a frequent misdiagnosis (as tumors, autoimmune bowel disease, etc.), the nonspecific clinical presentation, and the need for strict conditions for bacterial growth through standard microbiological methods are the challenges faced by the physician in making the diagnosis of all types of actinomycosis, including abdominal    . For this reason, a detailed patient assessment through history taking may be crucial in raising clinical suspicion. Physicians should inquire about recent abdominal trauma, gastrointestinal surgery, appendicitis, or the use of an IUD  . Furthermore, the role of the physical examination is equally important, since the detection of a palpable mass is a key step in allowing a more thorough investigation. Imaging studies should be employed, and ultrasonography (US), regarded as a first-line study, is able to visualize a solid mass that is often misidentified as a tumor  . If, however, macroscopic features suggest an abscess, percutaneous drainage or biopsy of the mass, assisted by either computed tomography (CT) or endoscopic US, might be indicated   . Once appropriate samples are obtained, cultivation and gram-staining of Actinomyces are recommended strategies to confirm the diagnosis, but the very long incubation period (> 10 days) and strict anaerobic conditions impede the effectiveness of these procedures   . More advanced studies, on the other hand, such as polymerase chain reaction (PCR) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF), are showing very high success rates in detecting Actinomyces  , but their cost is a significant limitation.