Abdominal actinomycosis

INTRODUCTION — A number of disorders are associated with lesions in the ileocecal region. Examples frequently encountered in developed countries include colon cancer, Crohn's disease, and, less commonly, infection due to Yersinia enterocolitica and Y. pseudotuberculosis (see related topic reviews). Many other infectious, neoplastic, and drug-related causes of ileocecal lesions have been described.

This topic review will provide an overview of abdominal actinomycosis, which is one of the causes of ileocecal lesions that are frequently considered in specific clinical settings or when more frequent causes have been excluded or are unlikely. The others (including mucoceles, tuberculosis, typhlitis, carcinoid, and lesions due to nonsteroidal anti-inflammatory drugs) are discussed separately. (See "Abdominal tuberculosis" and "Neutropenic enterocolitis (typhlitis)" and "Clinical features of carcinoid syndrome" and "NSAIDs: Adverse effects on the distal small bowel and colon" and "Clinical manifestations, diagnosis, and prognosis of Crohn disease in adults" and "Clinical presentation, diagnosis, and staging of colorectal cancer".) (See appropriate topic reviews.)

EPIDEMIOLOGY — Actinomycosis is an uncommon, chronic granulomatous disease caused by filamentous, gram-positive, anaerobic bacteria [1]. Actinomyces israelii is the major human pathogen [1,2]. Actinomycosis has a worldwide distribution, affects mostly middle-aged individuals, and is two to four times more common in men [2-4].

PATHOGENESIS — Actinomycetes are commensal inhabitants of the oral cavity and intestinal tract [5] but acquire pathogenicity through invasion of breached or necrotic tissue. As the infection progresses, granulomatous tissue, extensive reactive fibrosis and necrosis, abscesses, draining sinuses, and fistulas are formed [2].

Infection involving the cervicofacial area is most common (50 percent), followed by abdominal involvement (20 percent) and thoracic involvement (15 to 20 percent) [1]. In abdominal actinomycosis, the appendix and ileocecal region are usually involved [1,6]. The disease tends to remain localized as the infection spreads contiguously, disregarding tissue planes. Lymphadenopathy is not a clinical feature. Hematogenous dissemination is also rare [1,2]. (See "Cervicofacial actinomycosis".)

Actinomycotic abscesses can also present in the abdomen following cholecystectomy complicated by spilled gallstones during gallbladder removal [7,8]. Because of the slow growth characteristics of the pathogen, such patients may present months to years after cholecystectomy.

Factors that predispose to abdominal actinomycosis include recent abdominal surgery, trauma, neoplasia, or a perforated viscus [4]. In addition, there have been multiple reports of abdominopelvic actinomycosis associated with the use of intrauterine contraceptive devices [3-5,9,10]. (See "Intrauterine contraception: Candidates and device selection".)

CLINICAL MANIFESTATIONS — Actinomycosis is a difficult disease to diagnose preoperatively by virtue of its rarity, nonspecific symptoms, and imitation of more common conditions such as malignancy, Crohn's disease, and tuberculosis. It has been estimated that fewer than 10 percent of cases are diagnosed preoperatively [2,11]. As a result, a high index of suspicion is required in patients presenting with constitutional or nonspecific abdominal symptoms and an abdominal mass. The disease is characterized by a chronic, indolent course with symptoms such as fatigue, fever, weight loss, and abdominal pain. Physical findings may include a palpable mass, visible sinus tracts, or fistulas. Laboratory abnormalities may show anemia and leukocytosis.

DIAGNOSIS — Abdominal actinomycosis can be easily confused with Crohn's disease, tuberculosis (TB), or carcinoma [5,12]. The diagnosis is usually made postoperatively, since most patients undergo exploratory laparotomy for a suspected neoplasm. The presence of extraintestinal manifestations of inflammatory bowel disease (eg, uveitis, ankylosing spondylitis) may be helpful in distinguishing ileocecal Crohn's disease from actinomycosis. The lack of improvement with conventional anti-inflammatory or immunosuppressive drugs for a presumptive diagnosis of Crohn's disease usually leads to surgery, where a diagnosis of actinomycosis is eventually made. Clues in differentiating TB from actinomycosis include the presence of multisystem involvement (eg, lungs) in patients at high risk for TB. In contrast, actinomycosis is usually a localized, single-organ disease.

Radiologic findings — Radiologic findings are nonspecific in abdominal actinomycosis. Barium enema may show luminal narrowing, extrinsic compression, or fistulization. Computed tomography (CT) is the most useful imaging modality; it determines the location and extent of disease, occasionally contributes to an accurate preoperative diagnosis through fine-needle aspiration, and is used for monitoring the radiologic response to treatment on follow-up exams [11,13,14]. CT may show the infiltrative nature of the disease with disruption of tissue planes and demonstrate one or more solid masses with focal low-attenuation areas or cystic masses with thickened walls (image 1). However, these findings are nonspecific and, in one study, were felt to be indicative of a malignant process [13].

When feasible, CT-guided percutaneous aspiration may permit identification of the characteristic actinomycotic sulfur granules in pus and is also a good means of collecting material for culture [13]. In conjunction with antibiotics, this maneuver can be therapeutic, thus precluding a surgical intervention.

Colonoscopic findings — Colonoscopic findings are varied and include normal or thickened-appearing mucosa, colitis, ulceration, a nodular lesion, and button-like elevation of an inverted appendiceal orifice (picture 1) [6,15-19]. The main differential diagnoses at endoscopy include neoplasia, Crohn's disease, and tuberculosis. Endoscopic biopsies occasionally allow a preoperative diagnosis to be made when characteristic histologic findings are found (see below) [6,12].

Histologic findings and culture — A definitive diagnosis is usually based upon histologic identification of actinomycotic sulfur granules and/or culture of Actinomyces [1]. The preferred specimen for culture is pus.

Sulfur granules represent colonies of Actinomyces and are characterized by a zone of granulation tissue surrounding one or more oval eosinophilic granules. Beaded or filamentous, non–acid-fast, gram-positive bacilli radiate from these granules (picture 2) [11]. The sulfur granules are scarce so that multiple tissue sections should be studied. Sulfur granules are highly suggestive but not pathognomonic of actinomycosis, since organisms like Nocardia or Aspergillus spp can have a similar appearance.

Actinomyces are indistinguishable from Nocardia on Gram stain, but only the latter are positive on modified acid-fast staining. Culture is more specific, but the diagnosis is confirmed by culture in less than 50 percent of suspected cases [1,2].

An anaerobic environment is required for isolation of the organism, and the specimen should be sent under anaerobic conditions. Growth is faster in semi-selective medium (five to seven days) [3], but identification can often take two to four weeks even after growth has initially been observed.

MANAGEMENT — As mentioned above, many patients undergo resection before the diagnosis has been established. Initial medical treatment is reasonable in patients in whom the diagnosis is established prior to surgery. Penicillin is the treatment of choice for actinomycosis. Details of the treatment of actinomycosis are discussed elsewhere. (See "Treatment of actinomycosis".)

SUMMARY AND RECOMMENDATIONS

●Epidemiology − Actinomycosis is an uncommon, chronic granulomatous disease caused by filamentous, gram-positive, anaerobic bacteria. Actinomyces israelii is the major human pathogen. Actinomycosis has a worldwide distribution, affects mostly middle-aged individuals, and is two to four times more common in men. (See 'Epidemiology' above.)

●Pathogenesis − Actinomycetes are commensal inhabitants of the oral cavity and intestinal tract but acquire pathogenicity through invasion of breached or necrotic tissue. As the infection progresses, granulomatous tissue, extensive reactive fibrosis and necrosis, abscesses, draining sinuses, and fistulas are formed. (See 'Pathogenesis' above.)

●Clinical manifestations − Actinomycosis is a difficult disease to diagnose preoperatively by virtue of its rarity, nonspecific symptoms, and imitation of more common conditions such as malignancy, Crohn's disease, and tuberculosis. It has been estimated that fewer than 10 percent of cases are diagnosed preoperatively. As a result, a high index of suspicion is required in patients presenting with constitutional or nonspecific abdominal symptoms and an abdominal mass. The disease is characterized by a chronic, indolent course with symptoms such as fatigue, fever, weight loss, and abdominal pain. Physical findings may include a palpable mass, visible sinus tracts, or fistulas. (See 'Clinical manifestations' above.)

●Radiologic findings − Radiologic findings are nonspecific in abdominal actinomycosis. Computed tomography (CT) is the most useful imaging modality; it determines the location and extent of disease, occasionally contributes to an accurate preoperative diagnosis through fine-needle aspiration, and is used for monitoring the radiologic response to treatment on follow-up exams. CT may show the infiltrative nature of the disease with disruption of tissue planes and demonstrate one or more solid masses with focal low-attenuation areas or cystic masses with thickened walls (image 1). (See 'Radiologic findings' above.)

●Histopathologic findings − A definitive diagnosis is usually based upon histologic identification of actinomycotic sulfur granules and/or culture of Actinomyces. The preferred specimen for culture is pus. Sulfur granules represent colonies of Actinomyces and are characterized by a zone of granulation tissue surrounding one or more oval eosinophilic granules. Beaded or filamentous, non–acid-fast, gram-positive bacilli radiate from these granules (picture 2). Actinomyces are indistinguishable from Nocardia on Gram stain, but only the latter are positive on modified acid-fast staining. An anaerobic environment is required for isolation of the organism. (See 'Histologic findings and culture' above.)

●Management − Many patients undergo resection before the diagnosis has been established. Initial medical treatment is reasonable in patients in whom the diagnosis is established prior to surgery. Penicillin is the preferred choice. Details of the treatment of actinomycosis are discussed elsewhere. (See "Treatment of actinomycosis".)