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Fig. 6.4 A-C. Actinomycosis is not restrained by tissue planes. A A large peripheral lung abscess with an overlying left pleural reaction. There is fluid within the abscess and hilar lymphadenopathy. B A few weeks later the abscess had spread through the chest wall, invading the soft tissues and ribs. There is a hypertrophic periosteal reaction along the left clavicle. C In a different patient it is impossible to know where the infection started. There is consolidation and fluid in the left apical region, and periosteal new bone around the clavicle, scapula, and humerus. Irregular nodules can be seen in the soft tissues.

Fig. 6.5 A-C. Pelvic actinomycosis. A 50-year-old female had a 4-month history of constipation, ill health, and weight loss. A A barium enema some years previously showed an IUCD and normal large bowel. B, C A repeat barium enema showed a long irregular stricture of the rectosigmoid colon and adjacent sigmoid colon (arrows). There is still an IUCD. Ultrasonography showed mild bilateral hydronephrosis and some splenic enlargement. The stricture could not be passed on sigmoidoscopy. At laparotomy there was a large pelvic "mass" infiltrating the left wall of the pelvis and involving the colon, uterus, fallopian tubes, ovaries, and distal ureters. There was no pus in the uterus. Biopsy showed multiple colonies of Actinomycetes israelii. There was no evidence of malignancy. After antibiotic therapy a barium enema 12 months later was entirely normal. (Courtesy of Drs. A.E. Turnbull and M. E. L. Cohen and Clin Radiol, 1991)



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Imaging Diagnosis

There are few other infections which spread directly from soft tissues to bone and/or neighboring organs. This, together with the finding of multiple abscesses and sinuses, is an important indicator of actinomycosis at any site.


The soft tissue mass appears before the bony changes, which start with periosteal reaction followed by irregular, moth-eaten bone destruction. As the intraosseous granulomas develop, there will be apparent expansion of periosteal bone around lytic lesions. At this stage there will already be sinus tracts between the bone and soft tissues. Early and extensive soft tissue involvement preceding the bone infection, with associated fibrosis and sinus formation, distinguishes actinomycosis from osteomyelitis caused by other pyogenic organisms. Computed tomography (CT) and magnetic resonance imaging (MRI) are important to delineate exactly the location and exent of the infection and to track spread of the infection, particularly upwards through the para-nasal sinuses to the base of the skull, and occasionally even to the meninges and brain. Ultrasonography may be used to show the multiple abscesses within the thick soft tissue tumor and is particularly helpful in the neck. Actinomycosis will result in a thick irregular conglomerate mass, ignoring tissue planes and fixing together all layers as it spreads.


Actinomycotic granulomas may occur anywhere along the gastrointestinal tract, and be intraluminal, intramural, or outside the bowel. The lumen may be narrowed or distorted by external pressure. Localized stricture formation can be difficult to differentiate from other tropical infections (e. g., amebiasis, schistosomiasis, tuberculosis) or malignancy.

Pelvic actinomycosis is common, particularly in women in whom an intrauterine device has been in place for many years (Figs. 6.5, 6.6). Actinomyces israelii may be found on cervical smears when there is endometrial or endocervical infection, even when there is no other clinical evidence of systemic disease. Ultrasonography may show tubo-ovarian abscesses, or an apparently unrelated pelvic abscess elsewhere. Almost all other organs in the abdomen and pelvis have been involved (the bowel, bladder, liver, ureters, kidney, gallbladder, and pancreas), as well as the soft tissues. When actinomycosis is suspected, the whole abdomen must be scanned by ultrasonography or CT, including the subphrenic region. Spread through the diaphragm is common in amebiasis, but uncommon in pyogenic infection: only actinomycosis will show multiple sites with abscess formation. Actinomycosis of individual organs may be difficult to diagnose. When the ileum or cecum is infected, there will be distortion due to an abscess or pseudotumor, with internal or external sinuses: the terminal ileum is nearly always involved and partially obstructed. Eventually pelvic actinomycosis will directly involve the pelvic bones, unlike other infections or malignancies.

When the stomach is involved, actinomycosis may present (a) as an infiltrating tumor, (b) as an ulcer or ulcers which may resemble a diverticulum or may penetrate the full thickness of the stomach, or (c) as thickening of the gastric wall without a localized tumor, resembling linitis plastica. The lastmentioned form is least common, but in all three varieties the stomach loses its capacity to expand and becomes locally fixed. Only the multiple sinuses will allow differentiation from carcinoma, lymphoma, tuberculosis, schistosomiasis, and syphilis.

In the duodenum, actinomycosis produces longitudinal ulcers which eventually progress to fistulae and adhesions. It is only the fistulae which will suggest the correct diagnosis and allow exclusion of malignant disease or tuberculosis, but Crohn's disease may cause similar deformities.

Actinomycosis of the colon produces a mass or a stricture, and either may result in obstruction. Perirectal inflammation narrows and distorts the bowel and causes mucosal irregularity and fistulae. This appearance can resemble lymphogranuloma venereum, schistosomiasis, tuberculosis, amebiasis, and Crohn's disease. It is often impossible to make an accurate diagnosis by imaging alone.
Renal actinomycosis may affect one or both kidneys and be mistaken for tuberculosis or malignancy. The calyces are distorted, with enlargement of the kidney or with a localized mass. When there is a sinus tract to the skin, the diagnosis is straightforward, but when there is only renal or perirenal infection the differential diagnosis is difficult, if not impossible.


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