Pelvic actinomycosis is a rare but serious infection caused by Actinomyces spp., an opportunistic gram-positive bacteria usually introduced by foreign bodies, particularly intra-uterine contraceptive devices, surgery, or trauma. It generally falls under the broader spectrum of pelvic inflammatory disease.
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Pathology
Pelvic infection from several Actinomyces spp. can occur, which include:
- Actinomyces israelii: the most common causative organism, by far 3
- Actinomyces naeslundii
- Actinomyces viscosus
- Actinomyces eriksonii
The organisms are indigenous to the oral cavity, gastrointestinal tract, and genital tract, with opportunistic infection occurring when the mucosal barrier is broken.
Associations
- placement of intra-uterine contraceptive devices: usually when it has been present for a prolonged period
- ~25% of IUCDs eventually get colonized by Actinomyces spp.
- 2-4% of IUCDs that are colonized ultimately develop a serious actinomycotic infection
Radiographic features
Actinomycosis infection can mimic many other pelvic pathologies on imaging. The spread of infective/inflammatory change across tissue planes, and in particular retroperitoneal extension into the psoas muscle may suggest the diagnosis. The most common site of involvement of the GI system is the ileocecal junction.
CT
- tend to be denser than tubo-ovarian abscesses originating from other organisms
- can mimic a locally invasive malignancy
- enhancement in the solid component
- rim-enhancing abscesses within the solid component
MRI
- T2: intermediate-low signal intensity
- post-contrast enhancement
Associated findings
- indurated pelvic fat
- pelvic free fluid
- pelvic abscess
- hydronephrosis
Complications
- wider intra-abdominal extension: mainly through contiguous spread
- formation of tubo-ovarian abscess 2
- subsequent infertility
Treatment and prognosis
Treatment is usually with intravenous penicillin in uncomplicated cases. Presence of an associated complication, such as a tubo-ovarian abscess, warrants surgical intervention.
Differential diagnosis
Due to its non-specific imaging appearances, pelvic actinomycosis can mimic several pathologies, such as:
- other forms of pelvic inflammatory disease
- pelvic malignancy
-
ovarian cancers
- as a general rule, these incite more ascites and lymphadenopathy
-
lymphoma
- associated with lymphadenopathy elsewhere
-
ovarian cancers
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