Pelvic actinomycosis

Pelvic actinomycosis infection is a rare but serious infection caused by Actinomyces sp., an opportunistic gram-positive bacteria usually introduced by foreign bodies specially IUCDs, particularly intra-uterine contraceptive devices, surgery, or trauma. It generally falls under the broader spectrum of pelvic inflammatory disease.

Pathology

Pelvic infection from several Actinomyces sp. can occur, which include:

• Actinomyces israelii: by far the most common causative organism ³
• Actinomyces naeslundii
• Actinomyces viscosus
• Actinomyces eriksonii

The organisms are indigenous in 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 colonised by Actinomycosis sp.
  • 2-4% of IUCDs that are colonised 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 ileocaecal 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 IVintravenous penicillin in uncomplicated cases. The presence of an associated complication such as a tubo-ovarian abscess would warrant 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
  • tuberculous pelvic inflammatory disease
• pelvic malignancy
  • ovarian cancers
    • ​as a general rule, these incite more ascites and lymphadenopathy
  • lymphoma
    • associated with lymphadenopathy elsewhere