QUIZ: No. 19, 12/07/2025

USG

CT

MRI

ANS – Abdominal wall actinomycosis.

Actinomycosis is a rare chronic bacterial suppurative infection caused by Gram-positive anaerobic bacilli belonging to Actinomyces spp. Actinomyces israelii is the most common organism causing human infections. Normally actinomycetes are seen as commensals and they typically require a disruption of mucosal barriers to become pathogenic.

Ø  The aggressive infiltration pattern of abdominopelvic actinomycosis is one of the disease’s key radiologic features, which are attributed to the production of proteolytic enzymes by the bacilli.

Ø  This causes the abdominal wall to become extensively infiltrated with inflammatory fat, leading to the formation of abscesses.

Ø  In actinomycosis, the organism typically does not spread by hematogenous or lymphatic pathways, and regional lymphadenopathy is uncommon.

Ø  The presence of extensive and dense fibrosis in actinomycosis is responsible for T1/T2 hypointense signal change on MRI.

Conventional treatment for actinomycosis involves intravenous penicillin for 2–6 weeks followed oral penicillin for 6 months. Surgical debulking may be performed for localized abdominal actinomycosis, followed by short course oral antibiotics. 

TEACHING POINTS

1.     Actinomycosis should be a diagnostic consideration in chronic irregular hard masses extending across the tissue plane with surrounding inflammation

2.     Earlier diagnosis of actinomycosis can help the patient get cured by antibiotic therapy alone without the need for surgery. Knowledge about the clinical and radiological findings helps to avoid unnecessary surgical interventions

3.     Infiltrative T2 hypointense masses in atypical locations should raise the possibility of actinomycosis.