P0895 - Primary Hepatic Actinomycosis as Source of Acute Abdominal Pain in Adolescent

Introduction
Abdominal pain is commonly encountered in the pediatric population and prompts medical evaluation in both clinic and emergency department settings. In a 2007 study by Leoning-Baucke, et al., as many as 9% of pediatric patients 4 to 18 years of age required medical assessment for acute onset abdominal pain. In this case, abdominal actinomycosis, a rare etiology of abdominal pain in an adolescent female, is explored.

Case Description
A 14 year old AAF with no significant medical history developed acute onset right upper quadrant abdominal pain with associated fever and vomiting. History was negative for diarrhea, recent travel, and animal exposure. Initial work-up was significant for leukocytosis with a white blood cell count of 19,200, normal transaminases, and CT abdomen/pelvis with a hepatic mass and hepatic and splenic hypo-attenuating foci. MR abdomen revealed a caudate lobe lesion with an avascular, heterogeneous central component and thin rim of peripheral enhancement concerning for abscess versus necrotic malignancy. Endoscopic ultrasound with fine needle aspiration revealed fibrinopurulent exudate consistent with abscess; fluid culture was positive for Actinomyces odontolyticus. Despite intravenous (IV) antibiotic therapy based on sensitivities, the patient remained febrile with abdominal pain and ultimately required surgical drainage and change of antibiotic course before clinical improvement was achieved. Patient was continued on IV Penicillin G for 6 weeks followed by oral Penicillin VK for 6 months.

Discussion
Actinomyces odontolyticus is an anaerobic, gram-positive bacterium that often colonizes the oral, gastrointestinal, and urogenital tracts. Despite this commonality, it is a known pathogen causing cervicofacial, pulmonary, and abdominopelvic manifestations. When the abdomen is involved, the ileocecal junction and appendix are most frequently affected. Infection in these locations typically occurs after an insult to the intestinal mucosa or as a post-surgical complication. Primary hepatic actinomycosis is rare; when it does occur, it is typically seen in the right lobe of the liver and often misdiagnosed as malignancy. This presentation is almost exclusively reported in adults, in which the diagnosis is made post-operatively after hepatic resection has been performed.

Conclusion
The rarity of abdominal actinomycosis certainly limits its inclusion in the differential of abdominal pain in pediatric patients. For patients with abdominal pain of unclear etiology, abdominal imaging studies may be helpful. When imaging reveals spontaneous abscess formation or a potential mass, actinomyces should be considered because failure to successfully make the diagnosis and initiate proper treatment may lead to significant morbidity and mortality. While most intra-abdominal abscesses can be drained and treated with a short course of IV or PO antibiotics, abdominal actinomycosis requires a much longer course of IV antibiotics, approximately 4-6 weeks, before transitioning to continued PO therapy for several months thereafter.