Hepatic abscess on CT: pearls, pitfalls and diagnostic challenges

Hepatic abscess (HA) poses a diagnostic challenge worldwide, with up to around 80% of cases initially missed in emergency settings. This can be attributed to their clinical and imaging appearance varying considerably depending on the underlying pathogen and abscess type. Computed tomography (CT) remains the primary imaging modality for evaluation, and this pictorial essay highlights the characteristic imaging features of the subtypes of HA which include pyogenic, amebic, fungal, and hydatid infections. Key imaging findings discussed include the cluster sign and double target sign in pyogenic abscesses, the solitary right subcapsular morphology of amebic abscesses, the disseminated microabscess pattern of fungal infections in immunocompromised hosts, and the daughter cysts with peripheral calcifications characteristic of hydatid disease. Furthermore, HA has neoplastic mimickers which can demonstrate similar imaging characteristics. The diagnosis is further complicated as patients with known malignancies or surgical intervention are prone to developing HA. This pictorial review highlights the key imaging features that enable radiologists to recognize HA on CT in emergency settings and differentiate it from its most clinically significant mimics.