Clinicopathological heterogeneity and complexity of polymicrobial brain abscesses

Polymicrobial brain abscess (PBA) is a complex infection caused by two or more pathogens and a life-threatening condition with diagnostic and therapeutic challenges. We retrospectively identified PBAs in 31 patients (24 males and 7 females) and examined their clinical, radiological and pathological characteristics. These characteristics of PBAs were compared with those of monomicrobial BAs (MBAs) in a previously reported cohort of 113 patients in our institution. PBAs and MBAs had a few similarities such as nonspecific clinical presentations, a male predilection, and similar prognosis following surgical intervention with broad-spectrum antimicrobial therapy. However, PBAs were highly heterogeneous with more complexity on magnetic resonance imaging (MRI)/computed tomography imaging and histopathology. While PBAs were typically rim-enhancing lesions at late-stages, 30/31 (97 %) of PBAs showed lobulation of enhancing rims/walls; on MRI, 14/26 (54 %) of cases demonstrated marked variation in the thickness of enhancing rim, marked difference in the degree of diffusion-weighted imaging (DWI) signal, and/or marked variation in intra-lesional MRI signal. PBA histopathology was characterized mainly by alternating early-stage and late-stage features with regional differences, variable distribution and combinations of 2-4 pathogens. Compared to MBAs, PBAs were more frequently unifocal (94 % of cases) as well as caused by pathogens of otogenic, odontogenic and/or rhinogenic sources. Our findings suggest that, despite some shared features between PBAs and MBAs, PBAs are more heterogeneous with greater complexity on imaging and histopathology. Their diagnosis and disease staging require an integrative clinico-radiologico-pathological approach. PBAs deserve more awareness for prompt diagnosis and appropriate treatment.