Concomitant parasagittal meningioma and adjacent intracranial abscess of occult etiology

Introduction: Abscesses associated with tumors are a rare entity. Imaging to differentiate abscess from other entities is often non-diagnostic, and often the source of infection is unknown. We present an unusual case of peritumoral abscess infected with both gram-negative and gram-positive bacteria. Methods: A 70-year-old, previously healthy male presented with a 1-day history of right-sided facial weakness sparing the forehead, as well as concomitant right upper and lower extremity numbness. A homogenously enhancing mass with adjacent rim-enhancing lesion with diffusion restricting cavity seen on magnetic resonance imaging (MRI) raised the possibility of abscess. Results: Separate biopsy specimens of both the tumor and adjacent fluid collection during drainage of the collection confirmed World Health Organization (WHO) grade I meningioma and bacterial abscess containing Streptococcus constellatus, Fusobacterium species, Prevotella dentalis, and Parvimonas micra. The histologic diagnosis therefore confirmed the preoperative radiologic findings of two different but associated lesions. Investigations to determine a definitive source of infection were inconclusive, including urinalysis, blood cultures, respiratory cultures, endoscopy, and an orthopantomogram. Conclusions: Gram-negative and gram-positive bacteria can both be culprits in the formation of peritumoral abscess. Although the source of infection is unconfirmed, the presence of oropharyngeal flora in the abscess suggests a subclinical odontogenic infection with hematogenous spread to the tumor and adjacent brain.