Cryptogenic HACEK (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, and Kingella) CNS Abscess in an Otherwise Healthy Patient With a Patent Foramen Ovale.

and HACEK ( and ) organisms are part of the oral microbiome and rarely affect the central nervous system (CNS). CNS infections with these agents can be caused by contiguous or hematogenous spread. We present a case of a 25-year-old immunocompetent male who presented with a one-week history of progressively worsening generalized headaches, photophobia, nausea, and vomiting. Despite a normal physical exam and the absence of leukocytosis, head imaging showed a right frontal lobe abscess. The patient was started empirically on vancomycin, ceftriaxone, and metronidazole, and surgery was performed. Surgical cultures grew organisms from the HACEK spectrum (, ), , , and . Serial imaging studies showed a rapid increase in the size of the residual abscess, and the patient needed repeat intervention within five days. He was discharged five days after the repeat surgery on IV therapy prior to the transition to oral antibiotics. While the patient was found to have a small patent foramen ovale, there was no evidence of bacteremia or valvular vegetation, and no evidence of dental or sinus disease was seen on imaging. This case suggests that even in the absence of any clear sources of infection, cryptogenic brain abscesses can still occur sporadically in young, healthy patients.