Roughly 1-2% of cerebral abscesses are caused by Nocardia spp. and usually occur in immunocompromised patients. Mortality of Nocardia is around three times higher than other bacterial abscesses, making early diagnosis critical. Lesions are usually supratentorial and multiloculated due to daughter abscesses. 

A healthy 70-year-old male with history of diabetes mellitus and hypertension presented with new onset right upper extremity weakness, right-sided facial droop, and expressive aphasia. Brain MRI revealed an enhancing left-sided pontine mass with surrounding vasogenic edema. Lumbar puncture was obtained which was remarkable for leukocytosis, monocyte predominance (WBC 13thou/cmm). Cultures and PCR of cerebrospinal fluid were negative with no bacterial or fungal growth. He was started on intravenous steroids with improvement in his symptoms and discharged with close follow up. Three days later, he returned with worsening right upper arm weakness. Repeat MRI brain showed an expanding mass at the left aspect of the brainstem extending into the cerebral peduncle and medulla oblongata. MR spectroscopy favored abscess formation over metastasis or hematoma, and the patient was started on intravenous ampicillin empirically for presumed Neurolisteriosis.  As the patient experienced only minimal neurologic and radiologic improvement after two weeks, the decision for surgical biopsy was pursued. Left retromastoid craniotomy was performed and cultures grew Nocardia cyriacigeorgica, and the patient was started on trimethoprim-sulfamethoxazole, imipenem and amikacin.

While Nocardia CNS infections are typically supratentorial lesions, we present an atypical presentation of a patient who presented with progressive neurologic deficits from an expanding pontine mass. Nocardia abscesses are extremely rare and usually present in immunocompromised hosts. Despite being healthy with no significant prodrome prior to presentation, our patient had radiologic evidence of cirrhotic liver morphology which may have predisposed him to infection. This case highlights that Nocardia should be considered as an infectious agent in brainstem abscesses.