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Case Five - Cerebral Abscess

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Clinical History: 37-year-old female presents with a left parietal mass.

Findings: CT scan was performed before and after the administration of IV contrast and reveals a left cerebral mass abutting the falx. There is in addition surrounding edema extending superiorly with slight midline shift to the right. Subsequent to the administration of contrast, a rim of enhancement is evident.

Differential Diagnosis: Brain abscess, neoplasm, granuloma, cerebral infarct, resolving hematoma.

Diagnosis: Cerebral abscess

Discussion: Brain abscesses reveal an incidence of (0.18% to 1.3%) with a median age of presentation between 30 and 40 years. They may result from multiple causes; extension of a contiguous focus of infection (from otitis, sinusitis, or dental infection), hematogenous spread, or secondary to cranial trauma or surgery. They occur in the following regions in decreasing order of frequency; frontal >= frontoparietal > parietal > cerebellar >occipital.

Between (30% and 60%) of pyogenic abscesses are mixed infections, with aerobic isolates outnumbering anaerobic isolates approximately 2 to 1. Organisms include streptococci, staph aureus, and now more frequently gram negative bacilli. It is also important to note that the immune status of the patient can influence the organism causing the abscess. In neutropenic patients, brain abscesses may be caused by candida or aspergillus. In patients with abnormal cell mediated immunity, the causes may include toxoplasma gondii, mycobacterium, nocardia, cryptococcus, or listeria.

There are four stages in the evolution of a brain abscess.

Early cerebritis developing around one to three days.
Late cerebritis.
Early capsule formation occurring at approximately 10 to 13 days.
Late capsule formation.

Most patients present with signs of mass effect rather than those of infection. The clinical manifestation is also dependent on factors such as virulence of the organisms, patient immune status, and the location of the abscess. CT can detect the existence and location of the abscess, the extent of edema, the presence of hydrocephalus, and whether a midline shift exists. The abscess appears as in this case as an area of hypodensity surrounded by a contrast enhancing ring. MRI is however the desired modality in the work up of suspected brain abscess as it allows for greater tissue characterization, lacks bony artifacts and ionizing radiation, and has less toxic contrast agents.

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Submitted by:
Vito Basile, M.D.