Abscess formation within cerebellar metastatic carcinoma--report of two cases and review of the literature.

BACKGROUND

The occurrence of an abscess in conjunction with a tumor in the brain is very rare. Only presumptions exist about their origin and manner of dissemination. Preoperative discrimination between a brain tumor with cystic degeneration and a brain abscess within a tumor may be difficult or even impossible. The purpose of this report is to demonstrate the difficulty of such discrimination using conventional CT diagnostics alone.

METHODS

Two patients with abscess formation in association with metastatic carcinoma in the cerebellum are presented and compared with similar cases in the literature. The etiology and the route of dissemination are discussed.

RESULTS

In our first patient with previously diagnosed lung carcinoma and a CT showing suspected cerebellar metastasis only, an abscess caused by Propionibacterium acnes was found in the cerebellum and treated surgically. No tumor was recognised during the operation. Post-mortem examination six weeks later revealed the coexistence of remnants of a chronic abscess as well as metastatic lung carcinoma at the operation site. The second patient presented with an enhanced, ring-like cystic cerebellar lesion. During surgery, a purulent exudate with a coagulase-negative type of Staphylococcus species was found within the metastatic carcinoma of unknown origin. Both were radically excised and the patient recovered well. Neither patient had a history of previous infection and the pathway for abscess formation in both patients remained unclear. About 30 cases of abscesses associated with intracranial neoplasms were found in the literature. Including our own report, only three cases of abscesses within metastatic carcinoma have been published.

CONCLUSIONS

Modern diagnostic tools reported to differentiate more reliably between an abscess and a tumor are diffusion-weighted MR and proton MR spectroscopy techniques. Brain imaging using CT alone may not reliably demonstrate both coexisting lesions or differentiate between them. It is important to know that a metastatic brain lesion can occur in association with a brain abscess and that tissue sampling for pathological as well as microbiological testing is of crucial importance for optimal therapy for both lesions.