Patient Data
A nodular mass is demonstrated centered in the right basal nuclei with an irregularly thick contrast enhancing rim. Significant surrounding T2/FLAIR high signal extends via the cerebral peduncle into the midbrain and inferiorly to the right cerebral peduncle which is expanded. There is moderate regional mass effect with effacement of the frontotemporal sulci and effacement of the right lateral ventricle, resulting bowing of the septum pellucidum after 4 mm to the left.
The central portion of the mass is mildly hypointense to grey matter on T1-weighted imaging and hyperintense on T2-weighted imaging with poor suppression on FLAIR. Diffusion weighted imaging demonstrates patchy high signal predominantly at the peripheral portion of the mass and centrally decreased ADC. There is mildly increased rCBV in the rim of the mass. Spectroscopy demonstrates metabolite depletion and prominent lactate peak.
Conclusion: In an immunocompetent patient, this rim-enhancing mass has features favoring a high-grade glioma. Features are not typical of a pyogenic abscess however abscesses secondary to atypical organisms (e.g. Toxoplasmosis) may have this appearance; HIV / immunosuppressed status needs to be assessed. A less likely diagnosis is lymphoma, which may have this appearance in an immunocompromised patient.
MICROSCOPIC DESCRIPTION: Paraffin sections of the two specimens submitted for frozen section confirm the presence of numerous tacchyzooites of Toxoplasma and scattered encysted braddyzooites. There are present in a background of extensive necrosis of brain parenchyma which is sharply demarcated from adjacent viable parenchyma. Within the area of necrosis there are ghosts of necrotic blood vessels with peri and paravascular accumulation of neutrophils and chronic inflammatory cells and karryorhectic debris. There is reactive proliferation of small vessels in viable parenchyma. No evidence of tumor is seen. 3. The sections show cerebral cortex and white matter. Within an area of congestion and focal necrosis within deep white matter there are numerous tacchyzoites of Toxoplasma as well as scattered encysted braddyzoites. Scattered encysted braddyzoites are also identified in more superficial white matter and in the cortex. The features are of cerebral toxoplasmosis. No evidence of tumor is seen.
DIAGNOSIS: Cerebral toxoplasmosis
Case Discussion
It is not uncommon to not be aware of the immune state of a patient at the time of imaging, either because lab results are still pending or because the information has not been passed on along with the imaging request. It is thus essential to keep that possibility in mind.
This is a fairly typical appearance for Toxoplasmosis and would certainly be the favored diagnosis if the patient was known to be immunocompromised.