Abscess, left thalamus with ventriculitis
Findings:
Multiple MR images without and with contrast demonstrate a rim enhancing lesion in the left thalamus associated with surrounding vasogenic edema. The lesion is associated with a hypointense rim on T-2 weighted imaging and faint increased T1 signal along the periphery on the T1 precontrast images. There is also heterogeneous material within the left occipital horn and left frontal horn. The core of the ring enhancing lesion demonstrates marked restricted diffusion and there is also restricted diffusion within the intraventricular material.
Differential Diagnosis:
Abscess w ventriculitis most likely. If no intraventricular material could consider metastasis or primary tumor but the central DWI signal argues against neoplasm.
Discussion:
Please refer to multiple other cases of abscess on this site for discussion. Complex inflammatory fluid and cells within an abscess cavity have a relatively high viscosity which also restricts the motion of free water therefore marked diffusion restriction is expected within the core of an abscess. Leakage of this pus into another space such as the ventricular system will also be associated with restricted diffusion.