What is the differential diagnosis?
Viral encephalitis, limbic encephalitis, seizure related increased signal.
Which would you favour and why?
Overall appearances, in a patient with memory disturbances who is otherwise relatively well, and without seizures, favour a limbic encephalitis (paraneoplasitc / autoimmune). Viral encephalitis (e.g. HSV) could have similar appearances although patients are usually unwell, often with a reduced concious state.
Bilateral mesial temporal lobe increased T2 signal is demonstrated, more marked on the right, and seen extending in along the hippocampal head, body and tail, but also involving the fornicies, amygdala, and parahippocampal gyrus. There is no convincing contrast enhancement. No evidence of haemorrhage. MR spectroscopy demonstrates minor elevation of the choline peak (not shown). MR perfusion demonstrates and some apparent reduction in the right mesial temporal (not shown).