Rasmussen's disease fluoro-2-deoxyglucose positron emission tomography computed tomography as a complementary role in neuroimaging

Rasmussen's encephalitis (RE) is rare inflammatory neurodegenerative disease usually affecting single cerebral hemisphere. It manifests as progressive neurological deterioration and intractable seizures. Imaging plays a vital role in the diagnosis. The diagnosis of RE is clinically challenging and based on exclusion in patients with intractable seizures and progressive motor cognitive deterioration. Epilepsy surgery has a major role in RE and it remains the curative treatment for disease progression and has achieved wide range of seizure control. Due to refractory and progressive disease, the treatment options are disconnective techniques such as functional hemispherectomy (resection of affected cerebral hemisphere sparing frontal and occipital lobe) and hemispherotomy, to achieve seizure control. Thus, as a guiding tool for definitive surgical intervention, particularly in cases of nonspecific clinical findings, anatomical neuroimaging and metabolic neuroimaging are of critical importance. A lateralization of diffuse unilateral hypometabolism in 2-deoxy-2(¹⁸F)fluoro-D-glucose positron emission tomography computed tomography (FDG PET CT) and corresponding equivalent region of cerebral atrophy on magnetic resonance images supports the diagnosis of RE and gives precise information on the metabolic extent of disease. FDG PET CT has got a potential benefit in this to localize and lateralize the seizure focus. Here, we report four cases of RE in which FDG PET CT showed varied distribution of disease and proved an added benefit in neuroimaging. FDG PET CT shows a characteristic pattern of asymmetrical cerebral atrophy with ipsilateral hypometabolism and contralateral cerebellar atrophy associated with hypometabolism, i.e., crossed cerebellar diachiasis, probably due to propagation of seizure activity along corticopontocerebellar pathway