Diagnostic difficulties in childhood bilateral thalamic astrocytomas.

We report on two children with bilateral thalamic astrocytomas. The first patient developed psychomotor regression at the age of 20 months followed by rapidly progressive ataxia, intention tremor, slurred speech, and bouts of drowsiness. Magnetic resonance imaging (MRI) of the brain showed swelling and high signal intensity in both thalami accompanied by supratentorial hydrocephalus. The second patient presented with progressive cerebellar ataxia, headache, and vomiting at the age of 11 years. MRI of the brain revealed symmetrical, hyperintense and sharply delineated swelling of both thalami. Additional lesions were seen in the cerebellum and the right temporal lobe. In both cases proton magnetic resonance spectroscopy (MRS) of the lesions showed a striking decrease of the neuronal marker N-acetylaspartate, an increase of choline-containing compounds, and a minimal lactate peak. Stereotactic biopsies from the thalamus of the first patient and from a cerebellar lesion of the second patient finally revealed glial tumors, namely a diffuse astrocytoma of World Health Organization (WHO) grade II in the first patient and an anaplastic astrocytoma of WHO grade III in the second patient. We conclude that the clinical manifestations and MRI patterns of bilateral thalamic astrocytomas are very similar to those of encephalitis and neurometabolic disorders and should therefore be included in the differential diagnosis of these encephalopathies.