Multimodal target point assessment for stereotactic biopsy in children with diffuse bithalamic astrocytomas

Abstract

Introduction.Diffuse glial tumors with bithalamic involvement are rare in children. Diagnostic assessment can be difficult as the radiological findings can be unspecific.

Materials and methods.In order to enhance the diagnostic yield metabolic imaging with MRS and PET using FET (O-(2-[¹⁸F]fluoroethyl)-L-tyrosine) was performed in two children (2 and 10 years of age). Co-registered images were used for image-guided biopsy, which was planned with neuronavigation and stereotaxy simultaneously.

Results.Biopsies from the right thalamus were planned, but locations were changed in both cases after metabolic imaging was available. MRS (thalamic voxel) was typical for a glial tumor in one child. In the older girl FET-PET revealed an unexpected lesion in the left cerebellar hemisphere, with a tumor-to-cortex ratio of 3.8, as against 1.7 in the thalamus. Accordingly, a stereotactic biopsy specimen was taken from the left cerebellar hemisphere, and a final diagnosis of anaplastic astrocytoma was made. The other patient showed a higher uptake (tumor-to-cortex ratio 1.6) in the left dorsal thalamus, compared with bilateral homogeneous hyperintensity of the thalamus structures on MRI. Stereotactic biopsy revealed a low-grade diffuse astrocytoma.

Conclusion.Stereotactic biopsy using metabolic imaging and image fusion can enhance the diagnostic yield in cases of diffuse pediatric gliomas disclosing unexpected ’hot spots’.