47 year old female, a case of right perisylvian low-grade astrocytoma showing no contrast enhancement on MRI being followed up since 2014 had a recent episode of seizure for which she had undergone Brain PET/MRI with 18F-DOPA and with 18F-FDG as a correlative study in May 2019.
F-18 DOPA avid non enhancing FLAIR T2 hyperintense bulkiness is seen involving the right perisylvian region involving the right striatum, inferiorly the temporal lobe including the hippocampus and parahippocampus region encasing the right MCA & effacing the right basal cistern with signal changes in the right hypothalamus and chiasma and extending involving the right basifrontal region.
The lesion shows significantly increased DOPA uptake (lesion vs contralateral striatum: 2.11 vs 1.0 normal), increased perfusion and mild restricted diffusion and increased Cho/Cr and Cho/NAA ratios on MRS: all MRI parameters derived in a single examination are synergistic in favor of active disease.
Correlative FDG Brain PET done within the next 24 hours showed no appreciable FDG uptake corresponding to the nonenhancing bulkiness and DOPA avid region.
Fig.4 Axial T2W FLAIR image (a) showing hyperintense bulky lesion in the right perisylvian region extending involving the right striatum, inferiorly the temporal lobe including the hippocampus and parahippocampus region encasing the right MCA & effacing the right basal cistern with subtle signal changes in the right hypothalamus and chiasma, extending involving the right basifrontal region. Non-enhancing T1 axial images (b), but intense uptake in axial al DOPA PET (c) and fused axial PET MRI images (d). The lesion showed Diffusion restriction in ADC map (e) and no increased perfusion in axial CBV map (f), however, showed increased Choline on MRS (g) but not FDG avid: axial fused FDG PET MRI (h).
Teaching: DOPA can be avid in the nonenhancing region of a brain tumor
Contrast MRI is the mainstay in the evaluation of Gioma at all stages of the disease at diagnosis, residual/ recurrence after treatment or response to treatment based on its presence of enhancement and its pattern. Non enhancing tumor, appearing as hyperintense bulkiness on T2W FLAIR pose challenge for detection and accurate extent delineation of any underlying active/inactive disease from the commonly encountered presence of perilesional oedema or post RT gliosis as is in the case under discussion.
DOPA PET elegantly displayed in this case that there exists an active disease ( showing increased tracer uptake) in the entire extent of what appears as non enhancing bulkiness in the corresponding MRI scan with accurate spatial correlation because both PET and MR images acquired simultaneously.
FDG PET showing uptake in the corresponding area of DOPA avidity brings home the fact that unlike FDG, uptake of FDOPA does not depend on a break in blood-brain barrier the mechanism that makes a region in the brain appear enhanced in contrast MRI.
Delineation of the non-enhancing zone of a tumor with DOPA PET has an impact on defining tumor volume better, defining non enhancing residual disease after surgical resection and identifying unexpected recurrence beyond its usual presentation as enhancing mass after the treatment.
This short PET-MRI Scan case was compiled by Dr. Sangeeta Taneja and Dr. Amarnath Jena (Nuclear Medicine Physician at PET-Suite @ Indraprastha Apollo Hospital, Sarita Vihar).
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