Magnetic resonance spectroscopy guided brain tumor resection: Differentiation between recurrent glioma and radiation change in two diagnostically difficult cases

Background: It is often difficult to differentiate a recurrent glioma from the effects of post-operative radiotherapy by means of conventional neurodiagnostic imaging, Proton magnetic resonance spectroscopic imaging (H-1-MRSI), that allows in vivo measurements of the concentration of brain metabolites such as choline-containing phospholipids (Cho), may provide in vivo biochemical information helpful in distinguishing areas of tumor recurrence from areas of radiation effect. Patients and Methods: Two patients who had undergone resection and post-operative radiotherapy fbr a cerebral glioma became newly symptomatic. Computed tomographic (CT) and magnetic resonance imaging (MRI) performer: after the Intravenous infusion of contrast material, and in one case, [18F]fluorodeoxyglucose positron emission tomography (PET), could not differentiate between the possibilities of recurrent glioma and radiation effect. The patients underwent H-1-MRSI prior to reoperation and the H-1-MRSI results were compared to histological findings originating from the same locations. Results: A high Cho signal measured by H-1-MRSI was seen in areas of histologically-proven dense tumor recurrence, while low Cho signal was present where radiation changes predominated. Conclusions: The differentiation between the recurrence of a cerebral glioma and the effects of post-operative irradiation was achieved using H-1-MRSI in these two patients whose conventional neurodiagnostic imaging was equivocal for such a distinction. Where these two conditions are present, metabolite images from H-1-MRSI, such as that based on Cho, can be co-registered with other imaging modalities such as MRI and may also be integrated with functional MRI or functional PET within a multimodal imaging-guided surgical navigation system to assure maximal resection of recurrent tumor while minimizing the risk of added neurological damage.