MRI obtained 3 months after biopsy and at the end of combined chemoradiotherapy (Stupp protocol) demonstrates a left front burr hole with biopsy tract. Ring-enhancing mass within the left pons/midbrain extending into the left cerebral peduncle, which measures 24 x 19 x 35 mm in maximal dimensions, previously measures 17 x 11 x 27 mm. There is increased central low signal indicative of increased necrosis. Blooming surround this mass indicates surrounding blood product.
Surrounding more extensive high FLAIR signal, which tracts inferiorly to the medulla (new) and posteriorly to the left cerebellar hemisphere via the left cerebellar peduncle (new). It also newly crosses the midline into the right pons and midbrain, as well as increased FLAIR signal within the inferior left frontal lobe, left temporal lobe, extending into the left internal capsule / corona radiata and along the biopsy tract.
MRS demonstrated increased lactate peak with preserved NAA and mildly elevated choline. There is possibly some minor increase in CBV that corresponds with the enhancing margins of the mass, but this is minimal. There is also high DWI / low ADC signal indicating restricted diffusion within the enhancing margins of the mass but blood product in the region limits reliability.
Conclusion
Left midbrain/pons mass has increased in size with increased central necrosis. There is marked increase in surrounding FLAIR signal. At this time (3 months post biopsy, end of Stupp protocol) the absence of convincing elevation of CBV, and relatively mild MRS changes, favour a significant component of pseudoprogression.