A periventricular or deep grey matter mass that is T2-dark, restricts on diffusion and enhances homogeneously — suggest it before biopsy, because steroids can make it vanish and the biopsy non-diagnostic.
Orient first
- In immunocompetent patients: solid, homogeneously enhancing, crossing the corpus callosum or touching the ependyma.
- High cellularity gives low ADC and relatively low T2 signal.
- In immunocompromised patients lymphoma is often ring-enhancing and haemorrhagic, overlapping with toxoplasmosis.
Acquire the study
- MRI: T2, FLAIR, DWI/ADC, SWI, post-gadolinium 3D T1, DSC perfusion where available.
The manoeuvre
- DWI/ADC: low ADC in the solid tumour (lower than typical glioblastoma).
- T2: iso- to hypointense solid mass.
- Post-gadolinium T1: homogeneous enhancement, periventricular spread, callosal involvement.
- DSC perfusion: rCBV only mildly raised with signal overshoot above baseline — unlike glioblastoma.
- SWI: absence of haemorrhage and calcification favours lymphoma over glioblastoma.
- Recommend avoiding steroids before biopsy if clinically safe.
What confirms it
- A homogeneously enhancing periventricular mass with low ADC and low rCBV; stereotactic biopsy confirms.
What licenses you to exclude it
- Prominent necrosis with high rCBV favours glioblastoma; a restricting abscess cavity favours abscess.
The classic misread
- Imaging after steroids — the mass shrinks or disappears (ghost tumour).