What is the most likely diagnosis and the most relevant differential?
A high-grade glioma (GBM) s the most likely diagnosis and brain metastasis is a plausible, however unlikely, differential.
The patient found it difficult to remain still; as a result many sequences are severely degraded by motion artefact. MR spectroscopy could not be performed.
There is a large intra-axial mass centred on the left thalamus and basal nuclei.
This demonstrates areas of irregular nodular contrast enhancement with central areas of non-enhancement. The enhancing margin shows diffusion restriction and increased perfusion. There is surrounding abnormal FLAIR hyperintensity extending into the white matter of the frontal and temporal lobes, left insula, inferiorly into the left and across midline into the right thalamus.
There is marked mass effect on the third ventricle, dilation of both lateral ventricles, and periventricular FLAIR hyperintensity in keeping with transependymal fluid shift.
Conclusion:
Mass consistent with high-grade glial series tumour centred on left thalamus with extension into the right thalamus. Mass-effect on the third ventricle causing obstructive hydrocephalus.