A large heterogeneously enhancing mass replaces almost the entirety of the left temporal lobe, with evidence of prominent subependymal/ependymal spread along the trigone of the lateral ventricle. It demonstrates small areas of signal loss consistent with a blood product but no evidence of calcification. Markedly elevated cerebral blood volume is noted in the solid non-necrotic components. MR spectroscopy demonstrates elevation of choline, with prominent lipid and lactate components in the necrotic areas. Diffusion weighted imaging is unusual, with prominent diffusion restriction of the nonenhancing component (ADC values as low as 500 x 10^-6 mm^2/s) presumably representing thick necrotic material probably with blood products.
The mass exerts significant local mass effect with 5 mm of midline shift and left uncal herniation and distortion of the left cerebral peduncle. Scattered throughout the intracranial cavity are multiple other tiny punctate regions of contrast enhancement, most of them clearly leptomeningeal.
Conclusion: Despite the unusual appearance and subependymal spread, given the presence of pulmonary masses and leptomeningeal nodules, this large mass presumably represents a metastasis. If there were no systemic malignancy then a high-grade primary tumour with CSF seeding would be a differential.