Our patient was admitted under the medical team following development of left arm weakness, in addition to his left leg weakness.

A ct head with contrast has shown an enhancing frontal lesion, with perilesional oedema.

An urgent neurosurgical opinion is sought.

The differentials at this point are of CNS lymphoma, metastasis, other primary brain tumour or less likely an infective cause.

Systemic enquiry does not reveal any other symptoms.

The neurosurgery team suggest an mri brain to get additional information on this lesion. The patient also has an urgent CT chest thorax abdomen and pelvis does not reveal any primary tumour and no evidence of lymphadenopathy.

Urgent neurosurgical biopsy of the lesion is performed and following this the patient is started on dexamethasone.

The biopsy has come back showing diffuse large B cell lymphoma.

Given this information what other staging investigations do we need? Are there any blood tests we should do? What are the treatment options for primary CNS lymphoma?