The role of magnetic resonance imaging in the management of brain metastases: diagnosis to prognosis

Abstract

This article reviews the different MRI techniques available for the diagnosis, treatment and monitoring of brain metastases with a focus on applying advanced MR techniques to practical clinical problems. Topics include conventional MRI sequences and contrast agents, functional MR imaging, diffusion weighted MR, MR spectroscopy and perfusion MR. The role of radiographic biomarkers is discussed as well as future directions such as molecular imaging and MR guided high frequency ultrasound.

Figure 1

A patient known to have melanoma presents with a first seizure and (A) unenhanced CT brain (32-slice scanner, 10 mm slices) taken in the emergency department shows an abnormality in the left frontal lobe with surrounding oedema – they were referred for possible neurosurgical intervention. (B) T1 weighted MRI at 1.5 T with single dose (0.1 mmol/kg) gadolinium contrast detects this lesion but also delineates it further, allowing volume to be assessed accurately and in addition highlights two further areas of abnormality. After staging of the systemic disease and discussion with oncologists and surgeons, the patient was therefore treated with stereotactic radiosurgery to all three areas.

Figure 2

An elderly patient was referred with hemiparesis and suspected to have a stroke. MRI demonstrated a lesion in the left hemisphere which on (A) T1 weighted axial image post gadolinium at 1.5 T is shown to have a solid and ring enhancing portion. (B) The associated ADC map shows considerably reduced diffusion at the site of the solid portion of the lesion with increased diffusion due to vasogenic oedema in the white matter surrounding the mass. (C) Single voxel proton MRS of the lesion yields an abnormal spectrum with a large lipid and lactate peak, reduced NAA, reduced Cr and slightly elevated Cho. This pointed to a metastasis, glioma or lymphoma as opposed to an abscess. There was time to optimise the patient for surgery and begin steroid treatment before the lesion was resected and confirmed to be a renal cell carcinoma.

Figure 3

A patient known to have breast cancer with a manually dexterous job presented with intermittent left hand and arm weakness and was found (A) to have a solitary ring enhancing lesion in the premotor area on T1W MRI with gadolinium. (B) functional MRI performing a hand tapping and gripping task determined the location of hand function and this was used as the “seed” region of interest on a DTI scan to produce a representation of the motor tracts. (C) these were used to generate a 3D object and fused with an anatomical planning scan (1 mm slices) using commercially available software (StealthViz™ with StealthDTI™ by Medtronic, running on an S7 workstation) to produce images that were used intraoperatively for image guided resection, avoiding the tracts (shown in red, with tumour rendered in green).

Figure 4

Monitoring of treatment response after stereotactic radiosurgery. A patient with known metastatic melanoma underwent treatment to a left frontal lesion (A) and at 3 months (B) the characteristic changes of a blurred margin and necrosis followed by formation of a glial scar at 6 months (C) are seen. However in a similar appearing patient (D) with a right parietal lesion from metastatic renal cell carcinoma the lesion shows more florid changes at 3 months (E) with increased contrast enhancement at the margins and the possibility of progression as opposed to radionecrosis is raised. Multi-modal techniques described in the text may show promise in deciding how to proceed at this stage. The patient was well and on monoclonal antibody chemotherapy, with observation the lesion eventually regressed at 6 months (F) and is currently stable.