Brain metastases: the role of clinical imaging

Abstract

Imaging of brain metastases (BMs) has advanced greatly over the past decade. In this review, we discuss the main challenges that BMs pose in clinical practice and describe the role of imaging.Firstly, we describe the increased incidence of BMs of different primary tumours and the rationale for screening. A challenge lies in selecting the right patients for screening: not all cancer patients develop BMs in their disease course.Secondly, we discuss the imaging techniques to detect BMs. A three-dimensional (3D) T1W MRI sequence is the golden standard for BM detection, but additional anatomical (susceptibility weighted imaging, diffusion weighted imaging), functional (perfusion MRI) and metabolic (MR spectroscopy, positron emission tomography) information can help to differentiate BMs from other intracranial aetiologies.Thirdly, we describe the role of imaging before, during and after treatment of BMs. For surgical resection, imaging is used to select surgical patients, but also to assist intraoperatively (neuronavigation, fluorescence-guided surgery, ultrasound). For treatment planning of stereotactic radiosurgery, MRI is combined with CT. For surveillance after both local and systemic therapies, conventional MRI is used. However, advanced imaging is increasingly performed to distinguish true tumour progression from pseudoprogression.FInally, future perspectives are discussed, including radiomics, new biomarkers, new endogenous contrast agents and theranostics.

Figure 1.

The role of clinical imaging in brain metastasis management. A, B, C and D represent separate sections in this review.

Figure 2.

Axial, three-dimensional (3D) contrast-enhanced T1W image (ce-T1W) on the left, with the corresponding 3D contrast-enhanced T2W Fluid Attenuated Inversion Recovery image (ce-T2W FLAIR) on the right, from a patient with leptomeningeal disease (LMD, arrow). The ce-T2W FLAIR image shows the region of LMD much clearer than the ce-T1W image

Figure 3.

Axial contrast-enhanced T1W (ce-T1W) and native T1W images and a cerebral blood flow (CBF) map derived from arterial spin labelling (ASL), from a patient with a brain metastasis in the left parietal lobe, treated with stereotactic radiosurgery (SRS). The lesion increased in size 1 month after SRS and was histopathologically confirmed to be a combination of subacute haemorrhage and tumour progression. Most of the lesion is hyperintense before contrast administration, due to subacute haemorrhage. This portion has no perfusion on ASL. One small component is enhancing and shows increased perfusion on ASL (arrow), consistent with tumour progression.

Figure 4.

Axial contrast-enhanced T1W (ce-T1W) image, relative cerebral blood volume (rCBV) and cerebral blood flow (CBF) maps derived from dynamic susceptibility contrast enhanced (DSC) performed after a pre-load bolus with leakage correction and arterial spin labelling (ASL), respectively, from a 55-year-old male patient with a history of lung cancer and brain metastasis which was treated with high-dose radiation therapy. The ce-T1W image shows a ring-enhancing lesion adjacent to the left lateral ventricle with a waxing and waning course over time, suspicious of radiation necrosis. However, the lesion remained suspicious for metastasis recurrence due to the high rCBV as measured with DSC. CBF however is low, which is more consistent with the clinical diagnosis and time course of radiation necrosis. The discrepancy between findings with DSC and ASL is presumably due to leakage effects in the DSC images resulting in incorrect estimation of rCBV.