Role of Imaging in Central Nervous System Metastases

Specialties Article 4 Minute Read GE Healthcare Global

Systemic cancer often manifests in the form of central nervous system (CNS) metastases.1 It has been indicated that metastatic tumors are one of the most common forms of mass lesions in the brain, and that about 24-45 percent of cancer patients in the United States have brain metastases.2,3

Over the last decade or so, thanks to novel therapeutic strategies and technological advancements — more precise imaging techniques that can detect smaller tumor growths — in cancer diagnosis, the survival rate of such patients has improved.

Previously, standard magnetic resonance imaging (MRI) was reported to display high detection sensitivities, but did not have the capacity to differentiate the tumors accurately. And other methods could evaluate primary and secondary brain tumors, but often provided inconclusive data.1 

Therefore, some studies suggested the clinical management of patients can be designed in such a way to include physiologic or functional imaging (e.g., fMRI or functional MRI) as well as high-resolution structural imaging, where the main role of structural imaging scans was evaluating tumors and locating the lesions.5 

And with the rise of innovative concepts such as anti-angiogenic and immunogenic therapies, it was found that neuroimaging tools in such a combination could play a larger role in brain metastases management and disease monitoring.1

Imaging Techniques in Metastases Management

Computed tomography (CT)

Although CT scans have reported lesser sensitivity in tumor detection compared to MRIs, non-contrast CT has often been resorted to as an initial imaging option for new patients. This is because the technique is known to display the first signs of acute complications of metastatic disease.5  

Some investigations have shown the effectiveness of contrast-enhanced CT in detecting and tracking major leptomeningeal speed, a rare type of cancer affecting the CNS. Enhanced CT scanning, in fact, has also played a vital part in uncovering additional sites of metastases, apart from the primary site of cancer or solitary lesions, which could then positively impact the nature of treatment required.4 

But, in other cases, even enhanced CTs like double-dose delayed contrast are not preferred for brain metastases compared to more accurate and safer methods like MR imaging.1 

MRI

Advanced MRI techniques such as contrast-enhanced MR imaging have been called the method of choice when it comes to determination of CNS metastases. This procedure has proven its sensitivity and specificity in locating the presence of tumors.6 Findings from a study, conducted earlier and published in the ANJR journal, also showed the importance of contrast-enhanced MRI in diagnosing CNS lymphoma. The researchers of this project took the help of techniques like CT and metabolic imaging that helped differentiate the lymphoma from other CNS lesions.7  

In March 2018, a conversation between experts, Jack West of the Swedish Cancer Institute in Seattle and Hossein Borghaei of the Fox Chase Cancer Center in Philadelphia, offered greater insights on the subject of radiation and monitoring for non-small-cell lung cancer (NSCLC) patients.9 CNS metastases have been reported to occur in a large proportion of NSCLC patients.10 Borghaei said, “We come up with a good follow-up schedule for the patient, with occasional brain MRIs when we begin for monitoring.”9

Functional or fMRIs are minimally invasive and are favored over imaging methods that need radioactive markers.8 A few small studies have highlighted the role of a non-task based fMRI called resting-state fMRI (RS-fMRI), which is believed not only to be able to see the effects of brain tumors, but also visualize corresponding treatments. The technique can study the functional connectivity of the brain, thus making it a powerful tool for future research.

Nuclear Imaging: PET and PET/MRI

Side effects from harmful radiation, from techniques like whole brain radiation, loom large among cancer patients undergoing therapy. Positron emission tomography, and specifically brain PET, decrease the exposure to radiation to a small amount. Its most important advantage, in the past, was that the procedure could measure activities in the working brain and were superior in resolution and speed to other imaging. But this was a long time ago as PET’s drawbacks included monitoring only short tasks due to quick radioactive decay.8,11 

Now, for imaging brain activity, fMRIs that do not involve any radiation and show higher temporal resolution than PET are typically used.

However, systems with integrated PET/MRI are an interesting area of research that could overcome the limitations of the individual forms of imaging. Newer PET radiotracers can provide a good understanding of brain tumor physiology.5 

There are other imaging modalities such as magnetoencephalography (MEG) and electroencephalography (EEG) that have shown high temporal resolution in surveying brain action.8 Advanced MRIs like perfusion or diffusion-weighted imaging are radiological processes that can analyze high cellular tumors (i.e., CNS lymphoma and high-grade glioma).5 The latest of these methods is an MRI contrast-based concept called CEST (chemical exchange saturation transfer), which has the potential to reach several unexplored regions of the brain and thus tumors.1 But not many conclusive studies have been conducted in this domain yet. 

Determining the best and most ideal of these high-tech resources depends on the individual case and the extent of malignancies in each. In addition, it is a decision to be taken by experienced healthcare professionals, together with patients and their families. 

The role of imaging in monitoring the metastases of the central nervous system — whether it is a preoperative diagnosis, tumor categorization, prognosis, therapy or response to treatment5, or even the complete progression — is critical in cancer management and patient mortality. 

References

  1. Nowosielski, M. et al. (2015), The emerging role of advanced neuroimaging techniques for brain metastases, CCO, 4 (2)
  2. Brain metastases, 2018, Medscape, https://emedicine.medscape.com/article/1157902-overview, (accessed 15 Jul 2018)
  3. Nussbaum E. S. et al. (1996), Brain metastases. Histology, multiplicity, surgery and survival, Cancer, 78 (8), Pp 1781-1788
  4. Brain Metastasis Imaging, 2018, Medscape, https://emedicine.medscape.com/article/338239-overview, (accessed 15 Jul 2018)
  5. Mabrey, M. C. et al. (2015), Modern Brain Tumor Imaging, Brain Tumor Res Treat, 3 (1), Pp 8-23 
  6. Barajas, R. S. et al. (2016), Metastasis in Adult Brain Tumours, Neuroimaging Clin N Am, 26 (4), Pp 601-620
  7. Haldorsen, I. S. et al. (2011), Central nervous system lymphoma: characteristic findings on traditional and advanced imaging, ANJR Am J Neuroradiol, 32 (6), Pp 984-992
  8. Crosson, B. et al. (2010), Functional imaging and related techniques: an introduction for rehabilitation researchers, Journal of Rehabilitation Research and Development, 47 (2), Pp 7-34
  9. Which Lung Cancer Patients With CNS Metastases Can Avoid Radiation? 2018, Medscape, https://www.medscape.com/viewarticle/896954, (accessed 16 Jul 2018)
  10. Berger, L. A. et al. (2013), CNS metastases in non-small-cell lung cancer: Current role of EGFR-TKI therapy and future perspectives, Lung Cancer, 80 (3), Pp 242-248
  11. Nilsson, L. et al. (1999), Cognitive Neuroscience of Memory, Seattle: Hogrefe & Huber Publishers