How accurate is MR perfusion, an advanced MRI method, for differentiating low-grade gliomas from high-grade gliomas in children and adults?

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How accurate is MR perfusion, an advanced MRI method, for differentiating low-grade gliomas from high-grade gliomas in children and adults?

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Authors: 
Abrigo JM, Fountain DM, Provenzale JM, Law EK, Kwong JSW, Hart MG, Tam W

Why is differentiation of low-grade and high-grade gliomas important?

Low-grade gliomas (LGGs) are slow growing brain tumours that have a typical appearance on standard MRI. Patients with LGGs who have few or no symptoms may prefer to delay treatment until such time they experience progression of their symptoms or appearance of the tumour on MRI; this is called the watch-and-wait approach. However occasionally, high-grade gliomas (HGGs), which are aggressive and require early treatment, can mimic the appearance of LGGs. It is only by examining tissues obtained by surgery – either through sampling (biopsy) or removal of tumour (resection) – can LGG and HGG be definitively differentiated. But a patient with few or no symptoms may want to avoid risking early neurologic disability resulting from surgery. Thus an accurate noninvasive method to differentiate gliomas can aid patients’ decision making whether to opt for a watch-and-wait approach or undergo early treatment.

What is the aim of this review?

The review aims to determine how accurate MR perfusion is for differentiating LGGs and HGGs, and what factors affect its accuracy. Researchers in Cochrane included seven studies to answer this question.

What was studied in this review?

An advanced MRI technique called MR perfusion was studied. This method detects abnormal blood vessels which are increased from low- to high-grade gliomas. Unlike surgery, MR perfusion is noninvasive and allows clinicians to determine if a watch-and-wait approach can be adopted by patients, i.e. delay treatment including the initial tissue examination which requires surgery.

What are the main results of the review?

The analysis included results from 115 patients. The results indicate that in theory, if MR perfusion were to be used in 100 patients with brain tumours that look like LGG on standard MRI scan, of whom 72 actually have LGG, then:
– an estimated 74 will have an MR perfusion result indicating that they have LGGs, and of these 15 will have HGGs;
– an estimated 26 will have an MR perfusion result indicating that they have HGGs, and of these 13 will have LGGs.

How reliable are the results of the studies in this review?

In the included studies, the diagnosis of LGG or HGG was made by assessing all patients with tissue examination, and a majority underwent resection. This is considered a reliable method for deciding whether patients actually had LGGs or HGGs.

The small number of patients that were included in this review is a major limitation to the analysis. Estimates from individual studies and pooled data were variable and/or had a wide range. The numbers reported in the main results above are an average across studies in the review, but it is unknown if MR perfusion will always produce these results. Further, the included studies differed in how MR perfusion was performed, and pooling of data for the analysis may be inappropriate.

Who do the results of this review apply to?

The included studies were carried out in Europe (Italy, Sweden, Spain, France), Asia (Japan) and South America (Brazil) and MR perfusion was mostly performed in university hospitals. Most studies recruited adults so the results may not be representative of children.

What are the implications of this review?

Our results based on 115 patients showed that MR perfusion may detect 66% to 93% of LGGs, which means that 7% to 34% of people with LGGs may be misclassified as having HGGs and thus may undergo early invasive treatment with an accompanying risk of adverse events. Meanwhile, around half of people with HGGs may be misclassified as having LGGs, and thus may suffer from delayed treatment. Due to uncertainty in the estimates this may range from 9% to 90% of patients. Given the wide range of estimates, currently, it cannot be determined how accurate MR perfusion is for differentiating LGGs and HGGs. Future studies to inform evidence would need to include larger numbers of patients with LGG and HGG.

How up to date is this review?

We searched for and used studies published from 1990 to November 2016.

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