What is low-grade glioma? Low-grade glioma is not an imaging concept. What is diagnosed as “low-grade glioma” by MRI or CT alone is not necessarily a true low-grade glioma, but may be a pathologically graded high-grade glioma or not a glioma at all. In the field of neuro-oncology, low-grade glioma is essentially a generic term for a variety of pathological types of gliomas, and is a pathological concept. Moreover, as the WHO pathologic classification criteria evolved, what is meant by low-grade glioma also evolved. What is the scope of the previous low-grade gliomas referred to In the pathological grading before 2016, which was based on morphological diagnosis, low-grade gliomas referred to WHO grade II diffuse gliomas, while high-grade gliomas referred to WHO grade III and IV gliomas. The pathological types of low-grade gliomas here are mainly diffuse astrocytomas and oligodendroglial cell tumors, both with WHO grade II pathological classification. The median survival is 10-11 years for astrocytomas and 15 years for oligodendrogliomas, although of course the length of survival may vary considerably for each individual patient. Lower grade gliomas after modern introduction of molecular indicators From 2016, molecular indicators were introduced into the WHO pathological diagnostic grading system for neuro-oncology, and such a graded staging pathology system has a more accurate determination of survival time for patients with gliomas. The so-called low-grade glioma now refers to lower grade gliomas, including some of the WHO grade II and III gliomas previously referred to, which are not exactly the same as the content of the previous low-grade gliomas. Because it is sometimes difficult to distinguish pathomorphologically between WHO grade II and grade III gliomas, and after the introduction of molecular indicators to look back at this part of gliomas, it was found that the prognosis of grade II and grade III gliomas with IDH mutations is close, which means that patients with these two pathologically graded gliomas have similar survival times as long as they both have the same molecular indicator of IDH mutations. Furthermore, based on molecular indicators such as IDH mutation and the presence or absence of 1P19Q, low-grade gliomas can be further classified into oligodendrogliomas with IDH mutation, 1P19Q deletion, and astrocytomas with IDH mutation, 1P19Q absence, P53 mutation, and ATRX mutation. the median survival of low-grade gliomas with IDH mutation with 1P19Q deletion is 8 years, and the median survival of low-grade gliomas with IDH mutation without 1P19Q deletion had a median survival of 6.3 years. However, the prognosis for IDH wild-type gliomas without IDH mutations is poorer, with a median survival of 1.7 years. About 20% of lower grade gliomas without IDH mutations, especially grade III astrocytomas, have a median survival of 1.2 years if they are accompanied by EGFR amplification, H3F3A mutation, and TERT promoter mutation changes, and 7.6 years if they are free of these mutations. Therefore, even if the pathological grade of glioma is the same, but the molecular characteristics are different, the prognosis of glioma varies greatly.