Recurrence is a major characteristic of glioma and is both a cause of concern for glioma patients and a major challenge that has plagued physicians for decades. Whether it is extended surgical resection or postoperative adjuvant radiotherapy and chemotherapy, the main goal is to reduce the residual tumor cells in order to prolong the time of tumor recurrence. With a large number of clinical multicenter randomized controlled studies conducted internationally in recent years, there is a new understanding of what was thought to be the recurrence of glioma in the past. At the 2nd International Glioma Congress in 2006, the concept of pseudopregression after glioma treatment was introduced. When I listened to this presentation, I felt a great sense of enlightenment and clarity, which helped me solve a problem that had been bothering me for several years, that is, how to identify whether a glioma is a true recurrence or a pseudopregression. By summarizing my successful treatment cases over the years and the latest international research progress, I published a scientific paper entitled “Diagnosis and treatment of pseudoprogression after brain tumor radiotherapy” in the Chinese Journal of Neurosurgery in June 2010. It is expected to provide a reference for the differential diagnosis of glioma recurrence and pseudo-progression, and also to raise new hope for many patients who were misdiagnosed as glioma recurrence. Clinical manifestations of pseudoprogression: The clinical manifestations of pseudoprogression are very similar to those of tumor recurrence. Not only the symptoms of high cranial pressure such as headache appear in the early stage, but also the symptoms of neurological deficiency such as limb weakness, even hemiparesis and aphasia will appear. On MRI, it shows large foci of long T1 and long T2 abnormal signals with irregular gadolinium intensification foci within, with obvious occupancy effect. Analyzed from the clinical characteristics of recurrence of glioma after surgery, the time of tumor pseudo-progression to appear symptoms is often shorter, and some patients already have headache and other high cranial pressure symptoms at the end of radiotherapy. 2. Imaging diagnosis: During the follow-up of brain tumor patients after radiotherapy, MR enhancement scan has been the main imaging standard to evaluate the treatment effect and tumor progression – “Macdonald standard”. However, with the understanding of MRI enhancement images and the observation of a large number of clinical cases, it was found that gadolinium enhancement images only reflect the integrity of the blood-brain barrier, but not the tumor growth directly, therefore, any factors that can affect the integrity of the blood-brain barrier can change the gadolinium enhancement images on MRI. Radiation therapy can disrupt the blood-brain barrier, and the resulting radiation brain necrosis is capable of manifesting as abnormally enhanced images on MR. In addition, it has been recognized that radiation therapy can also cause a delayed response, especially when using localized high-dose radiotherapy techniques such as stereotactic radiotherapy and intra-stromal radiotherapy. This delayed response is also radionecrosis and can occur months to years after treatment. For simultaneous radiotherapy and chemotherapy, this proximal imaging change can appear much more rapidly and can occur immediately after radiotherapy. (1) MRI: Some scholars believe that gadolinium-enhanced MRI that shows multiple lesions and corpus callosum invasion often indicates tumor progression, while the presence of Swiss cheese-like manifestations (Swiss cheese-like) may suggest pseudo-progression of the tumor, but these so-called characteristic manifestations alone cannot fully distinguish tumor recurrence from pseudo-progression. (2) MRS: Since it can show the chemical metabolism of the tissues in the area of interest, it can theoretically distinguish tumor recurrence from tissue necrosis, and its validity has been confirmed in clinical practice. (3) PET: At present, the application of 18F-FDG-labeled PET images has been recommended as an important method to distinguish true tumor progression from pseudo-progression. In recent years, tracers such as 11C-methionine and 18F-FLT have emerged, which can suggest the recurrence of high-grade glioma in terms of amino acid and nucleic acid metabolism, but the accuracy and specificity of these tracers are still lacking. However, the accuracy and specificity of these tracers are still insufficient. At present, there is no international diagnostic standard for pseudo-progression of glioma after radiotherapy, which makes it extremely difficult to accurately identify tumor recurrence and pseudo-progression, and in clinical practice, the identification of the two still relies mainly on doctors’ personal experience and knowledge. The following points of my personal experience may be helpful for the differential diagnosis of glioma recurrence and pseudo-progression. 1.Inquire the patient’s medical history of radiotherapy in detail to determine whether there is any overdose of radiotherapy, and the possibility of pseudo-progression of tumor caused by inappropriate radiotherapy is high; 2.If clinical symptoms such as high cranial pressure appear early after radiotherapy, such as high cranial pressure symptoms appear within six months after radiotherapy, the possibility of pseudo-progression of tumor is high; 3.If MR examination shows large brain edema, it suggests that there may be radioactive brain edema 4. MRS and PET scans suggesting hypometabolism of the lesion can help the diagnosis of pseudoprogression; 5. For those suspected of pseudoprogression, experimental treatment with corticosteroids can be carried out first, if it is effective, the possibility of pseudoprogression of tumor is high and further observation should be made; 6. Surgery can be considered to remove the lesion and finally rely on histopathology to determine the diagnosis, which is still the gold standard.