The thalamus accounts for less than 2% of the volume of the neuraxis, so tumors originating in this area are relatively rare, accounting for l% to 5% of intracranial tumors. Gliomas are the most common thalamic tumors and are mainly of low grade. Because of their deep location and adjacent to important functional areas, their treatment has always been a difficult problem in neurosurgery. 1, Pathophysiology Thalamic glioma is a disease with unique anatomical structure and clinical process, mostly showing expansive growth. It is surrounded by brain parenchyma nuclei, so the tumor boundary is relatively clear. The most common sites include the anterior and superior parts of the thalamus (anterior thalamic nucleus, ventral nucleus and central nucleus) and the posterior nodes. The tumor may travel along the conduction tracts, subventricular tracts, or disseminate within the ventricles. The growth pattern of thalamic gliomas can be classified into the following three types: (1) the tumor is confined to the thalamus, and the surrounding important structures, such as the internal capsule and the nucleus accumbens, are damaged; (2) the tumor extends beyond the thalamus, and reaches upward or outward to the subcortical white matter in the neighboring lobes or gyrus; and (3) the tumor grows toward the ventricles, but does not penetrate through the walls of the ventricles. Depending on the site and extent of growth, the tumor may involve the ventricular system, destroying the thalamic nuclei, nerve fiber conduction tracts or optic radiation and causing patients to have different symptoms and signs. Jiang Tao, Department of Neurosurgery, Beijing Tiantan Hospital, Beijing, China 2. Clinical manifestations Thalamic glioma can occur in all age groups. It mainly occurs in adolescents. The rate of male and female is approximately equal. Some literature reports that the male rate is slightly higher. Age has an important influence on the prognosis of thalamic glioma, and the prognosis of patients under 40 years old is significantly better than that of patients of advanced age. The time interval between onset and clinical diagnosis is relatively short, and the diagnosis can often be made early, especially in children. Common clinical manifestations include intracranial hypertension, motor deficits, epilepsy, involuntary movements, sensory deficits and thalamic syndromes. Cranial hypertension and motor deficit symptoms are the most common, followed by epilepsy and sensory deficits. Involuntary movements are rare in patients with unilateral thalamic gliomas but are more common in patients with bilateral thalamic involvement. Visual field changes, oculomotor deficits, and mental behavioral abnormalities may also be present in some cases. A few patients also have psycho-skin syndrome. 3 .Imaging manifestations Thalamic glioma is generally large, spherical or round-like, with relatively clear margins. When the posterior part of the third ventricle is compressed and occluded, the ependymal ventricle will be enlarged, and the sign of non-traffic hydrocephalus will be obvious.CT shows that the lesion boundary is clear, and the peri-tumor edema is rare, and it is mainly in the form of low or mixed density, which can be accompanied by enhancement.MR:T1-WI shows that the tumor is homogeneous low-signal shadow(astrocytoma) or non-homogeneous low-signal shadow (mesenchymal astrocytoma or glioblastoma).T2-WI sees that the tumor is homogeneous or inhomogeneous slightly high-signal shadow, and the tumor is not homogeneous, and the tumor is not homogeneous, and the tumor is not homogeneous. T2-WI shows the tumor as a homogeneous or inhomogeneous slightly high signal shadow, with no edema bands adjacent to the tumor. After intravenous injection of contrast medium, the tumor is usually ring-enhancing, and in a few cases, ring-enhancing astrocytomas are similar to glioblastomas and are not easy to differentiate. Adult thalamic glioma may also infiltrate into the midbrain and spread to the contralateral thalamus through the intermediate block. Differential diagnosis 4.1 Germ cell tumor is one of the few curable intracranial malignant tumors. Most of them are found in pineal gland and saddle region, basal ganglia and thalamus are rare. Thalamic germ cell tumors account for l3% of all germ cell tumors, and 25% of basal ganglia and thalamus tumors. Thalamic germ cell tumors are almost always seen in adolescent males. Experimental radiotherapy can help diagnosis, radiation therapy is preferred, and combined with adjuvant chemotherapy can reduce the radiotherapy dose and improve the tumor-free survival of patients. On imaging, the tumor is morphologically heterogeneous, with heterogeneous signal, cystic changes, necrosis, and hemorrhage are common, paraneoplastic edema is relatively mild, and enhancement scanning reveals the lesion as a plaque or patchy enhancement. In addition, germ cell tumors of the basal ganglia may be associated with ipsilateral cortical atrophy. 4.2 Malignant teratoma: Rarely found in thalamus, the tumor rarely contains fat and calcification; it shows irregular low-signal shadow on T1-WI, and non-uniform high-signal shadow on T2-WI, with obvious paratumoral edema and “garland”-like enhancement. 4.3 Ganglion cell tumor of thalamus is rare, but it has unique imaging manifestations: T1-WI foci are not clearly demarcated from the surrounding brain tissues, and small focal low-signal shadows can be seen in the foci; T2-WI shows that the foci are cortical signal shadows, and the internal focal lesions are high signals; there is no paratesticular edema, and the tumor does not enhance after injection of contrast agent, but the internal focal lesions are obviously strengthened. It may be accompanied by ipsilateral cerebral hemispheric malformation and enlarged ventricles. Thalamic glioma is located deep in the midline of the brain. Adjacent to the internal capsule, hypothalamus, the third ventricle and other important structures, it is difficult to operate, and the rate of death and disability is high, so the treatment of thalamic glioma has not yet formed a consistent viewpoint. Most scholars hold a conservative attitude towards surgery and advocate radiotherapy after biopsy to prolong the survival time of patients. Some scholars for early diagnosis of patients to take the “wait” point of view In recent years, due to the improvement of neurosurgical techniques and thalamus surgical pathway improvement, surgical disability and mortality rate is greatly reduced, some hospitals surgical mortality rate has been reduced from 40% to less than 5%. Moreover, the effective radiotherapy dose is directly related to the size of the residual tumor, and too high radiation dose will lead to radiation brain injury, so the residual tumor of gliomas with large body is often difficult to achieve. Conventional radiotherapy after surgery is often difficult to be effective. In order to prolong the survival time of patients, more and more scholars advocate surgical treatment. Although the thalamic site is deep, except for its ventral and lateral surfaces adjacent to the basal nuclei and the internal capsule. Its medial, posterior and superior surfaces are free, and the above anatomical features determine the feasibility of surgery. The existing surgical approaches include transcortical (frontal, parietal, temporal, parieto-occipital) transventricular thalamotomy, transcallosal (anterior part of the corpus callosum, posterior part of the corpus callosum) transcortical thalamotomy, and transcallosal fornix thalamotomy. Translateral fissure thalamic tumor resection and transsubtentorial supratentorial thalamic tumor resection. The basic surgical principles are: to maximize the resection of tumor under the premise of preserving normal physiological function, to ensure smooth cerebrospinal fluid circulation, to relieve cranial hypertension, and to create conditions for radiotherapy and chemotherapy. 5.1 The choice of surgical access should be made by transcortical approach: if the tumor is located in the anterior part of thalamus, transfrontal cortical approach should be adopted. If the tumor is located in the anterior part of thalamus, transcortical approach should be adopted; if the tumor is located in the posterior part of thalamus (e.g. thalamus occipital), transparietal occipital cortical approach should be adopted. In order to avoid the complications arising from the destruction of the cerebral cortex by this approach, Prakasht used a transparietal interhemispheric approach for thalamic gliomas located in the dominant hemisphere. For tumors located in the ventral posterior aspect of the thalamus, the transsuperior temporal sulcus approach can be applied to reduce the damage of important blood vessels The disadvantage of the transcortical approach is that it requires incision of the cerebral cortex, especially when the ventricles of the patient are not large, the cerebral cortex and white matter are subjected to greater pulling effect, which can cause epilepsy or important neurological deficits (e.g., hemiparesis, impaired visual field, and aphasia) in the postoperative period. The advantages are simplicity of operation and ease of visualization of important refluxing veins low probability of injury. In order to reduce the occurrence of postoperative epilepsy and neurological deficits. Nowadays, more and more scholars advocate the use of transcallosal anterior lateral ventricular approach to resect tumors with the main body protruding into one lateral ventricle or transcallosal posterior lateral ventricular approach to resect tumors located in the thalamo-occipital region, which makes use of the natural gaps in the brain tissues and is unaffected by the size of the ventricles. The above approaches can be summarized as a transcallosal lateral ventricular approach for resecting thalamothoramic gliomas with lateral type of growth. A small number of thalamic gliomas originate from the medial thalamus, grow toward the midline and protrude into the third ventricle. The tumors are often found in the early stage and have a low degree of malignancy, so aggressive surgery and complementary radiotherapy can achieve more satisfactory results. Because the main body of the tumor protrudes into the third ventricle, surgery should be performed via the third ventricle. Surgery should be selected via the third ventricle approach. Some scholars in China have used transcallosal interforaminal approach to resect medial thalamic glioma, and achieved preliminary satisfactory curative effect. Surgical characteristics are: ① the use of potential cavities in the development of brain tissue for surgical operation, minimize surgical trauma. ② Short path to reach the third ventricle, adequate exposure, and separation of the internal cerebral vein or large cerebral vein adherent to the tumor under direct vision. ③ Explore the interventricular foramen and the superior port of the conduit under direct vision. According to the intraoperative situation, the bottom of the third ventricle fistula and the transparent septum fistula are performed. Maximize the release of hydrocephalus. ④ No damage to the cerebral cortex, fornix column, and thalamic vein is required to reduce postoperative complications. In addition, for thalamic gliomas that grow significantly toward the ventral posterior aspect of the thalamus and are closely connected to the insula, transverse lateral fissure thalamotomy is also an option. The full length of the lateral fissure needs to be opened intraoperatively. The posterior part of the insula cortex is clarified (because it is adjacent to the posterior border of the posterior limb of the internal capsule), and an incision is made in the middle of the central posterior sulcus of the insula. The subcortical tumor can then be identified and removed. In principle, this approach is less traumatic to the brain tissue than the transparieto-occipital cortical approach and the transsuperior temporal sulcus approach, and it is especially suitable for thalamic gliomas that are closely connected with the insula cortex. However, it is necessary to be familiar with the anatomy of the site. 5.2 Intraoperative points The following points should be noted in thalamic glioma surgery: ① Before opening the dura mater. Before opening the dura mater, intravenous drops of mannitol and dexamethasone should be administered, and the cerebrospinal fluid should be patiently aspirated after opening the lateral ventricles. ② When approaching via the anterior corpus callosum. 2cm in front of the coronal suture, separate the longitudinal fissure vertically to the body of the corpus callosum in the direction of the line between the two ears. The corpus callosum incision is controlled within 2 cm. ③ When separating the fornix to enter the third ventricle, enter along the midline and separate the fornix suture above the interventricular foramen. If necessary, a lateral septum pellucidum fistula is feasible, and the position of the interventricular foramen is determined via the lateral ventricle. ④ Fully expose the tumor and its surrounding important structures to facilitate tumor resection and hemostasis. ⑤ When removing the tumor, use cotton pads to separate the ventricular system from the tumor operative area first to prevent intraoperative blood dispersion to the distal area, and then open the cerebrospinal fluid pathway after near-total resection. (vi) The thalamic vein is used as an anatomical landmark of the ventral-lateral border of the thalamus to protect its lateral important structures. The tumor is first resected intratumorally in pieces, and then the edges of the tumor are separated after the tumor volume is reduced. ⑦ The choroid plexus in the operative field can be electrocoagulated, and if the interventricular foramen fails to be opened, a hyaline diaphragmatic fistula should be performed. ⑧ Tightly suture the layers, and the lateral ventricles are routinely drained with tubes. If hydrocephalus exists in the postoperative period, shunt operation should be performed as early as possible. Postoperative complications include hydrocephalus, intracranial infection, intraventricular hemorrhage, hemiparesis, hemiplegia, hemianopsia, visual field defect, aphasia, coma, etc. The patients should have good knowledge of anatomy. Good knowledge of anatomy. Choosing the correct surgical approach and skillful microneurosurgical operation can help the operator to reduce the occurrence of the above complications.