In 1888, Horsly and Gwers reported the first successful resection of an extramedullary subdural tumor. 1907, Elsberg reported the first resection of an intramedullary tumor. 1919, Dandy invented air myelography, and in 1921, Sicard and Forester applied contrast to myelography, which contributed to the development of spinal cord tumor surgery. In 1940, Greenwood invented bipolar electrocoagulation and reported several successful resections of intramedullary spinal cord tumors with complete preservation of spinal cord nerve function and no recurrence for a long time. Before the 1970s, because of the high surgical mortality and disability rate of intramedullary tumors, and because most neurosurgeons were concerned that resection of intramedullary tumors would aggravate spinal cord injury and cause complications such as postoperative paralysis, respiratory dysfunction, and urinary and fecal disorders, they generally preferred conservative treatment, which often involved decompression of the vertebral plate, biopsy, partial tumor resection, and radiation therapy. With the introduction of CT and MRI, the continuous progress of microsurgery technology, the update of surgical instruments, and the intraoperative application of electrophysiological monitoring technology, the surgery of spinal cord intramedullary tumors has developed considerably, and surgery has become the only effective method to treat most intramedullary tumors. The incidence and pathology of intramedullary tumors account for 2%-4% of CNS tumors and 20%-25% of intradural tumors. The incidence of intramedullary tumors in children is higher than that in adults, accounting for approximately 50% of intradural tumors. According to the pathological types, 45% of the intramedullary tumors are ventricular meningiomas, 40% are astrocytomas, 5% are vascular reticulocytomas, and 10% are other tumors such as lipomas, cavernous hemangiomas, and epidermoid cysts. Ventricular meningioma: It is the most common intramedullary tumor in adults, especially in middle-aged people, with the same incidence in both sexes. Although the spinal cord and end filaments account for only 3% of the CNS in terms of weight and volume, 1/2 of the ventricular meningiomas in the CNS occur in the spinal canal. The cervical segment is the preferred site. For those occurring in the terminal filaments, they are anatomically and surgically classified as extramedullary tumors. Most ventricular meningiomas of the spinal cord are benign tumors. Although they do not have an envelope, intra-tumoral hemorrhage and necrosis sometimes occur, they usually do not infiltrate the surrounding spinal cord tissue and are well defined from the spinal cord. There are many histologic subtypes of ventricular meningioma. Cellular ventricular meningioma is the most common, and other types such as epithelial, fibrous, subventricular, mucous papillary, and mixed types can also occur. Sometimes it is difficult to distinguish histologically from astrocytoma, but the diagnosis can be made if there are pseudo- or true rose petal-like cells around the blood vessels. 2. astrocytoma: 3% of astrocytomas in the central nervous system grow in the spinal cord and can occur at any age, but mostly in children under the age of 30. 90% of children under the age of 10 and 60% of adolescents are the most common type of intramedullary tumors in children. after the age of 60, the incidence of astrocytoma and ventricular meningioma is similar. About 60% of intramedullary astrocytomas occur in the cervical medulla or cervicothoracic junction, but are rare in the thoracolumbosacral medulla and conus, and even rarer in the terminal filum. Histologically, astrocytomas of the spinal cord include relatively benign fibrous and hairy cell astrocytomas, ganglioneuroblastomas, and malignant astrocytomas and glioblastomas. Approximately 90% of intramedullary astrocytomas in children are benign, mostly fibrous astrocytomas, while others are hairy cell astrocytomas or ganglion cell tumors. In children, 10% of intramedullary tumors are malignant astrocytomas and glioblastomas, which have a short history, rapid progression of clinical symptoms, and easy dissemination of tumors along the cerebrospinal fluid. Fibroblastic astrocytomas predominate in adults, while hairy cell astrocytomas and ganglion cell tumors are rare. About 20% of adult intramedullary astrocytomas are malignant. Vascular reticulocytoma: Vascular reticulocytoma accounts for about 3-8% of intramedullary tumors and can occur at any age in adults, mostly around 40 years of age, but is rare in children. Vascular reticulocytoma is a benign tumor that originates from blood vessels, has no envelope, but has clear boundaries with the spinal cord, and almost always has soft spinal membrane attachment, and mostly grows in the dorsal or dorsolateral part of the spinal cord. It can be combined with Von2Hippel2Lindous syndrome and cystic lesions of cerebellum or other organs. 4.Other types of tumors: metastatic cancer accounts for 2% of intramedullary tumors, and the low incidence may be related to the small size of the spinal cord and the lack of vascularity. The primary focus is often lung, breast tumor, melanocytoma, etc. There are also reports of fibrosarcoma metastasis to the spinal cord. Other intramedullary tumors include epidermoid cysts, cavernous hemangiomas, and lipomas. Clinical characteristics[5,6] Because of the lack of specific clinical manifestations of intramedullary tumors, early diagnosis is difficult. The course of the disease is usually 2-3 years, but the history of malignant and metastatic tumors is very short, a few weeks or a few months. Intratumoral hemorrhage and necrosis can accelerate the disease. Pain is the most common symptom of intramedullary tumors in adults, while dyskinesia and gait disturbances are more common in children. Pain occurs mostly at the level of the tumor and rarely at the radical level. 30% of patients have early sensory and motor disturbances. The progression and distribution of symptoms are related to the location of the tumor, with cervical medullary tumors having mainly upper extremity symptoms, typically presenting as unilateral, asymmetric sensory abnormalities. Tumors of the thoracic medulla may have spasticity and sensory disturbances, which often occur in both lower extremities and then develop proximally. Tumors of the lumbar medulla and conus often manifest as pain in the low back and lower extremities, and urinary and fecal dysfunction often occurs in the early stage. Radiological examination[6] In the past, the main method of radiological examination for intramedullary tumors was myelography, which had low accuracy and often had false positives, and this was one of the main reasons why only decompression and biopsy of the vertebral plate could be done for early intramedullary tumor surgery. In modern times, due to the introduction of high-resolution MRI, intramedullary tumors are often detected before the appearance of obvious neurological deficits, and MRI has become an important tool for confirming the diagnosis of intramedullary tumors, not only for precise localization, but also to clarify the nature of most intramedullary tumors, and to show the combination of tumor cystic changes and spinal cord cavities. If a vascular tumor is suspected, DSA can be performed again. MRI of intramedullary tumors commonly shows thickening of the spinal cord, with equal or low signal in the T1 phase and high signal in the T2 phase, but it is difficult to distinguish between the tumor and the spinal cord cavity at both ends in the T2 phase. After contrast injection, almost all tumors have enhancement in T1 phase. However, different tumors have their own characteristics. Most of the tumors are accompanied by spinal cord cavities at both ends, especially in the cervical medulla and cervicothoracic junction. If there is necrotic cystic lesion in the tumor, heterogeneous enhancement can be seen. Individual cystic ventricular meningioma has little enhancement, which is difficult to distinguish from intramedullary astrocytoma. 2, astrocytoma: compared with ventricular meningioma, because of the irregularity of the tumor boundary, we rarely see a well-defined enhancement image on MRI, it is often mild, heterogeneous, lamellar enhancement, especially when the tumor is necrotic, and this irregular enhancement may extend to several spinal cord segments. Vascular reticulocytoma: MRI shows obvious homogeneous enhancement, and vascular flow can be seen, and cysts at both ends of the tumor are common. However, it is sometimes difficult to make an accurate qualitative diagnosis on MRI films. 4. Congenital tumors: common ones are epidermoid cysts and dermatomal cysts. Epidermoid cysts and dermatomal cysts have high signal in both T1 and T2 phases of MRI, and the tumor may be surrounded by a circularly enhancing cyst wall. Some people believe that surgery for intramedullary tumors will aggravate spinal cord injury and lead to postoperative neurological dysfunction, and advocate observation and treatment for less severe intramedullary tumors, and then consider surgery when the neurological function deteriorates. However, a lot of clinical data show that the surgical effect of intramedullary tumors is closely related to the severity of preoperative symptoms. Patients with advanced intramedullary tumors often suffer from severe compression and damage to the spinal cord, and their limbs are close to paralysis or completely paralyzed, so surgery at this time increases the risk of further damage to the spinal cord, and the postoperative effect is poor, and the paralyzed limbs are difficult to recover. Therefore, most scholars believe that early diagnosis and timely surgery are the key to the success or failure of intramedullary tumor treatment, and the less severe the preoperative symptoms and signs, the better the postoperative recovery, even to a near-normal state. Grade III, moderate neurological deficits and limited limb function; Grade IV, severe motor and sensory deficits requiring assistance; Grade V, hemiplegia or paraplegia, or slight limb movement. They believe that patients with grade I-III have good postoperative recovery of neurological function; patients with grade IV have different degrees of recovery after surgery, but sometimes the results are not good; patients with grade V have poor postoperative results and are generally no longer considered for surgery. Surgery is the most effective treatment for most intramedullary tumors [7-11]. The extent of surgical resection depends on the boundary between the tumor and the spinal cord. If the boundary is clear, most of the tumors are benign, and modern microsurgical techniques can not only make complete resection, but also have a low disability rate, and often obtain satisfactory results. Almost all ventricular meningiomas, well differentiated astrocytomas and vascular reticulocytomas are clearly demarcated from the spinal cord, so surgery should strive for total or sub-total excision. A small incision in the spinal cord to obtain a small amount of tissue for biopsy should be avoided to avoid delaying treatment. In the case of intramedullary malignant tumors, although major resection or partial resection of the tumor can relieve the disease and reduce the symptoms. However, considering the poor prognosis of intramedullary malignant tumors and the high rate of postoperative disability, it is believed that in such cases, the operation should be terminated only after spinal dissection and histological diagnosis is obtained. For intramedullary dermatomal cysts and epidermoid cysts, it is difficult to completely remove the cyst wall from the spinal cord during surgery, so total excision is not required. It is not possible to completely excise the lipoma in the spinal cord, but it is possible to excise a large part of the tumor, which can also obtain a positive therapeutic effect. Intramedullary tumors can be detected in prone or lateral position, and intraoperative monitoring of somatosensory evoked potential (SEP) and motor evoked potential (MEP) is advisable when available. The value of intraoperative monitoring is: (1) to identify the nerve tissues around or within the tumor to improve the safety of spinal cord tumor surgery; (2) to guide and ensure the surgeon to perform the surgery correctly; (3) to reflect the acute injury and site of the spinal nerve conduction pathway; (4) to quickly clarify the changes of acute ischemia and hypoxia of the nerve tissue. Vertebroplasty should be used for pediatric patients, but still does not guarantee long-term spinal stability. The resection of intramedullary tumors depends on the relationship of the tumor to the spinal cord. Most of the tumors are buried in the spinal cord and are rarely exposed outside the medulla. Intraoperative ultrasonography is useful to localize the tumor and determine the extent of spinal cord dissection. If there is a cavity or cystic cavity in the spinal cord at both ends of the tumor, the cystic fluid will be released first, and then the tumor will be removed one by one. If there is a cavity or cystic cavity at both ends of the tumor, the cystic fluid should be released first, and then the tumor should be resected one by one. If the tumor is infiltrative growth, there is no obvious demarcation between the tumor and spinal cord, so do not excessively expand the resection range of the tumor. 1.Ventricular meningioma: The surface is smooth and gray-red, and more reticulated blood vessels can be seen, which is the main feature to distinguish it from astrocytoma. The surface of the tumor is clearly demarcated from the spinal cord, so it is easy to separate along the perimeter of the tumor during surgery. Some scholars prefer to separate the whole tumor from both ends. For large tumors, Epstain et al. advocated the use of a cavit ronult rasonic surgical aspirator (CUSA) or laser to perform a major intratumoral resection, followed by separation along the tumor border and electrocoagulation of the blood supply artery from the anterior spinal cord artery until the tumor is completely excised. It is believed that this can reduce the damage to the spinal cord. 2.Astrocytoma: For benign astrocytoma with certain boundaries, total excision should be strived for. However, sometimes the tumor is infiltrative growth without obvious boundary, so it should be biopsied for diagnosis. Usually, a pseudo-border can be created by separating the surface of the astrocytoma, and the tumor can be resected from the center to the periphery with CUSA or laser to achieve decompression. Although most astrocytomas do not have a clear border with the spinal cord, intraoperative differences in color between the tumor and the spinal cord can often be detected, facilitating surgical resection. If intraoperative SEP or MEP monitoring changes, or if the tumor is difficult to identify from the spinal cord, the operation should be terminated. 3. Vascular reticulocytoma: By separating the attachment point of the tumor in the soft spinal membrane and electrocoagulating the blood vessels on the surface of the tumor, surgical resection of vascular reticulocytoma is not very difficult, and the part buried in the medulla is easier to be separated. Intratumoral resection should be avoided to avoid difficulties in hemostasis and damage to the spinal cord. However, electrocoagulation can be used to reduce the size of the tumor by cauterizing the surface of the tumor. After resection of intramedullary tumor, the spinal incision does not need to be sutured, the dura is routinely sutured, or a biological dural patch or autologous fascial repair suture can be used to prevent postoperative dorsal spinal cord embolism. For secondary surgery, the wound should be tightly sutured to prevent postoperative cerebrospinal fluid leakage. Postoperative radiotherapy [7-11] is still controversial. In the past, many scholars advocated that postoperative radiotherapy should be given to intramedullary tumors. However, many studies in recent years have shown that most intramedullary ventricular meningiomas can be completely resected and do not recur for a long time, or even cured, so radiotherapy is not necessary for these patients. Radiation therapy is only indicated for patients with malignant ventricular meningioma with little growth and cerebrospinal fluid dissemination metastases. In vascular reticulocytomas, total resection is almost always obtained, and postoperative radiotherapy is not of any value. Intramedullary dermatomal cysts, epidermoid cysts, and lipomas are all benign tumors and do not require postoperative radiotherapy. Most scholars do not advocate postoperative radiotherapy for benign astrocytomas with good intramedullary differentiation, which can cause serious local adhesions and make secondary surgery after recurrence extremely difficult. Radiotherapy is the main treatment for intramedullary malignant astrocytoma, but the average survival time is only 6 months to 1 year. For sub-total resection of benign and malignant adenocarcinoma, the decision of radiotherapy should be based on postoperative clinical and imaging findings. Prognosis[10-12] The outcome of surgery is related to the patient’s preoperative neurological function and the tumor site, and most patients usually have different degrees of sensory loss after surgery, which may be related to the midline spinal cord incision. However, this postoperative sensory deficit can gradually improve. For patients with severe and long-lasting preoperative neurological deficits, the postoperative recovery was poor and even further aggravated after surgery, while patients with mild preoperative symptoms recovered quickly and with good results after surgery. This shows the importance of early diagnosis and early treatment.