1. Incidence and pathogenesis. In the case of trauma and degeneration, the protruding intervertebral disc tissue breaks through the posterior longitudinal ligament and is located freely in the epidural to form an epidural-type intervertebral disc protrusion compressing the spinal cord and nerves. Zhang Zuolun et al. reported that ECDE accounted for 24.3% in 400 patients with cervical spondylosis. Bertalanffy et al. reported that the incidence of ECDE was as high as 35%, and the authors speculated that it might be caused by the different standards of patients included in the statistics. Some scholars statistic 27~100% of patients have neck trauma history before the onset of the disease, presumably in the cervical intervertebral disc degeneration, trauma can lead to intervertebral disc annulus fibrosus rupture, pressure nucleus pulposus protrudes, can break through the weak posterior longitudinal ligament whole layer of violent protruding to reach the epidural cavity, and with the annulus fibrosus nucleus pulposus tissue separation, can be to the spinal canal or the foramen of the vertebral hole in any direction movement. On the contrary, in degenerative ECDE, the course of the disease progresses slowly and there is no history of trauma. Foreign scholars believe that there are two types of ECDE: the nucleus pulposus breaks through the posterior longitudinal ligament and reaches the epidural space and then stays at the level of the intervertebral space without moving up and down; or the nucleus pulposus moves up and down to the posterior part of the vertebral body, reaching half of the vertebral body height, i.e., NTSEMCDE. Currently, there are only 18 cases of NTSEMCDE reported in the English literature, and Carviy Nievas et al. retrospectively analyzed the clinical characteristics of these 18 cases and the surgical treatment options. After summarizing the literature and the clinical characteristics of the 28 patients we reported, we analyzed the possible causes of this type of cervical disc prolapse as follows: 1) The patient had pre-existing cervical degeneration, and the nucleus pulposus had prolapsed across the posterior longitudinal ligament and lodged in the epidural space at the level of the intervertebral space. The free nucleus pulposus is gradually absorbed by the body through vascularization and apoptosis and shrinks or splits into multiple nucleus pulposus fragments, and these shrunken and split nucleus pulposus fragments are more likely to sneak up and down to reach the posterior vertebral body than the larger nucleus pulposus.2) Usually, patients who have a clear history of traumatic injuries will receive timely medical consultation for ECDE, and the discovery of compression is usually treated by surgery, which is a missing opportunity for continuous and dynamic tracking.3) The patient’s cervical spine may have a history of cervical spine degeneration. 2. Clinical characteristics and MRI diagnosis. NTSEMCDE patients with relatively long onset, disc herniation penetrated the posterior longitudinal ligament to reach the epidural, and then continued to migrate to the posterior aspect of the vertebral body. Due to the long duration of the disease and the persistence of degenerative factors, the herniated material is usually large, and the compression of the anterior dural sac leads to injury of the anterior spinal artery or the sulcus artery, resulting in ischemia and hypoxia of the anterior horn of the spinal cord and the joint part of the gray matter, resulting in impaired function of the spinal cord, and the clinical manifestation is the symptom of the spinal cord compression of the vertebral bundle. If the dislodged nucleus is located laterally, it is typical of the hemisection syndrome of the spinal cord. Therefore, it is usually difficult to distinguish the common cervical disc herniation from NTSEMCDE from the patient’s clinical manifestations. However, this type of intervertebral disc prolapse has a unique signal alteration in its cervical MRI because it has a different disease mechanism from the conventional herniation, which is the best way to determine this type of prolapse. We observed that in our group of 10 cases, the free displaced nucleus pulposus tissue to the posterior part of the vertebral body could be clearly detected in the T1 loss position, and these nucleus pulposus tissues and their parent nucleus intervertebral space had the same isosignal signal. The number of free nucleus pulposus fragments in the posterior part of the vertebral body can also be roughly determined. The axial phase, on the other hand, shows the location of the nucleus pulposus compressing the spinal cord and the degree of compression. The T2 phase in the lost position shows a mass-like isosignal or high signal shadow in the posterior part of the vertebral body, but it cannot determine that these are free nucleus pulposus tissues. 3. Clinical treatment. Conservative treatment: The results of lumbar spine research show that the free type, penetrate the posterior longitudinal ligament, the larger the prolapse and the more nucleus pulposus components of the intervertebral disc is more easily absorbed. The mechanism may be to promote the resorption of the intervertebral disc through immuno-inflammatory response, re-vascularization and apoptosis. The phenomenon of resorption after lumbar disc herniation provides a theoretical basis for the conservative treatment of certain types of lumbar disc herniation. Accordingly, the free nucleus pulposus of the cervical spine reported in this article has the clinical characteristics of large free displacement distance, large protrusion, penetration of the posterior longitudinal ligament, and predominance of nucleus pulposus components, and it is presumed that the possibility of natural resorption is higher. However, because of the different anatomical environments of the cervical and lumbar spine, scholars usually hold the view that early decompression is desirable to save spinal cord function due to functional impairment of spinal cord compression caused by cervical disc herniation, and that late decompression may result in irreversible spinal cord function, so there are relatively few reports in the literature of cervical disc herniation being naturally resorbed by conservative treatment. shimomura et al. reported the natural absorption of cervical disc herniation through conservative management by reviewing 56 cases of non-surgically treated spinal cord-type Shimomura et al. showed in a retrospective study of 56 patients with non-surgical cervical spondylosis that good clinical outcomes could be achieved by conservative treatment in patients with mild (preoperative JOA score of 13-17) spinal cervical spondylosis, while surgical treatment was required in mild patients with annular compression of the spinal cord and loss of the subdural space in the axial position on MRI. In our group, 10 patients had a preoperative JOA score of 10 or less, so conservative treatment was not appropriate and surgical treatment was preferred. The JOA score at the endpoint of follow-up after surgery in our group was 13.6±1.90 significantly improved from the preoperative score of 7.2±1.55, with a mean improvement rate of 66.7%. In contrast, Srinivasan reported worsening of clinical symptoms due to refusal of surgical treatment in this type of patients. Surgical characteristics: We summarize the following characteristics of NTSEMCDE anterior surgery: 1. Because the free nucleus pulposus is located in the posterior part of the vertebral body, anterior sub-total vertebral body resection with composite posterior longitudinal ligament resection for decompression and bone grafting can fully reveal the posterior longitudinal ligament in the posterior part of the vertebral body, and the resection of posterior longitudinal ligament can remove all the free nucleus pulposus tissues completely without omission, so as to achieve the goal of complete decompression. 2. The posterior longitudinal ligament needs to be removed: complete resection of the posterior longitudinal ligament can fully reveal and remove the free nucleus pulposus. Sometimes, the preoperative MRI shows a whole nucleus pulposus image, whereas intraoperative incision of the posterior longitudinal ligament reveals several free nucleus pulposus fragments. It is easy to miss without ligament resection and difficult to achieve complete decompression. In addition, in some cases, the rupture of the medulla through the posterior longitudinal ligament healed again, and if the posterior longitudinal ligament is not excised for epidural exploration, it is also caused to be missed.3. Precautions for resection of the posterior longitudinal ligament: If the rupture of the medulla through the posterior longitudinal ligament can be observed, a small nerve stripper is used to expand along the rupture, and with the ultra-thin lance forceps to bite off the ligament step by step. If the rupture of the nucleus pulposus through the posterior longitudinal ligament had healed and the posterior longitudinal ligament was smooth, a small nerve stripper hook was carefully hooked into the ligament along the direction of ligament travel from the proximal vertebral body at the weak point of the lateral side of the ligament, then gently rotated by 90 degrees and lifted up, and then the posterior longitudinal ligament was cut transversely by scissors along the longitudinal grooves of the stripper hook, and then the ligament was carefully bitten by the ultrathin lance forceps to take out the free nucleus pulposus. Since all 10 cases in this group were soft free disc herniation without obvious hypertrophy and ossification of the posterior longitudinal ligament, and the free nucleus pulposus taken during the operation did not have obvious tight adhesion with the dural sac and posterior longitudinal ligament, it was not difficult to operate as long as the operation was performed with care and good illumination and drainage were maintained. There was no case of dural rupture and cerebrospinal fluid leakage in this group. On the contrary, it was reported in the literature that the adhesion between the nucleus pulposus and the dura mater was very heavy after some epidural-type disc herniation, which required microscopic resection. We analyzed the possible reason for this is that trauma-induced epidural disc herniations contain not only the nucleus pulposus, but also some endplates and annulus fibrosus, and the histological manifestations of these herniations may be different from those after pure nucleus pulposus herniation. Secondly, the herniation may not be a soft disc herniation, and if there is a hard herniation causing compression, the herniation and dura are more heavily adherent.4. Surgical options for NTSEMCDE combined with other segmental degeneration: usually, for patients with disc herniation of 3 segments and above and developmental cervical stenosis, posterior open-door plication surgery is the indication. However, for this type of ECDE, posterior laminoplasty with posterior recession of the spinal cord does not alleviate the compression of the free nucleus pulposus on the spinal cord. Srinivasan et al. reported a case of poor outcome and deterioration of neurological function after a routine posterior laminoplasty, supporting the above view. For this reason, in our case of ECDE combined with disc degeneration in the adjacent segment, we performed a single-gap disc removal and decompression with bone grafting and fixation of the adjacent segment. The surgery went smoothly and the recovery was good. In conclusion, for this kind of patients with epidural cervical disc herniation which is clinically rare and free to the posterior part of the vertebral body, if the MRI of the cervical spine is carefully read before surgery, and if a large mass of nucleus pulposus is found in the posterior part of the vertebral body on the T1 phase in the lost position, and the signals of these nucleus pulposus tissues and the signal of the nucleus pulposus and its mother nucleus intervertebral space are consistent and isotropic, the diagnosis of epidural cervical disc herniation can be basically confirmed. It is advisable to perform anterior cervical subtotal vertebral body resection and posterior longitudinal ligament resection with decompression and internal fixation at an early stage, and complete decompression with complete resection of the free mass and fragmented nucleus pulposus is the key to the success of the surgical treatment.