Abstract Objective To investigate the advantages and shortcomings of microsurgical treatment of cervical spinal canal tumors by the hemi-laminar approach. Methods Fifty-two cases were treated by microsurgical resection of cervical spinal canal tumors using a hemivertebral approach, including 37 cases using a simple hemivertebral approach and 15 dumbbell-type tumors using a hemivertebral and subtotal joint resection approach. The postoperative neurological function, tumor recurrence and spinal deformity were followed up. In 51 cases, the tumors were completely resected, and in one case, only a subtotal resection was performed, and no new symptoms of neurological impairment were observed. Conclusion The treatment of cervical intracanalicular tumors by microsurgery with a hemi-vertebral plate approach causes little damage to the posterior structures and is conducive to maintaining the stability of the spine, but when there is small joint destruction, the stability changes should be followed up for a long time. Exposure of the operative field is limited to extramedullary tumors growing on one side. Keywords hemivertebral plate; cervical spine; intradural tumor Spinal cord tumors are mostly extramedullary, with benign tumors such as nerve sheath tumors, neurofibromas, and spinal meningiomas predominating. With the development of microsurgery, the efficacy of surgical resection has improved significantly, and the function of the spine after surgery is of increasing concern. From June 2002 to February 2009, we treated 52 cases of cervical spinal canal tumors with microsurgery using a hemi-vertebral plate approach, which is reported below. 1. Clinical data and methods 1.1 General data The 52 cases in this group were 26 males and 26 females. The age ranged from 27 to 76 years old, with an average of 49.5 years old. The duration of disease ranged from 3 to 96 months, with an average of 43.2 months. All cases were diagnosed with unilateral extramedullary subdural tumor or intradural tumor in the cervical spinal canal by MRI examination, most of the tumors were biased to the side of the spinal canal, lateral or lateral back of the spinal cord, 15 cases had tumors growing toward the intervertebral foramen or riding across the intervertebral foramen, with a transverse diameter of 1 to 2 cm and a longitudinal diameter of 1 to 6 cm. patients had symptoms and signs of spinal cord compression: weakness of limbs in 31 cases, numbness of limbs in 33 cases, chest fasciculation in 11 cases. There were 37 cases of sensory impairment in the plane of spinal cord damage, 38 cases of radicular pain, and 3 cases of urinary and fecal disorders. There were no intramedullary or epidural tumors with this surgical method. 1.2 Surgical method Preoperative localization of the corresponding vertebral plate of the lesion was performed 1 day before surgery. The patient was positioned prone to simulate the position during surgery, and the corresponding spine of the lesioned segment was marked with a varicose needle or cod liver oil capsule, while the corresponding lesioned vertebral body was marked on the body surface with nail violet. A frontal and lateral cervical spine X-ray or MRI is taken to determine the surgical incision by the relative position of the marker to the bony structure or tumor. The skin was cut along the preoperative incision, the paravertebral muscles on the side of the tumor were separated and retracted (32 cases on the left side and 20 cases on the right side of the group), and the muscle and periosteum were peeled from the spinous process and the vertebral plate from the inside out with a periosteal stripper, generally not exceeding the medial edge of the articular eminence to avoid damage to the small joint capsule. 15 cases of tumors involving the intervertebral foramen In 15 cases of tumors involving the intervertebral foramen, the lateral side was exposed to the lateral edge of the articular eminence and the foramina was dissected. After exposing the vertebral plate on the side of the lesion, the number of plates removed was decided according to the size of the tumor (one case with one plate removed, 39 cases with two plates removed, 8 cases with three plates removed, and 4 cases with four plates removed in this group), preserving the spinous process and interspinous ligament, medially to the base of the spinous process, and laterally preserving the small articular process or cutting part of the foramen. The resection of intravertebral canal tumor was performed through the bone window after hemilaminectomy, starting from cutting the dura, using microscopic operation, cutting the dura near the tumor as much as possible, paying attention to protecting the adjacent spinal cord or nerve roots, first cutting the tumor envelope and performing intracapsular resection of the tumor, then separating the adhesions between the tumor envelope and the spinal cord or nerve roots after decompression, and removing the tumor and envelope piece by piece. The tumor supply artery is cut off by electrocoagulation, but attention is paid to avoid damaging the larger vessels supplying the spinal cord, complete hemostasis, and careful suturing of the dura to prevent cerebrospinal fluid leakage. The epidural cavity around the window was filled with gelatin sponge and the wound was sutured layer by layer. 1.3 Postoperative follow-up The patient’s preoperative symptoms were used as their own control, and the patient was followed up immediately after surgery, and 3 months after surgery for neurological function, tumor recurrence and spinal mobility and curvature, and for long-term follow-up. 2. Results Among the 52 cases in this group, 51 cases achieved complete resection of the tumor, and 1 case had only subtotal resection with unclear boundary between the tumor and surrounding structures. The operation time was 1-2 hours, with an average of 1.5 hours. The total hospital stay ranged from 9 to 12 days, with an average of 10 days. The bed activity started 3 days after surgery, and the bed activity started 5 days after surgery. None of the cases without small joint destruction required neck brace protection, and those with small joint destruction routinely wore neck brace protection for 1 month after surgery and exercised the neck muscles. The pathological diagnosis was nerve sheath tumor in 38 cases, spinal meningioma in 7 cases, neurofibroma in 2 cases, ganglion cell neuroma in 4 cases, and metastatic small cell carcinoma of the lung in 1 case. All of them showed improvement of their symptoms immediately after surgery: 38 cases had reduced or disappeared radicular pain, 11 cases had reduced the sensation of chest banding, and 31 of the 37 cases with sensory impairment of spinal cord damage had decreased in plane. The symptoms further improved at 3 months after surgery: the radicular pain and chest banding sensation disappeared, muscle strength was restored in 31 cases of limb weakness, numbness disappeared in 31 out of 33 cases of limb numbness, the plane decreased in 37 cases of sensory impairment of spinal cord damage, and there was only mild sensory impairment in 3 cases of urinary and fecal dysfunction; no tumor recurrence was seen on MRI; one patient with metastatic small cell carcinoma of the lung was lost at 1 year after surgery. One patient with metastatic small cell lung cancer was lost at 1 year after surgery, and the remaining 51 patients were followed up for a long period of 10 to 90 months, with a mean of 48 months. One case of nerve sheath tumor was found to have recurred 36 months after surgery, but no recurrence was found 48 months after reoperation. 38 patients (27 hemivertebral resections alone and 11 hemivertebral resections with small joint disruptions) were reviewed on plain radiographs of the cervical spine in hyperextension and hyperflexion, and no cervical deformity was observed in all patients. The cervical spine mobility was greater in those with small joint destruction (52.75±0.42°) than in those without small joint destruction (52.17±0.25°). 3 Discussion Intraspinal tumors are most commonly extramedullary tumors, commonly benign tumors such as nerve sheath tumors, which cause varying degrees of symptoms and neurological dysfunction [1]. Surgical resection is the accepted treatment of choice, and with advances in minimally invasive surgery, the rate of total resection and functional improvement has increased significantly [1]. Traditional laminectomy requires occlusion of the spinous process, supraspinous ligament, interspinous ligament, lamina and other structures to fully reveal the tumor, but because of the large damage to the posterior structures of the spine, it affects the biomechanical balance of the spine and can cause spinal deformity, which can affect the patient’s ability to live and work in severe cases [2]. How to maintain the biomechanical stability of the spine has become an increasing concern for neurosurgeons [3]. According to the “three-column” theory, the posterior column of the spine contains the posterior joint capsule, the ligamentum flavum, the attachments of the spine, the synovial and supraspinous and interspinous ligaments, and these structures are important for maintaining spinal stability [4]. Posterior tension bands (collateral, spinous, supraspinous and interspinous ligaments), small joints and/or multiple segments of the laminae are surgically removed can disrupt the biomechanical stability of the spine [5]. The center of gravity of the head is slightly anterior to the cervical spine, gravity has the effect of causing anterior flexion of the cervical spine, and the posterior muscles and ligaments resist its action. Sagittal stability of the cervical spine is maintained by the balance of anterior and posterior structures, and any alteration of the posterior cervical bone or ligamentous structures may cause displacement of the weight-bearing axis [6]. Cervical laminectomy shifts the weight-bearing axis ventrally to the anterior part of the vertebral body so that most of the weight is carried by the anterior vertebral body and intervertebral disc; when the load increases, the anterior spinal column tends to be deformed in compression and the posterior column is in tension; because the posterior tension band has weakened, its force against changing the cervical alignment is reduced, which causes the loss of anterior cervical convexity, straightening its alignment or changing it to retroconvexity [7]. In order to maintain the structural and functional integrity of the spine, minimally invasive and microsurgery has been used in recent years for intracanalicular tumors. We adopt a hemivertebral approach for some patients during resection of cervical intradural tumors. Since the cervical spinal canal is wide and most cervical spinal canal tumors are benign tumors such as nerve sheath tumors, which are mostly located in the extramedullary-subdural area, it is feasible to treat cervical spinal canal tumors using a hemi-plate approach by applying micro-neurosurgical techniques [8]. It can reveal well, remove the tumor smoothly and completely, reduce the damage to the posterior column of the spine, and preserve the structure and function of the spine to the maximum extent after surgery, which can improve the quality of life and work ability of patients [9]. Compared with the traditional procedure, this method is less invasive, has less postoperative epidural scar formation, faster recovery, allows early bedtime and functional exercise, and shortens the hospital stay [1, 10]. This method preserves structures such as the spinous process, ligaments, and articular processes, which can maintain the stability of the spine and reduce the appearance of postoperative spinal deformity or instability [3, 10]. Cervical spinal canal tumors that grow in a dumbbell shape are deep, difficult to reveal, and often closely related to the vertebral artery, making surgical operation difficult. The semilaminar approach is useful for cervical spinal canal dumbbell-shaped tumors with an extracanalicular portion <4 cm and is less invasive and does not affect the stability of the cervical spine [1, 11]. All 15 dumbbell-shaped tumors in our group except one metastatic small cell carcinoma of the lung were completely resected through this approach, similar to those reported in the literature. However, in order to fully reveal the tumor, it was often accompanied by small joint destruction. In the literature, it has been reported that for tumors less than 2 cm in length and diameter, only part of the small joint can be removed to completely resect the tumor, especially for tumors less than 1 cm, and even the small joint can be kept intact [11]. In contrast, for larger tumors outside the spinal canal, total resection of the small joint is required. The integrity of the small joints, however, is very important for the stability and maintenance of cervical spine alignment.Ng et al. found that resection of more than 50% of the small joints could cause increased segmental motion and stress on the fibrous ring and cortical bone through finite element modeling [12]. Patients with small joint disruption in this group did not develop cervical instability but had greater cervical motion than those without small joint disruption. It is evident that damage to small joints should be minimized during surgery; the effect on cervical spine stability in the presence of small joint disruption remains to be observed in the long term in a large number of cases. The preoperative localization should be accurate and reliable during the hemi-vertebral plate approach surgery. MRI can accurately localize the tumor and can clearly understand the relationship between the tumor and the spinal canal, spinal cord and vertebral artery, so that the surgical strategy can be formulated preoperatively. If the tumor occupies 1/3 of the vertebral canal, only half laminectomy is needed; when the tumor occupies 1/3-1/2 of the vertebral canal, half laminectomy and part of the spinous process root should be removed; when the tumor occupies 1/2-2/3 of the vertebral canal, in addition to half laminectomy, part of the spinous process and supraspinous and interspinous ligaments should be removed to facilitate greater subterranean resection of the spinous process root. If the dumbbell tumor involves only the foramen externally, only 1/4 of the lesser articular processes need to be resected; if the outward growth is <4 cm and only the vertebral artery is compressed or encircles <1/2 of the vertebral artery, 1/2-3/4 of the lesser articular processes need to be resected; if the outward growth is <4 cm, when encircling >1/2 of the vertebral artery, the lesser articular processes need to be completely resected. Microsurgery with a semilaminar approach to remove tumors in the cervical spinal canal has the characteristics of less surgical trauma, faster postoperative patient recovery, and maintaining the stability of the cervical spine, but also has the disadvantage of limited exposure. If it is a dumbbell type tumor, the destruction of small joints should be minimized. When there is destruction of small joints, long-term postoperative follow-up should be performed.