Spinal dumbbell tumors: Long-term outcome and risk factors

Objective There is limited literature on long-term outcomes after resection of intraspinal dumbbell tumors. To identify the progression-free survival (PFS) and outcomes associated with these tumors, we retrospectively reviewed data from 74 patients. Methods From 2007 to 2016, data from 74 patients who underwent surgical treatment for dumbbell tumors were reviewed. Patient outcomes were determined with the Japanese Orthopaedic Association (JOA) score. The median follow-up time was 7.3 years Results Gross total resection (GTR) was performed in 39 patients (52.70%) and subtotal resection (STR) in 35 patients (47.30%). The progression-free survival (PFS) at 11 years was 82.43%. A good outcome was observed in 85.13% of patients based on the JOA. Moreover, the univariate analysis showed that surgical recession was related to tumor recurrence, and that tumor location and multiplicity were associated with tumor prognosis. However, the multivariate regression analyses showed that no factors were associated with poor prognosis and recurrence. nerve as possible.

subtotal resection (STR) in 35 patients (47.30%). The progression-free survival (PFS) at 11 years was 82.43%. A good outcome was observed in 85.13% of patients based on the JOA. Moreover, the univariate analysis showed that surgical recession was related to tumor recurrence, and that tumor location and multiplicity were associated with tumor prognosis. However, the multivariate regression analyses showed that no factors were associated with poor prognosis and recurrence.
Conclusion The general standard treatment for spinal dumbbell tumors is complete resection, but the surgery needs to protect nerve function as much as possible.
Thus, our principle is to maximize tumor removal with functional preservation.

Background
Spinal cord tumors are relatively common; the overall incidence rate is 4-16% of all central nervous system (CNS) tumors, with 13-18% being dumbbell tumors 1 − 3 .
Spinal dumbbell tumors refer to tumors that connect two or more separate regions, such as intradural, epidural, and paravertebral spaces, and not just the dumbbell shape 1  Therefore, appropriate selection of the surgical approach is the key to the successful management of spinal dumbbell tumors. There have been many kinds of classifications used for dumbbell tumors in recent years, with Eden's classification and Toyama typing being the most commonly used 5 .
Due to a dearth of published reports, the effect of specific features and related recurrence factors on the outcome of patients with spinal dumbbell tumors is nor extremely clear. The aim of this study was to evaluate the long-term clinical efficacy of 74 patients surgically treated for dumbbell tumors. The outcome data were then analyzed for correlations with preoperative variables, surgical morbidity, progression-free survival (PFS), resection degree, and histology, and there was a long follow-up time of 11 years.

Patients characteristics
This retrospective study of spinal dumbbell tumors included patients who received microsurgery treatment between 2007 and 2016 at our hospital. This study was approved by the Ethics Committee of our hospital and informed consent was obtained from each patient before surgery. Of 512 spinal cord tumor patients, 74 patients included in our study.
We collected the following data from each patient: the age at surgery, sex, presenting symptoms, location of the tumor (surgical level), tumor size (maximal diameter on MR images), surgical resection (gross total resection GTR or subtotal resection STR), tumor multiplicity (number of tumors), histological diagnosis, recurrence and Toyama typing. These data were assessed by the same physician.
We evaluated patients' clinical symptoms and neurological function used the Japanese Orthopaedic Association (JOA) 6 . The JOA score was divided into four main categories: motor and sensory functions of the four extremities, activities of daily living (ADLs) and bladder sphincter function, with a total score of 29. All patients underwent magnetic resonance imaging (MRI) scans to determine the tumor location and size as well as the relationship with the surrounding tissue.

Surgical techniques
All patients were administered general anesthesia. Combined with preoperative Xray, MRI and intraoperative C-arm localization, the range of the posterior median incision was determined. Posterior surgery can be used for tumors confined to the spinal canal and intervertebral foramen. The patients were placed in the prone position and the lamina and spinous process of the lesion were removed. The extradural tumors were excised first; then, the subdural part that compressed the spinal cord was excised, after which the part involved the intervertebral foramen was gradually separated to the lateral side and was excised in blocks. If exposure was limited during the operation, the osteotomy time could be extended until total resection of the tumors was complete. Most tumors often adhered to the nerve root at the injured nerve cuff; then, the tumors were dissected from the nerve root to conserve the nerve root at the lesion site as much as possible. After resection of the tumor, the field was washed with normal saline, and the dura mater was tightly sutured. Thirteen patients required spinal fixation and pedicle screws were placed in the adjacent vertebral body. Contoured rods were installed to prevent deformities.
For patients with no internal fixation, a titanium plate or titanium nail was used to fix the laminae. Finally, the outer layers were sutured step by step to achieve anatomical reduction. Additionally, 9 patients underwent second-stage thoracoscopic surgery after 3-6 months. Patients were placed in the lateral position.
After ipsilateral lung collapse and single-lung ventilation, anterior resection of the paraspinal tumors was performed through a small surgical approach combined with thoracoscopy by thoracic surgeons.

Statistical analysis
All statistical data were analyzed using statistical software (SPSS Version 22.0).
Categorical variables were analyzed using the Pearson χ2 test, and the Wilcoxon rank sum test was used for continuous variables. Furthermore, we also used univariate analyses when testing for associations between outcome and recurrence.
The variables included gender, age, pathology, tumor level, surgical resection, tumor multiplicity and blood loss. A P value less than 0.05 was considered statistically significant. Moreover, PFS analyses were done using Kaplan-Meier

Patient demographics
Of 512 patients surgically treated for spinal cord tumors during the study period, 74 patients were included in this study. Table 1 summarizes the patient characteristics.
The mean age at surgery was 45.7 years (range 10-78 years), with a slight male predominance (M/F = 1.05). The major presenting symptoms were pain, numbness, muscle weakness and sphincter disturbances, of which the most common symptom was pain (62.16%). Furthermore, the most pathological type of tumor was Neurilemmoma (63.51%) and most tumors were located in the cervical region (39.19%). Moreover, tumor sites and distributions are also summarized in Table 1.
Thirteen patients (17.57%) experienced tumor recurrence or progression of residual tumor. Ten patients underwent a second operation to treat recurrent tumors, and the rest did not undergo an operation because they could not tolerate general anesthesia. Tumor recurrence might have been associated with STR or malignant tumors. During our follow-up period, 7 patients died because of advanced age and other internal diseases.
To explore the variables possibly associated with prognosis and recurrence, we adopted both univariate and multivariate regression analyses (Tables 3 and 4).
Univariate analysis showed that surgical recession was related to tumor recurrence and that tumor location and multiplicity were associated with tumor prognosis.
However, the multivariate regression analyses showed that no factors were associated with poor prognosis and recurrence.

Discussion
Previous studies have described the incidence of spinal dumbbell tumors as 13-18% 1− 3 . In our study, the rate was 14.45%, which is consistent with these reports.
Therefore, dumbbell tumors are not unusual. Moreover, many studies have reported that dumbbell tumors occur most commonly in the cervical spine and that most are   22,23 . Thus, it is significant to understand the risk factors for tumor recurrence and prognosis. The univariate analysis showed that recurrence and poor outcome were related to STR and tumor location, respectively (P < 0.05). However, multivariate regression analyses did not show any positive results. The difference between the two analyses may be due to the limitation of the small sample size in our study.

Conclusion
Data from seventy-four patients with spinal dumbbell tumors were reviewed. The PFS at 11 years was 82.43% and a good prognosis was considered in 85.13% of patients based on the postoperative JOA score. The gold standard treatment for dumbbell tumors is GTR, but the premise is to ensure good neurologic outcomes. It is noteworthy that this study had limitations because this was a retrospective follow-up study, and we had a sample size of only 74 dumbbell tumors, which may affect the credibility of our findings. We believe that our findings may have

Ethics approval and consent to participate
Our research was retrospective study which is not applicable for consent.

Consent for publication
The manuscript has not been published previously, in any language, in whole or in part, and is not currently under consideration elsewhere.