Tumors were totally removed in all patients via microsurgery. In assessment of neurological functions based on McCormick classification, 39 of the 51 patients demonstrated improved neurological status at the latest follow-up (16 in free-hand group, 23 in ITFN group; between 3 months and 16 months postoperatively). The other 12 patients (7 in free-hand group and 5 in ITFN group) reported that symptoms remained the same. In these 12 patients, statistical analysis demonstrated that the duration of preoperative symptoms might be the potential factor that affects the surgical outcome (t = 4.639, P < 0.005) [Figure 6]. No tumor recurrences were found during follow-up.
Postoperative CT scan demonstrated satisfactory results in all cases. Based on the intraoperative CT, 25 pedicles were completely or partially destroyed in free-hand group and 29 pedicles were destroyed in ITFN group due to the tumoral invasion. Eight pedicles in ITFN group were thought to be impassable because of altered pedicle anatomy and size. In the free-hand group, 145 screws (92.4%) were Grade I, 9 screws (5.7%) were Grade II, and 3 screws (1.9%) in Grade III. In the ITFN group, 192 screws (97.4%) were Grade I, 5 screws (2.6%) were Grade II, and no Grade III screw was detected in this study. Statistical analysis showed that the accuracies of pedicle screws in two groups were significantly different (χ2 = 4.981, P = 0.026) [Figure 7].
Furthermore, among the screw pedicles of Grade II in ITFN group, we analyzed the factors that affect the accuracy of PSP, and the result demonstrated that the number of vertebral bodies between the screws and the tracker were statistically different in ITFN group (Grade I vs. Grade II: 2.93 ± 0.93 vs. 4.29 ± 0.48, t = 6.279, P < 0.001). No medial cortical penetration or anterior vertebral cortical penetration was observed. No cases of iatrogenic neurological injury were found [Figure 8].
The term of PIST has not been proposed in prior literature; however, earlier articles reported some specific spinal tumors with this invasive nature. Sridhar et al. defined giant invasive spinal schwannoma as a tumor that extends more than two vertebral levels with extraspinal extension of >2.5 cm and those with vertebral body erosion and posterolateral extension into myofascial planes. Tureyen et al. described a series of idiopathic spinal epidural arachnoid cysts with obvious vertebral erosion because of long-term compression. Varying lesions with an invasive nature in spinal canal have been described in sporadic case reports as well, pathological types most commonly include epidermoid cysts, neurofibroma, spinal giant-cell tumor, and hemangioblastoma. Surgery plays an important role in the treatment of PISTs. The treatment goals include the restoration and preservation of neurological function, pain relief, and local lesion control. Total resection is recommended because inadequate removal may be followed by recurrence. In our study, 39 of 51 patients showed significant symptoms’ improvement postoperatively based on McCormick classification, and 12 patients’ symptoms remained the same. We further analyzed some factors that affect the surgical outcome, such as patients’ age and the duration of preoperative symptoms. The statistical result demonstrated that the duration of preoperative symptoms has positive correlation to the surgical outcome. We considered that the neurological deficits were caused by direct tumor compression of the cord, and preoperative duration of compression may affect the surgical outcome. Thus, early surgical treatment allows rapid neurological function recovery. The accuracy of pedicle screw was not considered to be associated with the neurological status.
In achieving total tumor resection, multilevel laminectomy with facet removal has to be done. Meanwhile, operators should further consider the influence to spinal stability. Tumor erosion plus surgical destruction may worsen the spinal deformity or instability. This situation following procedure has raised concerns by more and more surgeons. Contemporary pedicle-based spinal instrumentation is thought to be the most effective method with the aim of reconstructing spine stability until now. Although this technique has been widely used among different medical centers in the world, PSP in the thoracic spine is still full of risks because of the smaller pedicle size and more complex 3D anatomy. In practice, screw malposition may lead to highly severe vascular and neurological complications, especially when the patient's anatomy is changed or destroyed by some certain reasons, such as scoliosis, idiopathic deformities, or tumor erosion. In our study, 29 pedicles were totally destroyed and 8 pedicles became extremely slim in furthermore, the spinal cord was compressed to the one side in spinal canal, which leads to a safe zone reduction between the cord and pedicles. The odds of neurological structure injury significantly increased because of the above reasons while inserting pedicle screws.
Given these potential risks, multiple studies of varying pedicle screw installation have been developed to evaluate the accuracy of its usage. Puvanesarajah et al. reviewed a series of reported studies and concluded the accuracy rate in the thoracic spine by free-hand ranging from 71.9% to 98.3%. Of note, the lowest accuracies were associated with the mid-thoracic spine. Parker et al. found that screws inserted into T4 and T6 were most likely to breach while Modi et al. found that screws inserted into the pedicles of T5–T8 had a greater incidence of breaches. Furthermore, as expected, free-hand techniques have been noted to have a significant learning curve. In this study, our rate in the free-hand technique was 92.4%. Although three screws showed penetration 2–4 mm on CT images, none of the misplaced screws resulted in neurological deficits.
For overcoming the disadvantages of free-hand techniques, some surgeons identify anatomical landmarks via K-wires placement based on fluoroscopy guidance into the pedicles, and the incidence of pedicle screw misplacement ranges from 1.5% to 25% using the K-wire-guided methods. Although previous researches showed only 1.5% misplacement, they admitted that the actual rate would be higher on those patients who have severe spine deformity or destroyed pedicles. Meanwhile, the conventional K-wire-guided technique could not allow direct visualization of the starting point on the intraoperative fluoroscopy and/or radiography. The accuracy of PSP depends largely on the patient's anatomic landmarks and the surgeon's experience. Furthermore, radiation exposure of surgeon and operating room personnel has raised concerns as well.
Despite the advantages of using ITFN system, we cannot ignore the fact that there are still 2.6% screws breaching the cortex, although they are all silent clinically. Imaging shifting is thought to be a major reason for this error. Patient's position can be shifted while the screws are placed. Thus, we suggest the operator should manipulate gently in pedicle screw insertion to avoid touching the patient. Meanwhile, in analyzing the position of every single screw, we discovered a gradual rise in screw misplacement rate was demonstrated with increasing distance between instrumented segment and the tracker by Spearman rank correlation analysis. The screws closing to the tracker (within two segments) have significantly higher accuracy compared to the ones that extend the range of two vertebras. As a result, we considered that the increasing distance to tracker is an important factor of impacting the accuracy of screw placement. Last but not least, Scheufler et al. reported that ventilatory arrest during scan acquisition and registration of the lower thoracic does not appear to be warranted. The impact of ventilation on chest cage and spinal motion depends on several factors, such as tidal volume, chest cage volume, configuration, and rigidity, as well as positioning of the patient. Therefore, we suggest that the surgeon should verify the accuracy of the navigation system during the operation if there is any doubt.
There may be some bias in our study. First, the quantity of samples in each group is less. Second, there could be a learning curve that may have influenced our results. Before this study, we sufficiently performed thoracic tumor resection without ITFN system. Thus, we believe that the effect of a learning curve in using 3D ITFN may be minor.
Conclusively, the treatments of PISTs include total tumor resection and reconstruction of spine stability. The ITFN system could provide high accuracy of PSP, especially for incomplete pedicles in thoracic spine. The promising result suggests that this technique is feasible and safe. However, considering the accuracy rate, further studies will be required in the future.
This work was supported by the grant from the Ministry of Science and Technology of China (No. 2015BAI12B04).
There are no conflicts of interest.
1. Baruah D, Chandra T, Bajaj M, Sonowal P, Klein A, Maheshwari M, et al A simplified algorithm for diagnosis of spinal cord lesions Curr Probl Diagn Radiol. 2015;44:256–66 doi: 10.1067/j.cpradiol.2014.12.004
2. Chamberlain MC, Tredway TL. Adult primary intradural spinal cord tumors: A review Curr Neurol Neurosci Rep. 2011;11:320–8 doi: 10.1007/s11910-011-0190-2
3. Guzik G. Surgical treatment in patients with spinal tumors – Differences in surgical strategies and malignancy-associated problems. An analysis of 474 patients Ortop Traumatol Rehabil. 2015;17:229–40 doi: 10.5604/15093492.1162422
4. Li WS, Chen C, Wang H, Liang CF, Luo L, Guo Y. Hemilaminectomy approach combined with in situ
restoration of vertebral laminae for thoracic intraspinal tumors Turk Neurosurg. 2013;23:630–8 doi: 10.5137/1019-5149.JTN.7859-12.0
5. Moussazadeh N, Rubin DG, McLaughlin L, Lis E, Bilsky MH, Laufer I. Short-segment percutaneous pedicle screw fixation with cement augmentation for tumor-induced spinal instability Spine J. 2015;15:1609–17 doi: 10.1016/j.spinee.2015.03.037
6. Yukawa Y, Kato F, Ito K, Horie Y, Hida T, Nakashima H, et al Placement and complications of cervical pedicle screws in 144 cervical trauma patients using pedicle axis view techniques by fluoroscope Eur Spine J. 2009;18:1293–9 doi: 10.1007/s00586-009-1032-7
7. Allam Y, Silbermann J, Riese F, Greiner-Perth R. Computer tomography assessment of pedicle screw placement
in thoracic spine: Comparison between free hand and a generic 3D-based navigation
techniques Eur Spine J. 2013;22:648–53 doi: 10.1007/s00586-012-2505-7
8. Gertzbein SD, Robbins SE. Accuracy of pedicular screw placement in vivo
Spine (Phila Pa 1976). 1990;15:11–4 doi: 10.1097/00007632-199001000-00004
9. Mueller CA, Roesseler L, Podlogar M, Kovacs A, Kristof RA. Accuracy and complications of transpedicular C2 screw placement without the use of spinal navigation
Eur Spine J. 2010;19:809–14 doi: 10.1007/s00586-010-1291-3
10. McCormick PC, Torres R, Post KD, Stein BM. Intramedullary ependymoma of the spinal cord J Neurosurg. 1990;72:523–32 doi: 10.3171/jns.1990.72.4.0523
11. Sridhar K, Ramamurthi R, Vasudevan MC, Ramamurthi B. Giant invasive spinal schwannomas: Definition and surgical management J Neurosurg. 2001;94:210–5 doi: 10.3171/spi.2001.94.2.0210
12. Tureyen K, Senol N, Sahin B, Karahan N. Spinal extradural arachnoid cyst Spine J. 2009;9:e10–5 doi: 10.1016/j.spinee.2009.03.006
13. Suk SI, Kim WJ, Lee SM, Kim JH, Chung ER. Thoracic pedicle screw fixation in spinal deformities: Are they really safe? Spine (Phila Pa 1976). 2001;26:2049–57 doi: 10.1097/00007632-200109150-00022
14. Onen MR, Simsek M, Naderi S. Alternatives to surgical approach for giant spinal schwannomas Neurosciences (Riyadh). 2016;21:30–6 doi: 10.17712/nsj.2016.1.20150242
15. Luksanapruksa P, Buchowski JM, Singhatanadgige W, Rose PC, Bumpass DB. Management of spinal giant cell tumors Spine J. 2016;16:259–69 doi: 10.1016/j.spinee.2015.10.045
16. Boriani S, Bandiera S, Casadei R, Boriani L, Donthineni R, Gasbarrini A, et al Giant cell tumor of the mobile spine: A review of 49 cases Spine (Phila Pa 1976). 2012;37:E37–45 doi: 10.1097/BRS.0b013e3182233ccd
17. Tobin MK, Geraghty JR, Engelhard HH, Linninger AA, Mehta AI. Intramedullary spinal cord tumors: A review of current and future treatment strategies Neurosurg Focus. 2015;39:E14 doi: 10.3171/2015.5.FOCUS15158
18. Yu NH, Lee SE, Jahng TA, Chung CK. Giant invasive spinal schwannoma: Its clinical features and surgical management Neurosurgery. 2012;71:58–66 doi: 10.1227/NEU.0b013e31824f4f96
19. Montano N, Trevisi G, Cioni B, Lucantoni C, Della Pepa GM, Meglio M, et al The role of laminoplasty in preventing spinal deformity in adult patients submitted to resection of an intradural spinal tumor. Case series and literature review Clin Neurol Neurosurg. 2014;125:69–74 doi: 10.1016/j.clineuro.2014.07.024
20. Kotani T, Akazawa T, Sakuma T, Koyama K, Nemoto T, Nawata K, et al Accuracy of Pedicle Screw Placement
in Scoliosis Surgery: A Comparison between Conventional Computed Tomography-Based and O-Arm-Based Navigation
Techniques Asian Spine J. 2014;8:331–8 doi: 10.4184/asj.2014.8.3.331
21. Ishikawa Y, Kanemura T, Yoshida G, Ito Z, Muramoto A, Ohno S. Clinical accuracy of three-dimensional fluoroscopy
-based computer-assisted cervical pedicle screw placement
: A retrospective comparative study of conventional versus computer-assisted cervical pedicle screw placement
J Neurosurg Spine. 2010;13:606–11 doi: 10.3171/2010.5.SPINE09993
22. Moses ZB, Mayer RR, Strickland BA, Kretzer RM, Wolinsky JP, Gokaslan ZL, et al Neuronavigation in minimally invasive spine surgery Neurosurg Focus. 2013;35:E12 doi: 10.3171/2013.5.FOCUS13150
23. Puvanesarajah V, Liauw JA, Lo SF, Lina IA, Witham TF. Techniques and accuracy of thoracolumbar pedicle screw placement
World J Orthop. 2014;5:112–23 doi: 10.5312/wjo.v5.i2.112
24. Parker SL, McGirt MJ, Farber SH, Amin AG, Rick AM, Suk I, et al Accuracy of free-hand pedicle screws in the thoracic and lumbar spine: Analysis of 6816 consecutive screws Neurosurgery. 2011;68:170–8 doi: 10.1227/NEU.0b013e3181fdfaf4
25. Modi H, Suh SW, Song HR, Yang JH. Accuracy of thoracic pedicle screw placement
in scoliosis using the ideal pedicle entry point during the freehand technique Int Orthop. 2009;33:469–75 doi: 10.1007/s00264-008-0535-x
26. Scheufler KM, Franke J, Eckardt A, Dohmen H. Accuracy of image-guided pedicle screw placement
using intraoperative computed tomography-based navigation
with automated referencing. Part II: Thoracolumbar spine Neurosurgery. 2011;69:1307–16 doi: 10.1227/NEU.0b013e31822ba190
27. Heary RF, Bono CM, Black M. Thoracic pedicle screws: Postoperative computerized tomography scanning assessment J Neurosurg. 2004;100:325–31
28. Bransford R, Bellabarba C, Thompson JH, Henley MB, Mirza SK, Chapman JR. The safety of fluoroscopically-assisted thoracic pedicle screw instrumentation for spine trauma J Trauma. 2006;60:1047–52 doi: 10.1097/01.ta.0000215949.95089.18
29. Larson AN, Polly DW Jr, Guidera KJ, Mielke CH, Santos ER, Ledonio CG, et al The accuracy of navigation
and 3D image-guided placement for the placement of pedicle screws in congenital spine deformity J Pediatr Orthop. 2012;32:e23–9 doi: 10.1097/BPO.0b013e318263a39e
30. Dang L, Liu X, Dang G, Jiang L, Wei F, Yu M, et al Primary tumors of the spine: A review of clinical features in 438 patients J Neurooncol. 2015;121:513–20 doi: 10.1007/s11060-014-1650-8
31. Roy-Camille R, Saillant G, Berteaux D, Salgado V. Osteosynthesis of thoraco-lumbar spine fractures with metal plates screwed through the vertebral pedicles Reconstr Surg Traumatol. 1976;15:2–16
32. Wu JS, Lu JF, Gong X, Mao Y, Zhou LF. Neuronavigation surgery in China: Reality and prospects Chin Med J. 2012;125:4497–503 doi: 10.3760/cma.j.issn.0366-6999.2012.24.031
Edited by: Qiang Shi