Introduction: Chiari-I Malformation (CM-I) is characterized by a shallow posterior fossa and hindbrain herniation through the foramen magnum. Posterior fossa decompressive craniectomy (PFDC) is the standard treatment for symptomatic patients. However, there are many variations to this approach, definitive treatment remains unresolved and there is no consensus on the optimal surgical technique. The authors report their experience with a minimally invasive occipitocervical decompression (MIOCD) for patients with CM-I and compare this novel technique with the traditional open approach.

Methods: We conducted a retrospective review of 23 consecutive patients who underwent surgical treatment for symptomatic CM-I. Patient records were appraised and statistical analyses were performed on clinical status, intraoperative factors, length of hospitalization and postoperative results. Findings were used to compare the outcomes after minimally invasive and standard open approaches.

Results: Ten patients underwent MIOCD, and thirteen standard open PFDC. All 23 procedures included duraplasty and resection of the posterior arch of C1. Patient age ranged from 9 to 60 years (mean 32.4) and follow-up duration varied from 1 to 57 months (Mean 14.7 months). There were no statistically significant differences between the 2 groups in terms of neurological recovery, pain scores, length of stay, diameter of the craniectomy and complications. Nevertheless, the MIOCD group showed a tendency to present better results when compared to the PFDC in terms of blood loss (Mean 320ml Vs. 400ml), operation time (Mean 134.9min Vs. 164.5min) and immediate POP pain scores (1.9 Vs. 2.9 in the VAS).

Conclusions: We present a novel technique for minimally invasive decompression of the posterior fossa that provides similar outcomes as the standard PFDC in the surgical treatment of CM-I. Preservation of the posterior tension band and musculature could result in better postoperative pain control, lower incidence of craniocervical instability and better cosmetic results. However, further prospective studies are needed to confirm these hypotheses.

Patient Care: Minimally invasive occipito-cervical decompression can represent an effective treatment for symptoms associated with CM-I with similar outcomes as the standard open technique. It is a feasible and simple surgical alternative that takes advantage of an anatomical corridor to avoid excessive exposure, muscle disinsertion and preserves the posterior tension band; hence it could result in better postoperative pain control, cosmetic results and lower incidence of craniocervical instability. We open a window for further studies that could eventually validate the importance of a less invasive approach to the patient with CM-I, hence improving surgical outcomes and lowering surgery-related morbidity.

Learning Objectives: By the conclusion of this session, participants should be able to identify the minimally invasive occipito-cervical decompression approach as an effective treatment alternative for patients with Chiari Type I malformation. Furthermore, they should understand the anatomical and biomechanical implications of preserving the posterior tension band and neck musculature. Finally, we seek to open a window for further studies that aim to validate the advantages of an MIS approach and improve postoperative results in patients with Chiari Type I malformation

References: 1. Nishikawa M, Sakamoto H, Hakuba A, Nakanishi N, Inoue Y. Pathogenesis of the Chiari malformation: a morphometric study of the posterior cranial fossa. J Neurosurg. 1997;86:40-47. 2. Lazareff J, Galarza M, Gravori T, Spinks T. Tonsillectomy without craniectomy for the management of infantile Chiari I malformation. J Neurosurg. 2002;97:1018–1022. 3. Hoffman CE, Souweidane MM. Cerebrospinal fluid-related complications with autologous duraplasty and arachnoid sparing in type I Chiari malformation. Neurosurgery. 2008;62:156-160. 4. Klekamp J. Surgical treatment of Chiari I malformation--analysis of intraoperative findings, complications, and outcome for 371 foramen magnum decompressions. Neurosurgery. 2012;71(2):365-380. doi:10.1227/NEU.0b013e31825c3426 5. Hu Y, Liu J, Chen H, et al. A minimally invasive technique for decompression of Chiari malformation type I (DECMI study): study protocol for a randomised controlled trial. BMJ Open. 2015;5(4):e007869-e007869. 6. Durham SR, Fjeld-Olenec K. Comparison of posterior fossa decompression with and without duraplasty for the surgical treatment of Chiari malformation type I in pediatric patients: a meta-analysis. J Neurosurg Pediatr. 2008;2:42-49. 7. Oro JJ, Mueller DM. Posterior fossa decompression and reconstruction in adolescents and adults with the Chiari I malformation. Neurol Res. 2011;33:261-271. 8. Meadows J, Kraut M, Guarnieri M. Asymptomatic Chiari Type I malformations identified on magnetic resonance imaging. J Neurosurg. 2000;92(6):920-926. 9. Chou YC, Sarkar R, Osuagwu FC. Suboccipital craniotomy in the surgical treatment of Chiari I malformation. Childs Nerv Syst. 2009;25(9):1111-1114. 10. Lee HS, Lee SH, Kim ES, et al. Surgical results of arachnoid-preserving posterior fossa decompression for Chiari I malformation with associated syringomyelia. J Clin Neurosci. 2012;19:557-560. 11. Litvack ZN, Lindsay RA, Selden NR. Dura splitting decompression for Chiari I malformation in pediatric patients: clinical outcomes, healthcare costs, and resource utilization. Neurosurgery. 2013;72:922-929. 12. Dyste GN, Menezes AH, VanGilder JC. Symptomatic Chiari malformations. An analysis of presentation, management, and long-term outcome. J Neurosurg. 1989;71:159-168. 13. Alden TD, Ojemann JG, Park TS. Surgical treatment of Chiari I malformation: indications and approaches. Neurosurg Focus. 2001;11(1):1-5. 14. Hosono N, Sakaura H, Mukai Y, Fujii R, Yoshikawa H. C3–6 laminoplasty takes over C3–7 laminoplasty with significantly lower incidence of axial neck pain. Eur Spine J. 2006;15(9):1375–1379. 15. Nolan JP, Sherk HH. Biomechanical evaluation of the extensor musculature of the cervical spine. Spine (Phila Pa 1976). 1988;13(9):9-11. 16. Steinbok P, Boyd M, Cochrane D. Cervical spinal deformity following craniotomy and upper cervical laminectomy for posterior fossa tumors in children. Childs Nerv Syst. 1989;5:25-28. 17. Takeshita K, Seichi A, Akune T, Kawamura N, Kawaguchi H, Nakamura K. Can laminoplasty maintain the cervical alignment even when the C2 lamina is contained? Spine (Phila Pa 1976). 2005;30:1294-1298. 18. Lam FC, Irwin BJ, Poskitt KJ, Steinbok P. Cervical spine instability following cervical laminectomies for Chiari II malformation: a retrospective cohort study. Childs Nerv Syst. 2009;25:71-76. 19. Camino WGO, Bosio ST, Puigdevall MH, Halliburton C, Sola CA, Maenza RA. Craniocervical spinal instability after type 1 Arnold Chiari decompression: a case report. J Pediatr Orthop B. 2017;26(1):80-85. 20. McLaughlin MR, Wahlig JB, Pollack IF. Incidence of postlaminectomy kyphosis after Chiari decompression. Spine (Phila Pa 1976). 1997;22(6):613-617. 21. Bell DF, Walker JL, O’Connor G, Tibshirani R. Spinal deformity after multiple-level cervical laminectomy in children. Spine (Phila Pa 1976). 1994;19(4):406-411. 22. Aronson DD, Kahn RH, Canady A, Bollinger RO, Towbin R. Instability of the Cervical Spine After Decompression in Patients Who Have Arnold-Chiari Malformation. J Bone Jt Surg. 1991;73(6):898-906. 23. Santiago P, Fessler RG. Minimally invasive surgery for the management of cervical spondylosis. Neurosurgery. 2007;60(Suppl 1):S160-165. 24. Coric D, Adamson T. Minimally invasive cervical microendoscopic laminoforaminotomy. Neurosurg Focus. 2008;25(2):E2. 25. Evaniew N, Khan M, Drew B, Kwok D, Bhandari M, Ghert M. Minimally invasive versus open surgery for cervical and lumbar discectomy: a systematic review and meta-analysis. C Open. 2014;2(4):E295–E305. 26. Fessler RG, O’Toole JE, Eichholz KM, Perez-Cruet M. The development of minimally invasive spine surgery. Neurosurg Clin N Am. 2006;17(4):401-409. 27. Kim CW, Siemionow K, Anderson DG, Phillips F. The current state of minimally invasive spine surgery. Instr Course Lect. 2011;60:353-370. 28. Schijman E, Steinbok P. International survey on the management of Chiari I malformation and syringomyelia. Childs Nerv Syst. 2004;20(5):341-348. 29. Haroun RI, Guarnieri M, Meadow JJ, Kraut M, Carson B. Current opinions for the treatment of syringomyelia and Chiari malformations: survey of the Pediatric Section of the American Association of Neurological Surgeons. Pediatr Neurosurg. 2000;33:311-317. 30. Gambardella G, Caruso G, Caffo M, Germano` A, La Rosa G, Tomasello F. Transverse microincisions of the outer layer of the dura mater combined with foramen magnum decompression as treatment for syringomyelia with Chiari I malformation. Acta Neurochir (Wien). 1998;140(2):134-139. 31. Logue V, Edwards M. Syringomyelia and its surgical treatment—an analysis of 75 patients. J Neurol Neurosurg Psychiatry. 1981;44(4):273-284. 32. James H, Brant A. Treatment of the Chiari malformation with bone decompression without durotomy in children and young adults. Childs Nerv Syst. 2002;18(5):202-206. 33. Won D, Nambiar U, Muszynski C, Epstein F. Coagulation of herniated cerebellar tonsils for cerebrospinal fluid pathway restoration. Pediatr Neurosurg. 1997;27(5):272-275. 34. Parker S, Harris P, Cummings T, George T, Fuchs H, Grant G. Complications following decompression of Chiari malformation Type I in children: dural graft or sealant? J Neurosurg Pediatr. 2011;8(2):177-183. 35. Takeuchi K, Yokoyama T, Ito J, Wada K, Itabashi T, Toh S. Tonsillar herniation and the cervical spine: a morphometric study of 172 patients. J Orthop Sci. 2007;12(1):55-60. 36. Kelly MP, Guillaume TJ, Lenke LG. Spinal Deformity Associated with Chiari Malformation. Neurosurg Clin N Am. 2015;26:579-585. 37. Menezes A. Chiari I malformations and hydromyelia—complications. Pediatr Neurosurg. 1991;17(3):146-154. 38. Sakaura H, Hosono N, Mukai Y, Oshima K, Iwasaki M, Yoshikawa H. Preservation of the nuchal ligament plays an important role in preventing unfavorable radiologic changes after laminoplasty. J Spinal Disord Tech. 2008;21(5):338-343. 39. Riew DK, Raich AL, Dettori JR, Heller JG. Neck Pain Following Cervical Laminoplasty: Does Preservation of the C2 Muscle Attachments and/or C7 Matter? Evid Based Spine Care J. 2013;13(4):42-53. 40. Kato M, Nakamura H, Konishi S, et al. Effect of preserving paraspinal muscles on postoperative axial pain in the selective cervical laminoplasty. Spine (Phila Pa 1976). 20089;33(14):E455-459. 41. Takeuchi K, Yokoyama T, Aburakawa S, et al. Axial symptoms after cervical laminoplasty with C3 laminectomy compared with conventional C3-C7 laminoplasty: a modified laminoplasty preserving the semispinalis cervicis inserted into axis. Spine (Phila Pa 1976). 2005;30(22):2544-2549.