A fibrous structure located dorsal to the dura at the posterior craniocervical junction stretches horizontally between the bilateral occipital condyles and the upper borders of the C-1 laminae. Partially covered by the occipital bone, this structure is always encountered when the bone is removed from the foramen magnum rim during approaches to the posterior cranial fossa. Although known to surgeons, this structure has not been defined, studied, or named. The most appropriate name for this structure is “the suboccipital ligament,” and a detailed rationale for this name is provided.
This 3-year-long study included 10 cadaveric specimens and 39 clinical patients: 31 consecutive surgically treated patients with Chiari Type I malformations (CM-I subgroup) and 8 other patients with posterior fossa pathologies (non–CM-I subgroup). The dimensions were defined, the function of this ligament was hypothesized, size and histological composition were compared between patient subgroups, and its origin and relationship to the surrounding structures were analyzed. Possible statistical differences in the parameters between the 2 groups were also evaluated.
The suboccipital ligament consists of horizontally oriented hyaline fibers and has a median length of 35 mm, height of 10 mm, and thickness of 0.5 mm. These dimensions are not significantly different between the CM-I and non–CM-I patients. The median age of the patients was 43 years, with CM-I patients being significantly younger (median 35 years) than non–CM-I patients (median 57 years). There was no statistically significant difference in weight, height, and body mass index between patient subgroups. There was no significant correlation between the body mass index or height of the patients and the dimensions of the ligament. No statistically significant differences existed between the subgroups in terms of smoking history, alcohol consumption, and the presence of diabetes mellitus, hypertension, hydrocephalus, or headaches. The ligament tissue in the CM-I patients was disorganized with poorly arranged collagen bands and interspersed adipose tissue. These patients also had more hyalinized fibrosis and showed changes in the direction of fibers, with hyaline nodules ranging from 0 to 2+. The result of the histological evaluation of the suboccipital ligament for hyaline nodules, calcification, and ossification was graded as 2+ if present in 3 or more medium-power magnification fields (MPFs); 1+ if present in 1–2 MPFs; and 0, if present in less than 1 MPF. Histological examination of the ligaments showed structural differences between CM-I and non–CM-I patients, most notably the presence of hyaline nodules and an altered fiber orientation in CM-I patients.
The suboccipital ligament extends between the occipital condyle and the superior edge of the C-1 lamina, connecting the contralateral sides, and appears to function as a real ligament. It is ventral to the occipital bone, which covers approximately two-thirds of the height of the ligament and is loosely attached to the dura medially and more firmly laterally. Because of its distinctive anatomy, characteristics, and function, the suboccipital ligament deserves its own uniform designation and name.
ABBREVIATIONSBMI = body mass index; CM-I = Chiari malformation Type I; MPF = medium-power magnification field.
Correspondence Kenan I. Arnautovic, Semmes-Murphey Clinic, 6325 Humphreys Blvd., Memphis, TN 38120. email: firstname.lastname@example.org.INCLUDE WHEN CITING Published online April 14, 2017; DOI: 10.3171/2016.10.JNS162161.Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.
AndersonRC, EmersonRG, DowlingKC, FeldsteinNA: Improvement in brainstem auditory evoked potentials after suboccipital decompression in patients with Chiari I malformations. 98:459–464, 200310.3171/jns.2003.98.3.0459)| false
ArnautovicASplavskiBBoopFAArnautovicKI: Pediatric and adult Chiari malformation Type I surgical series 1965–2013: a review of demographics, operative treatment, and outcomes. J Neurosurg Pediatr15:161–1772015
ArnautovicA, SplavskiB, BoopFA, ArnautovicKI: Pediatric and adult Chiari malformation Type I surgical series 1965–2013: a review of demographics, operative treatment, and outcomes. 15:161–177, 201510.3171/2014.10.PEDS1429525479580)| false
ArnautovicKI, MuzevicD, SplavskiB, BoopFA: Association of increased body mass index with Chiari malformation Type I and syrinx formation in adults. 119:1058–1067, 201310.3171/2013.4.JNS12201123662826)| false
AydinS, HanimogluH, TanriverdiT, YenturE, KaynarMY: Chiari type I malformations in adults: a morphometric analysis of the posterior cranial fossa. 64:237–241, 200510.1016/j.surneu.2005.02.02116099255)| false
CaldarelliMNovegnoFVassimiLRomaniRTamburriniGDi RoccoC: The role of limited posterior fossa craniectomy in the surgical treatment of Chiari malformation Type I: experience with a pediatric series. J Neurosurg106:3 Suppl187–1952007
CaldarelliM, NovegnoF, VassimiL, RomaniR, TamburriniG, Di RoccoC: The role of limited posterior fossa craniectomy in the surgical treatment of Chiari malformation Type I: experience with a pediatric series. 106:3 Suppl187–195, 200717465383)| false
EickerSO, MendeKC, DührsenL, SchmidtNO: Minimally invasive approach for small ventrally located intradural lesions of the craniovertebral junction. 38:4E10, 201510.3171/2015.2.FOCUS1479925828486)| false
GodilSSParkerSLZuckermanSLMendenhallSKMcGirtMJ: Accurately measuring outcomes after surgery for adult Chiari I malformation: determining the most valid and responsive instruments. Neurosurgery72:820–8272013
GodilSS, ParkerSL, ZuckermanSL, MendenhallSK, McGirtMJ: Accurately measuring outcomes after surgery for adult Chiari I malformation: determining the most valid and responsive instruments. 72:820–827, 201310.1227/NEU.0b013e318289734123381490)| false
KlekampJ: Surgical treatment of Chiari I malformation—analysis of intraoperative findings, complications, and outcome for 371 foramen magnum decompressions. 71:365–380, 201210.1227/NEU.0b013e31825c3426)| false
KotilK, TonT, TariR, SavasY: Delamination technique together with longitudinal incisions for treatment of Chiari I/syringomyelia complex: a prospective clinical study. 6:7, 200910.1186/1743-8454-6-7)| false
NashLNicholsonHLeeASJohnsonGMZhangM: Configuration of the connective tissue in the posterior atlanto-occipital interspace: a sheet plastination and confocal microscopy study. Spine (Phila Pa 1976)30:1359–13662005
NashL, NicholsonH, LeeAS, JohnsonGM, ZhangM: Configuration of the connective tissue in the posterior atlanto-occipital interspace: a sheet plastination and confocal microscopy study. 30:1359–1366, 20051595936310.1097/01.brs.0000166159.31329.92)| false
RomeroFR, PereiraCA: Suboccipital craniectomy with or without duraplasty: what is the best choice in patients with Chiari type 1 malformation?. 68:623–626, 20102073032110.1590/S0004-282X2010000400027)| false
StovnerLJ, BerganU, NilsenG, SjaastadO: Posterior cranial fossa dimensions in the Chiari I malformation: relation to pathogenesis and clinical presentation. 35:113–118, 199310.1007/BF005939668433785)| false
TakayasuMTakagiTHaraMAnzaiM: A simple technique for expansive suboccipital cranioplasty following foramen magnum decompression for the treatment of syringomyelia associated with Chiari I malformation. Neurosurg Rev27:173–1772004
TakayasuM, TakagiT, HaraM, AnzaiM: A simple technique for expansive suboccipital cranioplasty following foramen magnum decompression for the treatment of syringomyelia associated with Chiari I malformation. 27:173–177, 200410.1007/s10143-004-0338-515138848)| false
TubbsRSWellonsJCIIIOakesWJBlountJP: Reformation of the posterior atlanto-occipital membrane following posterior fossa decompression with subsequent constriction at the craniocervical junction. Pediatr Neurosurg38:219–2212003
TubbsRS, WellonsJCIII, OakesWJ, BlountJP: Reformation of the posterior atlanto-occipital membrane following posterior fossa decompression with subsequent constriction at the craniocervical junction. 38:219–221, 20031264674310.1159/000069092)| false
VanaclochaV, Saiz-SapenaN, Garcia-CasasolaMC: Surgical technique for craniocervical decompression in syringomyelia associated with Chiari type I malformation. 139:529–540, 199710.1007/BF02750996)| false
YundtKDParkTSTantuwayaVSKaufmanBA: Posterior fossa decompression without duraplasty in infants and young children for treatment of Chiari malformation and achondroplasia. Pediatr Neurosurg25:221–2261996
YundtKD, ParkTS, TantuwayaVS, KaufmanBA: Posterior fossa decompression without duraplasty in infants and young children for treatment of Chiari malformation and achondroplasia. 25:221–226, 199610.1159/0001211299309784)| false
ZamelK, GallowayG, KosnikEJ, RaslanM, AdeliA: Intraoperative neurophysiologic monitoring in 80 patients with Chiari I malformation: role of duraplasty. 26:70–75, 20091927949910.1097/WNP.0b013e31819f9058)| false