Craniocervical Junction Fusions in Patients With Hindbrain IOWA 08

ATIENTS with hindbrain herniation or the so-calledCM-I and/or syringohydromyelia are often treatedwith dorsal decompression alone. However, the small

percentage of patients with other associated bone abnor-malities at the CCJ have a high failure rate in terms ofsymptomatic improvement (that is, without additional sta-bilization). Some of these patients may present with find-ings typical of hindbrain herniation or a localized syrinx,but have bone anomalies that would not be responsive to aPFD alone; these patients require an associated ventralbrainstem decompression. Others may have symptoms of

hindbrain herniation or a syrinx may develop, only withoutany bone abnormalities; brainstem compression (usually inflexion) due to a number of causes is diagnosed in these pa-tients on dynamic MR imaging, and they require a dorsaldecompression as well as a dorsal fusion for stabilization.Still others may have undergone repeated attempts at PFD,rendering the musculature and ligaments lax and causingoccipitocervical instability.

The presence of syringohydromyelia in patients withCM-I is well known, with these entities occurring togetherin 50–76% of patients with CM-I.6,25 However, the presenceof concomitant bone abnormalities with CM-I and/or sy-ringohydromyelia is reportedly much more rare.22 There-fore, the extant literature is limited and presents variousopinions on the best method of treatment in these condi-tions. We sought to survey the indications for CCJ fusionsin this select population.

J. Neurosurg.: Spine / Volume 9 / July 2008

J Neurosurg Spine 9:1–9, 2008

Craniocervical junction fusions in patients with hindbrainherniation and syringohydromyelia

ALBERT J. FENOY, M.D., ARNOLD H. MENEZES, M.D., AND KATHLEEN A. FENOY, A.R.N.P.

Department of Neurosurgery, University of Iowa Hospitals and Clinics, Iowa City, Iowa

Object. Patients with hindbrain herniation or the so-called Chiari malformation Type I (CM-I) and/or syringo-hydromyelia are treated with dorsal decompression alone; however, a small percentage of patients with other asso-ciated abnormalities require concomitant dorsal craniocervical junction (CCJ) fusion. The authors surveyed the indi-cations for CCJ fusions in this population.

Methods. A retrospective review of University of Iowa medical records and radiographs obtained between 1996and 2005 was performed. Inclusion criteria encompassed patients with diagnoses of CM-I and/or syringohydro-myelia requiring dorsal CCJ fusions, and others with CCJ abnormalities who had CM-I and/or syringohydromyelia.

Results. Two hundred thirty-four patients were identified, all of whom were symptomatic at presentation. Theirages ranged from 2.5 to 86 years; 33% of the patients were , 16 years of age. Patients were categorized as follows,with some being assigned to . 1 category: Group I, congenital or acquired CCJ abnormalities with reducible bonecompression (25% of patients); Group II, previous anterior CCJ/upper brainstem decompression (44%); Group III,occipitocervical complex instability with CM-I and/or syringohydromyelia but without CCJ bone abnormalities re-quiring adjunctive posterior fossa decompression (26%); and Group IV, musculoligamentous instability, either frompathological states or from muscle dehiscence from repeated posterior fossa procedures (14%). Instrumentation wasused in 96% of patients, with all 96% receiving semirigid fixation with titanium loop and sublaminar cables; all fu-sion constructs incorporated autologous bone. At last follow-up evaluation, fusion was radiographically completein 97%, and symptom improvement was seen in 92%.

Conclusions. Dorsal CCJ fusions are required in patients with CM-I and/or syringohydromyelia who have con-comitant CCJ abnormalities (Groups I and II). A definite group (CM-I and/or syringohydromyelia) without boneabnormality exists (Groups III and IV). This may be due to muscle weakness secondary to a high syrinx. (DOI: 10.3171/SPI/2008/9/7/001)

KEY WORDS • Chiari malformation Type I • craniocervical fusion • dorsal fusion •syringohydromyelia

P

1

Abbreviations used in this paper: BMP = bone morphogeneticprotein; CCJ = craniocervical junction; CM-I = Chiari malformationType I; CMJ = cervicomedullary junction; CSF = cerebrospinalfluid; CVJ = craniovertebral junction; FMD = foramen magnum de-compression; PFD = posterior fossa decompression.

Methods

A retrospective review of University of Iowa medical re-cords and radiographs obtained between 1996 and 2005was performed. Inclusion criteria were patients with diag-noses of hindbrain herniation and/or the presence of a syr-inx in the cervical spinal cord and who required a dorsalcraniocervical fusion; this included patients with other CCJabnormalities associated with CM-I and/or syringohydro-myelia. Hindbrain herniation was defined as cerebellar ton-sillar descent to below the level of the foramen magnum,and the patient needed to have referable symptomatologyfor inclusion.

Patient Presentation

Over this 10-year period, 234 patients were identifiedwho met the aforementioned criteria. The patient age atpresentation ranged from 2.5 to 86 years (mean 36 years);33% of the patients were , 16 years old.

The duration of symptoms ranged from 1 month to 150months (mean 29.75 months). All patients were symp-tomatic on presentation, with head or neck pain (78% ofpatients) being the most common feature (suboccipitalheadache alone was present in 59% of patients). A catego-rization of presenting signs and symptoms is shown inTable 1.

Diagnosis of the Anomaly

Diagnosis of the anomaly was made by assessing thepresenting symptoms and signs and evaluating them in thecontext of adequate imaging studies. This preoperativeinvestigation was critical and was believed to be thorough-ly conducted to obtain the maximum benefit of a surgicalprocedure. This was most effectively accomplished bycomplete imaging of the CVJ with both preoperative CTand MR imaging studies. When possible, these studieswere performed at our institution and included a 3D re-construction of the craniocervical CT to better define thesurgical anatomy and bone anomalies. Also, dynamic MRimaging in both flexion and extension views, which wereobtained to evaluate the extent of ventral and dorsal cervi-comedullary compression, respectively, was found to be akey component in determining the reducibility of the ab-normality at the CCJ. Such comprehensive preoperativeimaging of the neck in flexion and extension was also nec-essary to assess the stability of the cervical spine. Asreviewed previously,16 unstable configurations at the CCJare outlined in Table 2. Stabilization is of paramount im-portance for reducible lesions to maintain the neural de-compression. Irreducible lesions require decompression atthe site of compression, followed by fusion. Relief ofsymptomatic ventral compression seen on flexion MR im-ages obtained with the spine in the extended position was ared flag indicating the need to fuse. The position of theodontoid was taken into consideration when positioning thepatient for surgery, because cervical flexion could exagger-ate the ventral compression on the CMJ.29,30

In an effort to further explore the indications for dorsalfusions in patients presenting with hindbrain herniationand/or syringomyelia, the patients were categorized as fol-lows, with some in . 1 category: Group I, patients withreducible CCJ bone abnormalities causing compression;

Group II, patients having undergone a previous anteriordecompression of the ventral brainstem; Group III, patientshaving occipitocervical complex instability without CCJbone abnormalities; and Group IV, patients with muscu-loligamentous instability. A summary of these patient cate-gories, definitions, and the number included in each group-ing is presented in Table 3.

Sixty-five patients presented with syringohydromyelia inaddition to their bone abnormalities. The bone anomaliesassociated with CM-I/syringohydromyelia in these patientswere numerous and sometimes superimposed, as presentedin Table 4.

Management of the Disease

All patients underwent dorsal fusions. Of such fusionsperformed, the most common concomitant decompressionwas that of the posterior fossa (170 patients), either alone(119 patients) or combined with a ventral decompression of the brainstem (51 patients) via the transoral approach.Dorsal fusion was the only procedure performed in 33patients; these individuals comprised Group IV (see Table3). In the cases in which potentially reducible bone com-pression was present at the CCJ (that is, in patients com-

A. J. Fenoy, A. H. Menezes, and K. A. Fenoy

2 J. Neurosurg.: Spine / Volume 9 / July 2008

TABLE 1Presenting signs and symptoms in 234 patients with

hindbrain herniation and/or syringohydromyelia treated between 1996 and 2005

Signs & Symptoms No. of Patients (%)*

headache 136 (58)neck pain 46 (20)dysphagia 46 (20)decreased gag response 91 (39)upper-extremity weakness 56 (24)upper-extremity numbness/paresthesia 86 (37)lower-extremity weakness 5 (2)lower-extremity numbness/paresthesia 16 (7)gait instability 62 (27)hyperreflexia 143 (61)C-2 numbness 46 (20)facial numbness 28 (12)torticollis 34 (15)dizziness 23 (10)

* Many patients had . 1 sign or symptom.

TABLE 2Unstable configurations at the CCJ*

Criteria for Unstable Configurations

predental space .5 mm in patients ,8 yrs of age, .3 mm in those 8–10 yrs & older

separation of atlas lat masses .6 mmvertical clivus odontoid translation .2 mmgap btwn occipital condyles & atlas facets on lat cervical radiographsabnormal relationship btwn spinal canal & foramen magnumabnormal craniocervical motion dynamics

* Adapted from Menezes and VanGilder.

posing Group I), the patient was placed in halo-ring tra-c-tion preoperatively to obtain the optimum degree of de-compression; this was maintained by instrumentation andfusion in an extended position after the PFD.

The PFD Surgical Procedure

The PFD procedure followed by dorsal occipitocervicalfusion was performed in the 59 patients comprising GroupI as well as in the 60 patients in Group III. The extent ofPFD varied on a per-patient basis, but always involved thefollowing: an occipital craniectomy; partial C-1 (superiortwo-thirds) laminectomy; intraoperative ultrasonographyconfirmation of dorsal decompression; intradural explo-ration and removal of constricting intradural bands (whenpresent, in ~ 30% of patients); adequate tonsillar shrinkageand lysis of arachnoid adhesions to visualize CSF flow;watertight dural closure with a cervical fascia graft; andmeticulous, layered muscle closure.

Transoral–Transpalatopharyngeal Surgical Procedure

The 103 patients comprising Group II underwent a stan-dard transoral–transpalatopharyngeal approach for ven-tral decompression of the brainstem by the senior author(A.H.M.). This procedure was combined with a PFD andconcomitant dorsal craniocervical fusion in 51 patients; in52 patients a limited dorsal FMD was made to allow for theoccipitocervical fusion. The transoral approach is describedin detail elsewhere18,19 but is summarized as follows: in-duction of general anesthesia is followed by intraoral place-ment of the Dingman self-retaining retractor, which allowsample exposure to the soft palate. A midline incision ismade here, followed by one in the posterior pharyngealmidline raphe. Magnification provided by the operatingmicroscope is introduced where the prevertebral fascia andlongus colli musculature are mobilized laterally; this allowsthe anterior inferior clivus as well as the anterior arches ofthe atlas and axis vertebrae to be visualized. The anteriorarch of the atlas and the odontoid process are then removedusing a high-speed drill, allowing for visualization of theretroodontoid space and ensuring that there is adequateventral decompression of the brainstem. After ensuring thatthe integrity of the dura mater is preserved, the wound isthen copiously irrigated and closed in multiple layers.

Dorsal Occipitocervical Fusion Procedure

Overall, 96% of patients underwent instrumented and4% had noninstrumented fusions. Of these, 96% underwentfusion from the occiput to C-2 or C-3, with semirigid fixa-tion via titanium loop and sublaminar titanium cables andbone. Rigid constructs included posterolateral C1–2 platingsystems, C1–2 transarticular screws, and C-1 lateral massto C-2 pedicle screw fixation constructs, and these wereused in the remainder of cases. All fusion constructs incor-porated autologous bone; either grafts from the patient’sright ninth rib, from posterior spinal elements, or from thecalvarium. A micro-air impactor was used to harvest bone.We used BMP and/or bone graft composite in most cases.In children , 6 years of age, rib-graft strut fusion was usu-ally performed (90%); instrumented fusion took place inthe 10% who had adequate bone mass.


Fusion of the CCJ for hindbrain herniation and syringohydromyelia

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Results

Occipitocervical fusion was found to be radiograph-ically complete in 97% of patients based on CT scans andlateral cervical spine imaging performed at last follow-up.Symptomatic improvement was seen in 92%. Not surpris-ingly, the symptoms of suboccipital headache and posteri-or cervical pain were those that were most commonly re-lieved by treatment. No change from the preoperativeexamination or persistence of symptoms was observed in7%, with headaches again comprising the largest compo-nent (5%). Two patients reported a return of dysphagia anddysarthria, as well as lower-limb paresthesias in 1S, al-though these were subjective findings and were not sub-stantiated by imaging or clinical examination.

In 4% of patients with continued symptoms, repeatedtonsillar descent was seen following PFD on follow-upimaging. However, in half of these, dynamic imaging re-vealed CSF space around the tonsils, and thus no interven-tion was undertaken. Tonsillar impaction was found to berepeated in the remaining half of patients; 2 of these alsohad an associated residual cervical syrinx. These patientsunderwent repeated dorsal decompression and fusion, withplacement of a fourth ventricle–subarachnoid shunt in the 2with residual syringes. Radiographic and symptomatic im-provement was confirmed at follow-up.

Sixty-five patients presented with syringohydromyelia inaddition to their bone abnormality. Of these, 23 patientspresented with syringohydromyelia alone, in the absence of hindbrain herniation. The most common anatomicalconcurrent finding in these patients was the Klippel–Feilanomaly, with . 1 cervical segmentation failure as well asdystopic os odontoideum. On evaluation of this group to-gether at last follow-up, however, 60 of 65 patients werefound to have radiographic improvement or resolution oftheir syrinx. The remaining 5 patients had persistent syr-inges, in one of whom a syringosubarachnoid shunt wasplaced; the other 4 patients had stable conditions and noother treatment plans were formulated.

Follow-Up Duration

The mean duration of follow-up was 20.2 months (range1 month–10 years). Twenty-eight patients were lost to fol-low-up, either continuing their care at their referring insti-tutions or failing to return after discharge. No deaths werereported in those patients who continued through to the lastfollow-up evaluation.

Illustrative Cases

Case 1 (Group I)

This case provides an example of atlas assimilation withbasilar invagination that is reducible on extension.

History and Physical Examination. This 11-year-old boyhad a history of progressive posterior headache and neckpain over several months, with an even longer history ofdifficulty walking. He and his family also reported worsen-ing difficulty with gait. Physical examination revealed anabsent gag reflex and a broad-based gait, but the remainderof his examination results were normal.

Neuroimaging. Sagittal dynamic MR images obtained inflexion and extension views demonstrated tonsillar hernia-tion as well as a large syrinx extending from C-2 to the thoracic spinal cord. The ventral osseous cervicomedullarycompression caused by atlas assimilation seen on flexionviews was relieved in extension (Fig. 1A).

Operation. The patient underwent PFD, with intradurallysis of adhesions and tonsillar shrinkage, and concomitantdorsal Oc–C2 fusion with titanium loop and cable instru-mentation, calvarial bone grafts, and BMP (Fig. 1B and C).This fusion kept the patient in moderate extension.

Postoperative Course. The patient noted complete symp-tom resolution after the 12-month follow-up visit and con-tinues to do well, with complete fusion confirmed by radi-ographic assessment.

Another example of a CM-I with atlas assimilation andreducible atlantoaxial dislocation in extension can be seenin Fig. 1D; this patient was treated with a PFD and dorsaloccipitocervical fusion.

Case 2 (Group II)

This case provides an example of a fixed ventral bonecompression in which treatment was anterior decompres-sion of the upper cervical cord followed by PFD and fu-sion.

History and Physical Examination. This 12-year-old girlpresented initially to an orthopedist with a 7-month historyof progressive claw deformity of her hands, to the extentthat she was unable to play her clarinet. She was ultimatelyreferred to our institution, where detailed questioning re-vealed that she sometimes aspirated liquids while drinking.Physical examination confirmed clawing of her hands, theright worse than the left, with weak interosseous muscles, aswell as absent upper-extremity reflexes and hyperactivelower-extremity reflexes; the remainder of her examination,including cranial nerve and gait assessments, was normal.

Neuroimaging. Sagittal and coronal neutral MR imagingdemonstrated hypoplastic occipital condyles resulting inbasilar invagination and ventral compression of the CMJ;this, combined with cerebellar tonsillar herniation, resulted



TABLE 4Associated diagnoses in 234 patients with hindbrain herniation

and/or syringohydromyelia treated between 1996 and 2005*

Diagnosis No. of Patients†

syringomyelia 65Klippel–Feil anomaly 57atlas assimilation 50basilar invagination 56Down syndrome 10osteogenesis imperfecta 3Ehlers–Danlos syndrome 3VATER complex 2Noonan syndrome 1Goldenhar syndrome 1spondylometaphyseal dysplasia 1Crouzon syndrome 1Apert syndrome 1

* VATER = vertebral defects, anal atresia, tracheoesophageal fistula withesophageal atresia, and radial and renal anomalies.

† Many patients demonstrated . 1 associated diagnosis.

in a large syrinx extending from the CMJ to the conus infe-riorly (Fig. 2).

Operation. The patient underwent transoral–transpalato-pharyngeal resection of the odontoid and anterior arch ofC-1, followed by PFD and dorsal Oc–C2 fusion with tita-nium loop and cable instrumentation, calvarial bone grafts,and BMP. This fusion kept the patient in mild extensionand relieved compression on the spinal cord.

Postoperative Course. The patient has noted improve-ment in her claw deformity after 24 months of follow-upcare, and she continues to do well; her fusion is completeaccording to radiographic studies.

Case 3 (Group III)

This case is an example of reduction of a ventral abnor-mality in the extended position, so that treatment was PFDand fusion.

History and Physical Examination. This 22-year-old wom-an presented to a local facility after colliding with one ofher dance partners at practice and hitting her occiput,prompting evaluative imaging, which led her to our institu-tion. She reported posterior cervical and suboccipital painon presentation to our institution, but further investigationrevealed that she had experienced lifelong trouble swal-lowing solids more than liquids, painful extension of theneck, posterior headaches, and occasional ringing in herears. Physical examination confirmed a decreased gag re-

sponse as well as decreased sensation in the left V1 and V2distributions; the remainder of the results were normal.

Neuroimaging. Dynamic MR imaging in flexion and ex-tension views demonstrated CVJ buckling as well as cere-bellar tonsillar ectopia to C-2. At the level of the posteriorarch of C-1, no CSF was seen surrounding the brainstem orspinal cord. There was no syringohydromyelia noted. Onflexion of her neck, it was noted that her anterior brainstemwas severely compressed, which was relieved in extension.There was no bone abnormality (Fig. 3).

Operation. The patient underwent PFD and dorsal Oc–C2 fusion with titanium loop and cable instrumentation,calvarial bone grafts, and BMP. This fusion kept the patien-t’s spine in mild extension (Fig. 3).

Postoperative Course. The patient has noted completesymptom resolution and at 30 months of follow-up hasreturned to her previous occupation, with complete fusionbased on radiographic assessment.

Case 4 (Group IV)

This case is an example of musculoligamentous instabil-ity after repeated PFDs, which caused poor muscle approx-imation and fibrotic scars after repeated operation.

History and Physical Examination. This 13-year-old girlhad a long, complex history of symptomatic CM-I withbrainstem abnormalities, including 10th cranial nerve dys-



5

FIG. 1. Case 1. Sagittal dynamic T1-weight-ed MR images (A) demonstrating tonsillar her-niation and ventral bone CMJ compression inflexion that is relieved on extension. A large syrinx extending from C-2 to the thoracic cord is noted. Intraop-erative photographs show the PFD with intradural lysis of adhesions and tonsillar shrinkage (B) and dorsalOc–C2 fusion with titanium loop and cable instrumentation, calvarial bone grafts, and BMP (C). Sagittal MRimages (D) depict another example of a CM-I with atlas assimilation and reducible atlantoaxial dislocation inextension; the patient was treated with a PFD and dorsal occipitocervical fusion.

function, which had required tracheostomy and gastrosto-my when she was an infant. This was concomitant with hy-drocephalus and a cervicothoracic syrinx, for which sheunderwent 2 PFDs between the ages of 3 and 6 months,with placement of a fourth ventricle–subarachnoid shunt.At her third PFD at the age of 7 months, a large fat graft hadbeen placed over the dural closure to prevent scarring. Shesubsequently had a ventriculoperitoneal shunt placed andunderwent 32 shunt revisions for headache before she firstpresented to us in early 2006 with severe occipital head-aches, quadriparesis, ataxia, and an old tracheostomy. Shehad no ventriculomegaly. Physical examination findingswere as follows: gross hyperreflexia, clonus, unsteady gait,and generalized weakness. Neuroophthalmological find-ings of upgaze paresis, diplopia, convergence–retractionnystagmus, and lid retraction localized the anomaly to thedorsal midbrain.

Neuroimaging. Sagittal MR imaging and CT scanning aswell as 3D CT reconstruction revealed an abnormal clivus–odontoid C-1 arch relationship, as follows: angulation ofthe clivus–odontoid articulation of ~ 95° in flexion and120° in extension, with indentation into the ventral medul-la. The dorsal fat graft and a displaced fourth ventricleshunt catheter were visualized. Axial CT and MR imagingstudies at the C-2 vertebral body level demonstrated thecervical muscles separated by fat (Fig. 4).

Operation. The patient underwent transoral–transpalato-pharyngeal resection of the odontoid process and lowerclivus. The PFD procedure was followed by intradural ex-ploration of the fourth ventricle and syrinx, with lysis ofadhesions. Gross occipitocervical instability was present,and we found intradural scarring. The Oc–C2 fusion wasperformed with titanium loop and cable instrumentation,calvarial bone grafts, and BMP.



FIG. 2. Case 2. Sagittal (A) and coronal (B) neutral T1-weighted MR images demonstrating hypoplastic occipitalcondyles resulting in basilar invagination and ventral compression of the CMJ as well as tonsillar herniation to C-2. Alarge syrinx extending from the CMJ to the thoracic cord is noted. Sagittal T1-weighted MR image obtained 12 monthsafter ventral and dorsal decompression surgeries (C) reveals marked relief of CMJ compression and significant reductionin the syrinx.

FIG. 3. Case 3. Sagittal dynamic T2-weighted MR images in flexion (A) and extension(B) demonstrating CVJ buckling as well as cerebellar tonsillar ectopia to C-2. The anteri-or brainstem is severely compressed on flexion but relieved on extension, with no associ-ated bone abnormality. Postoperative lateral cervical spine radiograph (C) shows the dor-sal occipitocervical fusion with titanium loop and cable instrumentation, following thePFD.

Postoperative Course. The patient attained complete neu-rological recovery within 3 weeks after the dorsal proce-dure and fixation. At her 1-year follow-up evaluation sheremained symptom free. A follow-up postfusion MR im-age demonstrates marked reduction in the syrinx commen-surate with symptomatic improvement (Fig. 4F).

Discussion

Osseous anomalies of the CVJ are believed to arise dur-ing the origination of the occipital bone and vertebrae fromsclerotomes in the mesoderm and ensuing complex dif-ferentiation processes that occur from Week 4 to Week 12of gestation.22–24 The CM-I is one such complication, butsometimes these bone anomalies may be superimposed,5,14,

21,28,32,33 reducing the volume of the posterior fossa. Syringo-myelia may develop when the CSF is also obstructed at theforamen magnum.26 The presence of such concurrent ab-normalities at the CCJ makes the site subject to instability,both anteroposteriorly and on horizontal rotation of thehead, which further complicates matters, especially whentreatment plans must be formulated.

The simultaneous presence of CM-I and syringohydro-myelia has long been recognized, but the literature hasvarying opinions on the appropriate treatment to be provid-ed.1,3,4,7–11,20,22,27 The PFD procedure alone, which is the stan-dard treatment for CM-I, is considered inadequate in asmall subgroup in which the risk of postoperative instabil-ity at the CCJ requires stabilization by a fixation proce-dure.2,6,8,11,12,15 However, few large-scale studies have report-ed in detail the indications for treating such combinedanomalies of the CCJ, and these entities are often the topicof isolated, smaller studies. Furthermore, the presence ofconcomitant CCJ bone anomalies with CM-I and/or syrin-gohydromyelia is the subject of only a few case reports,with different treatment plans and choices for dorsal fu-sion.13,14

The incidence of CM-I with concurrent bone anomaliesis reported to be rare. In a series of 364 patients with symp-tomatic CM-I, Milhorat et al.22 reported basilar invagina-tion in 12%, atlas assimilation (together with condylar hy-poplasia and other occipital bone atypias) in 5.2%, and theKlippel–Feil anomaly in 4.9%, but reported that none ofthese were superimposed. The incidence of these concur-



7

FIG. 4. Case 4. Sagittal CT (A) and T2-weighted MR (B) image composites show an abnormal clivus–odontoid C-1arch relationship with angulation of the clivus–odontoid articulation of ~ 95° in flexion and 120° in extension. Note thedisplaced fourth ventricle shunt catheter (small arrow), and the cervical muscles, which were separated by fat (largearrows), again seen on axial CT (C) and MR (D) images at the level of the C-2 vertebral body. Postoperative lateral cer-vical spine radiograph (E) shows the dorsal occipitocervical fusion with titanium loop and cable instrumentation, fol-lowing the PFD. A follow-up postfusion MR image (F) demonstrates marked reduction in the syrinx.

rent anomalies is far below the present series’ reportedinstances of basilar invagination (31%), atlas assimilation(24%), and Klippel–Feil anomaly (24%). Such disparitiesare most probably a direct result of the fact that we focusedonly on those patients with CM-I and/or syringohydromy-elia who required dorsal CCJ fusions, the need for fusionbeing largely attributed to the inherent instability or con-comitant bone abnormalities causing ventral compression.Also, the referral patterns to our hospital skew the popula-tion of patients with CM-I and/or syringohydromyelia whoundergo evaluation, because the 234 patients in this seriesrequiring dorsal fusion comprise ~ 20% of all patients withCM-I who were treated. Thus, a comparison to other stud-ies of patients with CM-I is less meaningful.

In their study of 130 pediatric and young adult patientswith CM-I, Tubbs et al.29 reported on 7 patients with Klip-pel–Feil anomaly, and basilar invagination was present in5 patients; a syrinx was reported in 58%, and preoperativecervical instability was found in 1 patient. Treatment waswith the PFD procedure, and 83% of patients attained alle-viation of symptoms postoperatively. No patient initiallyunderwent a dorsal fusion; 1 patient with subsequent ven-tral brainstem compression later underwent a transoraldecompression followed by occipitocervical fusion. Otherpast studies have recognized that concomitant bone abnor-malities with CM-I and/or syringohydromyelia may re-quire adjunctive procedures to the dorsal decompression toaddress the ensuing instability. Goel and colleagues7,9 re-ported the importance of performing a posterior decom-pression followed by occipitocervical fusion via plate and screw fixation in patients with CM-I and atlantoaxialdislocation. Nishikawa et al.24 reported on 2 patients withCM-I as well as concomitant basilar invagination and at-las assimilation who required simultaneous PFD and pos-terior fixation for their fixed anomalies. We have pointedout before that atlas assimilation and segmentation failuresof the upper cervical spine may contribute to ligamentouslaxity and proliferation of granulation tissue at the CCJ.17

Such instability may eventually lead to basilar invaginationand irreducibility, and thus a stabilization procedure is in-dicated.

In their study of 40 pediatric and young adult patientswith CM-I, Grabb et al.10 sought to determine the amountof ventral brainstem compression that can be successful-ly treated with a PFD alone. They reported that 75% of pa-tients had some degree of ventral brainstem compression,with 55% having syringohydromyelia. Four of the patientswith severe ventral compression underwent preoperativehalo-ring traction in an attempt to reduce the compression;in 3 of these patients a subsequent dorsal CCJ fusion wasperformed after PFD, whereas 1 patient had a transoraldecompression and then fusion. One of the 3 patientsreceiving a PFD and fusion had residual compression anddeclined neurologically, however, necessitating a secondoperation and a ventral decompression.

Such a sequela of clinical worsening because of ventralcompression after PFD for CM-I is not unknown;3 indeedwe have reported it at our institution.6 It is thus imperativeto be able to quantify the amount of ventral compression at the time of initial evaluation so as to provide the appro-priate initial operative approach, either ventral or dorsal de-compression, as well as during long-term follow-up. Thiscan be most effectively performed through comprehensive

preoperative neuroimaging studies, including dynamic MRimaging of the patient with the spine in cervical flexion andextension. Our long experience with CCJ abnormalities hastaught us that, when presented with such combined prob-lems of ventral and dorsal compression, the safest and mosteffective procedure of choice is to address the vector caus-ing maximal cervicomedullary compression.31

The patients presenting with musculoligamentous in-stability (Group IV) were a relatively small component ofthe overall patient population studied (14%). However, thesource of such instability is important to elucidate so that acourse of treatment may be fashioned to address the un-derlying problem most correctly. Although musculoliga-mentous laxity at the CCJ can be found in patients withcongenital syndromes (that is, Ehlers–Danlos and Downsyndromes), often muscular weakness is an acquired find-ing and can possibly be attributed to one of several states:1) repeated muscle retraction with disturbed neurovascularsupply to muscle; 2) fibrotic changes occurring in muscledue to repeated operation; 3) inadequate closure at surgery;and 4) possible loss of innervation of cervical musculaturesecondary to high cervical cord syrinx. Fibrosis due to re-peated operation or poor muscular reapproximation may beaddressed at the time of surgery by lysis of adhesions orexcellent muscular–fascial closure, respectively, whereas a high cervical syrinx causing denervation atrophy of cer-vical musculature may ultimately require decompression of the syrinx before musculoligamentous stability returns.These possible causes should be entertained when a patientpresents with recurrent symptomatology of brainstem com-pression despite previous posterior decompression surgery,so that the best treatment may be provided.

Conclusions

In addition to PFD/FMD, dorsal CCJ fusions are re-quired in those patients with CM-I and/or syringohydromy-elia who have concomitant CCJ abnormalities that causecompression of the brainstem and upper cervical spinalcord. Such bone abnormalities causing ventral compressioncan be further categorized into those that are reducible oncervical extension (Group I) and those that require an addi-tional ventral surgical decompression (Group II). A definitegroup (CM-I and/or syringohydromyelia) without boneabnormalities exists, requiring dorsal CCJ fusion to main-tain relative decompression in cervical extension (GroupsIII and IV). This may be due to muscle weakness secondaryto a high syrinx, ligamentous laxity, or from repeated pos-terior procedures. In any of these cases, it is imperative thatthe treating physician obtains a comprehensive preopera-tive imaging survey of the CCJ, including dynamic MRcervical extension and flexion images, to be able to formu-late the best treatment plan.

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Manuscript submitted September 27, 2007.Accepted March 4, 2008.Address correspondence to: Arnold H. Menezes, M.D., Depart-

ment of Neurosurgery, University of Iowa Hospitals and Clinics,200 West Hawkins Drive, Iowa City, Iowa 52242. email: [email protected].



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Craniocervical Junction Fusions in Patients With Hindbrain IOWA 08