Cranial Settling Research Articles

Advances, Challenges, and Future Directions in the Management of Craniovertebral Junction Pathologies

In this third article in a 3-article series on the craniocervical junction, we define the terms "basilar impression," "cranial settling," "basilar invagination," and "platybasia," noting that these terms are often used interchangeably but represent distinct entities. We then provide examples that represent these pathologies and treatment paradigms. Finally, we discuss the challenges and future direction in the craniovertebral junction surgery space.

Gorham-Stout disease of skull base leading to cranial settling and rhinorrhea: a case-based review.

Gorham-Stout disease (GSD) is a rare progressive osteolytic disorder, theoretically caused by lymphovascular endothelial proliferation. Spinal involvement carries a dismal prognosis because of neurological consequences. Lesions of the skull base are extremely rare and entail even more devastating prognosis due to cervical instability and cerebrospinal fluid (CSF) leakage. Due to scarcity of this condition, the aim of this study was to give an overview of skull base GSD and review the cases with such condition reported in the literature. In this case-based review, different aspects of skull base GSD are discussed, and a sample clinical case of GSD leading to cranial settling and rhinorrhea is presented. The characteristics, symptoms, and managements of all English-language PubMed-reported cases were reviewed, and different features of presentation and methods of treatments were analyzed. Based on the literature review, most of the cases encountered serious problems in the course of the disease. Meningitis/CSF leakage was detected in 12 of 26 collected cases, followed by hearing loss/tinnitus/otitis media in 10 cases, headache in 8, and neck pain/stiffness in 8 patients. Despite a variety of treatments, improvement was only observed in 8 of 26 collected cases. The reminders showed either stable condition or worsening and death. All cases of GSD of the skull base should be evaluated for rhinorrhea/otorrhea and cranial settling, both of them being among the most life-threatening conditions. Since definite treatment, in order to stop disease progression, is sometimes impossible, symptomatic and supportive treatment should be started as possible.

Odontoid Resorption After Posterior Occipitocervical Fusion in Rheumatoid Basilar Invagination

Background Context: Inflammatory arthritis of the cervical spine is common and begins early after the onset of rheumatoid arthritis. Atlantoaxial instability is the most common pattern followed by cranial settling or basilar invagination, with subaxial subluxation being least common. Vertical migration of the odontoid (basilar invagination) poses an increased risk of sudden death from compression of the brain stem. A combination of transoral decompression and posterior occipitocervical fusion has been described, although a single posterior approach stabilization may suffice and avoid the associated comorbidities with an anterior/posterior surgery in a high-risk rheumatoid patient. Purpose: To report a case of odontoid resorption and cervicomedullary angle improvement after occipitocervical fusion. Study Design: A retrospective case report. Methods: Radiographic analysis. Results: After posterior occipitocervical fusion alone for basilar invagination there was a reduction of cervicomedullary angle to 127 degrees at 3 years follow up. This was improved from an initial 115 degrees through odontoid remodeling. Conclusions: Basilar invagination treated with posterior alone occipitocervical stabilization may suffice in providing stability and long term decompression of the cervicomedullary junction through resorption and remodeling of the odontoid. This case study supports the viability of avoiding a transoral resection for an irreducible severely migrated odontoid.

Cervical spine manifestations of rheumatoid arthritis: a review.

Rheumatoid arthritis (RA) is a progressive autoimmune inflammatory disease affecting 1% of the population with three times as many women as men. As many as 86% of patients suffering from RA have cervical spine involvement. Synovial inflammation in the cervical spine causes instability and injuries including atlantoaxial subluxation, retroodontoid pannus formation, cranial settling, and subaxial subluxation. While many patients with cervical spine involvement are asymptomatic, symptomatic patients often present with nonspecific symptoms resulting from inflammation and additional secondary symptoms that are due to compression of the brainstem, cranial nerves, vertebral artery, and spinal cord. Radiographs are the imaging modality used most often, while MRI and CT are used for assessment of neural element involvement and surgical planning. Multiple classification systems exist. Early diagnosis and treatment of cervical spine involvement is critical. Surgical management is indicated when patients experience symptoms from cervical involvement that result in biomechanical instability and, or a neurological deficit. Atlantoaxial instability managed with atlantoaxial fusion, retroodontoid pannus with neural element compression is managed with posterior decompression and atlantoaxial fusion or occipitocervical fusion. Cranial settling is managed can be managed with anterior decompression and posterior fusion or with dorsal only approaches. Subaxial subluxation is managed with circumferential fusion or posterior only decompression and fusion. Patients with atlantoaxial instability have better functional and neurologic outcomes. RA patients have higher complication rates and more frequent need for revision surgery than the general population of spine surgery patients.

Restabilization of the Occipitocervical Junction After a Complete Unilateral Condylectomy: A Biomechanical Comparison of Unilateral and Bilateral Fixation Techniques.

Occipitocervical instability may result from transcondylar resection of the occipital condyle. Initially, patients may be able to maintain a neutral alignment but severe occipitoatlantal subluxation may subsequently occur, with cranial settling, spinal cord kinking, and neurological injury. To evaluate the ability of posterior fixation constructs to prevent progression to severe deformity after radical unilateral condylectomy. Eight human cadaveric specimens (Oc-C2) underwent biomechanical testing to compare stiffness under physiological loads (1.5 N m). A complete unilateral condylectomy was performed to destabilize one Oc-C1 joint, and the contralateral joint was left intact. Unilateral Oc-C1 or Oc-C2 constructs on the resected side and bilateral Oc-C1 or Oc-C2 constructs were tested. The bilateral Oc-C2 construct provided the greatest stiffness, but the difference was only statistically significant in certain planes of motion. The unilateral constructs had similar stiffness in lateral bending, but the unilateral Oc-C1 construct was less stiff in axial rotation and flexion-extension than the unilateral Oc-C2 construct. The bilateral Oc-C2 construct was stiffer than the unilateral Oc-C2 construct in axial rotation and lateral bending, but there was no difference between these constructs in flexion-extension. Patients who undergo a complete unilateral condylectomy require close surveillance for occipitocervical instability. A bilateral Oc-C2 construct provides suitable biomechanical strength, which is superior to other constructs. A unilateral construct decreases abnormal motion but lacks the stiffness of a bilateral construct. However, given that most patients undergo a partial condylectomy and only a small proportion of patients develop instability, there may be scenarios in which a unilateral construct may be appropriate, such as for temporary internal stabilization.

Ehlers-Danlos syndrome-associated craniocervical instability with cervicomedullary syndrome: Comparing outcome of craniocervical fusion with occipital bone versus occipital condyle fixation.

Introduction:Ehlers–Danlos syndrome (EDS) predisposes to craniocervical instability (CCI) with resulting cranial settling and cervicomedullary syndrome due to ligamentous laxity. This study investigates possible differences in radiographic outcomes and operative complication rate between two surgical techniques in patients with EDS and CCI undergoing craniocervical fusion (CCF): occipital bone (OB) versus occipital condyle (OC) fixation.Methods:A retrospective search of the institutional operative database between January 07, 2017, and December 31, 2019, was conducted to identify EDS patients who underwent CCF with either OB (Group OB) or OC (Group OC) fixation. For each patient, pre- and post-operative radiographic measurements and operative complications were extracted and compared between groups (OB vs. OC): pB-C2, clivoaxial angle (CXA), tonsillar descent, C2C7 sagittal Cobb angle, C2 long axis, and operative complications.Results:Of a total of 26 patients, 13 underwent OV and 13 underwent OC fixation. Eighty-five percent of the patients underwent OC underwent fusion from occiput to C2, while the remaining 15% fusion from occiput to C3. Radiographic outcome in the OC versus OB group was preoperative measurements were similar between OC and OB group: pB-C2 8.8 mm (1.5, 6–11) versus 8.3 mm (1.7, 4–9.6), P = 0.43; CXA 128.2° (5.4, 122–136) versus 131.9° (6.8,122–141), P = 0.41; tonsillar descent 6.2 mm (4.8, 0–15) versus 2.9 mm (3.4, 0–8), P = 0.05; C2 long axis 75.2° (6.7, 58–85) versus 67.2° (21.4, 1–80), P = 0.21; postoperative change of CXA + 14.4° (8.8, 0–30) versus 16.2° (12.4, −4–38), P = 0.43; change of pB-C2 − 2.6 mm (1.8, −-5.3 to 0) versus − 1.2 mm (4, −4.6–8), P = 0.26; and postoperative C2C7 sagittal Cobb angle − 2.6° (19.5, −43–39) versus − 2.6° (11.4, −21–12). Operative complications were seen in 1 out of 13 patients (8%) versus 2 out of 13 patients (16%), P = 1.Conclusions:In EDS, patients with CCI undergoing CCF radiographic and clinical outcome were similar between those with OC versus OB fixation. Both techniques resulted in sufficient correction of pB-C2 and CXA measurements with a low complication rate.

Chiari I Malformation and Basilar Invagination in Fibrous Dysplasia: Prevalence, Mechanisms, and Clinical Implications

Fibrous dysplasia (FD) is a mosaic disorder of benign fibro-osseous lesions, which may be associated with extraskeletal features as part of McCune-Albright syndrome (MAS). Cranial base abnormalities, including Chiari I malformation (CM1), in which the cerebellum extends below the foramen magnum, and secondary basilar invagination (BI), in which the odontoid prolapses into the posterior cranial fossa, are potentially serious complications of metabolic bone disorders. The purpose of this study was to determine the prevalence, natural history, and risk factors for CM1 and BI in patients with FD/MAS, and to determine mechanisms of cranial base deformities. Clinical and radiographic data from subjects in an FD/MAS natural history study were evaluated and compared to normal controls. In 158 patients with craniofacial FD, 10 (6.3%) cases of CM1 and 12 (7.6%) cases of BI were diagnosed. No cranial base abnormalities were identified in 10 control subjects. Craniomorphometric and volumetric analyses identified cranial constriction and cranial settling as the primary mechanisms of cranial base abnormalities, whereas intracranial hypertension was a contributing factor in a minority of subjects. Longitudinal analyses found progression of odontoid position with age, but no progression of tonsillar position. No endocrinopathies were associated with CM1. MAS endocrinopathies associated with BI included hyperthyroidism (odds ratio [OR] 12.0; 95% confidence interval [CI], 2.9 to 55.6; p < 0.01), precocious puberty (OR 5.6; 95% CI, 1.2 to 26.0; p < 0.05), and hypophosphatemia (OR 7.7; 95% CI, 1.9 to 27.0; p < 0.01). Scoliosis was associated with both CM1 (OR 4.8; 95% CI, 1.1 to 22.8; p < 0.05) and BI (OR = infinity; 95% CI, 4.7 to infinity; p < 0.01). This study successfully characterized cranial base abnormalities in FD/MAS and the pathophysiological connection between them. These findings support routine screening for cranial base abnormalities in patients with craniofacial FD, as well as aggressive management of contributory risk factors. © 2018 American Society for Bone and Mineral Research.

Cervical spine instability in the course of rheumatoid arthritis - imaging methods.

Cervical spine is affected in more than a half of patients with rheumatoid arthritis (RA). Depending on the degree of damage to the individual joints and ligaments RA-related cervical spine instability takes the form of atlanto-axial subluxation, subaxial subluxation or cranial settling. In the advanced cases spinal stenosis can occur as well as spinal cord injuries with typical neurological symptoms. The identification of patients with cervical spine instability before the occurrence of neurological complications still constitutes a diagnostic challenge.The article presents the methods of cervical spine imaging with the use of plain radiographs, magnetic resonance imaging (MRI) and computed tomography (CT). We discuss the advantages and disadvantages associated with each method and the possibility of its application in the diagnosis of cervical spine instability in RA. The knowledge of the above mentioned issues is indispensable to select an appropriate time for surgical intervention.

How I do it? Cranial setup for cranial settling.

Expanded endonasal endoscopic techniques allow us to treat several pathologies related to the odontoid process and craniocervical junction. Cases such as giant basilar invagination represent a surgical challenge. The authors provide technical nuances and describe how to complete an endoscopic endonasal odontoidectomy and release the craniocervical junction with the aim of restoring a correct sagittal balance in cases with giant basilar invagination. The study of cadaveric specimens adds clarifying dissections. Endonasal endoscopic odontoidectomy and craniocervical junction joint release allow the treatment of irreducible basilar invagination and restoration of better sagittal balance before posterior cervical occipitocervical fusion.

Occipitocervical Instability After Far-Lateral Transcondylar Surgery: A Biomechanical Analysis.

After a far-lateral transcondylar approach, patients may maintain neutral alignment in the immediate postoperative period, but severe occipitoatlantal subluxation may occur gradually with cranial settling and possible neurological injury. Previous research is based on assumptions regarding the extent of condylar resection and the change in biomechanics that produces instability. To quantify the extent of bone removal during a far-lateral transcondylar approach, determine the changes in range of motion (ROM) and stiffness that occur after condylar resection, and identify the threshold of condylar resection that predicts alterations in occipitocervical biomechanics. Nine human cadaveric specimens were biomechanically tested before and after far-lateral transcondylar resection extending into the hypoglossal canal (HC). The extent of condylar resection was quantified using volumetric comparison between pre- and postresection computed tomography scans. ROM and stiffness testing were performed in intact and resected states. The extent of resection that produced alterations in occipitocervical biomechanics was assessed with sensitivity analysis. Bone removal during condylar resection into the HC was 15.4%-63.7% (mean 35.7%). Sensitivity analysis demonstrated that changes in biomechanics may occur when just 29% of the occipital condyle was resected (area under the curve 0.80-1.00). Changes in occipitocervical biomechanics may be observed if one-third of the occipital condyle is resected. During surgery, the HC may not be a reliable landmark to guide the extent of resection. Patients who undergo condylar resections extending into or beyond the HC require close surveillance for occipitocervical instability.

Single-Stage Posterior Decompression and Occipitocervical Fusion Using a Screw-Rod-Plate System for Basilar Invagination with Anterior Spinal Cord Compression and Craniocervical Instability

Purpose: To review our experience with surgical management of basilar invagination causing foramen magnum compression, focusing on selection of the surgical approach. Methods: Twelve consecutive patients underwent posterior foramen magnum decompression with occipitocervical fixation and fusion for treatment of basilar invagination causing brain stem compression and instability. Gentle traction and reduction during positioning of the patients also were performed. Ventral decompression (odontoid resection) was performed in none of the patients. Pre- and postoperative neurologic status was graded according to JOA and Nurick scales. Results: All patients had anterior spinal cord compression due to cranial settling of the cervical spinal column as well as instability at the craniocervical junction. The average follow-up period was 31 months (range, 24–42 months). All patients’ JOA and Nurick scores improved after surgery, but postoperative neurologic improvement and odontoid reduction were better in patients with atlas assimilation compared with patients with other pathologies. Conclusion: Odontoid reduction using an occipitocervical fixation system and decompression of the foramen magnum through a single-stage posterior approach is an effective treatment for basilar invagination, particularly in patients with atlas assimilation. Since odontoid reduction and foramen magnum decompression can be achieved through a single-stage posterior approach in most patients, odontoid resection should remain as a secondary procedure when these decompression efforts are insufficient.

Transoral Decompression and Posterior Stabilization in Fixed Anterior Pathology of the Craniocervical Junction

Introduction Management of the anterior compressive pathology of the craniovertebral junction (CVJ) is complex and demanding. We review our experience with the transoral surgical decompression of fixed anterior CVJ lesions, with particular attention to the decision making and to the indication for a consecutive stabilization. Patients and Methods Retrospective study (2000–2013) of 47 consecutive patients (14 males and 13 females). Mean age was 59.2 years (range, 32–82 years). Encountered lesions were rheumatoid arthritis with pannus (29, 9 of which with associated cranial settling), ankylosing spondylitis (four), tumors (seven: six extradural chordomas/chondrosarcomas and one metastasis), odontoid fractures with hypoporosis, and rotational instability (seven). Patients presented with a variety of following symptoms: high cervical pain (82%), varying degrees of quadriparesis (64%), lower cranial nerve deficits (23%), and central cord syndrome with neurogenic bladder (14%). All patients underwent one-stage transoral decompression and consecutive posterior atlantoaxial or occipitocervical stabilization. Clinical evaluation was made pre- and postoperatively using the Ranawat score. Follow-up period ranged between 6 and 48 months (average, 22 months). Results According to the Ranawat score, we had 21 grade I patients, in 20 of which pain was eradicated, 10 grade II patients, 8 of which passed to grade I, 11 grade IIIA patients, of which 6 passed to grade I and 5 to grade II, and 5 grade IIIB patients of which 4 passed to grade IIIA. In seven patients, the transarticular screws crossed the anterior cortex of the atlas, without clinical manifestations. In five patients, complete reduction of the C1–C2 rotation was not possible, because of the chronic nature of the defect. Surgical morbidity occurred in five cases (three dural tears and two occipital wound infections). There were two perioperative deaths ([a] dural rupture, pneumoencephaly, meningitis, and massive pulmonary embolism, [b] pulmonary infection, and cardiorespiratory arrest). Conclusion Successful and stable decompression of the CVJ requires extensive preoperative evaluation, appropriate tailoring, and adequate expertise. The transarticular C1–C2 fixation is a safe and effective stabilization method when the atlanto-occipital joints remain competent. Complications appear mostly in patients with rotational deformity of the C1–C2 complex. Patients with clinical and radiological findings of myelopathy improve less even if surgery is successful.

Posterior-Only Approach for Reduction of Occipitocervical Instability with Vertical Migration of the Dens

Introduction Occipitocervical instability with vertical odontoid migration is a rare but potentially debilitating anomaly. Anterior decompression followed by posterior stabilization is commonly used to address the pathology, but the former is associated with significant morbidity. More recently, posterior-only techniques have been described to obtain reduction and stabilization for nonfused cases of cranial settling. Patients and Methods Retrospective analysis of seven cases of patients (four males, three females, age range 34–73 years) who suffered from occipitocervical instability with reducible vertical dislocation of the odontoid in the setting of various underlying pathology. Six patients were myelopathic preoperatively. The neurological status was classified according to the Nurick scale. Pain was assessed according to the Visual Analog Scale. Radiological measurements included preoperative and postoperative evaluation of the position of the tip of the odontoid process in relation to Chamberlain, McGregor, McRae, and Wackenheim lines, and measurement of the Ranawat line, the clival angle, and the Klaus height index. Follow-up ranged from 8 to 42 months. Results Five patients improved neurologically, and one remained stable. Pain improved significantly in these patients, and was completely eliminated in three of them. Obvious reduction of the deformity was demonstrated by the postoperative radiological craniometric measurements. One patient did not improve neurologically. Postoperative imaging revealed a very small reduction with practically unchanged ventral compression of the cord. He underwent transoral decompression at a second stage. No patient suffered from severe complications. No screw pullout, loosening, or fracture of implant has been observed so far. Conclusion Modern screw–rod systems enable intraoperative correction of nonfused deformity and indirect decompression of the cervicomedullary junction obviating the need for ventral decompression or preoperative traction. Patient selection is critical to ensure successful application of the reduction maneuvers.

Rheumatoid Arthritis and the Cervical Spine: A Review on the Role of Surgery.

Rheumatoid arthritis (RA) is a chronic systemic inflammatory disease affecting a significant percentage of the population. The cervical spine is often affected in this disease and can present in the form of atlantoaxial instability (AAI), cranial settling (CS), or subaxial subluxation (SAS). Patients may present with symptoms and disability secondary to these entities but may also be neurologically intact. Cervical spine involvement in RA can pose a challenge to the clinician and the appropriate role of surgical intervention is controversial. The aim of this paper is to describe the pathology, pathophysiology, clinical manifestations, and diagnostic evaluation of rheumatoid arthritis in the cervical spine in order to provide a better understanding of the indications and options for surgery. Both the medical and surgical treatment options for RA have improved, so has the prognosis of the cervical spine disease. With the advent of disease modifying antirheumatic drugs (DMARDs), fewer patients are presenting with cervical spine manifestations of RA; however, those that do, now have improved surgical techniques available to them. We hope that, by reading this paper, the clinician is able to better evaluate patients with RA in the cervical spine and determine in which patients surgery is indicated.

Advantages and limitations of endoscopic endonasal odontoidectomy. A series of nine cases

IntroductionTransoral odontoidectomy is the treatment of choice in cases of anterior bulbo-medullary compression. The development of endoscopic procedures has made it possible to perform odontoidectomy via a minimally invasive endoscopic endonasal approach. We discuss the feasibility, advantages, and limitations of this surgical approach. Materials and methodsWe report a two-center retrospective series of patients who underwent endoscopic endonasal odontoidectomy between September 2011 and February 2013. Preoperative characteristics, intraoperative data, clinical course, and postoperative complications were studied. The patients were followed for a minimum of 6 months. Cervico-occipital posterior fusion was performed during the same hospital stay in cases of preoperative instability. ResultsNine patients underwent decompressive odontoidectomy, for rheumatoid pannus in five cases and basilar impression in four cases. All had progressive neurological symptoms. Seven patients also underwent posterior fusion. In six patients, the C1 anterior arch was preserved. Decompression was achieved satisfactorily in all nine cases. The patients were able to resume oral feeding the day after the intervention. No patient required tracheostomy. We observed no dural fistulae or infectious complications. One patient died 2 months after the intervention of a pulmonary embolism. All patients improved in terms of their preoperative neurological status. ConclusionThis short series shows the feasibility of the endoscopic endonasal approach for resection of the dens. This approach allows optimal viewing when using angulated instrumentation and seems to result in low morbidity. In some cases, this approach makes it possible to preserve the C1 anterior arch, thus limiting the risk of cranial settling. LevelIV retrospective study.

Commentary on: "To the Occiput or Not? C1-C2 Ligamentous Laxity in Children with Down Syndrome".

Siemionow and Chou review the surgical management of atlantoaxial instability in the context of Down syndrome, using two interesting illustrative cases with different craniocervical abnormalities (atlantoaxial rotatory subluxation and os odontoideum). Both patients present with significant craniocervical spinal cord compression, and in this context, they highlight the specific case nuances that prompt occiptocervical fusion in one case and isolated atlantoaxial fixation in the other. However, it is important to note that while the authors refer to the presence of basilar invagination (and cranial settling) in these cases, a review of the accompanying radiographic images suggests that while significant craniocervical deformity and atlantoaxial instability is present, neither case truly has a diagnosis of basilar invagination nor cranial settling.

Endoscopic transnasal odontoid resection to decompress the bulbo-medullary junction: a reliable anterior minimally invasive technique without posterior fusion

Anterior decompression of the craniovertebral junction is reserved to patients with irreducible ventral bulbo-medullary lesions and rapidly deteriorating neurological functions. Classically performed through the transoral approach, the exposure of this region can be now achieved by a minimally invasive endonasal endoscopic approach (EEA). Four patients with irreducible, anterior bulbo-medullary compression due to rheumatoid pannus and basilar invagination were enrolled. The imaged-guided EEA was used to resect the odontoid process, trying to preserve the C1 anterior arch. Neurological improvement and adequate bulbo-medullary decompression were obtained in all patients. In two cases, anterior C1 ring was preserved. These patients did not required a posterior fusion. Compared with the standard transoral technique, the EEA provides the same good exposure but with potentially less complications. The preservation of the anterior C1 arch can contribute to avoid cranial settling and posterior fusion with its related risk of subaxial instability.

Cervicomedullary Compression at the Craniovertebral Junction by Clivus Hyperplasia

The craniovertebral junction (CVJ), which is composed of the distal third of the clivus, the occiput, the atlas, the axis, and the foramen magnum, is complex anatomically and includes important neurovascular structures1,2. Together, these structures enclose the cervicomedullary junction (CMJ) and the lower four cranial nerves. Signs and symptoms of abnormal conditions affecting the CVJ are varied and typically begin insidiously. They may be referable to the brainstem, cervical cord, cerebellum, cervical nerve roots, or lower cranial nerves or the vascular supply to these structures. Anterior compression at the CVJ can occur in many types of abnormalities: malformations (basilar invagination or cranial settling, atlas assimilation, os odontoideum, and atlantoaxial fixed dislocation), tumor, trauma, chronic inflammatory diseases (most frequently, rheumatoid arthritis [RA]), and osteomyelitis3-7. Not uncommonly, congenital ventral compression of the CVJ is discovered on postmortem examination8. We present an unusual case of anterior CVJ compression in a healthy woman due to hyperplasia of the clivus with horizontal segmentation and degeneration of the atlanto-occipital and atlantoaxial joints. The presenting symptoms were suggestive of carpal tunnel syndrome. The patient was informed that the data concerning the case would be submitted for publication, and she provided consent. A forty-two-year-old female school bus driver presented to our neurology clinic with bilateral upper-arm, forearm, and hand numbness and tingling, which she had experienced for two years; the left side was more symptomatic than the right. She had minimally impaired sensation in the thumb and index finger of the left hand. Deep tendon reflexes were intact bilaterally. Physical examination demonstrated positive Phalen and Tinel signs over the carpal tunnel bilaterally. An electrophysiology study revealed mild demyelination in the left distal median nerve and notable demyelination in the right distal median nerve consistent with bilateral carpal tunnel …

A Novel Technique of Odontoidoplasty and C1 Arch Reconstruction: Anatomical and Biomechanical Basis

Transoral odontoidectomy and resection of the anterior C1 arch destabilize the atlantoaxial joint and risk its stability. To preserve stability in such cases we devised and evaluated a proof-of-concept study. The arch and dens were dissected and decompression was performed on cadavers. The dens was replaced with an odontoid screw, and the C1 arch was replaced with a rib-graft substitute using miniplates. We assessed the biomechanical strength of the C1 ring and 3D occipitoatlantoaxial flexibility before and after the repair. Five silicon-injected fixed cadaver heads were dissected. The arch of C1 and dens were preserved and reconstructed using odontoid screws and miniplates. Once the feasibility of the technique was established, we biomechanically tested 6 cadaveric occiput-C2 specimens in 3 phases: (1) intact/normal range of motion (ROM), (2) after transection of dens and C1 arch, and (3) with odontoidoplasty using odontoid screws and C1 arch reconstruction. After odontoidectomy and arch removal, angular ROM increased significantly in all directions of loading. Resection increased flexion-extension at the occiput-C1 and at C1-C2 by 21% and 129%, respectively. Reconstruction slightly increased flexion-extension stability (16% and 107%, respectively) relative to normal.With 70 N applied compression, the C1 ring separation was 1145% greater than normal. After reconstruction, the separation was only 89% greater than normal (statistically significant, P = .002). C1 arch reconstruction with or without odontoidoplasty restores only partial angular stability of the atlantoaxial joint but provides restoration of the ability of the C1 lateral masses to resist splaying, often observed as postodontoidectomy cranial settling.

Mechanisms of cerebellar tonsil herniation in patients with Chiari malformations as guide to clinical management.

BackgroundThe pathogenesis of Chiari malformations is incompletely understood. We tested the hypothesis that different etiologies have different mechanisms of cerebellar tonsil herniation (CTH), as revealed by posterior cranial fossa (PCF) morphology.MethodsIn 741 patients with Chiari malformation type I (CM-I) and 11 patients with Chiari malformation type II (CM-II), the size of the occipital enchondrium and volume of the PCF (PCFV) were measured on reconstructed 2D-CT and MR images of the skull. Measurements were compared with those in 80 age- and sex-matched healthy control individuals, and the results were correlated with clinical findings.ResultsSignificant reductions of PCF size and volume were present in 388 patients with classical CM-I, 11 patients with CM-II, and five patients with CM-I and craniosynostosis. Occipital bone size and PCFV were normal in 225 patients with CM-I and occipitoatlantoaxial joint instability, 55 patients with CM-I and tethered cord syndrome (TCS), 30 patients with CM-I and intracranial mass lesions, and 28 patients with CM-I and lumboperitoneal shunts. Ten patients had miscellaneous etiologies. The size and area of the foramen magnum were significantly smaller in patients with classical CM-I and CM-I occurring with craniosynostosis and significantly larger in patients with CM-II and CM-I occurring with TCS.ConclusionsImportant clues concerning the pathogenesis of CTH were provided by morphometric measurements of the PCF. When these assessments were correlated with etiological factors, the following causal mechanisms were suggested: (1) cranial constriction; (2) cranial settling; (3) spinal cord tethering; (4) intracranial hypertension; and (5) intraspinal hypotension.