Craniocervical junction fusions in patients with hindbrain herniation and syringohydromyelia

Chiari malformation: are children little adults?

OBJECTIVES

To discuss the controversies, variability of opinion and approach, and special considerations in pediatric Chiari malformation.

METHODS

PubMed-based literature review with focused discussion on clinically relevant pediatric issues.

RESULTS

Compared to adults, children with Chiari more often present with congenital anomalies, scoliosis, and deficits in oropharyngeal control. Those with a syrinx present more with scoliosis than with deficits in sensation or pain. Surgical intervention has varied widely in its level of invasiveness though there has been a trend towards less invasive procedures with bony decompression only, especially in children where their dura may be more flexible and minimal procedures may lead to fewer complications and faster recovery.

CONCLUSIONS

Pediatric Chiari management must consider the effect of development, increased activity, and a longer life course on the decision to surgically treat. However, little is known about predicting the natural history of Chiari in the young. There is also difference in opinion regarding activity restriction since the number of asymptomatic children with Chiari is not known. The long-term effectiveness of less invasive procedures remains to be determined.

Morphometry of the outlet of the foramen magnum in crania with atlantooccipital fusion

Object

Assimilation of the atlas to the occiput may result in symptoms that are often compressive in nature around the outlet of the foramen magnum. The aim of the present study was to elucidate the morphological features of the bone through this foramen.

Methods

Thirteen adult skulls with atlantooccipital fusion underwent morphometrical analysis of the outlet of the foramen magnum.

Results

All specimens but one were found to have a decreased area of the outlet of the foramen magnum. In those 12 specimens, a decrease of 15%–35% was seen. Fusions of the atlas that were based primarily along the anterior rim of the foramen magnum resulted in more obstruction of its outlet. In general, the horizontal diameters of the outlet of these foramina were more decreased from the normal range.

Conclusions

These findings demonstrate that in the majority of cases, assimilation of the atlas to the occiput results in a compromised outlet of the foramen magnum.

Osteopetrosis with Chiari I malformation: presentation and surgical management

Osteopetrosis is a heterogeneous group of rare, inherited disorders of the skeleton that results in neurological manifestations due to restriction of growth of cranial foramina and calvarial thickening. A 25-year-old woman with a history of autosomal dominant osteopetrosis presented to the authors' institution with headache worsened by exertion and radiating from the occipital region forward with episodes of choking/coughing when eating and a loss of gag reflex on physical examination. On MR imaging, she was found to have severe posterior fossa calvarial thickening resulting in a small posterior fossa and tonsillar ectopia of 9 mm and compression and deformation of the brainstem. She underwent posterior fossa craniectomy, foramen magnum decompression, and partial C-1 laminectomy with external durotomy. The patient did well postoperatively with resolution of symptoms. This case describes a new neurological manifestation of autosomal dominant osteopetrosis. To the authors' knowledge, this report represents the first described case of extreme posterior fossa calvarial thickening from autosomal dominant osteopetrosis with associated Chiari I malformation (CM-I) requiring posterior fossa decompression and extradural decompression. Given previously published MR imaging data that demonstrate the association of osteopetrosis and CM may be more common than in this case alone, the authors discuss the need for further investigation of the incidence of CM-I in patients with autosomal dominant osteopetrosis. Additionally, they review osteopetrosis and other diagnoses of calvarial hyperostosis presenting as CM-I.

Correlation of Functional Outcome and Natural History With Clinicoradiological Factors in Surgically Managed Pediatric Chiari I Malformation

BACKGROUND:

Chiari I malformation occurs because of an underdeveloped posterior fossa with reduced volume that cannot accommodate the normally developed hindbrain.

OBJECTIVE:

To study the clinical presentation and surgical outcome of pediatric Chiari I malformation and to correlate outcome with demographic and clinical factors and radiological changes in the syrinx, spinal cord, and preoperative intracranial, posterior fossa, and foramen magnum dimensions.

METHODS:

This retrospective study spanning 9 years included 20 symptomatic patients who underwent foramen magnum decompression, shrinkage of tonsils, and duraplasty. Improvement at follow-up was assessed with a modified Asgari scoring system. Mean differences in the dimensions of the syrinx and cord, foramen magnum morphometry, and intracranial and posterior fossa for 2 groups (with or without improvement) were analyzed with the independent-sample Student t test. Correlation of outcome in relation to change in radiological factors and influence of variables such as age, type and duration of symptoms, and presence of syrinx were evaluated with the Pearson χ2 test.

RESULTS:

Sixty percent of patients showed functional improvement at follow-up. Of various demographic and radiological factors assessed, there was significant difference in mean values of change in cord diameter for the entire cohort (P = .05) and for the subgroup with preoperative syringes (P = .03). There was no correlation between change in any of these factors and functional improvement (χ2 range, 0-4.673; P > .05).

CONCLUSION:

More than half the pediatric patients with Chiari I malformation improve after surgery. The age at presentation, duration and type of symptoms, cranial and foramen magnum morphometry, and syrinx-related changes have no bearing on outcome at short-term follow-up. The spinal cord diameter differs significantly in patients with and without functional improvement.

Chiari type I malformation in children

The diagnosis of Chiari type I malformation (CIM) is more and more frequent in clinical practice due to the wide diffusion of magnetic resonance imaging. In many cases, such a diagnosis is made incidentally in asymptomatic patients, as including children investigated for different reasons such as mental development delay or sequelae of brain injury. The large number of affected patients, the presence of asymptomatic subjects, the uncertainties surrounding the pathogenesis of the malformation, and the different options for its surgical treatment make the management of CIM particularly controversial.This paper reports on the state of the art and the recent achievements about CIM aiming at providing further information especially on the pathogenesis, the natural history, and the management of the malformation, which are the most controversial aspects. A historial review introduces and explains the current classification. Furthermore, the main clinical, radiological, and neurophysiological findings of CIM are described to complete the picture of this heterogeneous and complex disease.

Pathophysiology of persistent syringomyelia after decompressive craniocervical surgery. Clinical article

OBJECT

Craniocervical decompression for Chiari malformation Type I (CM-I) and syringomyelia has been reported to fail in 10%-40% of patients. The present prospective clinical study was designed to test the hypothesis that in cases in which syringomyelia persists after surgery, craniocervical decompression relieves neither the physiological block at the foramen magnum nor the mechanism of syringomyelia progression.

METHODS

The authors prospectively evaluated and treated 16 patients with CM-I who had persistent syringomyelia despite previous craniocervical decompression. Testing before surgery included the following: 1) clinical examination; 2) evaluation of the anatomy using T1-weighted MR imaging; 3) assessment of the syrinx and CSF velocity and flow using cine phase-contrast MR imaging; and 4) appraisal of the lumbar and cervical subarachnoid pressures at rest, during a Valsalva maneuver, during jugular compression, and following the removal of CSF (CSF compliance measurement). During surgery, ultrasonography was performed to observe the motion of the cerebellar tonsils and syrinx walls; pressure measurements were obtained from the intracranial and lumbar intrathecal spaces. The surgical procedure involved enlarging the previous craniectomy and performing an expansile duraplasty with autologous pericranium. Three to 6 months after surgery, clinical examination, MR imaging, and CSF pressure recordings were repeated. Clinical examination and MR imaging studies were then repeated annually.

RESULTS

Before reexploration, patients had a decreased size of the CSF pathways and a partial blockage in CSF transmission at the foramen magnum. Cervical subarachnoid pressure and pulse pressure were abnormally elevated. During surgery, ultrasonographic imaging demonstrated active pulsation of the cerebellar tonsils, with the tonsils descending during cardiac systole and concomitant narrowing of the upper pole of the syrinx. Three months after reoperation, patency of the CSF pathways was restored and pressure transmission was improved. The flow of syrinx fluid and the diameter of the syrinx decreased after surgery in 15 of 16 patients.

CONCLUSIONS

Persistent blockage of the CSF pathways at the foramen magnum resulted in increased pulsation of the cerebellar tonsils, which acted on a partially enclosed cervical subarachnoid space to create elevated cervical CSF pressure waves, which in turn affected the external surface of the spinal cord to force CSF into the spinal cord through the Virchow-Robin spaces and to propel the syrinx fluid caudally, leading to syrinx progression. A surgical procedure that reestablished the CSF pathways at the foramen magnum reversed this pathophysiological mechanism and resolved syringomyelia. Elucidating the pathophysiology of persistent syringomyelia has implications for its primary and secondary treatment.

Direct posterior reduction and fixation for the treatment of basilar invagination with atlantoaxial dislocation

OBJECTIVE

To report the surgical technique and clinical results for the treatment of basilar invagination (BI) with atlantoaxial dislocation (AAD) by direct posterior reduction and fixation using intraoperative distraction between the occiput and C2 pedicle screws.

METHODS

From May 2004 to June 2008, 29 patients who had BI with AAD were surgically treated in our department. Pre- and postoperative dynamic cervical x-rays, computed tomographic scans, and 3-dimensional reconstruction views were performed to assess the degree of dislocation. Ventral compression of the cervicomedullary junction was evaluated by magnetic resonance imaging. For all patients, reduction of the AAD was conducted by intraoperative distraction between the occiput and C2 pedicle screws using a direct posterior approach.

RESULTS

Follow-up ranged from 6 to 50 months in 28 patients. Clinical symptoms improved in 26 patients (92.9%) and were stable in 2 patients (7.1%) without postoperative deterioration. Radiologically, complete or more than 50% reduction was achieved in 27 of 28 patients (96.4%). In 1 patient, the reduction was less than 50% because the direction of the facets on 1 side of the C1-C2 joint was vertically oriented, instead of horizontal. Overall, good decompression and bone fusion were shown on postoperative magnetic resonance imaging, computed tomography, or x-ray scans for all patients. There was 1 death in the series because of basilar artery thrombosis 1 week after the operation.

CONCLUSION

The direct posterior distraction technique between occiput and C2 pedicle screws is an effective, simple, fast, and safe method for the treatment of BI with AAD. Transoral odontoidectomy and cervical traction for the treatment of BI with AAD should be reconsidered.

Nuances of Occipitocervical Fixation

OBJECTIVE

To describe the indications and techniques for occipitocervical (OC) fixation.

METHODS

The operative nuances of current OC fixation techniques are described. A surgical technique video is included.

RESULTS

Pertinent literature is reviewed regarding OC fixation techniques.

CONCLUSION

OC fixation systems have evolved from wire and cable techniques to plates, rods, and screws. Screw-rod constructs are easy to implant and biomechanically more rigid than wire techniques.

Morphometric analysis of foramen magnum dimensions and intracranial volume in pediatric Chiari I malformation

PURPOSE

Foramen magnum dimensions and intracranial volume in Chiari I malformations in children were studied, and the statistical relationship between patient demographics, radiological features and foramen magnum morphometry was investigated.

METHODS

Linear measurements were used to calculate the intracranial volume using preoperative magnetic resonance images and computed tomogram images. The area of the foramen magnum was obtained independently using computer imaging software and a regression formula. The result of 21 pediatric patients was compared with a matched control group.

RESULTS

The area of the foramen magnum was within the range of the expected value deduced using a formula based on the intracranial volume. There was no statistical difference in the area and linear dimensions of the foramen magnum in the study and control groups. Six patients (28%) had a foramen magnum in close proximity to a spherical shape.

CONCLUSION

The authors provide a simple, accurate and reproducible method of estimating foramen magnum area in the pediatric Chiari I group. The irregular shape of the foramen magnum is accentuated by developmental bony and soft tissue anomalies at the cranio-vertebral junction in Chiari malformation. Consequently, an individualized cross-sectional assessment of the foramen magnum in relation to the hindbrain tissue in the same plane is required to study the initiation and propagation of the Chiari I symptomatology.

Visualização radiológica intraoperatória da região occipitocervical e coluna cervical superior: nota técnica

Relatamos nota técnica para melhor visualização radiológica intraoperatória em cirurgias da região occipitocervical e coluna cervical superior.