Posterior Fossa Reconstruction: A Surgical Technique for the Treatment of Chiari I Malformation and Chiari I/Syringomyelia Complex???Preliminary Results and Magnetic Resonance Imaging Quantitative Assessment of Hindbrain Migration

Surgical treatment of Chiari malformation with and without syringomyelia: experience with 177 adult patients

Object

This study aims to show the relationship between clinical outcome in patients who underwent surgical decompression for Chiari malformation (CM) and postoperative imaging studies, with particular emphasis on the subarachnoid cisterns of the posterior fossa.

Methods

One hundred seventy-seven patients with CM, including 97 with syringomyelia, underwent posterior fossa decompressive surgery. Both the dura and arachnoid were opened in 150 of these patients, and 135 underwent reduction of the cerebellar tonsils. The patients' clinical signs and symptoms were evaluated at 2 time points after surgery. Their imaging studies were analyzed specifically for the size of the retrotonsillar and subtonsillar cisterns and the syringomyelic cavities. The authors evaluated the relationship between these imaging findings and clinical parameters.

Results

Clinical improvement correlated strongly with enlargement of the subarachnoid cisterns, and enlargement of the cisterns also correlated with reduction in size of the syrinx cavities. Symptoms related to syringomyelia responded to reduction in size of the syrinx cavities.

Conclusions

Surgical decompression of the posterior fossa should aim to create relatively large subarachnoid cisterns and reduce the size of the syrinx cavity. Reduction of the cerebellar tonsils by surgical means, together with duraplasty, achieves this goal and thereby improves the clinical outcome for patients with CM. An incidental observation of the study is that obesity increases the likelihood of headache in patients with CM.

Long-term results after posterior fossa decompression in syringomyelia with adult Chiari Type I malformation

Object

There is little information about the long-term effectiveness and complications following decompressive surgery for syringomyelia related to Chiari malformation Type I (CM-I).

Methods

Examining long-term clinical and radiological follow-up, the authors studied a mixed retrospective and prospective single-institution cohort of 109 consecutive surgically treated adult patients with syringomyelia and CM-I. All patients underwent a standardized surgical protocol: decompression of the craniocervical junction, arachnoid exploration, and shrinkage of the cerebellar tonsils. Factors predicting outcome were investigated.

Results

The retrospective arm consisted of 41 cases treated between 1990 and 1994, and the prospective arm comprised 68 patients treated between 1994 and 2001. The mean overall age was 45.9 years, and 58.8% of the population was female. The median follow-up period was 12.7 years. The most frequent initial symptoms were pain and sensory and gait disturbances. There was no perioperative death or neurological deterioration. The comprehensive perioperative complication rate was approximately 11%, with 3 cases (2.7%) of CSF leakage. Regression analysis showed that the best combination of clinical and radiological outcome predictors was age and duration of symptoms. Clinical follow-up confirmed surgical result stability with clinical improvement of greater than 90% of the spinal and cranial manifestations over a long-term period. Two patients had radiological recurrences of syringomyelia without clinical signs 85 and 124 months after surgery.

Conclusions

Certain clinical predictors of poor clinical and radiological prognosis were identified—namely, age at time of surgery and symptom duration. The results of the study provide additional long-term data that support the effectiveness and safety of relieving CSF block at the craniocervical junction in CM-I–related syringomyelia.

Posterior fossa volume increase after surgery for Chiari malformation Type I: a quantitative assessment using magnetic resonance imaging and correlations with the treatment response

OBJECT

The aim of this paper was to measure the posterior fossa (PF) volume increase resulting from a given-sized occipital craniectomy in Chiari malformation Type I surgery and to analyze its correlations with the PF size and the treatment response, with the perspective of tailoring the amount of bone removal to the patient-specific PF dimensions.

METHODS

Between January 2005 and June 2006, 11 adult patients with symptomatic Chiari malformation Type I underwent a standardized PF decompression. A prospective evaluation with clinical examination, functional grading, and MR imaging measurement protocols was performed pre- and postoperatively. A method is reported for the measurement of PF volume (PFV) after surgery. The degree of PFV increase was compared with the preoperative size of the PF and with the clinical outcome.

RESULTS

All 11 patients improved postoperatively, with complete and partial recovery in 4 and 7 patients, respectively. No postoperative complication occurred after a mean follow-up period of 45 months. The mean relative increase in PFV accounted for 10% (range 1.5%-19.7%) of the initial PFV; the increase was greater in cases in which the PF was small (r = -0.52, p = 0.09) and the basiocciput was short (r = -0.37, p = 0.2). A statistically significant positive correlation was found between the degree of PFV increase and the treatment response (p = 0.014); complete recovery was observed with a PFV increase of 15% and partial recovery with an increase of 7%.

CONCLUSIONS

The treatment response is significantly influenced by the degree of PFV increase, which is dependent on the size of the PF and the extent of the craniectomy, suggesting that the optimal patient-specific PFV increase could be predicted on the basis of preoperative MR imaging and enhancing the perspective that the craniectomy size could be tailored to the individual PFV.

The effects of posterior fossa decompressive surgery in adult patients with Chiari malformation and sleep apnea

Object

One of the feared consequences of craniovertebral junction diseases is apnea. Although several cases of patients with central apnea have been described, obstructive sleep apnea has been identified as the most frequent manifestation of sleep respiratory disorder. Neuronal involvement may be responsible for both central and obstructive apneas. The objective of this work was to study the effect of posterior fossa decompressive surgery on respiratory parameters during sleep in patients with craniovertebral junction malformations and breathing-related sleep disorders.

Methods

In this study, prospectively enrolled consecutive symptomatic adult patients were monitored with full-night polysomnography before and after surgical decompression of the cranial posterior fossa.

Results

Of the 25 patients who were evaluated, 68% received a diagnosis of sleep apnea. After surgery, the mean number of respiratory events decreased from 180.70 to 69.29 (p = 0.005); the mean number of obstructive events decreased from 107.37 to 60.58 (p = 0.01); and the mean number of central events decreased from 38.45 to 8.05 (p = 0.01). The mean preoperative apnea/hypopnea index decreased from 26.68 to 12.98 (p = 0.06), and the mean central apnea index decreased from 13.81 to 1.68 (p = 0.01).

Conclusions

Decompressive surgery in patients with craniovertebral junction malformations resulted in decreased respiratory events during sleep, lowered sleep fragmentation, and enhanced the sleep apnea index in a significant number of patients. The effect was more pronounced in patients with central apnea.

Collagen matrix duraplasty for posterior fossa surgery: evaluation of surgical technique in 52 adult patients

Object

Complete dural closure is not always possible following posterior fossa surgery, often requiring a graft to secure complete closure. The authors report their experience of using a collagen matrix as an onlay dural graft for repair of a posterior fossa dural defect.

Methods

A retrospective analysis was performed in 52 adult patients who had undergone collagen matrix duraplasty for the posterior fossa. Complications directly related to the dural graft, the presence or absence of hydrocephalus, and the role of closed suction wound drainage in relation to postsurgical pseudomeningoceles were analyzed.

Results

The indication for posterior fossa surgery was tumors in 32 patients, vascular abnormalities in 9 patients, and spontaneous cerebellar hemorrhage in 11 patients. Closed suction wound drainage was used in 23 patients (44.2%). Forty-eight (92.3%) of 52 patients had a dural defect > 2 cm. Nine (81.8%) of 11 patients with hydrocephalus required ventriculoperitoneal shunts. Complications of the surgery included pseudomeningoceles in 2 patients (3.8%; no closed suction wound drainage); superficial wound infections in 1 patient (1.9%; with closed suction wound drainage); and unexplained eosinophilia in 1 patient.

Conclusions

Duraplasty using a collagen matrix is safe and effective in the posterior fossa, and is easy to use and time efficient. Meticulous layered wound closure, the detection and effective control of hydrocephalus, and the use of closed suction wound drainage reduces complications related to collagen matrix duraplasty for the posterior fossa.

Decompression for Chiari type I-malformation (with or without syringomyelia) by extreme lateral foramen magnum opening and expansile duraplasty with arachnoid preservation: comparison with other technical modalities (Literature review)

Posterior craniocervical decompression is the procedure most currently used for treating Chiari I malformation (alone or in association with syringomyelia in the absence of hydrocephalus). We reviewed the various technical modalities reported in the literature. We present a personal series of 44 patients harboring Chiari type I malformation (CM-I) operated with a suboccipital craniectomy and a C1 (or C1/C2) laminectomy, plus an extreme lateral Foramen Magnum opening, a "Y" shaped dural incision with preservation of the arachnoid membrane, and an expansile duraplasty employing autogenous periosteum. Outcomes were analyzed with follow-up ranging from 1 to 10 years (4 years on average). The presented technique was compared with the other surgical modalities reported in the literature. This comparative study shows that this type of craniocervical decompression achieved the best results with minimal complications and side-effects. Syringomyelia associated with CM-I must be treated by craniocervical decompression alone. Shunting no longer appears to be an appropriate method of treatment for syringomyelia.

Basilar invagination: craniocervical instability treated with cervical traction and occipitocervical fixation. Case report

The upward odontoid displacement observed in basilar invagination (BI) is generally associated with a horizontal clivus and craniocervical kyphosis, conditions that exert ventral compression at the spinomedullary junction. Ventral brainstem decompression by reduction or elimination of the odontoid invagination is part of the desired treatment. The authors describe a case of BI in an adult, who was effectively treated with the easy and safe reduction of odontoid invagination via cervical traction. Normalization of kyphosis at the craniovertebral junction and the vertical position of both a previously horizontal clivus and the cerebellar tentorium demonstrated that these conditions were not part of the original malformation but instead were caused by a reducible craniovertebral instability.

The role of limited posterior fossa craniectomy in the surgical treatment of Chiari malformation Type I: experience with a pediatric series

OBJECT

Despite progress in the understanding of the causes and pathophysiology of Chiari malformation Type I (CM-I), definitive surgical treatment remains unresolved. Various techniques have been propounded over the years, but there is no general consensus on the most appropriate surgical management for this condition. The authors report their experience with the surgical treatment of 30 pediatric patients with CM-I.

METHODS

The results obtained in 30 patients who underwent surgery for symptomatic CM-I with a purely extradural procedure were retrospectively reviewed. The patient age at operation ranged from 2 months to 16 years (mean 68 months). In 26 patients the CM-I occurred as an isolated disease, whereas in four a recognized bone anomaly involving the cranial base (achondroplasia) was observed. All patients underwent suboccipital craniectomy, which was accompanied by C-1 laminectomy in 22. In all cases a thick fibrous band at the level of foramen magnum was resected; in 11 children serial incisions of the outer layer of the dura mater were performed as well to expand the posterior fossa volume. The follow-up duration varied from a minimum of 12 months to 12.6 years (mean 4.7 years). The most frequent symptoms and signs were head and/or neck pain (56.7%), followed by vertigo (27.7%), upper-and lower-extremity weakness (20.0%), and ataxia (20.0%). Syringomyelia was noted in 12 patients (40.0%) on magnetic resonance (MR) images. Improvement in or resolution of clinical symptoms and signs was observed in all patients. However, only minimal or no modifications could be found in the position of cerebellar tonsils on postoperative MR images in most patients (only occasional improvement in tonsillar herniation), whereas syringomyelic cavitations reduced in size in half of the cases. Nevertheless, in only two patients was a reoperation necessary.

CONCLUSIONS

In the authors' experience, suboccipital craniectomy and C-I laminectomy (eventually integrated by dural delamination) can represent an effective treatment for symptoms associated with CM-I.

Posterior fossa volume in children with Chiari malformation Type I

OBJECT

The authors sought to establish whether the volume of the posterior fossa in children suffering from Chiari malformation Type I (CM-I) is smaller than normal, as has been suggested previously. They also investigated the role of syringomyelia in posterior fossa development.

METHODS

Both posterior fossa volume (PFV) and intracranial volume (ICV) were measured using segmentation techniques on preoperative magnetic resonance images obtained in 42 children who underwent surgery for CM-I (mean age 127 months, range 36-204 months); 25 (59%) of the patients had syringomyelia. The PFV/ICV ratio was calculated to eliminate differential supratentorial growth. Patients who had deformities potentially interfering with skull growth or who had undergone a shunt insertion procedure prior to craniovertebral decompression were excluded. The results were compared with measurements of 51 healthy children using one-way analysis of variance. In patients with CM-I only, the mean PFV and PFV/ICV ratios were not statistically different than those for healthy children. In patients with both CM-I and syringomyelia (CM-S), the mean PFV and PFV/ICV ratios were statistically smaller than those for healthy children. The ICV was 1383 cm3 in the healthy group, 1459 cm3 in the CM-I only group, and 1400 cm3 in the CM-S group (p = 0.363); the PFV was 186 cm3 in the healthy group, 196 cm3 in the CM-I only group, and 171 cm3 in the CM-S group (p = 0.036); the PFV/ICV ratio was 0.135 in the healthy group, 0.134 in the CM-I only group, and 0.122 in the CM-S group (p = 0.004). These differences were more prominent in the first 10 years of life.

CONCLUSIONS

Children with isolated CM-I do not have a PFV smaller than normal, whereas children with both CM-I and syringomyelia have a PFV significantly smaller than normal. This result indicates that the two subgroups may represent different phenotypic expression or even a different pathogenesis.

Toward a rational treatment of Chiari I malformation and syringomyelia

In patients with Chiari I malformation with and without associated syringomyelia, aberrant cerebrospinal fluid (CSF) dynamics and a spectrum of posterior fossa pathological findings are demonstrated. In this study, the authors test the validity of using prospective cardiac-gated phase-contrast cine-mode magnetic resonance (MR) imaging to define the malformation, delineate its pathophysiology, and assist in implementing a rational treatment plan.

Eighty-five cases were prospectively analyzed using cine MR imaging. Sixty-five patients, adults and children, with symptomatic Chiari malformation, with and without syringomyelia, were surgically treated from 1990 to 1999. All patients underwent pre- and postoperative cine MR evaluation. Ten patients were treated after a previous surgical procedure had failed. To establish CSF flow characteristics and normative CSF profiles, 20 healthy volunteers were examined.

Compared with normal volunteers, in Chiari I malformation patients with and without syringomyelia, uniformly abnormal craniocervical junction CSF flow profiles were revealed. After intradural exploration, nearly all patients with Chiari I malformation experienced clinical improvement and CSF flow profiles, paralleling those of normal volunteers, were shown. In all patients in whom treatment had failed, abnormal preoperative CSF flow profiles, which correlated with suspected physiological abnormalities and the pathological findings noted at reoperation, were demonstrated.

Symptomatic Chiari I malformation is a dynamic process characterized by the impaction of the hindbrain in an abnormal posterior fossa. This compression obstructs the normal venting of CSF in and out of the craniocervical sub-arachnoid space, throughout the cardiac cycle. Therefore, decompression or enlargement of the posterior fossa to establish normal CSF pathways should be the primary goal of surgical intervention. Aberrant CSF flow appears to be only one aspect of the pathological condition found in patients with Chiari I malformation. Arachnoid scarring in the posterior fossa and selective vulnerability of the spinal cord may also be factors in the pathogenesis and maintenance of associated syringomyelia. Phase-contrast cine MR imaging is a useful tool in defining physiological and anatomical problems in patients with Chiari I and syringomyelia, and it can help guide an appropriate primary or salvage surgical therapy.

Chiari 1/syringomyelia complex in a King Charles Spaniel

A 9-year-old King Charles Spaniel presented with a history of progressive forelimb weakness and paroxysmal involuntary flank scratching over a 2-year period. Neurological examination suggested a myelopathy of C1 to C4 spinal cord segments. Advanced imaging studies revealed hydrocephalus, caudal herniation of part of the caudal lobe of the cerebellum through the foramen magnum and marked syrinx formation to the level of the caudal thoracic spine, resembling Arnold-Chiari malformation with secondary hydromyelia in humans. Mechanical obstruction at the craniocervical junction, altering CSF flow dynamics, may lead to syrinx formation. Response to diuretic therapy was moderate but surgical decompression may offer better long term prognosis.