Sleep apnea represents a relative indication for posterior fossa decompression in pediatric patients with Chiari malformation type 1. Duraplasty was associated with improvement of sleep apnea in 100% of patients and dural splitting with improvement in 50% of patients. Duraplasty and dural splitting were associated with a similar reduction in tonsillar herniation on radiographic imaging of 58% (37% excluding tonsillectomy) and 35%, respectively. Longitudinal follow-up studies of patients with either neurologic deficits or severe symptoms will further elucidate the natural history of Chiari malformation type 1 and more appropriately gauge the risk-benefit tradeoff of surgical intervention.
Key points
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Sleep apnea represents a relative indication for posterior fossa decompression (PFD) in pediatric patients with Chiari malformation type 1 (CM-1).
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Duraplasty was associated with improvement of sleep apnea in 100% of patients and dural splitting with improvement in 50% of patients.
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Duraplasty and dural splitting were associated with a similar reduction in tonsillar herniation on radiographic imaging of 58% (37% excluding tonsillectomy) and 35%, respectively.
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Intraoperative ultrasound can be beneficial in determining restoration of cerebrospinal fluid (CSF) circulation in the posterior fossa.
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Longitudinal follow-up studies of patients with either neurologic deficits or severe symptoms will further elucidate the natural history of CM-1 and more appropriately gauge the risk-benefit tradeoff of surgical intervention.
Introduction
CM-1 has become increasingly recognized as a significant clinical burden in approximately 3.6% of children undergoing brain and cervical spinal cord imaging. Although approximately two-thirds of children are asymptomatic and present with incidental findings, symptoms can result from compression of neural structures in the posterior fossa and be associated with syrinx of the spinal cord or brainstem. Children can also have more occult findings, such as ataxia, sensory and motor deficits, lower cranial nerve abnormalities, or merely irritability or neck arching.
The association between Chiari-related herniation and sleep apnea syndromes is described elsewhere. Although sleep apnea syndromes are rare in childhood, with a prevalence of approximately 1% to 3%, recent series have reported upwards of 60% in children with CM-1. Sleep-related breathing disruption results from compression of the medullary respiratory control centers and manifests in central or obstructive sleep apnea, hypoventilation, or even sudden death. Brainstem compression in addition to strain on lower cranial nerves may also result in dysphagia, hoarseness of voice with decreased vocal cord mobility, dysarthria, palatal and hypoglossal weakness, and recurrent aspiration. Although surgical decompression serves as the preferred treatment of sleep-disordered breathing in patients with Chiari malformation, the effect of surgery differs among patients and respiratory failure can be a complication of treatment. Reports have proposed not only increased incidence of respiratory arrest and death during sleep but also nocturnal respiratory depression during the immediate postoperative period (up to 14% of patients in the first 5 days), presumably secondary to edema formation.
Without a widely recognized, definitive correlation between magnitude of tonsillar herniation and clinical manifestations of cervicomedullary junction compression, debate lingers over the indications for operative versus nonoperative management of CM-1. As such, there are no generally accepted criteria for selecting patients with CM-1 for surgical treatment and the decision for suboccipital decompression for symptomatic relief can be subjective. A recent review by the current authors (Pomeraniec, Ksendzovksy, Jane Jr, personal communication, 2015.) of 95 consecutive cases of Chiari type 1 malformation in pediatric patients identified dysphagia and sleep apnea as symptoms indicating surgical management.
The purpose of this review is 2-fold: (1) review the long-term clinical and radiographic information for surgically managed pediatric patients with concurrent sleep apnea and CM-1 and (2) review the literature and provide a representative case series comparing 2 different surgical techniques (duraplasty and dural splitting) as well as their correlation to symptomatic and radiographic resolution or progression.
Introduction
CM-1 has become increasingly recognized as a significant clinical burden in approximately 3.6% of children undergoing brain and cervical spinal cord imaging. Although approximately two-thirds of children are asymptomatic and present with incidental findings, symptoms can result from compression of neural structures in the posterior fossa and be associated with syrinx of the spinal cord or brainstem. Children can also have more occult findings, such as ataxia, sensory and motor deficits, lower cranial nerve abnormalities, or merely irritability or neck arching.
The association between Chiari-related herniation and sleep apnea syndromes is described elsewhere. Although sleep apnea syndromes are rare in childhood, with a prevalence of approximately 1% to 3%, recent series have reported upwards of 60% in children with CM-1. Sleep-related breathing disruption results from compression of the medullary respiratory control centers and manifests in central or obstructive sleep apnea, hypoventilation, or even sudden death. Brainstem compression in addition to strain on lower cranial nerves may also result in dysphagia, hoarseness of voice with decreased vocal cord mobility, dysarthria, palatal and hypoglossal weakness, and recurrent aspiration. Although surgical decompression serves as the preferred treatment of sleep-disordered breathing in patients with Chiari malformation, the effect of surgery differs among patients and respiratory failure can be a complication of treatment. Reports have proposed not only increased incidence of respiratory arrest and death during sleep but also nocturnal respiratory depression during the immediate postoperative period (up to 14% of patients in the first 5 days), presumably secondary to edema formation.
Without a widely recognized, definitive correlation between magnitude of tonsillar herniation and clinical manifestations of cervicomedullary junction compression, debate lingers over the indications for operative versus nonoperative management of CM-1. As such, there are no generally accepted criteria for selecting patients with CM-1 for surgical treatment and the decision for suboccipital decompression for symptomatic relief can be subjective. A recent review by the current authors (Pomeraniec, Ksendzovksy, Jane Jr, personal communication, 2015.) of 95 consecutive cases of Chiari type 1 malformation in pediatric patients identified dysphagia and sleep apnea as symptoms indicating surgical management.
The purpose of this review is 2-fold: (1) review the long-term clinical and radiographic information for surgically managed pediatric patients with concurrent sleep apnea and CM-1 and (2) review the literature and provide a representative case series comparing 2 different surgical techniques (duraplasty and dural splitting) as well as their correlation to symptomatic and radiographic resolution or progression.
Methods
The authors retrospectively reviewed 8 consecutive pediatric patients (less than 18 years old) with suspected symptomatic sleep apnea and concurrent CM-1 (defined as herniation of the cerebellar tonsils at least 5 mm below the foramen magnum) who were treated at the University of Virginia between 2004 and 2014. One patient was treated conservatively and followed in the outpatient setting. Seven patients received PFD and were grouped based on operative technique: 3 patients underwent duraplasty (1 with tonsillectomy, 1 with tonsillopexy, and 1 with tonsils untouched) and 4 patients underwent a dural splitting technique.
Clinical Evaluation
Patients underwent comprehensive multidisciplinary evaluation, including child neurology, sleep specialist, and otolaryngology consultations with information available about history, neurologic examinations, polysomnography data, vocal cord mobility, upper airway motor dysfunction, and swallowing difficulty. The patients were treated/operated on by the same pediatric neurosurgeon.
Imaging
All patients underwent high-resolution MRI using standard T1- and T2-weighted spin-echo sequences. Imaging studies were independently reviewed at diagnosis by a neuroradiologist and pediatric neurosurgeon for amount of cerebellar tonsillar ectopia, CSF flow dynamics at the foramen magnum, and spinal cord syringomyelia. The authors defined a syrinx as a contiguous fluid collection (hypointense on T1-weighted images with corresponding T2 hyperintensity) of at least 2 mm in maximal anteroposterior diameter on sagittal or axial imaging suggesting fluid within the spinal cord. If a syrinx was present, its widest diameter in millimeters as viewed on sagittal imaging and its length according to number of spanning vertebral levels were reported. Presyrinx states (T2 hyperintensity with indistinct T1 prolongation and without cavitation) were separately classified. CSF flow at the foramen magnum was evaluated by cine MRI. Sagittal CSF flow studies at the craniocervical junction were evaluated for CSF pulsations across the anterior and posterior midline foramen magnum as well as for any abnormally exaggerated cranial or caudal pulsations of the lower brainstem, upper cervical cord, or cerebellar tonsils. Baseline imaging parameters were compared with findings on postoperative imaging.
Sleep Evaluation
Patients were evaluated in the University of Virginia Sleep Disorders Laboratory. Standard testing consisted of electroencephalogram (C3/A2, C2/A1, O1/A2, and O2/A1), electromyogram (chin), electro-oculography (right/left), ECG, oxygen saturation by digital pulse oximetry, nasal/oral airflow by thermistor or nasal pressure cannula, end-tidal CO 2 by nasal cannula, and qualitative thoracic/abdominal movement by respiratory inductive plethysmography. Natural sleep was observed overnight. No sedation was administered. Central apneas, obstructive apneas, hypopneas, periodic breathing, the adequacy of gas exchange, and heart rate were recorded during sleep.
Surgical Technique
For patients undergoing PFD, a midline incision was made from the inion to the C2 level and carried down the midline using sharp dissection through the midline raphe to expose the suboccipital region of C1 and upper portion of C2. A suboccipital craniectomy was performed with a high-speed drill ( Fig. 1 A) with the foramen magnum decompression measuring a minimum of 2 cm wide and 2 cm above the foramen (see Fig. 1 B, C). C1 laminectomy was performed in all patients and a C2 laminectomy was performed in those patients whose tonsils extended to that level. Intraoperative ultrasound was performed before and after duraplasty and/or dural splitting but in no case was a planned dural splitting technique converted to a duraplasty on the basis of ultrasound. For duraplasty cases, arachnoid adhesions were released with sharp dissection and tonsillar coagulation or tonsillar resection was performed if these techniques were judged necessary to restore normal 4th ventricular CSF outflow. Duraplasty was performed using collagen-based dural substitutes. For those who underwent dural splitting, the superficial layer of the dura was split and opened without completely cutting through the inferior layer until the dura was translucent. The dural band at the foramen magnum was released.
Duraplasty
Under microscope visualization, a Woodson elevator was used to elevate the thick and tense band constituting the outer leaf of the foramen magnum dura and periosteum, which was encountered invariably in all patients ( Fig. 2 ). With thinning of the dural band, there was a subsequent release of pressure at the cervicomedullary junction, giving more room for expansion of herniated cerebellar tonsils, which were visualized pulsating under the microscope. The dura was then incised in a Y-shape under the microscope and held open by sutures tacked laterally and superiorly. The arachnoid was inspected for any scarring and adhesions, which were sharply dissected if present, and the thick band of arachnoid between the tonsils and dura was sharply released. For tonsillectomy (n = 1), dissection was taken circumferentially around the tonsils, which were subsequently elevated with careful dissection from underneath C2. The inferior portion of the tonsils were cauterized, incised and internally debulked. For tonsillopexy (n = 1) ( [CR] ; available online at http://www.neurosurgery.theclinics.com/ ), tonsils were mobilized from below the level of the dural opening and subsequently cauterized superiorly with bipolar electrocautery. For duraplasty with tonsils untouched (n = 1), the tonsils themselves were not scarred down and an easy dissection was taken between and beneath the tonsils. A fashioned piece of artificial dura (Duragen [Medtronic] or Durepair [Integra]) was used for the duraplasty and tacked into place. A central tacking suture was placed in the dural graft through the fascia or muscle to avoid adherence of the dural graft to underlying arachnoid. The dural graft was covered with DuraSeal (in 1 patient) or gel foam and the closure was performed in standard layered fashion. All patients were admitted to the neurosurgical ICU postoperatively.
Dural Splitting
Adherent fibers between the posterior atlanto-occipital membrane and dura were similarly removed and the fibrous band was released sharply ( Fig. 3 ). Once the thick fibrous band was incised, a dissector was used to split the dura caudally and laterally to the inferior and lateral extent of the bony exposure. A vertical incision was made of the outer layer of the dura, laterally from the midline. Using blunt dissection the outer layer of the dura was removed without breaching the inner layer or the arachnoid membrane. The cerebellar tonsils were then easily seen pulsating through the thinned dura ( [CR] ; available online at http://www.neurosurgery.theclinics.com/ ). The ultrasound was used to visualize the tonsils, which were seen to move freely ( [CR] ; available online at http://www.neurosurgery.theclinics.com/ ). CSF was identified posterior to the tonsils and between the dura as well as below the inferior aspect of the tonsils. The tonsils, which had been compressed and were pointed preoperatively, had been obviously freed and had a much more rounded appearance, indicating their decompression. The dura appeared transparent and bluish. Muscular and subcutaneous planes were closed without any tension.
Results
Patient Characteristics
In total, 8 pediatric patients were evaluated for and diagnosed with CM-1 and attendant central sleep apnea. One patient was treated conservatively without surgery and 7 patients received PFD with either duraplasty (n = 3) or dural splitting (n = 4). The average age at presentation was 11.9 years (range 2.2–17.1 years). Median clinical follow-up was 47.4 months (range 3.2–98.3 months) and median imaging follow-up was 45.7 months (range 3.2–107.4 months).
Imaging Characteristics
The mean extent of tonsillar herniation below foramen magnum at presentation was 22.2 mm (range 9.5–37.0 mm). Across all surgical patients, preoperative tonsillar descent ranged from 14.0 to 37.0 mm. On average, duraplasty reduced tonsillar herniation by 58% and dural splitting by 35%. Excluding the 1 patient with tonsillectomy and 100% reduction in herniation, duraplasty reduced tonsillar herniation by 37%. There was no significant difference of reduction in tonsillar herniation between duraplasty (16.2 mm) and dural splitting (9.7 mm, average) ( P = .40), which was further elucidated when excluding the patient who underwent tonsillectomy ( P = .92) ( Table 1 ).
| Below, Average (mm) | Below, Most Recent (mm) | Difference, Average, mm (% Change) | |
|---|---|---|---|
| Nonsurgical | 9.5 | 15.5 | 6.0 (63) |
| Duraplasty | 23.0 | 6.7 | −16.2 (−58) |
| Dural splitting | 24.8 | 18.6 | −9.7 (−35) |
One patient (33%) in the duraplasty group and 1 patient (25%) in the dural splitting group presented with syrinx. One patient in the duraplasty (tonsillopexy) group developed syrinx after the first decompression, which resolved with repeat tonsillopexy and reconstruction of the subarachnoid space. All patients with a syrinx had at least 1 repeat MRI study of the spine. These repeat imaging studies revealed resolution of syrinx size (eg, no evidence of syringomyelia on postoperative MRI) in both patients with surgery. Two patients (50%) in the dural splitting group developed presyrinx before surgery and both of these patients exhibited resolution of presyrinx after surgery ( Table 2 ).
Related posts:
Definitions and Anatomic Considerations in Chiari I Malformation and Associated Syringomyelia
Pathogenesis and Cerebrospinal Fluid Hydrodynamics of the Chiari I Malformation
Prevalence of Chiari I Malformation and Syringomyelia
Clinical Outcome Measures in Chiari I Malformation
Craniovertebral Junction Instability in the Setting of Chiari I Malformation
Complex Chiari Malformations in Children
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