This article is a discussion of the surgical technique for posterior fossa decompression as treatment for Chiari I malformation. It includes a brief discussion of the indications for surgical treatment as well as a discussion of the risks and benefits of bone-only decompression or decompression with accompanying duraplasty. Most of the text is dedicated to the technical description of the surgical procedure for decompression of the Chiari I malformation with particular attention to techniques aimed at avoiding common complications.
Key points
- •
Anatomic Chiari I malformation is common, so selection of patients likely to benefit from posterior fossa decompression is crucial.
- •
Soft tissue dissection need not extend more lateral than the level of the lateral edge of the foramen magnum, thus lowering the risk of vertebral artery injury.
- •
Dural opening should proceed from caudal to rostral to allow greatest control of potential venous lakes in the occipital dura.
- •
Bone-only decompression has a higher risk of requiring repeat operation for lack of improvement, whereas decompression with duraplasty has a higher rate of cerebrospinal fluid (CSF) complications. No definitive evidence favors either technique.
- •
Assuring adequate CSF outflow from the fourth ventricle should be the primary goal, especially in redo Chiari decompression.
Introduction: nature of the problem
The Chiari I malformation is characterized by low position of the tonsils of the cerebellum. The definition of Chiari I is typically expressed by a measurement of the distance that the most inferior tip of the cerebellar tonsil lies below the foramen magnum. However, the prevalence of Chiari I malformation, based on this anatomic definition, is potentially as high as 1% of the general population. However, only a small proportion of these Chiari I malformations are symptomatic or cause secondary pathologic phenomena like syringomyelia. The only accepted treatment for patients with symptomatic Chiari I malformation is surgical decompression of the hindbrain.
Although the typical symptoms of Chiari I malformation and syringomyelia, as well as the indications for undertaking surgical treatment, are discussed elsewhere in this issue, we briefly cover them here. The presence of a syrinx seems to be reasonable justification for operation. Although some patients have been shown to have spontaneous syrinx resolution, the decision for surgery rests with the likelihood that a fixed neurologic deficit as a consequence of the syrinx is more probable than spontaneous syrinx resolution.
In the absence of syringomyelia, an indication for operative treatment of the Chiari I malformation is often the presence of headache. Headaches that most reliably improve with Chiari I decompression are occipital or high cervical, are reproducibly brought on with Valsalva maneuver, and are of short duration. Relief of headaches that do not meet all of these criteria is less likely.
The purpose of this article is not to discuss indications for surgical treatment of Chiari I malformation. Rather, herein we describe the surgical technique and nuance for the operative treatment of the Chiari I malformation, including preoperative planning, patient positioning, surgical approach, the detailed surgical procedure, postoperative care, and recovery. We include a brief discussion of controversies surrounding opening of the dura and manipulation of the cerebellar tonsils, but the bulk of this text is a description of the surgical technique preferred at the authors’ institution.
Introduction: nature of the problem
The Chiari I malformation is characterized by low position of the tonsils of the cerebellum. The definition of Chiari I is typically expressed by a measurement of the distance that the most inferior tip of the cerebellar tonsil lies below the foramen magnum. However, the prevalence of Chiari I malformation, based on this anatomic definition, is potentially as high as 1% of the general population. However, only a small proportion of these Chiari I malformations are symptomatic or cause secondary pathologic phenomena like syringomyelia. The only accepted treatment for patients with symptomatic Chiari I malformation is surgical decompression of the hindbrain.
Although the typical symptoms of Chiari I malformation and syringomyelia, as well as the indications for undertaking surgical treatment, are discussed elsewhere in this issue, we briefly cover them here. The presence of a syrinx seems to be reasonable justification for operation. Although some patients have been shown to have spontaneous syrinx resolution, the decision for surgery rests with the likelihood that a fixed neurologic deficit as a consequence of the syrinx is more probable than spontaneous syrinx resolution.
In the absence of syringomyelia, an indication for operative treatment of the Chiari I malformation is often the presence of headache. Headaches that most reliably improve with Chiari I decompression are occipital or high cervical, are reproducibly brought on with Valsalva maneuver, and are of short duration. Relief of headaches that do not meet all of these criteria is less likely.
The purpose of this article is not to discuss indications for surgical treatment of Chiari I malformation. Rather, herein we describe the surgical technique and nuance for the operative treatment of the Chiari I malformation, including preoperative planning, patient positioning, surgical approach, the detailed surgical procedure, postoperative care, and recovery. We include a brief discussion of controversies surrounding opening of the dura and manipulation of the cerebellar tonsils, but the bulk of this text is a description of the surgical technique preferred at the authors’ institution.
Surgical technique
Preoperative Planning
Before surgery, a detailed history and physical examination, routine preoperative laboratory evaluation, and pre-anesthetic risk profiling are performed. It is important that before surgery, patients and families understand the goals of surgical therapy. In the patient with syringomyelia, the goal is most often to prevent future neurologic deficit and to affect a decrease in the size of the syrinx. In the patient with headaches, the goal of therapy is to reduce the frequency and severity of the headaches that are attributable to the Chiari, as described previously. When the patient and family accept the risks and potential benefits of surgery, Chiari I decompression can proceed.
Preparation and Patient Positioning
The patient is positioned prone on a standard operating table with the head flexed ( Fig. 1 ). Gel rolls or appropriate padding is used to support the chest and hips, leaving the abdomen free to facilitate ventilation. The head is secured using pin fixation. Pin fixation is an option in infants, particularly if a combination face support/pin fixation device is available. This type of device allows the weight of the infant’s head to be supported by the forehead support, while the pins maintain the flexed position required for optimal surgical exposure.
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
Surgical History of Sleep Apnea in Pediatric Patients with Chiari Type 1 Malformation
Craniovertebral Junction Instability in the Setting of Chiari I Malformation
Complex Chiari Malformations in Children
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
