CHIARI I MALFORMATION

Abstract

The Chiari I malformation (CMI) is a caudal displacement of the cerebellar tonsils into the cervical spinal canal. It is generally agreed that CMI is defined by tonsillar herniation more than 5 mm below the plane of the foramen magnum. The disorder affects children and adults and may be congenital or acquired. Although advances in magnetic resonance (MR) imaging have significantly enhanced our ability to diagnose CMI, management of this condition remains controversial. In patients with CMI, the most common presenting symptom is pain. Presenting signs include brainstem, cerebellar, and spinal cord dysfunction. The widespread use of MR imaging has led to CMI being diagnosed with increased frequency earlier in a patient’s life and sometimes even prior to the onset of symptoms. Despite advances in neuroimaging, major questions about CMI remain unanswered. What are the indications for surgery? What type of operation should be performed? Should patients with significant hydrosyringomyelia be treated differently? How should patients with asymptomatic CMI be managed? In this issue of Neurosurgical Focus, we explore the complexities of CMI with a diversity of reports that answer some of the aforementioned questions and pose new ones. Leading off is Bejjani with a discussion of the adult CMI. The author provides a historical review of CMI, beginning with the earliest descriptions of the disorder in the nineteenth century and ending with a detailed account of the radiological criteria in the modern MR imaging era. Alden and colleagues discuss the clinical presentation of CMI and review the evolution of different surgical approaches. These authors then present their clinical experience and provide an algorithm, which suggests that the surgical approach be tailored to treat the predominant clinical problem. Next, Alzate, et al., review a series of 66 consecutive patients with CMI who underwent surgical decompression of the craniovertebral junction. More than half the patients in this series had hydrosyringomyelia, and the authors recommend placing a syringosubarachnoid shunt at the time of foramen magnum decompression if there is a large symptomatic syrinx. Although patients in this series had an excellent outcome, the authors call for further studies to determine whether or when a shunt should be placed. Pandey and coworkers report on a subset of children with symptomatic CMI who presented with so-called “cerebellar fits.” Preoperatively, these children had a fulminant course with drop attacks, abnormal posturing, and varying degrees of respiratory compromise. Recognition of this entity is important because the diagnosis can be confused with cardiogenic syncope or cortical epilepsy, and patients recover promptly following foramen magnum decompression. In Menick’s paper on phase-contrast MR imaging he examines the use of preand postoperative noninvasive real-time imaging to look at cerebellar tonsillar motion at the craniovertebral junction. This technique provides information about the physiological status of the subarachnoid space at the foramen magnum and may be of predictive value in patients with hydrosyringomyelia. Along the same lines, Alperin and colleagues use phase-contrast MR imaging to evaluate blood and cerebrospinal fluid flow before and after surgery in patients with CMI. They found a markedly abnormal intracranial volume change waveform in patients with symptomatic CMI and suggest that MR imaging measurement of hemodynamic and hydrodynamic changes may provide useful information for guiding therapy. The final paper by Hida and Iwasaki describe the treatment of patients with CMI and hydrosyringomyelia by syringosubarachnoid shunt placement without foramen magnum decompression. This work will probably be judged as controversial because the authors have gone against the mainstream approach of foramen magnum decompression for symptomatic CMI. Their results were generally good, although 17% of patients in their series required repeated surgery. Of interest is the authors’ suggestion for improving the patency of syringosubarachnoid shunts by placing the proximal catheter into the ventral subarachnoid space. We hope you will find this issue of Neurosurgical Focus to be informative and provocative and that it will serve as a stimulus for further investigation. Alan R. Cohen, M.D., Rainbow Babies & Children’s Hospital, Cleveland, Ohio Sarah J. Gaskill, M.D., Pediatric Neurosurgery of South Texas, San Antonio, Texas