Key points

Introduction

Scoliosis is associated with the presence of a Chiari I malformation (CM) in up to 20% of patients, and even more frequently associated with CM in the setting of syringomyelia, with rates as high as 60%. Although this clinical entity is not particularly rare in practice, there is a paucity of published research regarding spinal deformities associated with CM. Thus, the pathophysiology of the spinal deformity, and the effects of the CM with or without syringomyelia, remain poorly understood. Some clinicians have proposed that the formation of a syrinx may cause anterior horn cell dysfunction, with scoliosis as a result. Because syringomyelia is not necessary for concomitant scoliosis, other clinicians have proposed that cerebellar tonsil compression is the inciting event. However, identifying patients with this constellation of diagnoses is essential, because there may be some neurologic risk to corrective surgery for the spinal deformity performed in the setting of an untreated syrinx or CM. Furthermore, early diagnosis of scoliosis associated with CM may allow for nonoperative management of the spinal deformity, thus avoiding a spinal fusion. This article reviews the current literature regarding scoliosis associated with CM, with and without syringomyelia.

Introduction

Scoliosis is associated with the presence of a Chiari I malformation (CM) in up to 20% of patients, and even more frequently associated with CM in the setting of syringomyelia, with rates as high as 60%. Although this clinical entity is not particularly rare in practice, there is a paucity of published research regarding spinal deformities associated with CM. Thus, the pathophysiology of the spinal deformity, and the effects of the CM with or without syringomyelia, remain poorly understood. Some clinicians have proposed that the formation of a syrinx may cause anterior horn cell dysfunction, with scoliosis as a result. Because syringomyelia is not necessary for concomitant scoliosis, other clinicians have proposed that cerebellar tonsil compression is the inciting event. However, identifying patients with this constellation of diagnoses is essential, because there may be some neurologic risk to corrective surgery for the spinal deformity performed in the setting of an untreated syrinx or CM. Furthermore, early diagnosis of scoliosis associated with CM may allow for nonoperative management of the spinal deformity, thus avoiding a spinal fusion. This article reviews the current literature regarding scoliosis associated with CM, with and without syringomyelia.

Clinical presentation

The presentation of scoliosis associated with CM varies significantly and, as such, it may remain undiagnosed, so spine surgeons should have some clinical suspicion when evaluating idiopathic scoliosis that shows any atypical features. Charry and colleagues reported a series of patient with syringomyelia in whom a small number had abnormal examinations (10 out of 25; 40%) and most were normal. Up to 10% of patients with suspected idiopathic scoliosis had some abnormality on preoperative MRI, most of which were syringomyelia (67%) followed by Chiari malformations (31%). However, a prospective, observational cohort of patients aged 10 to 19 years did not support these findings, and the clinical concern from disease presentation and physical examination findings are likely the most important factors. The diagnosis of scoliosis made in childhood is categorized by age, with children diagnosed as having infantile (birth to 3 years old), juvenile (4–10 years), and adolescent (>10 years old) scoliosis. The age of the child is important to consider, because young cases (infantile and juvenile, early onset scoliosis) of scoliosis are more frequently associated with some neural axis abnormality and an MRI study of the entire spine must be ordered. Age and skeletal maturity are important considerations, not only as predictors of the presence of a neural axis abnormality but also because there are implications for prognosis and potential for resolution with management of the CM and syrinx. Menarchal status is assessed in girls, because this may correlate with curve progression and allows for a more informed conversation with patient and parents.

In some cases, neurologic symptoms may precede the diagnosis of the spinal deformity. Perhaps the most common neurologic complaint is headaches, but sensory or motor disturbances may exist. The presence of any of these in an orthopedic clinic should elicit an MRI study of the entire spinal column, with referral to a neurosurgeon should the MRI find abnormalities. A complete neurologic examination must be performed at the initial visit for any child presenting with a spinal deformity. In many cases the examination is normal; however, in some instances a motor deficit, hyperreflexia, or a pathologic reflex may be present. Among the reflexes that must be examined are the abdominal reflexes, because these have been correlated with neural axis abnormalities, including syringomyelia. Gait should be examined and clonus should be checked to ensure symmetry and that there are no more than 2 to 3 beats per side, if present at all. Patients presenting as adults may have more profound neurologic abnormalities, which should prompt MRI before any surgical intervention for the spinal deformity.

Radiographic evaluation

A standard radiographic evaluation of spinal deformity includes upright, posteroanterior, and lateral full-spine images. The most commonly used classification system for adolescent idiopathic scoliosis (AIS) is the Lenke classification. The usual AIS deformity is an apex right, main thoracic curve, with a loss of thoracic kyphosis at the apex of the deformity ( Fig. 1 ). Atypical findings on posteroanterior (coronal plane) radiographs include an apex left thoracic deformity and sharp, angular deformities ( Fig. 2 A, B). Perhaps the most important detail related to identification of CM is the measurement of the sagittal Cobb angles. In our practice, a Lenke “+” modifier, indicating hyperkyphosis, undergoes MRI to ensure that there is no underlying neurologic abnormality (see Fig. 2 C). In the case of adolescent scoliosis, any atypia to the curve morphology or appearance warrants an MRI examination (see Fig. 2 D). As previously noted, early onset scoliosis is more frequently associated with neural axis abnormalities, such as CM. Clinicians must remember that a large deformity presenting as AIS was almost certainly present as a juvenile and, in such cases, MRI may be indicated.

( A ) Standing posteroanterior radiograph of a 17-year-old girl with typical radiographic findings of AIS: apex right, no angular deformity. ( B ) Standing lateral radiograph showing thoracic hypokyphosis, typical of AIS. ( C ) Standing clinical image showing a loss of thoracic kyphosis. ( D ) Lateral forward bending clinical image showing a loss of thoracic kyphosis.

( A ) Standing posteroanterior radiograph of a 13-year-old girl with typical coronal plane findings of AIS. ( B ) Standing lateral radiograph showing proximal thoracic kyphosis, atypical for AIS. ( C ) Lateral clinical image of 13-year-old girl with proximal thoracic kyphosis. ( D ) T2-weighted MRI of this young woman, showing Chiari I with syringomyelia.

Measurement of the coronal Cobb is important for prognostic factors, before decompression of the Chiari malformation. In general terms, the smaller the deformity at the time of presentation, the more likely the patient is to avoid surgery for the spinal deformity. However, risk of spinal deformity progression is multifactorial, and is also related to the skeletal maturity of the patient, which is related to future growth. The Risser score is a reasonable proxy for remaining growth potential and it should be noted on the posteroanterior radiograph, in addition to the descriptives of the spinal deformity itself. Given the varied presentations of these deformities, relationships between the spinal deformity and the underlying CM and syringomyelia have been difficult to describe. Yeom and colleagues and Qiu and colleagues found no relationships between curve magnitude or character and descriptives of tonsillar descent or syrinx character. In contrast, Godzik and colleagues found that larger syringes (maximum diameter >6 mm) were more commonly associated with the presence of a scoliosis. Those patients with severe tonsillar descent (>12 mm) were less likely to have a scoliosis than those with moderate tonsillar descent (5–12 mm). That these findings were not consistent emphasizes the varied nature of presentation and the poorly understood pathophysiology of this disease process.