What is the best testing to evaluate for Chiari (Arnold-Chiari) malformation?

From the Guidelines

The best testing to perform to evaluate for Chiari malformation is a noncontrast MRI scan of the brain, including a sagittal T2-weighted sequence of the cranio-cervical junction, as recommended by the American College of Radiology in 2018 1. This approach is supported by the ACR Appropriateness Criteria for headache in children, which suggests that MRI is the imaging modality of choice for evaluating Chiari I deformity, characterized by the herniation of the cerebellar tonsils through the foramen magnum 1. Some key points to consider when ordering an MRI for suspected Chiari malformation include:

• The importance of including a sagittal T2-weighted sequence of the cranio-cervical junction to best demonstrate the extent of tonsillar herniation
• The optional use of phase-contrast CSF flow study at the craniocervical junction to assess cerebrospinal fluid obstruction
• The preference for MRI over CT scans due to its superior soft tissue contrast and lack of radiation
• The need to correlate radiographic findings with the patient's symptoms, as some individuals with Chiari I malformation may be asymptomatic It is also important to note that a diagnosis of Chiari I malformation should be made with caution, as cerebellar tonsillar ectopia of >5 mm can also be seen in patients with pseudotumor cerebri syndrome (PTCS), and imaging and clinical consideration of PTCS are warranted to avoid misdiagnosis 1.

From the Research

Diagnostic Testing for Chiari Malformation

The best testing to evaluate for Chiari malformation involves the use of neuroimaging techniques, particularly:

• Magnetic Resonance Imaging (MRI) 2, 3, 4, 5
• Computed Tomography (CT) scans may provide additional information about skeletal anomalies 3

Key Features to Evaluate

MRI provides optimal anatomic detail of:

• Cerebellar tonsillar descent below the foramen magnum 2, 5
• Ventriculomegaly (potentially leading to the diagnosis of hydrocephalus) 2
• Characteristics of intracranial hypertension or hypotension 2
• Spinal cord syrinx 2, 6, 4, 5
• Scoliosis 2, 6, 4
• Tethered spinal cord 2, 6

Specialized Imaging Sequences

Specialized imaging sequences can provide enhanced visualization of:

• Ventral and dorsal cervicomedullary cisterns 2
• Cerebrospinal fluid flow 2
• Diffusion tensor imaging (DTI) and CSF flow studies can aid in clarifying the underlying fluid dynamics in CMI patients 4