From the Guidelines
The best test to diagnose an Arnold-Chiari malformation is a noncontrast MRI scan of the brain, including a sagittal T2-weighted sequence of the cranio-cervical junction, as it provides detailed images of soft tissues and allows clear visualization of the relationship between the cerebellum, brainstem, and spinal cord 1.
Key Considerations
- MRI is the imaging modality of choice for diagnosing Chiari I deformity, as it can detect the herniation of the cerebellar tonsils through the foramen magnum and potential associated conditions like syringomyelia 1.
- A noncontrast MRI scan is typically sufficient for initial diagnosis, but contrast enhancement may be useful in complex cases to rule out other conditions 1.
- The diagnostic criterion for Chiari I malformation is typically tonsillar descent of at least 5mm below the foramen magnum 1.
Imaging Modalities
- MRI is superior to CT scans for diagnosing Chiari malformation because it better demonstrates neural tissue, cerebrospinal fluid spaces, and potential associated conditions like syringomyelia 1.
- Other imaging modalities, such as CT, CTA, and MRV, may be useful in certain situations, but MRI is the gold standard for diagnosing Chiari malformation 1.
Clinical Context
- Chiari type 1 malformation is detected in 25-50% of children with X-linked hypophosphataemia (XLH) by use of cranial MRI or CT 1.
- Symptoms of Chiari malformation can include occipital or neck pain exacerbated by Valsalva maneuvers, peripheral motor and/or sensory defects, clumsiness, hyporeflexia or hyperreflexia, respiratory irregularities, and central apnoeas and lower cranial nerve dysfunction 1.
From the Research
Diagnostic Tests for Arnold Chiari Malformation
The best test to diagnose Arnold Chiari malformation is magnetic resonance imaging (MRI) of the head and spine, as it provides optimal anatomic detail of cerebellar tonsillar descent below the foramen magnum 2, 3, 4, 5.
Key Features of MRI in Diagnosing Arnold Chiari Malformation
- Obliteration of the retrocerebellar cerebrospinal fluid spaces 2
- Tonsillar herniation of at least 5 mm 2
- Varying degrees of post fossa anomalies 2
- Ventriculomegaly, characteristics of intracranial hypertension or hypotension, spinal cord syrinx, scoliosis, and/or tethered spinal cord 5
Comparison of Cranial and Cervical Spine MRI
Both cranial and cervical spine MRI can be used to determine the degree of tonsil ectopia, with no significant difference in measurements between the two 4.
Other Diagnostic Tests
- Computed tomographic (CT) scanning without injection of contrast agent can also detect nervous tissue abnormalities in Arnold Chiari malformation, although it may not be as effective as MRI 6
- Specialized imaging sequences can provide enhanced visualization of ventral and dorsal cervicomedullary cisterns and cerebrospinal fluid flow 5
Clinical Manifestations
Clinical manifestations of Arnold Chiari malformation include headaches, pseudotumor-like episodes, Meniere's disease-like syndrome, lower cranial nerve signs, and spinal cord disturbances in the absence of syringomyelia 2, 3