Chiari I Malformations – Primary Steps for Primary Care
Anxiety related to unexpected abnormal findings disclosed by imaging studies obtained during workup of headache or trauma is a frequent reason for referral to neurosurgery. A frequent incidental imaging finding is a Chiari I malformation, i.e., the presence of low-lying cerebellar tonsils, usually unaccompanied by other significant imaging findings. While the estimated prevalence of Chiari malformations is 1 per 1000 people, the overwhelming majority are asymptomatic. The extent of tonsillar descent, or herniation through the foramen magnum, differentiates so-called tonsillar ectopia (tonsillar tips descend < 5mm below the foramen magnum) from a Chiari I abnormality (tonsils extend further than 5mm below the foramen magnum).
Although many children with incidentally discovered tonsillar ectopia or Chiari I are asymptomatic, others may voice complaints that require accurate diagnosis, explanation and treatment.
What are common headache symptoms of Chiari I malformations?
The classic headache of Chiari I is episodic, tussive or aggravated with straining and suboccipital. It is easily differentiated from the boring, sustained pain of tension or muscle-contraction headache associated with chronically tight neck muscles. Generalized, frontal or bitemporal headache does not suggest tonsillar herniation, unless the latter is associated with chronically elevated intracranial pressure, findings and symptoms of which should be evident to any physician – especially when papilledema is present. In such cases, headache is not caused by the tonsillar herniation itself, but rather the intracranial hypertension.
Avoid posing leading questions while obtaining a history from child or parent, especially regarding headache location. Asking, “Where does it hurt?” is a wiser strategy than “Does the back of your head hurt?” Poorly defined symptoms, such as blurry vision or dizziness unaccompanied by objective neurological findings seldom signal a Chiari-related disorder.
What other symptoms might suggest a symptomatic Chiari I malformation?
A Chiari malformation or associated syrinx can disrupt lower brainstem and upper cervical cord function. Symptoms such as loss of pain/temperature in the upper torso and arms, difficulty swallowing, impaired balance, sleep apnea and loss of muscle strength in the upper extremities/hands are encountered. Even a cursory neurologic examination will identify pertinent objective findings, such as gait ataxia, spasticity, weakness, or cranial nerve palsy in these cases.
What imaging is of value in addition to MRI brain?
Because syringomyelia can be associated with Chiari I, experienced neuroimaging centers usually try to obtain a screening MRI image of the entire spinal cord. If the original brain study did not include spinal imaging, cervical spine MRI with survey view of the entire spine is necessary to completely evaluate for syrinx before the patient is referred to a neurosurgeon.
When is referral to neurosurgery suggested?
The presence of a syrinx or pre-syrinx findings (i.e., increased T2 signal within the brainstem or upper cervical cord parenchyma noted by the neuroradiologist), even in an asymptomatic patient, always demands evaluation by a neurosurgeon. Papilledema or other symptoms of increased intracranial pressure, as well as findings suggesting symptomatic Chiari as discussed above also warrant further evaluation.
Sometimes, it is hard to interpret a child harboring an incidental Chiari I who is voicing pain or other somatic complaints. Even experienced clinicians sometimes have to follow such patients with multiple visits for a time to see how things work out, an approach that may earn the family's trust and reassure the clinician that nothing is being missed.