7.7 Headache attributed to Chiari malformation type I (CM1)


Headache caused by Chiari type I malformation, usually occipital or suboccipital, of short duration (less than 5 minutes) and provoked by cough or other Valsalva-like manœuvres. It remits after the successful treatment of the Chiari malformation.

Diagnostic criteria:
  1. Headache fulfilling criterion C
  2. Chiari malformation type I (CM1) has been demonstrated1
  3. Evidence of causation demonstrated by at least two of the following:
    1. either or both of the following:
      • a) headache has developed in temporal relation to the CM1 or led to its discovery
      • b) headache has resolved within 3 months after successful treatment of the CM1
    2. headache has one or more of the following three characteristics:
      • a) precipitated by cough or other Valsalva-like manœuvre
      • b) occipital or suboccipital location
      • c) lasting <5 minutes
    3. headache is associated with other symptoms and/or clinical signs of brainstem, cerebellar, lower cranial nerve and/or cervical spinal cord dysfunction2
  4. Not better accounted for by another ICHD-3 diagnosis3.
  1. Diagnosis of Chiari malformation type I (CM1) by MRI requires a 5-mm caudal descent of the cerebellar tonsils or 3-mm caudal descent of the cerebellar tonsils plus crowding of the subarachnoid space at the craniocervical junction as evidenced by compression of the cerebrospinal fluid (CSF) spaces posterior and lateral to the cerebellum, or reduced height of the supraocciput, or increased slope of the tentorium, or kinking of the medulla oblongata.
  2. Almost all (95%) patients with CM1 report a constellation of five or more distinct symptoms.
  3. Patients with altered CSF pressure, either increased as in idiopathic intracranial hypertension (IIH) or decreased as in spontaneous intracranial hypotension secondary to CSF leak, may demonstrate MRI evidence of secondary tonsillar descent and CM1. These patients may also present with headache related to cough or other Valsalva-like manœuvre, and are correctly coded either as 7.1.1 Headache attributed to idiopathic intracranial hypertension or as 7.2.3 Headache attributed to spontaneous intracranial hypotension. Therefore, in all patients presenting with headache and CM1, abnormal CSF pressure must be excluded.

7.7 Headache attributed to Chiari malformation type I (CM1) is often descriptively similar to 4.1 Primary cough headache with the exception, sometimes, of longer duration (minutes rather than seconds).

Prevalence studies show tonsillar herniation of at least 5 mm in 0.24-3.6% of the population, with prevalence decreasing in older age.

The clinical context of CMI is important as many of these patients can be asymptomatic. There are conflicting data regarding the degree of herniation and the severity of associated headache and level of disability: patients can exhibit “Chiari-like” symptoms with minimal cerebellar tonsillar herniation, while others may be asymptomatic with large herniations.

These criteria for 7.7 Headache attributed to Chiari malformation type I (CM1) require validation: prospective studies with long-term non-surgical and surgical outcomes are needed. Meanwhile, rigid adherence to both clinical and radiological criteria is recommended in considering surgical intervention to avoid an unnecessary procedure with significant potential for surgical morbidity. Current data suggest that, in carefully selected patients, cough headaches more than headaches without Valsalva-like precipitants, and occipital headaches more than non-occipital, are responsive to surgical intervention.

Emerging data suggest a relationship between obesity and likelihood of headache in CM1; this finding warrants further research, particularly from a treatment viewpoint.