7.7 Headache attributed to Chiari malformation type I (CM1)

Description:
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:
A. Headache fulfilling criterion C
B. Chiari malformation type 1 (CM1) has been demonstrated1
C. 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
      b) headache has resolved within 3 months after successful treatment of the CM1

    2. headache has at least one of the following three characteristics:

      a) precipitated by cough or other Valsalva-like manœuvre
      b) occipital or suboccipital location
      c) lasting <5 min

    3. headache is associated with other symptoms and/or clinical signs of brainstem, cerebellar, lower cranial nerve and/or cervical spinal cord dysfunction

D. Not better accounted for by another ICHD-3 diagnosis2.

Notes:
1. Diagnosis of Chiari malformation 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 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. Patients with 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 as 7.2.3 Headache attributed to spontaneous intracranial hypotension). Therefore, in all patients presenting with headache and CM1, CSF leak must be excluded.

Comments:
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).

Almost all (95%) patients with CM1 report a constellation of five or more distinct symptoms.

An MRI database showed tonsillar herniation of at least 5 mm in 0.7% of the population. The clinical context of CMI is important as many of these subjects can be asymptomatic. Patients can exhibit “Chiari-like” symptoms with minimal cerebellar tonsillar herniation, while others may be asymptomatic with large herniations. No correlation exists between the amount of herniation and the severity of headache or level of disability in presenting patients. Rigid adherence to the clinical and radiological criteria described above is recommended prior to surgical intervention, to avoid an unnecessary surgical procedure which has significant potential for surgical morbidity.

These criteria for 7.7 Headache attributed to Chiari malformation type I (CM1) require validation. Prospective studies with long-term surgical outcome are needed.