Imaging-Based Features of Headaches in Chiari Malformation Type I

BACKGROUND:Suboccipital cough-induced headaches are considered a hallmark symptom of Chiari malformation type I (CMI). However, non--Valsalva-related suboccipital headaches and headaches in other locations are also common in CMI. The diagnostic significance and the underlying factors associated with these different headaches types are not well understood.OBJECTIVE:To compare cranial morphology and hydrodynamics in 3 types of headaches in CMI to better understand the pathophysiological basis for the different headache characteristics.METHODS:Twenty-two cranial physiological and morphological measures were obtained with specialized magnetic resonance imaging scans from 63 symptomatic pretreated CMI patients, 40 with suboccipital headaches induced by Valsalva maneuvers (34 women; age, 36 10 years), 15 with non--Valsalva-related suboccipital headaches (10 women; age, 33 9 years), 8 with nonsuboccipital non--Valsalva-induced headaches (8 women; age, 39 13 years), and 37 control subjects (24 women; age, 36 12 years). Group differences were identified with the use of the 2-tailed Student t test.RESULTS:Posterior cranial fossa markers of CMI were similar among the 3 headache subtypes. However, the Valsalva-related suboccipital headaches cohort demonstrated a significantly lower intracranial compliance index than the non--Valsalva-related suboccipital headaches cohort (7.5 3.4 vs 10.9 +/- 4.9), lower intracranial volume change during the cardiac cycle (0.48 +/- 0.19 vs 0.61 +/- 0.16 mL), and higher magnetic resonance imaging--derived intracranial pressure (11.1 +/- 4.3 vs 7.7 +/- 2.8 mm Hg; P = .02). The Valsalva-related suboccipital headaches cohort had smaller intracranial and lateral ventricular volumes compared with the healthy cohort. The non--Valsalva-related suboccipital headaches cohort had reduced venous drainage through the jugular veins.CONCLUSION:Valsalva-induced worsening of occipital headaches appears to be related to a small intracranial volume rather than the smaller posterior cranial fossa. This explains the reduced intracranial compliance and corresponding higher pressure measured in CMI patients with headaches affected by Valsalva maneuvers.ABBREVIATIONS:CMI, Chiari malformation type IICP, intracranial pressureMRICP, magnetic resonance--derived intracranial pressurePCF, posterior cranial fossa