Related Experiment Video
Updated: Oct 15, 2025
In Vivo Morphometric Analysis of Human Cranial Nerves Using Magnetic Resonance Imaging in Menière's Disease Ears and Normal Hearing Ears
Published on: February 21, 2018
Differentiation of Chiari malformation type 1 and spontaneous intracranial hypotension using objective measurements
Jessica L Houk1, Timothy J Amrhein1, Linda Gray1
11Department of Radiology, Division of Neuroradiology, Duke University Medical Center, Durham, North Carolina.
Insights
Objective midbrain measurements can differentiate Chiari malformation type 1 (CM-1) from spontaneous intracranial hypotension (SIH). Specific values for the third ventricular floor slope (3VF) and pontomesencephalic angle (PMA) accurately distinguish these headache causes.
Area of Science:
- Neurology
- Radiology
- Neurosurgery
Background:
- Chiari malformation type 1 (CM-1) and spontaneous intracranial hypotension (SIH) are common causes of headache.
- Cerebellar tonsillar ectopia (TE) can be present in both CM-1 and SIH, leading to diagnostic confusion.
- Objective imaging biomarkers are needed to differentiate CM-1 from SIH.
Purpose of the Study:
- To determine if objective midbrain morphology measurements can distinguish CM-1 from SIH on brain MRI.
- To identify specific imaging parameters that reliably differentiate these two conditions.
Main Methods:
- Retrospective case-control study comparing neuroimaging in adult subjects with CM-1 and SIH.
- Measurements included: cerebellar tonsillar ectopia (TE), slope of the third ventricular floor (3VF), pontomesencephalic angle (PMA), and displacement of iter (DOI).
- Comparison between CM-1, all SIH patients (SIHall), and SIH patients with >5mm TE (SIHTE).
Main Results:
- Significant differences found between SIHall and CM-1 groups in TE, 3VF, PMA, DOI, and clivus length (CL) (p < 0.0001).
- In the SIHTE subgroup, 3VF < -15° and PMA < 45° perfectly discriminated SIH from CM-1 (sensitivity and specificity = 1.0).
- DOI showed perfect specificity (1.0) for detecting SIH; SIH patients without other sagging findings did not present isolated TE.
Conclusions:
- Midbrain sagging measurements, particularly 3VF and PMA cutoff values, effectively differentiate CM-1 from SIH.
- These objective MRI measures can aid in preventing misdiagnosis and unnecessary surgical interventions for headache patients.
Objective:
Chiari malformation type 1 (CM-1) and spontaneous intracranial hypotension (SIH) are causes of headache in which cerebellar tonsillar ectopia (TE) may be present. An accurate method for differentiating these conditions on imaging is needed to avoid diagnostic confusion. Here, the authors sought to determine whether objective measurements of midbrain morphology could distinguish CM-1 from SIH on brain MRI.
Methods:
This is a retrospective case-control series comparing neuroimaging in consecutive adult subjects with CM-1 and SIH. Measurements obtained from brain MRI included previously reported measures of brain sagging: TE, slope of the third ventricular floor (3VF), pontomesencephalic angle (PMA), mamillopontine distance, lateral ventricular angle, internal cerebral vein-vein of Galen angle, and displacement of iter (DOI). Clivus length (CL), an indicator of posterior fossa size, was also measured. Measurements for the CM-1 group were compared to those for the entire SIH population (SIHall) as well as a subgroup of SIH patients with > 5 mm of TE (SIHTE subgroup).
Results:
Highly significant differences were observed between SIHall and CM-1 groups in the following measures: TE (mean ± standard deviation, 3.1 ± 5.7 vs 9.3 ± 3.5 mm), 3VF (-16.8° ± 11.2° vs -2.1° ± 4.6°), PMA (44.8° ± 13.1° vs 62.7° ± 9.8°), DOI (0.2 ± 4.1 vs 3.8 ± 1.6 mm), and CL (38.3 ± 4.5 vs 44.0 ± 3.3 mm; all p < 0.0001). Eight (16%) of 50 SIH subjects had TE > 5 mm; in this subgroup (SIHTE), a cutoff value of < -15° for 3VF and < 45° for PMA perfectly discriminated SIH from CM-1 (sensitivity and specificity = 1.0). DOI showed perfect specificity (1.0) in detecting SIH among both groups. No subjects with SIH had isolated TE without other concurrent findings of midbrain sagging.
Conclusions:
Measures of midbrain sagging, including cutoff values for 3VF and PMA, discriminate CM-1 from SIH and may help to prevent misdiagnosis and unnecessary surgery.
