MATERIALS AND METHODS

Brain MRIs of 30 patients with intracranial hypotension and 30 age-matched controls were evaluated by 2 fellowship-trained neuroradiologists for classic findings of intracranial hypotension and the interpeduncular angle. Group analysis was performed with a Student t test, and receiver operating characteristic analysis was used to identify an ideal angle threshold to maximize sensitivity and specificity. Interobserver reliability was assessed for classic findings of intracranial hypotension using the Cohen κ value, and the interpeduncular angle, using the intraclass correlation.

RESULTS

The interpeduncular angle had excellent interobserver reliability (intraclass correlation coefficient value = 0.833) and was significantly lower in the intracranial hypotension group compared with the control group (25.3° versus 56.3°; P < .001). There was significant correlation between the interpeduncular angle and the presence of brain stem slumping (P < .001) and in cases with ≥3 classic features of intracranial hypotension (P = .01). With a threshold of 40.5°, sensitivity and specificity were 80% and 96.7%, respectively.

CONCLUSIONS

The interpeduncular angle is a sensitive and specific measure of intracranial hypotension and is a reliably reproducible parameter on routine clinical MR imaging.

Intracranial hypotension is a neurologic syndrome with various etiologies that share a common final pathway of decreased CSF volume and pressure. The classic clinical presentation is orthostatic headache with associated nonspecific symptoms such as nausea and vertigo.1 In severe cases, the disease can progress to cranial nerve palsies and even coma.2⇓–4 The nonspecific nature of the clinical presentation can result in considerable delays in work-up, mimicking entities with drastically different treatments such as migraine, meningitis, or psychogenic disorders.5 The diagnosis is made clinically, based on the International Classification of Headache Disorders, 3rd edition, which requires a headache that develops in temporal relation with one of either low CSF pressure (< 60 mm of CSF) or imaging features demonstrating or suggestive of CSF leak.6 Currently, no criterion standard diagnostic test exists; the site of CSF leak in the spine is not always identified on imaging and a wide range of CSF opening pressures has been observed. For various clinical and practical considerations, contrast-enhanced MR imaging of the head is frequently the first-line investigation to confirm the diagnosis and rule out other mimics. However, even classically described imaging features are not always present and, at times, can be challenging to objectively report.7⇓⇓⇓⇓–12 For example, the most sensitive MR imaging finding for intracranial hypotension is pachymeningeal enhancement, but this can also be seen routinely in postoperative or post-lumbar puncture cases.7,8 Brain stem slumping has shown reasonable specificity for the syndrome, but the finding is only present in approximately 51% of cases and can be subjective.8⇓⇓⇓–12 These issues have led to attempts to develop more objective criteria in determining low CSF volume.11⇓–13 We propose a quantitative marker, the interpeduncular angle, to support the diagnosis of intracranial hypotension on MR imaging as a quick and reproducible measure. We aimed to investigate the relationship between this angle and the diagnosis of intracranial hypotension as well as its correlation to classically described imaging findings.