Evaluation of the C1-C2 False Localizing Sign in Spontaneous Intracranial Hypotension: Prevalence and Clinical Insights

BACKGROUND AND PURPOSE: Dural tears are a major cause of spontaneous intracranial hypotension. The existence of a dural tear can be inferred by the presence of extradural CSF on spine MRI. However, extradural CSF usually spans multiple spinal levels, precluding localization of the dural tear on MRI. The C1-C2 false localizing sign (C1-C2 sign) refers to preferential pooling of extradural CSF dorsally at C1-C2, even though this is typically not the site of leak. While this has been described as an important false localizing sign, other potentially important features of this imaging finding have not been studied. Here, we sought to estimate the prevalence of the C1-C2 sign in patients with spontaneous dural tears and determine whether presence of the C1-C2 sign correlates with length of disease. MATERIALS AND METHODS: We retrospectively identified all patients diagnosed with a dural tear on dynamic CT myelography at our institution between January 2024 and January 2026. We excluded patients who did not have SIH or lacked pre-myelographic spine MRI with T2-weighted fat suppressed sequences. For patients in the final cohort, we recorded the time between symptom onset and initial spine MRI. The presence or absence of the C1-C2 sign on spine MRI was assessed by two neuroradiologists, with any disagreements adjudicated by a third neuroradiologist. The prevalence of the C1-C2 sign was calculated, and correlation with length of symptoms prior to MRI was determined using logistic regression. RESULTS: Our final cohort consisted of 50 consecutive patients with ventral or lateral dural tears localized on dynamic CT myelography. The C1-C2 sign was present in 23/50 (46%) patients. There was a statistically significant negative correlation between symptom duration prior to MRI and presence of the C1-C2 sign (p < 0.05). Furthermore, we identified 11 patients who underwent two spine MRIs prior to myelography. In 6/11 patients, the C1-C2 sign was initially present and resolved over time. CONCLUSIONS: The C1-C2 false localizing sign is associated with a relatively shorter disease duration. Its presence may be helpful in determining optimal treatment strategies in patients with dural tears.