Assessment of 3D T2-weighted high-sampling-efficiency technique (SPACE) for detection of cerebellar tonsillar motion: new useful sign for Chiari I malformation

Abstract Objective To describe tonsillar blackout sign (TBS) on three-dimensional (3D)-SPACE, evaluate its performance in identifying Chiari malformation (CM1) as diagnostic marker, and investigate its role in differentiation of symptomatic and asymptomatic CM1. Methods One-hundred fifty-six patients were divided into two groups based on caudal displacement of cerebellar tonsils: CM1 (Group I) and non-CM1 (Group II). Group I was subclassified as symptomatic and asymptomatic by a neurosurgeon. Two radiologists evaluated TBS and cerebrospinal fluid flow abnormality. Results All subjects presenting TBS had CM1. Difference in presence of TBS between Group I and Group II was highly significant ( P < .001).Grading of TBS in symptomatic patients was significantly higher than that in asymptomatic patients ( P < .001). Conclusion TBS is highly suggestive of CM1 and potentially useful in differentiation of symptomatic and asymptomatic CM1.