In Reply: Spinal Intradural Arachnoid Cysts in Adults: An Institutional Experience and Literature Review

To the Editor: Liu and Lam raise excellent points regarding differences in management and clinical outcomes between primary and secondary spinal intradural arachnoid cysts.1 The authors described several cases of secondary cysts with variable clinical outcomes after surgical intervention.1 Our institutional experience has mostly consisted of lesions of primary origin of which the vast majority experienced a significant reduction in back pain after operative intervention.2 However, our literature review demonstrated significant differences in the natural history and clinical outcomes of spinal intradural arachnoid cysts depending on primary vs secondary etiology.2 Although both etiologies were most commonly found around the T5 level, primary lesions were more likely to be associated with a syrinx on imaging whereas secondary lesions were more often localized ventral to the spinal cord. Importantly, there was a disparity in clinical outcomes dependent on etiology. The rate of symptomatic improvement after operative intervention for primary cysts was more than double compared with secondary cysts. Moreover, compared with primary cysts, the rates of radiographic progression and repeat surgery were each more than double for secondary cysts. These data support surgical intervention for symptomatic primary spinal intradural arachnoid cysts.2 However, surgical intervention should be carefully considered when dealing with secondary lesions given a higher likelihood of radiographic progression, necessity of repeat surgical intervention, and worse clinical outcomes. Indeed, as stated by Liu and Lam, the optimal management strategies of secondary spinal intradural arachnoid cysts remain unclear.1 Additional studies are necessary to further elucidate the natural history of secondary lesions and better understand the best treatment paradigms for these rare entities.