ADC Mapping in the Differential Diagnosis of Choroid Fissure Cysts and Arachnoid Cysts: A ROC Analysis-Based Study

Background/Aims: This study aimed to investigate the differences in mean apparent diffusion coefficient (ADC) values between choroid fissure cysts (CFCs) and arachnoid cysts (ACs) and to evaluate the contribution of these measurements to radiological differential diagnosis. Methods: Seventy-two patients diagnosed with CFC (n=36) and AC (n=36) via brain MRI were retrospectively reviewed. Measurements were performed independently by two radiologists with 15 years of experience. Inter-observer agreement was assessed using the intraclass correlation coefficient (ICC). ADC measurements were obtained using standardized regions of interest (ROIs) placed at the cyst centers. Demographic data, cyst sizes, mean ADC values and MR signal characteristics were examined. Results: Cyst sizes and mean ADC values were significantly higher in the AC group compared to the CFC group (p<0.001). Inter-observer agreement was excellent in cyst size measurements (0.99-1.00) and high in ADC measurements (0.972 for CFC, 0.717 for AC). To differentiate CFC from AC, the optimal ADC cut-off value was determined as ≤2.85×10⁻³ mm²/s (sensitivity 63.9%, specificity 100.0%, AUC=0.831, p<0.001). Conclusions: Uncomplicated CFCs and ACs are benign cystic lesions that do not show diffusion restriction. Lesions such as epidermoid cysts and abscesses, which can be confused with CFC and AC, show diffusion restriction, which is diagnostic in these lesions. The higher ADC values found in ACs compared to CFCs are useful in resolving diagnostic confusion, especially in AC located near the choroid fissure. The ADC cut-off value determined for CFCs in this study is one of the rare quantitative data in the literature and may guide future studies.