OBJECTIVE. The purpose of this study was to assess the a priori chance that primary cystic lesions of the retrorectal space are malignant and to investigate MRI characteristics that indicate malignancy. MATERIALS AND METHODS. Patients referred to a center for colorectal surgery were recruited from 2000 to 2014. Lesions were proven by clinical assessment and histopathology. MRI was performed at 1.5 T with examinations evaluated by two radiologists. Interobserver agreement was assessed (Cohen kappa) and differences between malignant and benign lesions calculated (Fisher exact test). RESULTS. Twenty-eight patients (22 women, six men; age range, 18-70 years) with 31 lesions were included. Lesions were categorized as tailgut cysts (n = 16, 52%), teratomas (n = 9, 29%), lesions of colorectal origin (n = 4, 13%), or neurogenic lesions (n = 2, 6%). Five patients (18%) had malignant lesions. Colorectal lesions had the highest percentage of malignancy (3/4, 75%). A solid tissue component was found in all five (100%) malignant lesions and two (8%) of the benign lesions, which were both teratomas (p < 0.05). Sensitivity and specificity for malignancy according to the presence of a solid tissue component was 100% (5/5) and 92% (24/26). For unilocularity, multilocularity, debris, septa, and wall thickening, differences were not significant. Interobserver agreement was excellent (κ = 1) for all characteristics except debris (κ = 0.795). CONCLUSION. The majority of retrorectal cystic lesions are benign. The presence of a solid tissue component should raise suspicion for malignancy.

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doi.org/10.2214/AJR.16.17329, hdl.handle.net/1765/102191
American Journal of Roentgenology
Erasmus MC: University Medical Center Rotterdam

Dwarkasing, R., Verschuuren, S., Leenders, G., Braun, L.M.M. (Loes M. M.), Krestin, G., & Schouten, R. (2017). Primary cystic lesions of the retrorectal space: MRI evaluation and clinical assessment. American Journal of Roentgenology, 209(4), 790–796. doi:10.2214/AJR.16.17329