• Anousheh Sayah, Frank Berkowitz, and Rashmi S Thakkar.
• Division of Neuroradiology, Department of Radiology, Medstar Georgetown University Hospital, Washington, DC, USA.
• J Neuroimaging. 2021 Sep 1; 31 (5): 1028-1034.

Background And PurposeColloid cysts are relatively rare intracranial lesions located in the rostral aspect of third ventricle. They may produce acute hydrocephalus, brain herniation, and death. On conventional MRI, the appearance of a colloid cyst varies depending on its composition. Small isointense cysts can be missed. The purpose of this study is to introduce a new sign, "black rim susceptibility" sign for the accurate diagnosis of colloid cyst on susceptibility weighted imaging (SWI).MethodsA retrospective case-control study consisted of 100 MRI brain scans (19 cases and 81 controls) performed from January 2012 to September 2018. Two fellowship trained neuroradiologists individually interpreted SWI sequences for the presence of the "black rim susceptibility" sign (thin rim of dark signal along the periphery of a rounded, hyperintense focus).ResultsThe sample was 43% male and 57% female, with an average age of 51.8 ± 17.7. Out of 19 cases, 9 had undergone surgery in which pathology had confirmed colloid cyst. Sensitivity, specificity, and accuracy for reader 1 was 94.8%, 98.8%, and 98% and for reader 2 was 89.5%, 100%, and 98%, respectively. Positive predictive value and negative predictive value for reader 1 was 94.7% and 98.8% and for reader 2 was 100% and 97.6%, respectively. Interrater correlation between the two readers was calculated with kappa of 0.93.ConclusionThe black rim susceptibility appearance of colloid cyst on SWI is a novel description and an effective sign that can be used by radiologists for accurate diagnosis.© 2021 American Society of Neuroimaging.

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