Characteristic MRI Findings of Epidermal Cysts Categorized by Size

Abstract

Background: Epidermal cysts are lined with stratified squamous epithelium and filled with keratinous material.Magnetic resonance imaging (MRI) findings can be used for the diagnosis of epidermal cysts, but characteristic MRI findings related to cyst size in particular go unreported. Objective: To analyse characteristic MRI findings of epidermal cysts categorized by size. Materials and Methods: Unruptured epidermal cyst cases were analyzed according to 3 cyst size categories: large (≥4 cm), medium (≥2 to <4 cm), and small (<2 cm). MRI assessments focused on the keratinized material using low signal intensity on T2-weighted images because of intracystic diffuse foci (a sign of intracyst debris) and serpentine structures at the periphery (a sign of a peripheral lining) of cysts. Results: Thirty-three patients (26 males and 7 females; average age, 52.2 years; 33 cases) were grouped by cyst size: large (13 cases), medium (12 cases), and small (8 cases). MRIs revealed cyst walls via low signal intensity on T1- and T2-weighted images. On T1-weighted images, the signal intensity of cysts relative to that of muscle was hypointense (1 case, 3%), isointense (4 cases,12%), and slightly hyperintense (28 cases, 85%). On T2-weighted images, cysts were hyperintense in muscle relative to adipose tissue (20/33 cases, 61%) and isointense relative to adipose tissue (7/33, 21%) or hyperintense relative to adipose tissue (6/33, 18%). Overall, signal patterns were similar among groups. Signs of inner debris were observed in all large (13, 100%) and medium (2/12, 17%) cysts, but not in small cysts (0/8). Large, medium, and small cysts had signs of peripheral linings (12/13, 92%; 9/12, 75%; and 4/8, 50%, respectively). Conclusion: Slightly hyperintense signals on T1-weighted images were characteristic, even in small epidermal cysts. Signs of intracyst debris and a peripheral lining reflect the pathology and were considered useful for diagnosis. Larger cysts were more frequently positive for keratinous debris.