Radiologic Findings of Epidermal Cysts in the Trunk

ABSTRACT

PURPOSE: To evaluate the ultrasonographic (US) or computer tomography (CT) findings of surgically proven epidermal cysts in the trunk, and to compare the echogenicity of cysts with internal contents. MATERIALS AND METHODS: Forty-five patients were retrospectively evaluated. US and CT findings of epidermal cysts were assessed in regard to location, size, shape, number, echogenicity, posterior sound enhancement, internal density, septa, mural nodule and calcification, perilesional infiltration, contrast enhancement, and internal contents. RESULTS: All 45 patients (M: F=29: 16; US in 26, CT in 19) had only one cyst, and they were located in the buttocks (n=19), back (n=13), inguinal (n=4), posterior neck (n=3), perineum (n=2), abdominal wall (n=2), presternal (n=1), and axilla (n=1). Of 26 patients who underwent US, there were 8 cases of homogeneously hypoechoic mass (30.8%), 8 of inhomogeneously hypoechoic mass (30.8%), 7 of homogeneously hypoechoic mass with internal hypoechoic lines and echogenic spots (26.9%) and 3 of homogeneously hypoechoic mass with internal echogenic spots (11.5%). Posterior sound enhancement was noted in 21 patients (80.8%). Of 19 patients who underwent CT, there were 14 cases of simple cyst (73.7%) and 5 of abscess-like lesion (26.3%). Overlying skin thickening (n=13), contrast enhancement of cystic wall (n=11), perilesional infiltration (n=7), and internal septa (n=6) were demonstrated. The internal contents of the cysts were keratinous (n=27, 60.0%) or greasy (n=15, 33.3%) material. There was no statistical significance between the echogenicity of the cysts and the internal contents (p >0.2). CONCLUSION: Epidermal cysts showed homogeneous or inhomogeneous hypoechoic mass with posterior sound enhancement on US. There was no relationship between the echogenicity of the cysts and the internal contents. In the case of ruptured cyst, an abscess-like lesion with wall enhancement and perilesional infiltration was noted on CT scan.