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Epidermoid Cyst
Esther H. Y. Hung, MBChB, FRCR, FHKCR, FHKAM (Radiology); James F. Griffith, MD, MRCP, FRCR
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KEY FACTS

  • Terminology

    • Imaging

      • Top Differential Diagnoses

        • Diagnostic Checklist

          TERMINOLOGY

          • Synonyms

            • Epidermal inclusion cyst, epidermal cyst, infundibular cyst, sebaceous cyst
          • Definitions

            • Slow-growing subdermal cyst that contains keratin and is lined by stratified squamous epithelium
              • Most cysts are due to ductal blockage of hair follicles with downward rupture of obstructed pilosebaceous unit
              • Some cysts are due to traumatic or embryological subdermal sequestration of epithelial tissue
                • Histologically similar and hence grouped under general term "epidermoid cyst"
              • Wall of cyst must not contain dermal elements
                • Presence of dermal elements → designation as dermoid cyst
              • Epidermis = outer layers of skin
                • Contains keratinocytes, corneocytes, and melanocytes
              • Dermis = inner layers of skin that support epidermis
                • Contains hair follicles, nerves, sweat glands, small blood vessels, and sebaceous glands

          IMAGING

          • General Features

            • Radiographic Findings

              • CT Findings

                • MR Findings

                  • Ultrasonographic Findings

                    • Imaging Recommendations

                      DIFFERENTIAL DIAGNOSIS

                        PATHOLOGY

                        • General Features

                          • Gross Pathologic & Surgical Features

                            CLINICAL ISSUES

                            • Presentation

                              • Demographics

                                • Natural History & Prognosis

                                  • Treatment

                                    DIAGNOSTIC CHECKLIST

                                    • Consider

                                      Selected References

                                      1. Clarke R et al: Twinkle artefact in the ultrasound diagnosis of superficial epidermoid cysts. Ultrasound. 24(3):147-153, 2016
                                      2. Park HJ et al: Strain elastography features of epidermoid tumours in superficial soft tissue: differences from other benign soft-tissue tumours and malignant tumours. Br J Radiol. 88(1050):20140797, 2015
                                      3. Hung EH et al: Pitfalls in ultrasonography of soft tissue tumors. Semin Musculoskelet Radiol. 18(1):79-85, 2014
                                      4. Hung EH et al: Ultrasound of musculoskeletal soft-tissue tumors superficial to the investing fascia. AJR Am J Roentgenol. 202(6):W532-40, 2014
                                      5. Yuan WH et al: Differences in sonographic features of ruptured and unruptured epidermal cysts. J Ultrasound Med. 31(2):265-72, 2012
                                      Related Anatomy
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                                      Related Differential Diagnoses
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                                      References
                                      Tables

                                      Tables

                                      KEY FACTS

                                      • Terminology

                                        • Imaging

                                          • Top Differential Diagnoses

                                            • Diagnostic Checklist

                                              TERMINOLOGY

                                              • Synonyms

                                                • Epidermal inclusion cyst, epidermal cyst, infundibular cyst, sebaceous cyst
                                              • Definitions

                                                • Slow-growing subdermal cyst that contains keratin and is lined by stratified squamous epithelium
                                                  • Most cysts are due to ductal blockage of hair follicles with downward rupture of obstructed pilosebaceous unit
                                                  • Some cysts are due to traumatic or embryological subdermal sequestration of epithelial tissue
                                                    • Histologically similar and hence grouped under general term "epidermoid cyst"
                                                  • Wall of cyst must not contain dermal elements
                                                    • Presence of dermal elements → designation as dermoid cyst
                                                  • Epidermis = outer layers of skin
                                                    • Contains keratinocytes, corneocytes, and melanocytes
                                                  • Dermis = inner layers of skin that support epidermis
                                                    • Contains hair follicles, nerves, sweat glands, small blood vessels, and sebaceous glands

                                              IMAGING

                                              • General Features

                                                • Radiographic Findings

                                                  • CT Findings

                                                    • MR Findings

                                                      • Ultrasonographic Findings

                                                        • Imaging Recommendations

                                                          DIFFERENTIAL DIAGNOSIS

                                                            PATHOLOGY

                                                            • General Features

                                                              • Gross Pathologic & Surgical Features

                                                                CLINICAL ISSUES

                                                                • Presentation

                                                                  • Demographics

                                                                    • Natural History & Prognosis

                                                                      • Treatment

                                                                        DIAGNOSTIC CHECKLIST

                                                                        • Consider

                                                                          Selected References

                                                                          1. Clarke R et al: Twinkle artefact in the ultrasound diagnosis of superficial epidermoid cysts. Ultrasound. 24(3):147-153, 2016
                                                                          2. Park HJ et al: Strain elastography features of epidermoid tumours in superficial soft tissue: differences from other benign soft-tissue tumours and malignant tumours. Br J Radiol. 88(1050):20140797, 2015
                                                                          3. Hung EH et al: Pitfalls in ultrasonography of soft tissue tumors. Semin Musculoskelet Radiol. 18(1):79-85, 2014
                                                                          4. Hung EH et al: Ultrasound of musculoskeletal soft-tissue tumors superficial to the investing fascia. AJR Am J Roentgenol. 202(6):W532-40, 2014
                                                                          5. Yuan WH et al: Differences in sonographic features of ruptured and unruptured epidermal cysts. J Ultrasound Med. 31(2):265-72, 2012