Archives of the AFIP -- RadioGraphics

Figure Legend | Image

Figure 1: Schematics illustrate two theories of the formation of epidermoid and dermoid inclusion cysts. A, failure of surface ectoderm to separate from the developing neural tube. The surface ectoderm may "stick" to the underlying neural tube during early development. The surface ectoderm may then be drawn into the embryo, creating a fistulous tract or becoming completely sequestered as an enclosed cyst. Combinations of cyst and fistula may occur, and the cyst may be in the calvaria yet extradural, intradural yet extraaxial, intraaxial, or occasionally intraventricular. B, sequestration of surface ectoderm at lines of epithelial fusion during embryonic development. During the process of forming the eye, orbit, ear, and nose, there are secondary invaginations of surface ectoderm. Some of these invaginations close by fusion of the more superficial ectoderm, and some remain patent (eg, the external auditory canal, palpebral fissure). Inclusion cysts may form along the sites of fusion, as well as along the course of normal invaginations. (Reprinted, with permission, from reference 12.).

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