Presentation
Incidental finding on CT.
Patient Data
Midline posterior fossa tumor favored to be extra-axial, solid-cystic, with intrinsically dense solid content and flecks of peripheral calcification. It does not cause a significant mass effect in the posterior fossa; the fourth ventricle is preserved.
There is a midline posterior fossa tumor favored to be extra-axial and located posterior to the vermis and in between the cerebellar hemispheres, pushing against them. It appears to be predominantly cystic, showing heterogenous signal intensity, with the more solid portions having an intense intrinsic high T1 signal and patchy low T2 signal, with no convincing internal enhancement. There are marginal linear blooming artefacts on SWI, and flecks of calcifications have been shown on the previous CT. Heterogeneous restriction diffusion is noted throughout the lesion. The lesion does not cause a significant mass effect in the posterior fossa; there are no cerebellar signal abnormalities and the fourth ventricle is preserved. The remainder of the brain appears normal.
Case Discussion
The left posterior fossa tumor shows imaging features of an atypical "white" epidermoid. Absence of oily component makes this less likely to be a dermoid cyst, although they are essentially along a continuum.
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