Cerebellopontine angle epidermoid cyst
Headache with left tinnitus
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Left cerebellopontine angle well defined lobulated lesion with the same CSF signal on both T1 and T2 weighted sequences but is 'iso to high' on FLAIR. DWI demonstrates very bright signal with intermediate ADC values similar to brain parenchyma.
The major differential of an Epidermoid cyst of the cerebellopontine angle is an Arachnoid cyst . Both of them is well defined and with homogeneous low density, identical to cerebrospinal fluid on computerized tomographic scan, and never enhances. On MRI, both cysts usually appear of low signal on T1-weighted images and high signal on T2-weighted images. On fluid-attenuated inversion recovery, an arachnoid cyst demonstrate similar signal to the cerebrospinal fluid , whereas an epidermoid becomes of high signal. Unfortunately sometimes an epidermoid may have a low-intensity on fluid-attenuated inversion recovery, here it comes the role of a diffusion scanning, on which an epidermoid appears bright.