Click the arrow to see the next slide with the correct interpretation.
Right-Sided Hearing Loss
This case features a patient presenting with right-sided hearing loss, ultimately diagnosed with an epidermoid cyst of the external auditory canal (EAC).
Imaging overview:
Axial CT demonstrates smooth remodeling of the right external auditory canal consistent with slow-growing expansion without cortical destruction. Axial T2 3D SPACE MRI shows mixed signal intensity within the lesion rather than the typically expected CSF-like T2 hyperintensity. Coronal DWI HASTE demonstrates marked diffusion restriction within the lesion, a key feature distinguishing epidermoid cyst from other EAC masses.
Clinical insight:
Epidermoid cysts of the external auditory canal are slow-growing lesions that expand by accumulation of desquamated keratin. On CT, smooth osseous remodeling without cortical destruction reflects the indolent growth pattern, in contrast to EAC cholesteatoma, which typically demonstrates osseous erosion. T2 signal is usually hyperintense and similar to CSF, though mixed signal can be seen as in this case. Marked diffusion restriction on DWI is the most reliable imaging feature and is essential for diagnosis, particularly when T2 signal is atypical. Recognition of smooth remodeling versus erosion is critical for distinguishing epidermoid cyst from cholesteatoma, as the two entities have different management implications.
Case courtesy of Lindsey Wood, MD, and Brian Graner, MD, Indiana University School of Medicine.