Dermoid, retroauricular scalp

9-year-old male that presented with swelling behind the left ear. There is a well circumscribed, round, T1-hypointense, nonenhancing, T2/FLAIR-hypointense lesion which restricts diffusion. The lesion overlies the left occipitotemporal suture, and there is chronic remodeling/thinning of the outer cortical calvarial table at those sites. The findings are compatible with an epidermal inclusion cyst. While the diffusion restriction and off-midline location favor an epidermoid, the intimate association with the underlying suture favors a dermoid cyst. On resection, this was found to be a dermoid. Epidermal inclusion cysts are thought to be secondary to aberrant epidermal or dermal inclusion in the calvarium. Most present between 20 and 40 years of age with dermoids slight larger than epidermoids.