Classic Case

Figure Caption
Dermoid cysts are most commonly located at the floor of of the mouth in the head and neck region. When they occur in the anterior neck, midline and suprahyoid location is charateristic. Clinically, the cyst is soft, mobile, and slow growing (A). Histopathologically, the lumen of the cyst is filled with a mixture of keratin, sebaceous material, and occasionally, hair. On CT, the cyst may appear to be filled with marbles (arrows in B) due to the coalescence of fat into small nodules within the fluid matrix. This “sack-of-marbles” appearance (C) is virtually pathognomonic for a dermoid cyst in this location. On US, depending on the contents of the fluid, the cystic background can be heterogeneous or even hyperechoic, and the fat nodules become relatively hypoechoic (arrows in D); although, hyperechoic fat nodules are also common.