[Congenital dermoid cyst over the anterior fontanelle: case report].

We report a case of a 35-month-old Japanese boy harboring a dermoid cyst in the region of the anterior fontanelle, which is rarely reported among Japanese. A small soft subcutaneous mass was noticed in the mid-frontal region at the age of 6 months. On admission, a soft, nontender round mass (2.5cm in diameter) was located over the anterior fontanelle. Transillumination was negative. Neurological examination yielded normal findings. MRI showed a well-circumscribed mass, which was slightly hypointense on T1W1 and hyperintense on T2W1. Midsagittal MRI showed no intracranial extension. At operation, a well-encapsulated mass was found beneath the pericranium, which was easily dissected from the underlying dura mater and removed. The tumor contained caseous material and several hairs. Microscopically, the cyst wall consisted of connective tissues lined by stratified squamous epithelium. Sebaceous glands and hair follicles were found in the subepithelial layer. It is important to confirm preoperatively whether or not the extracranial mass extends into the intracranial cavity. For this purpose, midsagittal or coronal MRI seems to be most useful.