While rarely clinically significant, the distinction between hamartomas and choristomas is nevertheless often testable.
A hamartoma is an anomalous overgrowth of mature tissue at a normal site. For example, as in the above, capillary hemangioma, plexiform neurofibromas, and nevi are hamartomas. In each example, the primary type of tissue normally exists at that site. In the above examples, those would be endothelial cells, nerve tissue, or melanocytes, respectively.
A choristoma, on the other hand, is an overgrowth of normal tissue at an abnormal site. For example, dermolipomas, dermoid cysts, and teratomas are choristomas.
Dermoid cysts and dermolipomas are commonly associated with Goldenhar syndrome (aka oculo-auriculovertebral syndrome). Patients can have hemifacial microsomia, preauricular skin anomalies, and vertebral abnormalities in addition to dermoid cysts.