Rapidly enlarging orbital tumor in a facial fibrous dysplasia lesion.

Malignant change in fibrous dysplasia (FD) is a well-described phenomenon in the literature. When rapid enlargement is observed in an FD lesion, malignant change should be considered first. We present a case with McCune-Albright syndrome in which a rapidly enlarging orbital tumor developed in a facial FD lesion, which was subsequently proven to be a metastasis from an incidental esophageal carcinoma. Although metastasis of a malignant tumor to an FD lesion is quite rare and has been neglected as a differential diagnosis in the literature, it should be included in the important differential diagnosis because hematogenous metastasis could readily occur in FD due to its abundant blood flow. The importance of systemic examinations, such as positron emission tomography, is also emphasized.