Abstract: Objective To describe characteristic presentation of rare primary orbital malignant melanoma in Chinese, and analyze the differences between Chinese cases and Caucasian cases. Design Retrospective case series. Participants Three cases with primary orbital melanoma under the care of the Oncology Clinic at Beijing Tongren Hospital. Methods Retrospective review of clinical presentation, treatment, radiology and pathology characteristics for the three cases. Main Outcome Measures Clinical manifestation, MRI appearances, and pathology characteristics. Results Thorough physical examination of all the three patients demonstrated the absence of cutaneous or mucous melanoma, excluding the possibility of metastatic melanoma. No pigmentary disorders were visible on face, eyelid, conjunctiva, and sclera, excluding the pathologic basis of congenital melanosis. MRI of two cases was consistent with the typical characteristics of melanoma, but MRI of one case didn’t suggest melanoma. Pathologic examination revealed the pathologic type of the three cases, which was spindle cell, epithelial cell and mixed cell melanoma, respectively. One case originated from the inner wall of cyst, which is a definite cystic epithelial basis, so it could be presumed that the melanocytes migrated from the neural crest and adherent to the cystic wall epithelial cells might be the origination of orbital melanoma. All the three cases were treated by primary resection. After surgery, two cases accepted systemic chemotherapy and one patient did not. There has been no recurrence or metastasis in 40 to 48 months follow-up. Conclusion MRI may provide some clues for pre-operation diagnosis of primary orbital malignant melanoma. The melanocytes adherent to the inner wall of cysts may be the origination of the tumor. These encapsulated tumors may be treatable by primary resection.

Key words: melanoma, orbital, MRI, pathology