Novel Approach to Diagnosing Primary Orbital Melanoma: Case Report and Emerging Role of PET Imaging
Author: Shehnaz Bazeer
Base Hospital / Institution: Moorfields Eye Hospital
ePoster presentation
Abstract ID: 25-499
Purpose
Primary orbital melanoma (POM) is a rare and challenging malignancy that poses significant diagnostic difficulties due to its resemblance to other orbital pathologies in both clinical presentation and imaging findings. Conventional imaging techniques, remain the primary tools for evaluating orbital tumours. However, these modalities often fail to distinguish POM from benign or other malignant lesions accurately. We present a rare case in which a surveillance PET scan detected metabolic activity in a long-standing lesion with previously no signs of avidity for POM.
Methods
A 58-year-old female with history of primary colorectal adenocarcinoma was referred for evaluation of a right orbital mass. The lesion had been identified on an initial PET scan in 2021 but was not metabolically active at that time. However, a follow-up surveillance PET in 2024 revealed increased avidity at the same site, suggesting a change in tumour behaviour.
The patient was asymptomatic, with normal ocular and orbital exam findings.
Due to the suspicion of metastatic disease, an excisional biopsy was performed. Histopathological analysis confirmed the presence of large spindle-celled melanoma and GNAQ, a common marker for melanocytic neoplasms was found to be positive.
There were no abnormal findings on additional systemic workup, thus supporting POM. Patient was referred for a combination of orbital radiotherapy and immunotherapy.
Results
Histopathology remains the gold standard for POM diagnosis. Our case’s unexpected PET avidity raises key questions. While PET aids melanoma detection elsewhere, its role in POM is unclear. Variability in reported PET findings suggests fluctuating metabolic activity, possibly due to tumour dormancy or biology. Further research is needed to determine if PET can reliably track POM over time.
Conclusion
There is a strong rationale for integrating PET imaging into the diagnostic and surveillance strategy for POM. If scans can reliably detect metabolic activity at earlier stages than conventional imaging, they may serve as an invaluable tool for treatment planning and disease monitoring.
Additional Authors
| First name | Last name | Base Hospital / Institution |
|---|---|---|
| Mohsan M. | Malik | Moorfields Eye Hospital |
| Gabriella | Guevara | Moorfields Eye Hospital |
| Geoffrey E. | Rose | Moorfields Eye Hospital |
| David H. | Verity | Moorfields Eye Hospital |
