Imaging of gastrointestinal melanoma metastases: Correlation with surgery and histopathology of resected specimen.

Objective: To assess the appearance of gastrointestinal melanoma metastases on CT and PET/CT and evaluate the diagnostic value of CT and PET/CT compared with surgery and histopathology.
Methods: We retrospectively included 41 consecutive patients (aged 56.1 ± 13.5 years) with gastrointestinal melanoma metastases who underwent preoperative imaging (CT: all, PET/CT: n = 24) and metastasectomy. Two blinded radiologists assessed CT and PET/CT for gastrointestinal metastases and complications. Diagnostic accuracy and differences regarding lesion detectability and complications were assessed, using surgical findings and histopathology as standard of reference.
Results: Fifty-three gastrointestinal melanoma metastases (5.0 ± 3.8 cm) were confirmed by surgery and histopathology. Lesions were located in the small bowel (81.1 %), colon (15.1 %) and stomach (3.8 %), and described as infiltrating (30.2 %), polypoid (28.3 %), cavitary (24.5 %) and exoenteric (17.0 %). Fifteen patients (37 %) had gastrointestinal complications. Higher complication rates were associated with large and polypoid lesions (p ≤ .012). Diagnostic accuracy was high for CT and PET/CT (AUC ≥ .802). For reader B (less experienced), CT yielded lower diagnostic accuracy than PET/CT (p = .044).
Conclusion: Most gastrointestinal melanoma metastases were located in the small bowel. Large and polypoid metastases were associated with higher complication rates. PET/CT was superior for detection of gastrointestinal melanoma metastases and should be considered in patients with limited disease undergoing surgery.
Key Points: • Gastrointestinal melanoma metastases (GI-MM) are rare but often cause serious gastrointestinal complications. • Early detection of GI-MM is important to prevent complications and guide surgery. • PET/CT is superior to CT for detection of GI-MMs. • PET/CT should be considered for patients with limited disease before surgical resection.