Scar sarcoidosis: A rare entity found by 18F-FDG-PET/CT

Area of Science:

• Oncology
• Nuclear Medicine
• Pathology

Background:

• ¹⁸F-labeled fluoro-2-positron deoxyglucose emission tomography/computed tomography (FDG-PET/CT) is a standard imaging technique for cancer staging and recurrence detection.
• FDG-PET/CT uptake is not specific to malignancy and can be observed in various benign inflammatory and infectious conditions.
• Sarcoidosis, a systemic inflammatory disease, can rarely manifest as scar sarcoidosis.

Observation:

• A 60-year-old male patient with a history of colon adenocarcinoma and clear cell renal cell carcinoma presented with suspected tumor recurrence.
• FDG-PET/CT revealed increased fluorodeoxyglucose uptake in mediastinal and left supraclavicular lymph nodes.
• Hypermetabolic cutaneous foci were noted at previous surgical scar sites.

Findings:

• Skin biopsy of the cutaneous foci was performed.
• Histopathological examination of the skin biopsy was suggestive of sarcoidosis.
• The findings indicate that FDG-PET/CT can identify scar sarcoidosis, which may be mistaken for malignancy.

Implications:

• FDG-PET/CT findings in patients with a history of cancer should be interpreted cautiously, considering potential benign causes of increased uptake.
• Recognition of scar sarcoidosis on FDG-PET/CT is crucial to avoid misdiagnosis of tumor recurrence.
• Further investigation may be warranted in cases with atypical FDG-PET/CT findings, especially in patients with inflammatory conditions.