Vol. 6, Issue 2, Part A (2024)

Background: Skeletal metastases often present a diagnostic challenge, especially in cases of bone metastasis with an unknown primary tumor. Accurate identification of the primary tumor is crucial for optimal patient management. The integration of 18F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET/CT) into clinical practice has shown promise in enhancing diagnostic accuracy. This study evaluates the effectiveness of FDG-PET/CT in detecting primary tumors in patients presenting with bone metastasis of unknown origin.

Methods: This prospective study included 50 patients with bone lesions of unknown primary origin, referred from the outpatient oncology clinic at Benha University between April 2022 and February 2024. Patients underwent PET/CT scanning of the neck, chest, abdomen, and pelvis. The study population comprised 30 males and 20 females, aged 6 to 70 years. All patients fasted for 6-8 hours prior to FDG injection, and scans were performed one hour post-injection. The PET/CT images were analyzed for the detection of primary tumors, with histopathological findings used as the reference standard.
Results: FDG-PET/CT detected primary malignancies in 41 out of 43 malignant bone lesions, yielding a sensitivity of 95.3%. Specificity was recorded at 85.7%, with 6 out of 7 benign lesions correctly identified as non-malignant. The overall accuracy of FDG-PET/CT in detecting malignant bone lesions was 94%. Additionally, PET/CT identified extraosseous lesions in 33 cases, with lymph node involvement in 21 patients, and further organ involvement in 17 of these cases. Patients aged above 40 years exhibited statistically significant differences in the presence of extraosseous lesions (p=0.04) and a higher frequency of multifocal bone lesions (p=0.04) compared to younger patients. Sclerotic lesions were more prevalent in patients older than 40 years, while osteolytic lesions were more common in those under 40 years (p=0.03).

Conclusion: FDG-PET/CT is a highly sensitive and accurate imaging modality for detecting primary tumors in patients with bone metastasis of unknown origin. It demonstrates significant potential in guiding the diagnostic work-up and management of these challenging cases, particularly in identifying extraosseous disease and specific bone lesion characteristics.