Sequential Application of the Birmingham Atypical Cartilage Tumor Imaging Protocol and Radiological Aggressiveness Score in Long-Bone Intramedullary Cartilage Tumors: A Retrospective Cohort Study

Background: The Birmingham Atypical Cartilage Tumor Imaging Protocol (BACTIP) addresses referral triage, whereas the Radiological Aggressiveness Score (RAS) estimates resection-grade histology. We evaluated their sequential application in a selected tertiary-center cohort. Methods: This retrospective study included 99 patients during 2001–2025, combining consecutive eligible surgical chondrosarcomas with a nonconsecutive enchondroma sample. Groups comprised lesions outside BACTIP referral categories, referral-category lesions with RAS < 4, and referral-category lesions with RAS ≥ 4. Diagnostic performance for resection-grade disease (grade 2, grade 3, or dedifferentiated chondrosarcoma) and exploratory, unadjusted oncologic outcomes were assessed. Results: All 47 resection-grade tumors met BACTIP referral criteria (sensitivity 100%; 95% CI, 92.4–100%). Requiring RAS ≥ 4 increased whole-cohort specificity from 69.2% to 94.2% and reduced sensitivity to 91.5% (95% CI, 80.1–96.6%). RAS positivity alone and sequential classification identified identical patients. Four grade 2 tumors were RAS-negative despite BACTIP category 3 classification, and grade 2 sensitivity was 78.9% (15/19). Excluding dedifferentiated tumors, sensitivity was 83.3% (20/24). Oncologic events were concentrated in the referral/RAS-positive group, and global log-rank comparisons were significant for all three endpoints (p < 0.001). Conclusions: BACTIP may structure referral assessment, while RAS may further characterize imaging aggressiveness in lesions meeting referral criteria. The four RAS-negative grade 2 tumors underscore the importance of maintaining specialist referral when BACTIP referral criteria are met, even when RAS suggests lower imaging aggressiveness. Neither tool replaces clinical assessment, histopathological correlation, or multidisciplinary review. This selected cohort does not establish safe nonreferral, independent prognostic value, or improved management or outcomes. Prospective validation in the intended referral population is required.