Birmingham atypical cartilaginous tumour imaging protocol (BACTIP) revisited.
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AIM: To revalidate an MRI protocol for the management of solitary central cartilage tumours (CCTs) of the proximal humerus and around the knee, excluding the proximal fibula. MATERIALS AND METHODS: Data on 387 patients with a solitary CCT assessed in a specialist orthopaedic oncology unit between 2007 and 2016 was updated and combined with a further 393 patients referred from 2017 to 2023. The initial MRI images and any follow-up scans were evaluated for craniocaudal length of the CCT, presence/absence of endosteal scalloping or aggressive/malignant features. The cases were categorised according to the BACTIP. Patient outcome was assessed to ascertain if the application of the protocol led to any delay in the diagnosis of high-grade chondrosarcoma (HGCS). RESULTS: HGCS is rare (7%) in this large series of 780 patients with a solitary CCT. Ascending BACTIP type correlates with malignancy. All Type IA, IB, and IIA lesions were either benign enchondroma or atypical cartilaginous tumour (ACT), whereas 69% of Type III were diagnosed as HGCS. Only 4 cases on follow-up MRI showed a delay in diagnosis with progression to a BACTIP Type III (Type IC x1 and Type IIB x3). All were identified within seven months of presentation and were shown to be HGCS. Therefore, malignant transformation is remarkably rare (0.4%) and tends to occur relatively early (<1year). CONCLUSION: This combined retrospective and prospective study confirms that BACTIP remains a useful tool for the general radiologist in determining which cases of CCT of the proximal humerus and around the knee would benefit from onward referral to a specialist orthopaedic oncology service. It may also have a further role in the future as management preferences for borderline CCTs move away from surgical intervention to a watch-and-scan policy.