Retrospective validation of the Birmingham atypical cartilage tumor imaging protocol (BACTIP) in a single, United States tertiary care center.

Background: Central cartilage tumors are common incidental lesions around knee and shoulder joints. Differentiation of low-grade chondroid lesions, such as enchondroma from atypical cartilaginous tumor (ACT) is often difficult on imaging given pathologic and radiologic similarities. The Birmingham atypical cartilage tumor imaging protocol (BACTIP) provides a guide to initial assessment and imaging follow-up for incidental indeterminate central cartilage tumors.

Objective: This study retrospectively evaluates BACTIP in a United States tertiary care center.

Methods: Indeterminate central cartilage tumors in the proximal humerus, distal femur, and proximal tibia of adults were identified by a keyword search in the health network picture archiving and communications systems (PACS). These were categorized into one of seven BACTIP categories based on criteria including size and degree of endosteal scalloping.

Results: There were 292 cases that met the inclusion criteria. The final diagnosis of enchondroma was 100% for lesion types IA and IB, 66% for IC, and 50% for IIB; ACT was 33% for IC and 50% for IIB. Of the type IIC lesions, 43% were diagnosed as intermediate or high-grade chondrosarcoma. Pathology diagnosis was dedifferentiated chondrosarcoma in 75% of type III lesions. Chart review and follow-up imaging revealed no delay of diagnosis. The malignant transformation rate in this study was 0.3%.

Conclusion: There were no cases where the application of BACTIP would have led to a delayed diagnosis. The BACTIP would serve as a conservative and appropriate imaging follow-up guideline for patients with central cartilage tumors around the shoulder and knee joint.