Case discussion
01Clinical context
A middle-aged patient with long-standing left leg pain and swelling underwent MRI and radiographs due to abnormal tibial appearance on X-rays.
02Key imaging findings
MRI of the left tibia shows a long-segment expansile lesion involving the mid to distal tibial shaft, measuring approximately 3.5 × 2.4 cm transversely and anteroposteriorly, with cortical thickening and smooth periosteal new bone formation. Radiographs demonstrate a characteristic advancing geographic lytic front with adjacent sclerosis, producing the classic "blade of grass" appearance. MRI signal changes and post-contrast enhancement indicate active osseous remodeling consistent with the lytic/mixed phase of Paget disease. No cortical breakthrough, pathological fracture, aggressive periosteal reaction, or soft-tissue mass is seen.
03Diagnostic reasoning
The imaging interpretation correlates the reported radiographic "blade of grass" appearance—an advancing geographic lytic front with adjacent sclerosis—with MRI findings of cortical thickening and heterogeneous marrow signal. Post-contrast enhancement is compatible with active remodeling in this context, but is not specific by itself. No aggressive periosteal reaction, cortical breakthrough, or soft-tissue mass was reported; these negative findings do not independently exclude malignancy or infection.
04Questions for clinical practice
What is the significance of the "blade of grass" sign? It indicates an advancing lytic front typical of Paget disease's active phase. Does the MRI show any signs of malignant transformation? No, there is no cortical breakthrough, pathological fracture, or soft-tissue mass. What further tests are recommended? Correlation with serum alkaline phosphatase and other bone turnover markers is advised to assess disease activity and guide management.
05Teaching point
The combination of the radiographic "blade of grass" sign with cortical thickening and MRI remodeling features supports Paget disease of bone in its lytic/mixed phase. Recognizing this pattern helps distinguish Paget disease from other bone disorders. Correlation with the clinical findings and biochemical markers remains important.
Shown for education. De-identified — no identifiable patient data. A radiology report is a specialist opinion and must be read with the full clinical context by the treating physician.