Bone SPECT is more sensitive than MRI in the detection of early osteonecrosis of the femoral head after renal transplantation

We compared the diagnostic sensitivity of Tc-99m-methylene diphosphonate bone SPECT and MRI in the early detection of femoral head osteonecrosis after renal transplantation. Methods: The patients were 24 renal allograft recipients who underwent both bone SPECT and MRI within 1 mo of each other because of hip pain but normal findings on plain radiography. SPECT was considered positive for osteonecrosis when a cold defect was detected in the femoral head, and the defect was further classified according to the presence of adjacent increased uptake: type 1 = a cold defect with no adjacent increased uptake; type 2 = a cold defect with adjacent increased uptake. MRI was considered positive for osteonecrosis when a focal region with low signal intensity on T1 images was detected in the femoral head. Final diagnoses were made by surgical pathology or clinical and radiologic follow-up of > 1 y. Results: A total of 32 femoral heads, including 24 of 29 painful hips and 8 of 19 asymptomatic contralateral hips, were confirmed as having osteonecrosis. SPECT detected osteonecrosis in all 32 of the femoral heads, resulting in a sensitivity of 100% (32/32), whereas MRI detected osteonecrosis in 21 femoral heads, for a sensitivity of 66% (21/32, P < 0.005). SPECT showed the type 1 pattern in 13 and the type 2 in 19. Ten of the 13 femoral heads with the type 1 pattern were false-negative on MRI, whereas only 1 of 19 with the type 2 pattern was normal on MRI (P < 0.001). There were 6 femoral heads with normal MRI findings and abnormal SPECT findings (type 1 pattern) in 3 patients, for whom hip pain decreased and radiographic findings were normal during follow-up. Follow-up bone SPECT showed a decreasing area of cold defect in 4 femoral heads. Conclusion: Tc-99m-methylene diphosphonate SPECT is more sensitive than MRI for the detection of femoral head osteonecrosis in renal transplant recipients. Bone scintigraphy with SPECT is needed to diagnose osteonecrosis in patients with hip pain despite normal radiography results after renal transplantation. The significance of a transient SPECT abnormality needs to be clarified by further natural history studies.