MRI surpasses CT and plain film in bone marrow disease

Although plain-film radiography and CT can be used to image bone marrow, MRI provides the best results and should be the primary imaging tool for suspected bone marrow pathology, according to an ECR presentation by German researchers. With MRI, radiologists can not only detect bone marrow problems but also differentiate between yellow (fatty) marrow and red (hematopoietic) marrow. Changes in bone marrow type can also indicate a variety of pathology.

CT and plain film play a role in bone imaging for conditions that may involve the marrow. With plain films, the bone marrow can be seen only when the trabecular or cortical bone is destroyed or major calcification has taken place. CT can yield highly detailed information about bone disease and clearly shows trabecular destruction. MRI, however, provides the best overall view of both types of bone marrow and changes to normal marrow.

"MRI really is the only and most sensitive method to study bone marrow for signs of metastatic disease, lymphoma, and leukemia, and can also detect changes that occur with infection," said Prof. Dr. Maximilian Reiser, a professor of radiology at the Grosshadern Clinic in Munich, Germany. "In addition, MRI can give you an overview of the entire bone, something you don't have with bone marrow biopsies."

Reiser moderated a symposium at the ECR on Tuesday morning that covered the normal appearance of bone marrow, normal variations, and changes that occur with cancer, infection, and edema.

Optimal bone marrow imaging usually requires a combination of MR sequences. The most sensitive are fat saturation techniques such as STIR and T1-weighted spin-echo. MRI can show early changes in bone marrow and may significantly affect patient management.

Understanding the normal appearance of bone marrow on MRI is critical. In infants, all bone marrow is red but is gradually replaced by yellow marrow. In adults, red marrow is normally found only in the pelvis and bone close to the trunk of the body. T1-weighted spin-echo MRI sequences best reflect these changes that occur during bone marrow conversion and may also be the technique of choice for studying suspected lesions.

Normal bone marrow can have several variations on MRI. In middle-aged women, for example, MRI reveals hyperplasia of the red marrow that may be idiopathic or associated with mild anemia, obesity, or chronic infection. Hypercellular but normal red marrow may have moderately decreased signal on T1-weighted images.

Two types of major changes in bone marrow can be seen on MRI, appearing as focal areas of altered signal intensity or homogeneous diffuse changes. Metastatic disease normally has a focal hypointensive appearance on T1-weighted spin-echo sequences, with increased intensity on fat suppression images.

Homogeneous changes indicating diffuse malignancy may be more difficult to detect, said Dr. Andrea Baur, a radiologist at the Grosshadern Clinic. Calculating contrast agent uptake can be useful, and an uptake of more than 40% in adults over 35 strongly suggests malignant infiltration.

Whole-body MRI can be useful, especially in cancer patients with suspected metastatic disease at more than one site.

"PET may be more sensitive than whole-body MRI, but it's more expensive, and not all metastases can be detected with PET. MRI seems to have the highest accuracy and can be integrated into a protocol that also allows you to assess the liver," Reiser said.

Bone marrow edema and inflammation are also imaged well with MR. Edema caused by trauma may be associated with internal trabecular microtrauma with secondary capillary hemorrhage. Differentiating tumor from infection is usually straightforward, and MRI is extremely sensitive for detecting bone infections. Diffusion-weighted imaging helps clinicians determine whether vertebral column fractures are osteoporotic or result from neoplastic disease.