| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Letters to the Editor |
Department of Radiology, Leiden University Medical Center, PO Box 9600, Leiden 2300 RC, the Netherlands. e-mail: j.l.bloem@lumc.nl
Editor:
I totally agree with most of the general statements presented in the editorial by Dr Mosher (1) in the August issue of Radiology, which can be summarized as "only add expense and effort if it has been proven to pay back." Nevertheless, there are some comments that may cause confusion to the readership of Radiology. As Dr Mosher (1) and Schmid et al (2) suggest, we also do not use gadolinium-based contrast material at magnetic resonance (MR) imaging in such a population as that described by Schmid et al. As a matter of fact, I am not familiar with any practice that routinely uses or advocates the use of gadolinium-based contrast material enhancement at MR imaging in such a population. However, the absence of a blood-brain barrier in the musculoskeletal system (1) is not a good reason to discard the use of gadolinium-enhanced MR imaging in bone (marrow), since other mechanisms related to angiogenesis are also important. The speculation that the results of dynamic MR imaging would not have been different from those of equilibrium-phase imaging (1), as presented in the study of Schmid et al (2), is cutting corners. Dr Mosher does not provide references or data to back up his statement that hyperemia and increased vascular permeability are associated with high interstitial water content to such an extent that dynamic contrast-enhanced MR imaging will produce the same information as that in equilibrium-phase imaging. One of many examples can be found in giant cell tumor: Permeability is high, but interstitial water content is low, resulting in rapid wash in and rapid washout of gadolinium-based contrast material, as demonstrated with dynamic MR imaging (3). This information cannot be extracted from equilibrium-phase images.
Dr Mosher states that gadolinium-enhanced MR imaging cannot be used to differentiate osteomyelitis in the diabetic foot from bone marrow edema. However, it is not mentioned that it has been proven that gadolinium-enhanced MR imaging is useful in the diabetic foot to identify an abscess (4).
Dr Mosher rightfully mentions the use of gadolinium-enhanced MR imaging in monitoring response to therapy in bone marrow tumors. The remark that gadolinium-enhanced MR imaging cannot be used to differentiate benign from malignant tumors is, however, in contradiction with this statement and the literature. To monitor response to therapy, viable tumor must be identified. It has been shown that residual viable tumor can be identified and differentiated from benign tissue by using dynamic gadolinium-enhanced MR imaging (5).
The procedure of flattening a dead cat that is already flat makes a good comparison (1). One can only conclude, however, that flattening a flat dead cat is useless once a diagnosis of a dead flat cat has been made. In the study of Schmid et al (2), only patients with abnormal findings at short inversion time inversion-recovery (STIR) MR imaging are included (2). The study does not provide information about the usefulness of gadolinium-enhanced MR imaging in patients without abnormalities at STIR imaging. Schmid et al (2) therefore limit their conclusions to the data set that is available for analysis, and they refrain from making loose generalizations. Like Dr Mosher, I also think that in this population of patients without abnormalities at STIR MR imaging, gadolinium-based contrast enhancement will not add anything to normal STIR MR images, but this has not been shown in the study of Schmid et al (2). We should therefore refrain from making generalizations not supported by data.
REFERENCES
Department of Radiology, Penn State Milton S. Hershey Medical Center, PO Box 850, 500 University Dr, MRI Bldg M-108, Hershey, PA 17033. e-mail: tmosher@psu.edu
I appreciate the comments of Dr Bloem regarding my recent editorial (1) on the use of gadolinium-enhanced MR imaging in the evaluation of abnormal bone marrow signal. In general, I believe that comments reflected in my editorial are in complete agreement with points raised in Dr Bloem’s letter; however, I appreciate the opportunity to clarify my views. The major thesis expressed in my editorial is that application of gadolinium-based contrast enhancement in the evaluation of patients with abnormal bone marrow signal must be based on sound scientific evidence. My comments on specific applications were intended not to define guidelines for clinical practice but rather to highlight potential areas in need of further study.
Although the focus of my discussion was application of equilibrium-phase gadolinium-enhanced images, it is well known that additional information is obtained by using dynamic contrast-enhanced MR imaging. As I state in my editorial, dynamic contrast enhancement provides additional information on hyperemia and vascular permeability that is not present on equilibrium-phase images. I do not speculate "that the results of dynamic MR imaging would not have been different from those of equilibrium-phase imaging" but rather argue that it is not safe to assume that results of Schmid et al (2) would have been substantially different had they used dynamic rather than equilibrium-phase MR imaging. This is an important difference that addresses the basic tenet of my editorial. Experimental studies are needed to determine if additional mechanisms of tissue contrast obtained with dynamic gadolinium-based enhancement provide useful diagnostic information. Since inflammation, in response to either benign or malignant conditions, is associated with hyperemia and edema, there is at least a theoretic basis for hypothesizing that MR imaging results for most inflammatory conditions may be similar for the two techniques. As Dr Bloem illustrates with giant cell tumor, however, there are specific cases in which dissociation of vascular permeability and interstitial water content may provide useful information for tissue characterization. Rather than promote speculation, I encourage additional research in these areas.
With regard to the role of gadolinium-based contrast enhancement in the evaluation of osteomyelitis, my comments were made with specific regard to evaluation of bone marrow. As I state in my editorial, there is a role for gadolinium-based contrast material in identifying areas of devitalized bone, which may occur with an abscess. The major benefit of contrast enhancement in osteomyelitis is evaluation of not marrow edema but rather adjacent soft tissues. I routinely use gadolinium-based contrast material in patients suspected of having osteomyelitis for evaluation of soft-tissue and periosteal abscesses associated with osteomyelitis.
I appreciate the clarification regarding the role of contrast enhancement in the evaluation of tumors. Dynamic contrast enhancement provides relevant information on tumor viability that can be used for monitoring or for differentiating residual viable tumor from reactive edema. However, specificity is substantially lower once contrast material has equilibrated with interstial fluid.
With regard to my comments on the role of gadolinium-based contrast material in the evaluation of patients without abnormalities on STIR MR images, my intent was not to apply "loose generalizations" to interpretations of results of the study of Schmid et al (2). This population was not evaluated in their study. In providing an overview of the role of gadolinium-enhanced MR imaging in the evaluation of bone marrow lesions, however, I felt it was necessary to at least highlight potential applications in which greater signal-to-noise ratio of contrast-enhanced T1-weighted MR imaging had a potential benefit in increasing either diagnostic sensitivity or confidence.
REFERENCES
Department of Radiology, Penn State Milton S. Hershey Medical Center, PO Box 850, 500 University Dr, MRI Bldg M-108, Hershey, PA 17033. e-mail: tmosher@psu.edu
Department of Radiology, Orthopedic University Hospital Balgrist, Forchstrasse 340, 8008 Zurich, Switzerland. e-mail: mariusschmid@hotmail.com
We appreciate the comments by Dr Bloem regarding the editorial of Dr Mosher (1) and our own article (2). Our study population included only three patients with benign bone tumors and six patients with osteomyelitis. There were no malignant bone or soft-tissue tumors in our study group. Therefore, we excluded these abnormalities from our conclusion, regarding no additional value of contrast-enhanced MR imaging in bone marrow abnormalities of the foot. We agree with the statement of Dr Bloem that in patients with malignant bone tumors and infections in the foot, administration of gadolinium-based contrast material helps in the detection of necrosis (important for follow-up examinations) and abscess formation. In this context, Dr Van der Woude et al (3,4) indeed showed an additional benefit of dynamic contrast-enhanced MR imaging, especially after neoadjuvant chemotherapy of malignant musculoskeletal tumors.
We often get referrals from several radiologic institutions for contrast-enhanced MR examinations in patients with diffuse bone marrow signal intensity irregularities not related to tumor or infection. This means that there is uncertainty among many radiologists, which leads to almost routine use of gadolinium-enhanced MR imaging in such a population. The results and conclusion of our study may help colleagues in the decision not to perform contrast-enhanced MR imaging in cases of bone marrow abnormalities of the foot that are not related to tumor or infection.
REFERENCES
and
Mark E. Schweitzer, MD
Department of Radiology, Penn State Milton S. Hershey Medical Center, PO Box 850, 500 University Dr, MRI Bldg M-108, Hershey, PA 17033. e-mail: tmosher@psu.edu
Department of Radiology, Orthopedic University Hospital Balgrist, Forchstrasse 340, 8008 Zurich, Switzerland. e-mail: mariusschmid@hotmail.com
Department of Radiology, University Hospital Basel, Petersgraben 4, 4031 Basel, Switzerland* e-mail: hans-peter.ledermann@gmx.ch
Department of Radiology, Thomas Jefferson University Hospital, Philadelphia, Pa
We agree entirely with the comments of Dr Bloem concerning Dr Mosher’s editorial on the effectiveness of gadolinium-enhanced MR imaging in the evaluation of abnormal bone marrow signal in the foot and ankle (1). Dr Mosher states correctly that in most patients without tumor or infection, gadolinium-enhanced MR imaging may not demonstrate important additional information with the potential to alter therapy. He also points out that gadolinium-enhanced MR images cannot allow differentiation of osteomyelitis in the diabetic foot from bone marrow edema (1). There are, however, other aspects of pedal infections that may influence the choice of further therapy and that require contrast material administration for correct evaluation.
As already pointed out by Dr Bloem, it was shown that gadolinium-enhanced MR images aid considerably in the diagnosis of abscesses in infected feet (2). It is especially difficult or sometimes impossible to diagnose abscesses on nonenhanced images in diabetic patients because of the diffuse diabetic edema in the muscular and subcutaneous tissues in this patient group (2). More than 80% of all patients in our practice who were referred for evaluation of pedal infection had longstanding diabetes mellitus, and nearly one-fifth of patients suspected of having osteomyelitis had a pedal abscess (2). Almost all patients who are referred for MR evaluation of pedal infections have skin ulcers (3), which may be contiguous with sinus tracts. Skin ulcers and especially sinus tracts are much easier to recognize on contrast-enhanced MR images (4), and correct evaluation of these so-called secondary signs will help to differentiate osteomyelitis from other forms of bone marrow signal intensity alterations, such as diabetic neuroarthropathy, stress-related bone marrow edema, or inhomogenous fat suppression (4). Infection of a tendon may alter the choice of therapy, since spread of infection along tendons and advanced septic tenosynovitis may require surgical intervention (5). In our experience, tendon infections are also easier to diagnose after contrast material administration.
An important issue in MR imaging of infected feet is the presence and extent of necrotic tissue. It could be shown that necrotic tissue has variable signal intensities on T1- and T2-weighted MR images and that only contrast-enhanced MR images allow reliable diagnosis of devitalized tissue (6).
When considering the amount of clinically important information gained with contrast-enhanced MR images in patients suspected of having osteomyelitis, we advocate the use of gadolinium-enhanced MR imaging.
REFERENCES
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| RADIOLOGY | RADIOGRAPHICS | RSNA JOURNALS ONLINE |
