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Letters to the Editor |
Department of Nuclear Medicine, Ludwig-Maximilians-University of Munich, Ziemssenstrasse 1, D-80336 Munich, Germany* e-mail: hahn@med.uni-muenchen.de
Martin Charron, MD,
Department
of Radiology, Children’s Hospital of Philadelphia,
Pa
Barry L. Shulkin, MD,
Department of Pediatric Nuclear Medicine, University of Michigan Medical Center, Ann Arbor
Editor:
We read with great interest the article by Dr Siegel and colleagues in the April 2002 issue of Radiology (1). We believe that the subject addressed by the authors is very important, and we congratulate them on the very good statistical work-up of this multicenter study. There are two points concerning the study design, however, that probably deserve a more thorough explanation.
First, as stated in the article and as indicated in comparative studies in the literature, we know that magnetic resonance (MR) imaging is equal or superior to computed tomography (CT) in the diagnosis of pediatric neuroblastoma (2,3). Therefore, it is hard to comprehend why CT is reevaluated in a prospective study. The argument that these imaging studies were performed with older-generation equipment, that they were retrospective, and that each imaging modality was evaluated in isolation does not justify the use of ionizing radiation, unless clearly performed as part of routine clinical care. To our knowledge, there is no study that demonstrates the diagnostic superiority of CT over MR imaging in pediatric neuroblastoma. For that reason, MR imaging should be used as the primary imaging tool because of the lack of ionizing radiation.
Second, we do not understand the use of bone scintigraphy instead of metaiodobenzylguanidine (MIBG) scintigraphy as the primary nuclear medicine imaging modality. To define the disease stage, document the disease course, and evaluate the response to therapies in patients with neuroblastoma, imaging with MIBG is now essential. Accordingly, the recommendations of the International Neuroblastoma Staging System, or INSS, indicate that MIBG scintigraphy must be performed in patients with neuroblastoma at the time of initial staging and during therapy (4,5).
Shulkin et al (6) conclude that both MIBG and bone scintigraphy are useful for the detection of skeletal neuroblastoma. MIBG is the better agent for characterization of the extent of disease, and MIBG is clearly superior for the detection of extraskeletal neuroblastoma. Bone scintigraphy is a valuable adjunctive agent that provides skeletal landmarks for comparison.
As mentioned in the article of Dr Siegel and colleagues (1), differentiation between stage 4 neuroblastoma and the other three stages is most important. Therefore, a nuclear medicine method should be used that depicts skeletal and extraskeletal neuroblastoma lesions. Only MIBG scintigraphy matches this demand.
However, the study protocol of Dr Siegel and colleagues required that bone scintigraphy be performed in all patients and be allowed for additional MIBG scintigraphy only as an option at the discretion of the clinicians and surgeons at each institution.
In summary, it is clear that MIBG scintigraphy is the first-line nuclear medicine examination tool for staging of pediatric neuroblastoma.
REFERENCES
Mallinckrodt Institute of Radiology, Washington University School of Medicine, 510 South Kingshighway Boulevard, St Louis, MO 63110* e-mail: siegelm@mir.wustl.edu
Department of Radiology, St Jude Children’s Research Hospital, 332 North Lauderdale Street, Memphis, TN 38112
Drs Hahn, Charron, and Shulkin raise a question about the design of our study in which MR imaging and CT were compared for overall assessment of stage 4 neuroblastoma in children. They claim it is well known that MR imaging is superior to CT in the diagnosis of neuroblastoma. At the time our study was designed and conducted, CT represented the standard of care for imaging evaluation of neuroblastoma in the United States, and the purpose of our study was to assess the relative accuracies of CT, MR imaging, and scintigraphy for staging of newly diagnosed neuroblastoma. The authors refer to two other studies to support their statement that MR imaging is equal or superior to CT for the diagnosis of neuroblastoma, and, on the basis of these reports, they state that they find it hard to comprehend why CT was reevaluated in a prospective study. However, these studies were published several years after our study was initiated, and, moreover, unlike in our study, CT, MR imaging, and scintigraphy were not rigorously compared. The need for a rigorous prospective assessment was precisely the reason we undertook our multiinstitutional study.
Drs Hahn, Charron, and Shulkin also question our use of bone scintigraphy rather than MIBG scintigraphy as the primary scintigraphic method to evaluate stage 4 neuroblastoma. Although we agree that the superiority of MIBG imaging has been established, at the time of our study, MIBG was not widely available in the United States. Moreover, iodine 123 MIBG was even less accessible than iodine 131 MIBG (which is clearly inferior for pediatric imaging). Thus, our study was designed such that results would be generalizable to most U.S. institutions.
We agree with Drs Hahn, Charron, and Shulkin that differentiation between stage 4 neuroblastoma and the other three stages is important. They state that, therefore, an imaging method should be used that depicts both skeletal and extraskeletal lesions and that only MIBG scintigraphy meets this criterion. We agree that this differentiation is important, and that is the reason we performed our study. However, we are unaware of any large series in which MIBG imaging has been evaluated for local staging of neuroblastoma. As noted in our article, the purpose of our multiinstitutional study was not to assess the extent of local disease but rather to assess the accuracy of MR imaging for detection of distant metastases. Our patient population was too small to evaluate the accuracy of imaging methods for local staging. However, our results do show that MR imaging performs well in the detection of stage 4 neuroblastoma. We believe that a larger prospective study is needed to assess the value of MR imaging, as well as MIBG scintigraphy, for local staging.
Drs Hahn, Charron, and Shulkin recommend that a child with a newly diagnosed neuroblastoma undergo MIBG scintigraphy as the first-line scintigraphic examination for staging neuroblastoma. The authors’ contention may be correct, but to our knowledge, a direct comparison of MIBG imaging with MR imaging for neuroblastoma staging has not been done. Such a study needs to be performed to validate the authors’ opinion. Our results do show that MR imaging alone can replace the combination of CT and bone scintigraphy in the detection of stage 4 neuroblastoma. It is also notable that Drs Hahn, Charron, and Shulkin raise the concern that the use of CT is not justified because of the resulting exposure to ionizing radiation. Of course, the use of MIBG scintigraphy also exposes children to ionizing radiation. Avoiding radiation exposure was one of the principal reasons we sought to determine whether MR imaging could be substituted as the chief imaging method for neuroblastoma staging.
REFERENCES
This article has been cited by other articles:
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  M. Lindskog, C. Spenger, J. Jarvet, A. Graslund, and P. Kogner Predicting Resistance or Response to Chemotherapy by Proton Magnetic Resonance Spectroscopy in Neuroblastoma J Natl Cancer Inst, October 6, 2004; 96(19): 1457 - 1466. [Abstract] [Full Text] [PDF]
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