Role of MR imaging and iodine 123 MIBG scintigraphy in staging of pediatric neuroblastoma.

Abstract

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 firstline nuclear medicine examination tool for staging of pediatric neuroblastoma.