Original PaperComparative study of whole-body MRI and bone scintigraphy for the detection of bone metastases
Introduction
Malignant tumours are currently the third most common cause of death worldwide.1 Mortality due to malignant tumours and the probability of successful treatment depend primarily on the characteristics of the tumour, but they also depend on whether metastases are present. Knowing the stage of the patient’s disease is important to enable prognosis and individualized treatment.2, 3 Metastases very often affect the skeleton. The percentage of tumours with a tendency to metastasize to bone is 32%.4 The tumours that most often metastasize to bone are lung, breast, prostate, kidney, and thyroid carcinomas.4 About 75% of patients with these tumours will develop at least one bone metastasis.5
Plain-film radiography is the initial imaging study in the diagnostic work-up of bone metastases and the most frequently employed, together with bone scintigraphy. However, radiography can only show significant bone destruction with a mineral loss of greater than 50%;6 thus, there is a long latency period between the onset of bone destruction and its first signs on radiography. For this reason, other techniques are necessary for earlier diagnosis.
CT (computed tomography) is more sensitive than plain-film radiography; this technique is often used to study the extent of bone destruction,7 as well as to determine extension to soft tissues and to evaluate possible complications.8
Whole-body magnetic resonance imaging (MRI) is a method that does not use ionizing radiation. The protocol of combined T1-weighted and short-tau inversion recovery (STIR) sequences has proven very sensitive in discriminating benign from malignant bone marrow processes.9, 10 Recently the use of diffusion-weighted imaging (DWI) has been proposed.11, 12
Many centres consider bone scintigraphy the best imaging test for the early detection and staging of bone metastases. However, bone scintigraphy is prone to false positives from benign lesions that have increased bone formation7 and to false-negatives from metastases that do not have a sufficiently strong osteoblastic reaction.13 Nevertheless, bone scintigraphy is relatively inexpensive and fast, so it is still considered the reference standard for early detection and evaluation of the extent of bone metastases.2, 14, 15
Several studies have compared whole-body MRI with bone scintigraphy for screening for bone metastases.7, 13, 16, 17, 18, 19, 20 However, these few series were small and used a wide variety of protocols. Moreover, whole-body MRI is more expensive and less widely available than bone scintigraphy; thus, whole-body MRI has yet to be incorporated into diagnostic algorithms for screening for bone metastases.
The aim of the present study was to compare the diagnostic accuracy and reproducibility of whole-body MRI and bone scintigraphy in the diagnosis of bone metastases.
Section snippets
Patients
From November 2006 to May 2007, a prospective, cross-sectional study of 40 randomly selected patients diagnosed with primary malignant tumours was undertaken. All patients underwent bone scintigraphy and whole-body MRI to screen for bone metastases. Inclusion criteria were patients older than 18 years of age with (1) a histologically confirmed primary malignant solid tumour that required screening for bone metastases (breast and lung cancers), or (2) other malignant solid tumours and clinical
Results
Bone metastases were present in 18 patients and absent in 20. The results of the binary classification of patients by bone scintigraphy were: sensitivity 72.2% (13/18), specificity 75% (15/20), and diagnostic accuracy 73.7% (28/38). The four-point scale classification of patients by bone scintigraphy yielded a diagnostic accuracy (AUC) of 76.9% (Fig. 1).
The results of the binary classification of patients by whole-body MRI were: sensitivity 94.4% (17/18), specificity 90% (18/20), and diagnostic
Discussion
In the present study, the diagnostic accuracy for the detection of bone metastases was higher for whole-body MRI than for bone scintigraphy. These results are in line with those of other studies,13, 16, 18, 19, 20 although it is difficult to compare the results of the different studies due to differences in the selection criteria, techniques, and approach to data analysis used.
The high number of false-negative results for bone scintigraphy in the present study is probably due to this
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