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Keywords:

  • bone metastasis;
  • bone single photon emission computed tomography;
  • degenerative joint disease;
  • prostate cancer

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Objective:  To determine whether single photon emission computed tomography (SPECT) is useful in the detection of prostate cancer bone metastases in the lumbar vertebrae.

Methods:  Thirty-nine patients (12 with benign prostatic hyperplasia, 27 with prostate cancer) were considered and submitted to bone SPECT. All of them had increased uptake in lumbar vertebrae on bone scintigraphy. In those with prostate cancer, definitive diagnosis of bone metastases was established by magnetic resonance imaging (MRI). SPECT axial images were classified into five accumulation patterns: mosaic, large hot, diffuse, peripheral, and articular (or pediculate). Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of bone SPECT were calculated.

Results:  Overall, 116 vertebral lesions (49 metastatic, 67 degenerative) were studied. Mosaic, large hot and diffuse patterns were more frequently associated with metastatic lesions (84.2%, 70.3%, and 63.1% of the cases, respectively). On the other hand, peripheral and articular (or pediculate) patterns were mostly ascribed to degenerative lesions (100% and 87.5% of the cases, respectively). Sensitivity, specificity, PPV and NPV of bone SPECT were 95.9% (47/49), 73.1% (49/67), 72.3% (47/65), and 96.1% (49/51), respectively.

Conclusions:  Bone SPECT provides better accuracy than bone scintigraphy in differential diagnosis of lumbar vertebral lesions from prostate cancer.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Radionuclide bone scintigraphy using 99mTc-labeled phosphates is known to be more sensitive than plain radiographs in detecting bone metastasis. It is the most common imaging technique for detecting bone metastasis throughout the skeleton, as well as staging patients with prostate cancer. In elderly patients who have a high incidence of benign changes in the vertebral column, one or more abnormal vertebrae detected by bone scintigraphy is common in clinical practice. These lesions may be caused by early metastatic spread or by a benign process, therefore posing a diagnostic dilemma.1 The purpose of the present study was to determine whether bone single photon emission computed tomography (SPECT) is useful or not in differentiating malignant from benign lesions.

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Clinical subjects consisted of 12 patients with histologically proven benign prostate hyperplasia (age 65–88 years with a mean of 73.2) and 27 patients with prostate cancer (66–93 years with a mean of 77.6) whose anteroposterior and lateral lumbar spine radiographs showed the presence of bony sclerosis. On bone scintigraphy, all 39 patients demonstrated one to five hot spots in the lumbar vertebrae. In patients with prostate cancer, diagnoses of bone metastasis were established by magnetic resonance imaging (MRI). MR images were obtained on a 1.5T scanner (Magnetom Vision; Siemens, Germany) using a standard body coil. Axial, sagittal, and coronal images of the lumbar vertebrae were routinely obtained using T1-weighted, T2-weighted, and fat suppression techniques, including short-TI inversion recovery (STIR). If there were focal or diffuse areas of T1-low and STIR-high signal intensities within an area of normal signal intensities corresponding to marrow fat, the lesion was diagnosed as bone metastasis. Thus, this study included 116 lumbar vertebrae (49 with bone metastases and 67 with degenerative joint disease [DJD]) (Table 1). Using a gamma camera, bone scintigraphy was carried out 3–4 h after intravenous administration of 740 MBq 99mTc-HMDP. Anterior and posterior images of the whole body were obtained. SPECT images of the lumbar vertebrae were carried out immediately after bone scintigraphy using a high-resolution SPECT system (Toshiba 9300A/HG) with three-head rotating cameras equipped with high resolution, low energy, parallel-hole collimators. A Butterworth prefilter and a filtered back projection using a Shepp and Logan filter were used for imaging reconstruction of axial, coronal, and saggital sections in a 128 × 128 matrix. A single section was 6.4 mm thick. Actual imaging time was approximately 7 min.

Table 1.  Characteristics of patients undergoing single photon emission computed tomography (SPECT) imaging to detect prostate cancer bone metastases in the lumbar vertebrae
DiseasenNumber of abnormal findings on bone scintigraphyFinal diagnosis
Bone metastasisDJD
  1. BPH, benign prostate hyperplasia; DJD, degenerative joint disease.

BPH1239039
Prostate cancer27774928

The SPECT patterns of uptake were classified into five major groups: mosaic, large hot, diffuse, peripheral, and articular or pediculate pattern (Fig. 1). These classifications were outlined by Kosuda.2 Bone SPECT were interpreted by one attending radiologist who did not know the clinical information of the patient.

image

Figure 1. Accumulation patterns in the lumbar vertebrae obtained from the bone single photon emission computed tomography (SPECT) transaxial plane.

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Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

The final diagnoses of 116 lesions with relation to the pattern of uptake on bone SPECT images are summarized in Table 2. Mosaic patterns (n = 19) were more commonly observed in the metastatic foci (n = 16) than DJD (n = 3). Of the 16 metastatic foci, 10 were located not only in the vertebral body but also in the posterior element (spinous process or pedicle). Large hot patterns (n = 27) were also more commonly observed in the metastatic foci (n = 19) than DJD (n = 8). Of the 19 metastatic foci, 10 were located not only in the vertebral body, but also in the posterior element. However, of the eight DJD foci, only one resembled such an accumulation pattern. Diffuse patterns (n = 19) were also observed more commonly in cases of metastatic foci (n = 12) than DJD (n = 7). Six lesions showing diffuse uptake in the vertebral body and posterior element were all caused by metastases (Fig. 2). Not only the vertebral body metastasis but also extra-vertebral body metastases were clearly visualized on the saggital bone SPECT sections (Fig. 3).

Table 2.  The pattern of uptake on bone single photon emission computed tomography (SPECT) images in relation to the final diagnoses
SPECT patternBone metastasis (n = 49)DJD (n = 67)
  1. DJD, degenerative joint disease.

Mosaic16 (84.2%)3 (15.8%)
Large hot19 (70.3%)8 (29.7%)
Diffuse12 (63.1%)7 (36.9%)
Peripheral0 (0.0%)35 (100.0%)
Articular pediculate2 (12.5%)14 (87.5%)
image

Figure 2. A 69-year-old male with a history of prostate cancer. Transaxial bone single photon emission computed tomography (SPECT) image (a) and magnetic resonance imaging (MRI) image (b) of the L5 vertebrae. The SPECT image shows diffuse accumulations in the body, pedicle, and remaining posterior elements.

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image

Figure 3. An 86-year-old male with a history of prostate cancer. (a) T1-weighted sagittal magnetic resonance imaging (MRI) image of the lumbar vertebrae shows focal lesions of low signal intensity consistent with metastatic prostate cancer (arrow). (b) Sagittal section of bone single photon emission computed tomography (SPECT) clearly revealed increased accumulations in the lumbar vertebral body, which resembled the image of sagittal MRI. In addition, bone SPECT detected extra-vertebral body metastases (arrow).

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On the other hand, the lesions with peripheral patterns (n = 35) were all diagnosed as DJD (Fig. 4). Articular or pediculate patterns were more commonly recognized in DJD (n = 14) than metastatic foci (n = 2). The characteristic bilateral accumulation in the pars interarticularis showed DJD, while accumulation unilaterally involving the pedicle showed metastasis.

image

Figure 4. A 75-year-old male with a history of benign prostate hyperplasia (BPH). Transaxial bone single photon emission computed tomography (SPECT) images of the L2 vertebrae. The SPECT pattern was that of uptake projecting along the vertebral body surface, and beyond the vertebral body surface (peripheral pattern).

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Mosaic, large hot, and diffuse patterns were more frequently observed in patients with bone metastasis (84.2%, 70.3%, and 63.1%, respectively), whereas peripheral and articular or pediculate patterns were diagnosed as DJD (100% and 87.5%, respectively).

Consequently, the sensitivity of bone scintigraphy was 100% (49/49), and the positive predictive value (PPV) was 42.2% (49/116). On the other hand, assuming that the mosaic, large hot, and diffuse patterns indicate bone metastasis, the sensitivity of bone SPECT was 95.9% (47/49) and the PPV was 72.3% (47/65) (Table 3).

Table 3.  Comparison of the results of bone scintigraphy and bone single photon emission computed tomography (SPECT)
Imaging techniqueSensitivitySpecificityPPVNPV
  1. NPV, negative predictive value; PPV, positive predictive value.

Bone scintigraphy alone100.0% (49/49)42.2% (49/116)
Bone SPECT95.9% (47/49)73.1% (49/67)72.3% (47/65)96.1% (49/51)

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References

Early detection or exclusion of bone metastases is of high clinical importance in the management of patients with prostate cancer.3,4 The diagnosis of bone metastasis is usually made by an initial bone scintigraphy. It is well known that 99mTc bone scintigraphy is sufficiently sensitive in detecting metastatic bone lesions.5,6 The major advantage of bone scintigraphy is that it allows a whole skeletal survey. A particular problem is the enhanced diphosphonate uptake in degenerative processes, therefore a history of DJD could induce a false-positive bone scan.7 In most cases, this enhancement affects the vertebral column and the pelvis. Especially difficult is the differentiation of deforming spondylosis and spondylarthrosis, that is, degenerative disease of the facets, from metastases. In planar bone scintigraphy, superimposition hampers the exact anatomic localization of lesions. The addition of SPECT allows better distinction of benign from malignant changes because of the more exact localization of increased diphosphonate uptake. Bone SPECT improves image contrasts by separating the cross-sectional plane of medical interest from underlying and overlying distributions, and provides three-dimensional positional information.

In the present study, the SPECT patterns of uptake were classified into five major groups, which were outlined by Kosuda.2 Mosaic, large hot, and diffuse patterns were mostly diagnosed as bone metastasis, while peripheral and articular or pediculate patterns were frequently observed in patients with DJD. Assuming that the mosaic, large hot, and diffuse patterns indicate bone metastasis, bone SPECT maintains the sensitivity and improves the PPV of bone scintigraphy for the detection of bone metastases (Table 3). Consequently, the addition of bone SPECT to bone scintigraphy improves the diagnostic accuracy of bone scintigraphy. The detection rate of bone metastasis is thought to be equal to other tomography-based techniques such as MRI.7 MRI has been thought to be a more sensitive and specific modality than bone scintigraphy in detecting bone marrow metastasis, because the lesions are observed directly.8 However, because of the long acquisition time, cost, and inability to image the appendicular skeleton sufficiently, the use of MRI as a screening modality for metastatic prostate cancer is not always recommended. Bone SPECT can be carried out immediately after bone scintigraphy, and the ability to detect bone metastases in other locations, including the skull, upper vertebral column, rib cage, pelvis, and long bones, is also well known.9 The final aim of imaging techniques is to achieve correct diagnosis in a fast, non-invasive, comprehensive, and inexpensive way. Therefore, if some doubtful lesions are observed by bone scintigraphy, the addition of bone SPECT simultaneously is the most economical and available modality in clinical practice.

However, we should not neglect MRI because it offers significant additional information in the clinical practice. Recently, tumor detection using positron emission tomography (PET) has been rapidly growing. In spite of the high sensitivity and specificity of PET, it is expensive and the role of PET in patients with prostate cancer is still under investigation.10 Therefore, it is important to understand each advantage and to diagnose effectively.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. References