Abstract
Background/Aim: The aim of this study was to evaluate the diagnostic sensitivity, specificity and accuracy of endorectal magnetic resonance imaging (e-MRI), as a preoperative staging modality in the diagnosis of lymph node metastasis (LNM) in patients with prostate cancer (PCa). Patients and Methods: Retrospectively, we analyzed data from N=168 patients who underwent radical prostatectomy (RP) between 2004 and 2013 at two tertiary medical centres. Prior to RP all patients underwent an e-MRI. Inclusion criteria were: PSA levels >20 ng/ml or Gleason score >7. Examinations were performed on a closed 1.0-T system combined with an endorectal body phased-array coil, imaging results were correlated with histopathology. Results: 10.7% (N=18 patients) had histologically-proven LNM. e-MRI was true-positive in N=6 (33.3%) and false-negative N=12 patients (66.6%). N=150 (89.3%) patients without LNM e-MRI were true-negative in 96% and false-positive in 4%. Sensitivity was 96%, specificity was 33%, accuracy was 64.5%. Conclusion: e-MRI can be considered a useful preoperative staging modality in diagnosis of LNM.
The second most common cause of cancer death in Europe and the United States is prostate cancer (PCa). Around 30% of all newly diagnosed cancers in males are PCa (1). In general, in the early stage of the disease, radical prostatectomy including pelvic lymphadenectomy to detect metastatic spread to the lymph nodes is the most common therapy, however, it is well known that the presence of lymph node metastasis is a poor prognostic sign (1).
The aim of this study was to evaluate the diagnostic sensitivity, specificity, and accuracy of endorectal magnetic resonance imaging (e-MRI) of the prostate as a preoperative staging modality in the diagnosis of lymph node metastasis (LNM) in patients with biopsy-proven PCa.
Patients and Methods
A retrospective review of N=168 patients with biopsy proven PCa who subsequently underwent radical prostatectomy (RP) between April 2004 and April 2013 at two tertiary medical centres was conducted. Prior to RP all patients underwent an e-MRI of the prostate. Inclusion criteria for the study were PSA levels >20 ng/ml or Gleason score >7. The presence of one or more lymph nodes with a short axis diameter >1 cm was considered as LNM. Interpretation of the images was performed by a highly experienced radiologist blinded to patient clinical data. The examinations were performed on a closed 1.0-T system combined with an endorectal body phased-array coil and imaging results were correlated with histopathology. T1-weighted axial-oriented sequences were applied from the prostate base up to the aorta bifurcation. Regional lymph node resection included external iliac, internal iliac and obturator nodes. The clinicopathological parameters of the patients included age, PSA levels, Gleason score, e-MRI findings, histologically proven LNM, amount of lymph nodes dissected, size of lymph nodes dissected, sensitivity, specificity and accuracy.
Results
The clinicopathological characteristics of patients are listed in Table I. Out of the 168, 10,7% (N=18 patients) had histologically proven LNM. The e-MRI was true-positive in N=6 out of 18 patients (33,3%) and false-negative in N=12 cases (66,6%). N=150 (89.3%) patients had no LNM. The e-MRI was true-negative in N=144 out of 150 patients (96%) and false-positive in N=6 (4%). Concluding these results, a sensitivity of 96%, a specificity of 33% and accuracy of 64.5% were shown.
Discussion
The correct staging of the lymph status is critical to plan an optimal therapy for prostate cancer patients. Many studies demonstrated the supporting benefit of MRI in prostate cancer diagnostics (2-5). A sensitivity of 92% can be achieved respectively for the detection of the extracapsular extension of cancer. Thus, MRI seems a good preoperative support for example at the planning of a robot assisted nerve sparing radical prostatectomy (6-9).
An extended pelvic lymphadenectomy (obturator and external iliac lymph nodes, including the internal iliac lymph nodes) is associated with a high rate of lymph node metastasis outside of the fields of standard lymphadenectomy, in cases of clinically localized prostate cancer (10). For the preoperative detection of lymph node metastasis the conventional CT and conventional magnetic resonance imaging (MRI) seem to be equivalent in the current literature (11).
A meta-analysis in 2008 from Hövels et al. showed for both methods a sensitivity of 39% and 42% and a specificity of 82% (12). They showed that CT and MRI examination of patients have an equally poor quality in the detection of lymph node metastasis. Based on this, the patient will not receive the right therapy (12).
As Heesakers reported a few months later, the MR lymphoangiography (MRL) with use of lymph-node-specific MR-contrast agent ferumoxtran-10, had significantly higher sensitivity and negative predictive value than up-to-date multidetector CT for patients with prostate cancer, who had intermediate or high risk of having lymph-node metastases. In such patients, after a negative MRL, the post-test probability of having lymph-node metastases is low enough to omit a pelvic lymph-node dissection (13).
Choline-based PET/CT examinations demonstrated patient- and lymph node-based sensitivity from 41% to 64% and specificity from 90% to 100%. The limitation of choline-based PET/CT examinations seems to be at the detection of lymphatic metastases <5 mm (14-16).
The detection of micro-metastases is very complicated since the MRT is not a suitable method. In case of micro-metastases, high diagnostic experience is of great importance. Conventional MRI and diffusion-weighted MRI (DWI) have similar limitations (17, 18). Seyfer et al. showed in 2014 that a superparamagnetic iron oxide contrast agent MRI (USPIO-MRI) is able to differentiate inflammatory from malignant lesions (19). High-resolution USPIO-MRI with magnetic nanoparticles allows the detection of small and otherwise undetectable lymph-node metastases in patients with prostate cancer. In normal-sized lymph nodes having a diameter of 5-10 mm, the literature showed sensitivity of 96% and specificity of 93% for the detection of LNM. A drastic decrease of these values were shown for lymphatic sizes of <5 mm to 41% and 98% respectively (20, 21).
Thoeny et al. reported a sensitivity of 80% and specificity of 87% by the combination of diffusions enhanced MRI and USPIO enhanced MRI at the detection of smaller metastases (22). In a retrospective feasibility study the DWI was evaluated as a potential tool for characterization of pelvic lymph nodes in patients with prostate cancer (23). They showed a sensitivity of 86% and a specificity of 85% to distinguish between benign and malignant lymph nodes. A size-based analysis at a cu-toff of 8 mm was measured (23). Nowadays, only the prostate-specific antigen based screening (PSA level) has led to a downstaging of prostate cancer, due to the over-diagnosis and over-treatment of patients. Clinical nomograms for the prediction of insignificant disease provide more information than any diagnostic test alone; moreover, nomograms that incorporate MRI or MRI/ magnetic resonance spectroscopic imaging findings with clinical and biopsy data have been shown in the studyby Shukla et al. to improve the prediction of insignificant cancer, meaning cancer with low metastatic potential and good prognosis for the patients (24).
Patients' clinicopathological parameters.
Conclusion
The results of this study exhibited that although e-MRI can be considered a useful preoperative staging modality in the diagnosis of LNM, it has its limitations as seen through its specificity and accuracy. With the imaging methods only a staging accuracy of a PCa patient can be done, nevertheless, the question is, whether a lymphadenectomy improves the prognosis of a PCa patient significantly. Therefore, a large-scale multicentrical study should be performed to figure out the benefit of the imaging method and to highlight the benefit of a radical lymph node surgery.
- Received December 8, 2017.
- Revision received December 27, 2017.
- Accepted January 3, 2018.
- Copyright© 2018, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved
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