© Borgis - Postępy Nauk Medycznych 11/2016, s. 836-840
*Szymon Kawecki1, Mieszko Kozikowski1, Jakub Dobruch1, 2
The role of multiparametric magnetic resonance imaging (mpMRI) in the diagnosis of prostate cancer
Znaczenie wieloparametrycznego rezonansu magnetycznego (mpMRI) w rozpoznawaniu raka gruczołu krokowego
11st Unit of Didactics, Department of Urology, Centre of Postgraduate Medical Education, European Health Centre Otwock
Head of Department: Jakub Dobruch, MD, PhD
22nd Unit of Didactics, Department of Urology, Centre of Postgraduate Medical Education, Professor W. Orłowski Independent Public Teaching Hospital, Warsaw
Head of Department: Jakub Dobruch, MD, PhD
Rak stercza jest drugim co do częstości nowotworem wśród mężczyzn w Polsce. Skomplikowana patofizjologia i przebieg choroby sprawiają, że niektóre metody obrazowania sprawdzają się lepiej od innych w poszczególnych stadiach klinicznych raka stercza. Wieloparametryczny rezonans magnetyczny dostarcza złożonej informacji na temat morfologii i zmian czynnościowych w sterczu, co powoduje, że jest on przydatny w wielu sytuacjach, w których standardowe metody obrazowania stają się niewystarczające. Praca stanowi przegląd aktualnych metod obrazowania raka stercza ze szczególnym naciskiem na znaczenie wieloparametrycznego rezonansu magnetycznego.
Prostate cancer is the second most common neoplasm in men in Poland. Due to the complex pathophysiology and the course of disease, some imaging methods prove more effective than others in certain clinical stages of prostate cancer. Multiparametric magnetic resonance imaging provides complex information about morphology and functional changes in the prostate, therefore it is useful in many situations, where standard imaging methods are insufficient. The paper is a review of current imaging modalities in prostate cancer, with particular emphasis on the significance of multiparametric magnetic resonance imaging.
Prostate cancer (PCa) is one of the most common malignancies in men. The incidence of PCa varies among different countries, with the highest rates in Australia, New Zealand, Northern America, particularly among black males, and Western Europe (fig. 1). The lowest rates are reported in Asian countries. An estimated 1.1 million men worldwide were diagnosed with PCa in 2012, accounting for 15% of all malignancies diagnosed in men at that time (1). In Poland, prostate cancer is the second most common neoplasm after lung cancer. About 10,201 men were diagnosed with PCa in 2012 in Poland (2).
Fig. 1. Standardised incidence and mortality rates of prostate cancer in selected countries according to the Globocan database (WHO, 2012, www-dep.iarc.fr/globocan/globocan.html) (1)
PCa primarily develops in the peripheral zone of the prostate (fig. 2).
Fig. 2. The zonal structure of the prostate
AS – anterior commissure; TZ – transitional zone; CZ – central zone; PZ – peripheral zone; U – urethra (3)
Improved imaging methods for prostate scanning with enhanced biopsy accuracy for PCa diagnosis resulted in higher detection rates for tumours arising in the transition zone (TZ), located anterior to the urethra.
Initially, the cancer is limited to the prostate gland (organ-confined disease). However, with time it invades the periprostatic tissues (ECE – extraprostatic extension; locally advanced disease). Perineural invasion, i.e. tumour spread along a nerve, is a characteristic feature of PCa. Further development of PCa may result in the spread of cancer cells beyond the prostate gland, particularly to sites penetrated by the cavernous nerves, as well as lead to the invasion of the seminal vesicles as a result of cancer spread along the ejaculatory ducts, direct invasion of the seminal vesicles by the tumour itself or, least often, as a result of metastasis. The spread of cancer beyond the prostate gland can result in the invasion of the neck and the triangular region of the bladder. Ureteral invasion prevents the urine flow from the upper urinary tract, causing hydronephrosis, which may lead to renal failure. Anterior rectal wall invasion is rare as this part is protected against invasion by a strong structure known as the Denonvilliers fascia. Significant local progression of the primary tumour is usually accompanied by the presence of lymph node and distant metastases, bone metastases in particular.
Prostate-confined cancer is usually asymptomatic or causes scarce, non-specific symptoms. In some cases, clinical consequences of significantly advanced cancer, e.g. pain in bones, anaemia and/or renal insufficiency, are the first manifestations of PCa.
Transrectal ultrasound guided TRU-CUT core biopsy (TRUSTRU-CUT) of the prostate gland is the primary PCa diagnostic method. Indications for the TRU-CUT needle biopsy include abnormalities identified based on digital rectal examination (DRE), such as a nodular thickening in the prostatic parenchyma, generally increased prostate cohesion, asymmetry, blurred lateral boundaries and increased levels of serum prostate-specific antigen as well as lesions suspicious of PCa, which are detected by transrectal ultrasound (TRUS) or, recently increasingly often, by multiparametric magnetic resonance imaging (mpMRI). Prostate assessment based on DRE is very subjective and dependent on the experience of the examiner. TRUS-guided biopsy is superior in some respects when compared with DRE. It allows for an accurate determination of the size, boundaries and the internal structure of the prostate gland. Therefore, it is widely used for TRUSTRU-CUT. An hypoechoic area is a typical TRUS appearance of prostate cancer. Although about 50% of pathomorphologically confirmed prostate cancer foci are hypoechoic, the ultrasonographic pictures of poorly-differentiated cancers and cancers located outside the peripheral zone, where tumours most often develop, tend to vary (4, 5).
Clinical assessment of local tumour progression is based on DRE, TRUS, biopsy and, in some cases, computed tomography (CT) of the pelvis and/or mpMRI imaging. The mpMRI imaging technology is currently a method that most accurately reflects the structure of the prostate gland. This diagnostic method has been significantly improved in recent years. Currently, three-Tesla MRI scanners are available, which have better resolution of the obtained images, including dynamic contrast-enhanced images, compared to previous 1.5 Tesla MRI scanners. In addition to conventional morphology images, imaging using spectroscopy (magnetic resonance spectroscopic imaging – MRSI) and imaging based on water diffusion (diffusion-weighted MRI – DWMRI) have been introduced. Although collecting information obtained using all these technologies is very difficult, experience shows that combining at least two of them significantly improves the accuracy of evaluation, allowing for a final determination of the stage and the size of PCa. This information is useful in determining the extent of surgery (radical prostatectomy – RP) to minimise the risk of positive surgical margins (PSM) with the lowest possible impairment of quality of life.
MpMRI technology contributes to the improved diagnosis of PCa, which is of value for cancer patients at different stages of disease and in different clinical situations.
1. Localisation of PCa foci in patients with no abnormalities revealed by TRUS
As already mentioned, PCa tends to be isoechoic and thus invisible on TRUS. Only 60% of tumour foci are diagnosed based on transrectal ultrasonography (6). It was found based on the analysis of tissue material obtained during radical prostatectomy that mpMRI has a better PCa detection rate than TRUS, particularly in the case of tumours with Gleason score > 7 as well as tumours located in the anterior portion of the prostate gland, where it is very difficult to collect specimens during TRUSTRU-CUT biopsy.
Data analysis of 175 patients after radical prostatectomy demonstrated that mpMRI detection rate for tumour size < 0.5 mL, 0.5-2.0 mL and > 2.0 mL is 21-29%, 43-54% and 67-75%, respectively, 63%, 82-88% and 97% for Gleason score <6, 80% for Gleason score 7, 93% and 100% for Gleason score > 8 (7). Another study assessed the value of mpMRI in men, whose first biopsy did not find PCa. mpMRI scans were performed in 265 men, followed by another biopsy. PCa was detected in 41% of patients, with clinically significant cancer according to Epstein’s criteria in 87% of cases (8). Yuen et al. also investigated men after biopsy which failed to find PCa. The sensitivity, specificity, positive (PPV) and negative (NPV) predictive values as well as the accuracy of MRI, MRSI and the combination of MRI/MRSI in the detection of PCa were as follows: 57.1, 57.1 and 100.0% (sensitivity), 88.2, 82.4 and 70.6% (specificity), 66.7, 57.1 and 58.3% (PPV), 83.3, 82.1 and 100% (NPV) and 79.2, 75.0 and 79.2% (accuracy) (9). mpMRI is more effective than TRUS in detecting focal PCa. This method usually reveals abnormalities in patients with PCa volume > 0.5 mL and Gleason score > 6.
2. Assessment of local progression
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