The role of endorectal magnetic resonance imaging in predicting extraprostatic extension and seminal vesicle invasion in clinically localized prostate cancer.

Abstract

We aimed to assess the clinical value of endorectal magnetic resonance imaging (MRI) in predicting extraprostatic extension and seminal vesicle invasion in patients with clinically localized prostate cancer.
A total of 54 patients who underwent radical prostatectomy for clinically localized prostate cancer were retrospectively analyzed. The findings of endorectal MRI, performed at least 3 weeks after biopsy, were compared with the pathological results of radical prostatectomy specimens. The sensitivity, specificity, and accuracy of the detection of extraprostatic extension and seminal vesicle invasion were calculated.
The sensitivity, specificity, and accuracy of the endorectal MRI findings were 50.0%, 82.6%, and 77.8% for the detection of extraprostatic extension, respectively, and 75.0%, 92.0%, and 90.7% for the detection of seminal vesicle invasion, respectively. The sensitivity of endorectal MRI in the detection of extraprostatic extension improved as the Gleason score increased.
Endorectal MRI findings demonstrated modest sensitivity for predicting extraprostatic extension, whereas specificity was relatively high. In addition, endorectal MRI showed better sensitivity for detecting high-grade tumors.

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Korean Journal of Urology
Ⓒ The Korean Urological Association, 2010
308
Korean J Urol 2010;51:308-312
www.kjurology.org
DOI:10.4111/kju.2010.51.5.308
Urological Oncology
The Role of Endorectal Magnetic Resonance Imaging in Predicting
Extraprostatic Extension and Seminal Vesicle Invasion in
Clinically Localized Prostate Cancer
Seo Yong Park, Jung Jun Kim, Tae Heon Kim, Soo Hyun Lim, Deok Hyun Han, Byung Kwan Park1,
Chan Kyo Kim1, Ghee Young Kwon2, Han Yong Choi, Hyun Moo Lee
Departments of Urology, 1Radiology and Center for Imaging Science, 2Pathology, Sungkyunkwan University School of Medicine, Seoul,
Korea
Purpose: We aimed to assess the clinical value of endorectal magnetic resonance imag-
ing (MRI) in predicting extraprostatic extension and seminal vesicle invasion in pa-
tients with clinically localized prostate cancer.
Materials and Methods: A total of 54 patients who underwent radical prostatectomy
for clinically localized prostate cancer were retrospectively analyzed. The findings of
endorectal MRI, performed at least 3 weeks after biopsy, were compared with the patho-
logical results of radical prostatectomy specimens. The sensitivity, specificity, and ac-
curacy of the detection of extraprostatic extension and seminal vesicle invasion were
calculated.
Results: The sensitivity, specificity, and accuracy of the endorectal MRI findings were
50.0%, 82.6%, and 77.8% for the detection of extraprostatic extension, respectively, and
75.0%, 92.0%, and 90.7% for the detection of seminal vesicle invasion, respectively. The
sensitivity of endorectal MRI in the detection of extraprostatic extension improved as
the Gleason score increased.
Conclusions: Endorectal MRI findings demonstrated modest sensitivity for predicting
extraprostatic extension, whereas specificity was relatively high. In addition, endor-
ectal MRI showed better sensitivity for detecting high-grade tumors.
Key Words: Magnetic resonance imaging; Neoplasm staging; Prostatic neoplasms
Article History:
received 26 March, 2010
accepted 29 April, 2010
Corresponding Author:
Hyun Moo Lee
Department of Urology, Samsung
Medical Center, Sungkyunkwan
University School of Medicine, 50
Ilwon-dong, Gangnam-gu, Seoul
135-710, Korea
TEL: +82-2-3410-6543
FAX: +82-2-3410-3027
E-mail: besthml@medimail.co.kr
This study was supported by the
IN-SUNG Foundation for Medical
Research.
INTRODUCTION
Treatment of prostate cancer is greatly dependent on local
staging, particularly the presence or absence of extra-
prostatic extension. As a general rule, patients with disease
localized to the prostate are candidates for radical prosta-
tectomy, whereas those with tumor extension beyond the
prostatic capsule are probably more appropriately man-
aged with radiation therapy. Hence, we have to find a way
to perform accurate staging at diagnosis. A variety of imag-
ing modalities have been evaluated for staging prostate
cancer. However, none of these techniques is sensitive
enough to reliably detect extraprostatic extension and
seminal vesicle invasion of prostatic cancer [1,2]. For over
two decades, magnetic resonance imaging (MRI) has im-
proved our ability to delineate localized versus locally ad-
vanced prostate cancer [3]. Although it seems to have limi-
tations with respect to the diagnosis of microscopic extra-
prostatic cancer [4], MRI using an endorectal coil combined
with phased-array coils remains the most promising tech-
nique for the detection and staging of prostate cancer [5].
　The present study was undertaken to evaluate the ability
of endorectal coil MRI to predict extraprostatic extension
and seminal vesicle invasion in patients with clinically lo-
calized prostate cancer. In addition, we investigated the
changes in sensitivity, specificity, and accuracy when pa-
tients were subdivided into groups according to their Glea-
son scores and serum prostate-specific antigen (PSA) values.
MATERIALS AND METHODS
A total of 54 patients who underwent radical prostatectomy

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Korean J Urol 2010;51:308-312
Role of Endorectal MRI in Prostate Cancer Staging
309
TABLE 1. Clinicopathologic characteristics of patients included
in the study sample
No. of patients
Age (years)
Baseline PSA (ng/ml)
Interval between biopsy and MRI (days)
Max tumor diameter on endorectal MRI (cm)
Gleason score
6
7
8
9
Clinical stage
cT1
cT2
Surgical stage
pT2
pT3a-b
pT3c
54
63.5 (50-72)a
7.35 (3.5-41.2)a
37.5 (21-72)a
2.15 (0.5–4.8)a
30 (55.6%)
19 (35.2%)
3 (5.6%)
2 (3.7%)
32 (59.3%)
22 (40.7%)
45 (83.3%)
5 (9.3%)
4 (7.4%)
PSA: prostate-specific antigen, MRI: magnetic resonance imag-
ing, a: data are presented as the median value with the range in
parentheses
TABLE 2. Diagnostic performance of endorectal MRI for detecting extraprostatic extension of prostate cancer
No. of patients
No. of cases/total number (%)
Sensitivity (%)Specificity (%)PPV (%)NPV (%)Accuracy (%)
Overall
Gleason score
＜7
7
＞7
PSA
＜10
≥10
Partin tableb
54
30
19
5
37
17
54
4/8 (50)
0/3 (0)a
2/3 (67)a
2/2 (100)a
1/3 (33)
3/5 (60)
5/8 (63)
38/46 (83)
23/27 (85)
13/16 (81)
2/3 (67)
30/34 (88)
8/12 (67)
32/46 (70)
4/12 (33)
0/4 (0)
2/5 (40)
2/3 (67)
1/5 (20)
3/7 (43)
5/19 (26)
38/42 (90)
23/26 (89)
13/14 (93)
2/2 (100)
30/32 (94)
8/10 (80)
32/35 (91)
42/54 (78)
23/30 (77)
15/19 (79)
4/5 (80)
31/37 (84)
11/17 (65)
37/54 (69)
MRI: magnetic resonance imaging, PPV: positive predictive value, NPV: negative predictive value, PSA: prostate-specific antigen, a:
chi-square test: linear by linear association, p=0.034, b: data was presumed on the basis of the Partin tables [28]
for clinically localized prostate cancer were retrospectively
analyzed. By use of the same protocol, endorectal MRI (1.5
T) was performed before surgery in all patients. Patients
who received neoadjuvant treatment after the endorectal
MRI examination and patients who had undergone a prostate
biopsy and endorectal MRI within 3 weeks of each other
were excluded from the present study [6,7]. The criteria for
diagnosis of extraprostatic extension on endorectal MRI in-
cluded the following: a localized bulge of the prostatic con-
tour, a thickening or disruption of the prostatic capsule, an
infiltrative strand in the periprostatic fat, or asymmetry
of the neurovascular bundle [8-10]. Seminal vesicle in-
vasion was defined by abnormal tissue with low signal in-
tensity within the seminal vesicle or dilatation of the semi-
nal vesicle with asymmetry [8-10]. Radiologic inter-
pretations were made by the consensus of two radiologists.
The endorectal MRI findings were compared with the histo-
pathologic findings of the radical prostatectomy specimen
in each patient.
1. Protocol for endorectal MRI
The endorectal coil was inserted and the patient was posi-
tioned supine between the phased-array coils. All patients
underwent MRI with a superconducting MRI scanner op-
erating at 1.5 Tesla (Signa Horizon LX, GE Yokogawa
Medical Systems, Hino, Japan). Axial T2-weighted fast
spin echo (TR/TE 3,500 ms/102 ms, 16 echo train lengths,
256x192 matrix, 4-mm slice thickness, 0.5-mm interslice
gap, number of excitations: 4), T1-weighted spin echo
(TR/TE 400 ms/9 ms), and coronal T2-weighted fast spin
echo (TR/TE 3,200 ms/92 ms) images were obtained. After
precontrast image acquisition, 0.1 mmol/kg of gadopente-
tate dimeglumine was administered intravenously and ax-
ial T1-weighted spin echo images with the same imaging
parameters or axial T1-weighted fast spoiled gradient re-
called acquisition in steady state (GRASS) with fat sup-
pression (TR/TE/flip angle 200 ms/3.1 ms/90o) images were
obtained. The field of view was 14x14 cm. A four-channel
phased-array coil was used that consisted of four surface
coils (Pelvic Array, GE Yokogawa Medical Systems, Hino,
Japan) and one endorectal coil (MRInnervu BPX-15, Nihon
Medrad KK, Osaka, Japan) that were used together. One
channel of the phased-array coil was replaced with an en-
dorectal coil so that the detection system could encompass
the entire pelvis and prostate.
2. Statistical analysis
Because the number of positive cases was low, we per-
formed the chi-square trend test instead of the traditional
chi-square test to determine a statistically significant line-
ar trend in sensitivity for detecting extraprostatic ex-
tension based on the Gleason score. Differences were con-
sidered statistically significant at p＜0.05.
RESULTS
Clinicopathologic parameters are summarized in Table 1.

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Korean J Urol 2010;51:308-312
310
Park et al
TABLE 3. Diagnostic performance of endorectal MRI for detecting seminal vesicle invasion of prostate cancer
No. of patients
No. of cases/total number (%)
Sensitivity (%) Specificity (%)PPV (%) NPV (%)Accuracy (%)
Overall
Gleason score
＜7
7
＞7
PSA
＜10
≥10
54

30
19
5

37
17
3/4 (75)

0/1 (0)
2/2 (100)
1/1 (100)

1/2 (50)
2/2 (100)
46/50 (92)

26/29 (90)
16/17 (94)
4/4 (100)

32/35 (91)
14/15 (93)
3/7 (43)

0/3 (0)
2/3 (67)
1/1 (100)

1/4 (25)
2/3 (67)
46/47 (98)

26/27 (96)
16/16 (100)
4/4 (100)

32/33 (97)
14/14 (100)
49/54 (91)

26/30 (87)
18/19 (95)
5/5 (100)

33/37 (89)
16/17 (94)
MRI: magnetic resonance imaging, PPV: positive predictive value, NPV: negative predictive value, PSA: prostate-specific antigen
Surgical-pathologic analysis revealed eight (14.8%) pa-
tients with extraprostatic extension, including four (7.4%)
patients with seminal vesicle invasion. Endorectal MRI
demonstrated suspected extraprostatic extension in 12 pa-
tients and suspected seminal vesicle invasion in 7 patients.
The sensitivity, specificity, and accuracy of endorectal MRI
for the detection of extraprostatic extension were 50.0%,
82.6%, and 77.8%, respectively, and the sensitivity, specif-
icity, and accuracy for the detection of seminal vesicle in-
vasion were 75.0%, 92.0%, and 90.7%, respectively (Table
2, 3). The sensitivity of endorectal MRI for the detection of
extraprostatic extension and seminal vesicle invasion
tended to increase as the Gleason score or PSA increased.
In particular, chi-square trend analysis showed a signi-
ficant linear trend in groups with different Gleason scores
(p=0.034). When the Gleason score was 8 or greater, endor-
ectal MRI predicted seminal vesicle invasion perfectly.
DISCUSSION
The typical presentation of prostate cancer has changed
greatly over the past two decades. Currently, more men are
presenting with well-differentiated tumors, low PSA lev-
els, and nonpalpable disease. This dramatic shift in pre-
sentation, which may be due to PSA use, has caused a major
stage migration for prostate cancer, with nearly 80% of
newly diagnosed cases revealing only localized disease
[11,12]. In patients with localized prostate cancer, radical
prostatectomy is the most effective treatment tool and of-
fers the best chance of a cure [13]. However, over 30% of men
with clinically localized prostate cancer are found to have
extraprostatic extension by surgical pathologic analysis
[14,15]. Moreover, many of the long-term complications of
radical prostatectomy, such as urinary incontinence and
impotence, have a large impact on patients' quality of life
and, in some patients, may offset the clinical benefits [16].
Therefore, accurate cancer staging at diagnosis is crucial.
　The use of computed tomography and MRI to evaluate
the local extent of disease is not routinely recommended be-
cause of the low sensitivity and accompanying low cost-ef-
fectiveness of these modalities [1,10,17]. Nevertheless,
MRI using an endorectal coil combined with phased-array
coils remains the most promising technique for the de-
tection and staging of prostate cancer [5].
　The sensitivity of the detection and correct localization
of peripheral zone disease by use of T2 sequences was re-
ported to vary significantly between 37% and 96% [18]. For
the detection of extraprostatic extension, the sensitivity,
specificity, and accuracy of endorectal MRI has been re-
ported to range from 13-71%, 47-97%, and 58-91%, re-
spectively, whereas for the detection of seminal vesicle in-
vasion, the sensitivity, specificity, and accuracy of endor-
ectal MRI has been reported to range from 33-71%, 83-99%,
and 80-95%, respectively [19-21]. In the present study, the
sensitivity, specificity, and accuracy for the detection of ex-
traprostatic invasion was 50%, 83%, and 78%, respectively,
and that for the detection of seminal vesicle invasion was
75%, 92%, and 91%, respectively. As a result of the inability
of MRI to visualize microscopic disease, its sensitivity in
detecting extraprostatic extension is uniformly less than
75%. However, in clinical practice, a staging tool must have
a high sensitivity to prevent unnecessary surgeries that
could negatively impact quality of life. Therefore, it is im-
perative that we develop a method with an appropriately
high sensitivity. Ellis et al reported that high-grade tumors
are more likely to be detected on T2 sequences [22]. Later,
Ikonen et al confirmed that endorectal MRI detects poorly
differentiated prostate cancer lesions more accurately
than well-differentiated tumors, although there was no
statistically significant difference between PSA groups in
the detection of tumors [4]. In our study, chi-square trend
analysis also showed a significant linear trend in groups
with different Gleason scores. This observation seems to
be the result of greater variation in the tumor's micro-
structure [23]. Therefore, endorectal MRI could be advo-
cated in patients with high Gleason scores.
　There are several limitations to our study. First, the
number of enrolled cases was small and just eight (14.8%)
patients had extraprostatic extension. Therefore, the stat-
istical power is unavoidably weak. Second, we could not
compare the sensitivity of endorectal MRI for detecting
seminal vesicle invasion according to Gleason scores be-
cause the number of positive cases was too small. Third, on-
ly prostate cancer in the peripheral zone was assessed in

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Korean J Urol 2010;51:308-312
Role of Endorectal MRI in Prostate Cancer Staging
311
the present study; if prostate cancer in the central gland
had been included, the overall accuracy and sensitivity
might have been lower. Finally, the use of MRI in prostate
cancer is evolving. Recently, several studies have convinc-
ingly shown that dynamic contrast enhancement sequenc-
ing and spectroscopy each improve the detection rate and
sensitivity of MRI [24,25]. In addition, diffusion-weighted
imaging of standard T2-weighted sequences and 3T MRI
may improve cancer identification [26,27]. The use of these
tools will likely yield even better results.
CONCLUSIONS
Endorectal MRI demonstrated modest sensitivity and a
relatively high specificity for predicting extraprostatic ex-
tension of clinically localized prostate cancer in a small
sample of patients. The sensitivity was higher in poorly dif-
ferentiated prostatic cancer than in well-differentiated
prostate cancer. Using endorectal MRI, we were able to
more accurately predict seminal vesicle invasion than ex-
traprostatic extension.
Conflicts of Interest
The authors have nothing to disclose.
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