1990, The British Journal of Radiology, 63, 101-107
Magnetic resonance imaging of the normal prostate at 1.5 T By P. A. Gevenois, MD, * l . Salmon, MD, B. Stallenberg, MD, M. L van Sinoy, tG. van Regemorter and J. Struyven Departments of Radiology, 'Pathology and tUrology, Hopital Erasme, University of Brussels, Belgium {Received in March 1989 and in revised form August 1989)
Abstract. Prostatic magnetic resonance images of 22 male volunteers less than 30 years old and with no known genito-urinary tract disease were obtained at 1.5 T. Normal anatomical features of the prostate were studied with spin-echo techniques. Different zones of the normal gland are shown by r r weighted images: the anterior fibromuscular fascia, the central prostate, the peripheral prostate and the periurethral zone" can be differentiated. The normal prostate gland is shown on r,-weighted images as a homogeneous appearance. It is important to recognize the normal zonal anatomy of the prostate since prostatic disorders arise in different anatomical zones.
Previous papers have reported results of magnetic resonance imaging (MRI) of the prostate with lower field strengths (Hricak et al, 1983; Bryan et al, 1983; Berry et al, 1984; Poon et al, 1985; Gevenois et al, 1987a) and higher field strengths (Sommer et al, 1986; Philips et al, 1987a, b). The purpose of the following prospective study is to describe the anatomical aspects of the normal prostate and its adnexa. These features were studied with T2- weigh ted images, since 71,-weighted images do not show any differentiation in the prostate gland.
Results
The prostate showed a homogeneous low signal on r,-weighted images in all 22 volunteers (Fig. 1). Long TR/TE images (T2- weighted) demonstrated four
Materials and methods
We prospectively studied 22 healthy volunteers, with no known genito-urinary tract disorders, ranging in age from 21 to 30 years. Magnetic resonance images were obtained with a 1.5 T superconducting magnet (Philips SI5 Gyroscan), with a display matrix size of 256 horizontal by 256 vertical elements. A body coil with a field of view of 400 mm was used. Four data acquisitions were averaged for each image. Transaxial and sagittal images were obtained from each subject and, in addition, coronal images were obtained in two volunteers. All images were created using a two-dimensional Fourier transform technique. The same protocol for data acquisition was used. The examinations began with a r,-weighted sagittal multislice scan (spin-echo (SE), time to repeat (TR) 350, time to echo (TE) 20, two excitations) for positioning the prostate (Fig. 1). A r2-weighted transaxial multislice scan (SE, TR 2000, TE 50-100, two excitations) was then obtained with sections of 5 mm with 0.5 mm gaps. In two cases, additional coronal r2-weighted scans were obtained. A 1 h time limit was set for the examination of each volunteer. The appearances of the prostate, urethra, periprostatic fascia and venous plexus were analysed to determine anatomical detail and signal features. Address for correspondence: P. A. Gevenois, MD, Department of Radiology, Hopital Erasme, University of Brussels, Route de Lennik, 808, B-1070 Brussels, Belgium. Vol. 63, No. 746
Figure 1. On a sagittal SE 350/20 image of a young adult, the prostate (P) shows an intermediate homogeneous signal. The bulging of the bladder wall is always present (arrow). The seminal vesicles (SV) appear as a low signal (B = bladder, Pu = pubis).
101
P. A. Gevenois et al
Figure 2. On an axial SE 2000/50 image from the upper half of the prostate, the prostatic zonal differentiation is demonstrated, with the peripheral prostate (pp) being of higher signal intensity than the central prostate (cp). Anterior to the urethra (u) is a zone composed of fibromuscular stroma (f). The prostatic venous plexus (arrow heads) is seen posterolaterally, and the prostatic capsule is visualized (dark arrows) (B = bladder, R = rectum). 102
Figure 3. On an axial SE 2000/50 image from the lower half of the gland, peripheral prostate (pp) is discernible. The urethra (u) is surrounded by a thin low-signal margin (dark arrows). The prostatic venous plexus is seen posterolaterally (arrow heads) (P = pubis, la = levator ani muscle, R = rectum).
The British Journal of Radiology, February 1990
MRI of the normal prostate at 1.5 T
Figure 4. A coronal SE 2000/50 image shows the low-signal intensity of the central prostate (cp), which is lower than the peripheral prostate (pp). The prostatic capsule is discernible (arrow heads). The prostatic venous plexus (PVP) is visualized superolaterally. (la = levator ani muscle, cs = corpus spongiosum.)
separate zones within the gland in all cases. This zonal distinction was well defined on axial images but was also discernible on coronal images (Figs 2,3). McNeal describes four different anatomical regions of substantially different composition (McNeal, 1978, 1980a). One large region, the anterior fibromuscular stroma which is up to one third of the mass of the organ, is entirely non-glandular, consisting mainly of smooth muscle fibres. Another region surrounds the proximal or preprostatic half of the prostatic urethra above the verumontanum. This is a complex transitional region of mixed glandular and non-glandular tissue, which in the normal prostate is very small. The peripheral zone is the largest of the two major glandular regions of the prostate and represents roughly 75% of the total glandular tissue. The central zone is the second component of the functioning glandular prostate and makes up about 25% of its mass. It completes the proximal quadrant of the glandular tissue above and behind the verumontanum (McNeal, 1980a). The four zones visible by MRI were as follows (Fig. 2). a) A very low-intensity anterior region with maximal Vol. 63, No. 746
thickness in the images through the upper portion of the prostate. b) Two peripheral posterior symmetric crescents of high signal intensity. c) An intermediate-intensity region between these two regions in the central portion of the gland. This region is identifiable only on scanning the upper half of the prostate. d) A small circular area with a high signal lying posterior to the dark anterior region and in the anterior third of the gland. This region is bordered by a thin lowsignal margin in the lower half of the gland (Fig. 3). This small circle is thought to correspond to the urethra, surrounded by periurethral glands. The verumontanum was never seen. These four regions were observed in all cases. The T2weighted coronal image through the midportion of the prostate showed a zone of high intensity inferior and lateral to a region of lower intensity (Fig. 4). Between the two peripheral symmetric crescents, a high signal intensity was observed in three cases (Fig. 5). In one case, three points of quite high intensity were 103
P. A. Gevenois et al
(a)
Figure 5. On a transverse SE 2000/50 image from the upper half of the prostate, a very high-intensity signal (*) is observed between the two peripheral symmetric crescents (pp). This signal may represent the ejaculatory ducts or the prostatic utricle. The prostatic venous plexus (light arrows) courses laterally around the gland. The prostatic capsule is discernible (dark arrows) (B = bladder, f =fibromuscularstroma, cp = central prostate, pp = peripheral prostate, u = urethra, R = rectum).
seen, corresponding to the region of the ejaculatory Discussion ducts and prostatic utricle. In 10 cases, a thin rim of low Magnetic resonance imaging provides an ideal anatosignal intensity was poorly seen at the periphery of the mical image of the prostate. Spin-echo r2-weighted gland on r2-weighted scans, which may correspond to images obtained at 1.5 T allow distinction between peripheral and central zones and may reveal very small the prostatic capsule proper (Figs 2, 4-6). The relationships between the prostate gland, the structures such as the urethra or ejaculatory ducts. bladder floor, the rectum, the venous plexus within the Historically, the study of the anatomy of the prostate periprostatic fat, the symphysis pubis and the muscles has been characterized by a proliferation of contradictwere well seen. On the midline sagittal scan, a normal ory findings (McNeal, 1980b). McNeal (1980a) has bulging of the infero-posterior bladder wall was always defined a peripheral and a central zone, the histological present (Fig. 1). On T2- weigh ted images, a periprostatic differentiation of which leads to a zonal distribution of zone with high signal intensity was observed, repre- diseases. Cancer and benign prostatic hyperplasia senting the periprostatic venous plexus (PVP) in fatty (BPH) arise mainly in the peripheral and central zones, tissue (Figs 2-5), seen in the posterolateral and lateral respectively (Edwards et al, 1953; Franks, 1954; periprostatic tissue, but never in the posterior space McNeal, 1969; McNeal, 1978). Magnetic resonance between the prostate and rectum. In the coronal scan, depiction of the zonal anatomy of the prostate corresthe relationship of the prostatic gland to the urogenital ponds to McNeal's description (McNeal, 1972, 1980a). diaphragm was well defined (Fig. 6). McNeal described an anterior fibromuscular stroma, The seminal vesicles were well identified in all cases. which corresponds to the dark anterior signal The normal signal was always symmetrical, and (Figs 2, 5). Leiomyomas arising from this stroma have changed from low intensity on Tx -weighted images been described (Gevenois et al, 1987b). The central zone appears on T2-weighted images as an (Fig. 1) to high intensity on r2-weighted images (Fig. 7). The ampulla of the ductus deferens could not be differ- intermediate-intensity signal and the peripheral zone as a high-intensity signal (Fig. 2). The biochemical reasons entiated from the seminal vesicles. 104
The British Journal of Radiology, February 1990
MRI of the normal prostate at 1.5 T
Figure 6. A coronal SE 2000/50 image shows the prostatic urethra (u) and the relationships between the prostate and the perineum. (B = bladder, la = levator ani muscle, cc = corpora cavernosa, cs = corpora spongiosum, ICM = ischiocavernous muscle, BCM = bulbocavernous muscle, MUD = muscles of the urogenital diaphragm).
for this difference are not known. The peripheral zone should contain more free water than the central zone, and the central zone more than the fibromuscular stroma. The definition of these zones depends on differences in gland architecture. The peripheral zone ducts are long, narrow and straight, with short terminal branches ending in small, simple, round acini. The centra/ zone ducts are /arger with more compfex arborization. They produce large acini of irregular contour, partially compartmentalized by septa. The peripheral zone epithelium consists of pale cells in a simple columnar arrangement with basal, small dark nuclei. The central zone cells have granular, opaque cytoplasm (McNeal, 1980a). This striking histologic difference suggests a great difference in biological functions. The differences in signals by MRI confirm a chemical difference between central and peripheral glandular tissue. The urethral zone appears as a very high signal. This may result from urine in the utethral lumen or liquid secretions in the periurethral glands within the preprostatic sphincter. The thin, low-signal ring surrounding the urethra may represent this sphincter. Vol. 63, No. 746
The PVP is always seen. It courses laterally around the prostate to join anteriorly the plexus of Santorini. The plane directly posterior between the prostate and the rectum is known to be avascular. No PVP is ever seen in this region. The high signal of the PVP results from low venous blood flow. The bulging of the bladder wall is always seen and should not be misinterpreted as tumour infiltration of the inferior wall by prostatic carcinoma. Seminal vesicles appear as very high symmetrical signals, contrasting with the central prostatic zone. McNeal has shown that the architectural and histologic features of the central zone closely resemble those of the seminal vesicles (McNeal, 1980a), leading to the suggestion that the central zone may be of Wolffian duct origin, while the remainder of the glandular prostate arises from the urogenital sinus. Nevertheless, the intensities of the MR signal from these structures are completely different, reflecting biochemical differences between the structures. Recent studies have reported the results of MRI of the normal prostate (Sommer et al, 1986; Philips et al, 105
P. A. Gevenois et al
Figure 7. An axial SE 2000/50 image shows the seminal vesicles (SV). They appear as a symmetric high-signal intensity. (B = bladder, R = rectum).
1987a). These retrospective studies have been made with patients aged from 27 to 75 years (Sommer et al, 1986) or from 7 months to 67 years (Philips et al, 1987a), with no clinical evidence of prostatic disease. Berry et al (1984) have observed that the growth of BPH is probably initiated before the patient is 30 years old. The early phase of BPH growth (between 31 and 50 years old) is characterized by the shortest doubling time for the tumour weight (4.5 years). The prevalence of pathological BPH is only 8% at the fourth decade, but 50% of the male population have pathological BPH by the time they are 51-60 years old (Berry et al, 1984). McNeal has emphasized that BPH nodules originate selectively from a very small region near the cylindrical urethral sphincter above the verumontanum, and most nodules arise from the glands and the stroma of the transitional zone of the prostate (McNeal, 1978). Because of this, all 22 of our volunteers were chosen from adults less than 30 years old. Of the supposedly normal specimens examined by other authors, several were probably adenomatous. Since carcinomas arise frequently in the peripheral zone, any focal disruption of the normal high signal of this zone should arouse suspicion of malignancy. The examination of the prostatic contours and the PVP may 106
be of great interest in the evaluation of extracapsular neoplasic involvement. Although disruption of this high-signal zone can occur in prostatic carcinoma, some authors (Philips et al, 1987b) regard it as an unreliable sign. References BERRY, S. J., COFFEY, D. S., WALSH, P. C. & EWING, L.
L.,
1984. The development of human benign prostatic hyperplasia with age. Journal of Urology, 132, 474-479. BRYAN, P. J., BUTLER, H. E., LIPUMA, J. P., HAAGA, J. R., E L YOOSEF, S. J., RESNICK, M. I., COHEN, A. M., MALVIYA, V. K., NELSON, A. D., CLAMPITT, M., ALFIDI, R. J., COHEN, J. &
MORRISON, S. C , 1983. NMR scanning of the pelvis: initial experience with a 0.3 T system. American Journal of Roentgenology, 141, 1111-1118. EDWARDS, C. N., STEINTHORSSON, E. & NICHOLSON, D.,
1953.
An autopsy study of latent prostatic cancer. Cancer, 6, 531-534. FRANKS, L. M., 1954. Benign nodular hyperplasia of the prostate; a review. Annals of Royal College of Surgery, 14, 92-106. GEVENOIS, P. A., VAN REGEMORTER, G., VAN GANSBEKE, D., DELCOUR, C , CORBUSIER, A. & STRUYVEN, J., 1987a.
Pathologie prostatique en resonance magnetique. Journal de Radiologie, 68, 185-192. The British Journal of Radiology, February 1990
MRI of the normal prostate at 1.5 T GEVENOIS, P. A., GHYSELS, M., CORBUSIER, A., VAN REGEMORTER, G., DEPIERREUX, M. & STRUYVEN, J., 1987b.
MCNEAL, J. E., 1980b. Anatomy of the prostate: an historical survey of divergent views. The Prostate, 1, 3—13.
Leiomyome de la prostate. Aspect en IRM. Journal de Radiologie, 68, 631-634.
PHILIPS, M. E., KRESSEL, H. Y., SPRITZER, C. E., ARGER, P. H., WEIN, A. J., AXEL, L., WARREN, B. G. & POLLACK, H. M.,
HRICAK, H., WILLIAMS, R. D., SPRING, D. B., MOON, K. L., HEDGCOCK, M. W., WATSON, R. A. & CROOKS, L. E., 1983.
1987a. Normal prostate and adjacent structures: MR imaging at 1.5 T. Radiology, 164, 381-385.
Anatomy and pathology of the male pelvis by magnetic resonance imaging. American Journal of Roentgenology, 141, 1101-1110. MCNEAL, J. E., 1969. Origin and development of carcinoma in the prostate. Cancer, 23, 24-34. MCNEAL, J. E., 1972. The prostate and prostatic urethra: a morphologic synthesis. Journal of Urology, 107, 1008-1016. MCNEAL, J. E., 1978. Origin and evolution of benign prostatic enlargement. Investigative Urology, 15, 340-345. MCNEAL, J. E., 1980a. The anatomy heterogeneity of the prostate. In Models for Prostate Cancer. Ed by G. P. Murphy (Alan R. Liss, New York) pp. 149-160.
PHILIPS, M. E., KRESSEL, H. Y., SPRITZER, C. E., ARGER, P. H., WEIN, A. J., MARINELLI, D., ASEL, L., GEFTER, W. B. &
Vol. 63, No. 746
POLLACK, H. M., 1987b. Prostatic disorders: MR imaging at 1.5 T. Radiology, 164, 386-392. POON, P. Y., MCCALLUM, R. W., HENKELMAN, M. M., BRONSKILL, M. J., SUTCLIFFE, S. B., JEWETT, M. A. S., RIDER,
W. D. & BRUCE, A. W., 1985. Magnetic resonance imaging of the prostate. Radiology, 154, 143-149. SOMMER, F. G., MCNEAL, J. E. & CARROL, C. L., 1986.
MR
depiction of zonal anatomy of the prostate at 1.5 T. Journal of Computed Assisted Tomography, 10, 983-989.
107
Magnetic resonance imaging of the normal prostate at 1.5 T By P. A. Gevenois, MD, * l . Salmon, MD, B. Stallenberg, MD, M. L van Sinoy, tG. van Regemorter and J. Struyven Departments of Radiology, 'Pathology and tUrology, Hopital Erasme, University of Brussels, Belgium {Received in March 1989 and in revised form August 1989)
Abstract. Prostatic magnetic resonance images of 22 male volunteers less than 30 years old and with no known genito-urinary tract disease were obtained at 1.5 T. Normal anatomical features of the prostate were studied with spin-echo techniques. Different zones of the normal gland are shown by r r weighted images: the anterior fibromuscular fascia, the central prostate, the peripheral prostate and the periurethral zone" can be differentiated. The normal prostate gland is shown on r,-weighted images as a homogeneous appearance. It is important to recognize the normal zonal anatomy of the prostate since prostatic disorders arise in different anatomical zones.
Previous papers have reported results of magnetic resonance imaging (MRI) of the prostate with lower field strengths (Hricak et al, 1983; Bryan et al, 1983; Berry et al, 1984; Poon et al, 1985; Gevenois et al, 1987a) and higher field strengths (Sommer et al, 1986; Philips et al, 1987a, b). The purpose of the following prospective study is to describe the anatomical aspects of the normal prostate and its adnexa. These features were studied with T2- weigh ted images, since 71,-weighted images do not show any differentiation in the prostate gland.
Results
The prostate showed a homogeneous low signal on r,-weighted images in all 22 volunteers (Fig. 1). Long TR/TE images (T2- weighted) demonstrated four
Materials and methods
We prospectively studied 22 healthy volunteers, with no known genito-urinary tract disorders, ranging in age from 21 to 30 years. Magnetic resonance images were obtained with a 1.5 T superconducting magnet (Philips SI5 Gyroscan), with a display matrix size of 256 horizontal by 256 vertical elements. A body coil with a field of view of 400 mm was used. Four data acquisitions were averaged for each image. Transaxial and sagittal images were obtained from each subject and, in addition, coronal images were obtained in two volunteers. All images were created using a two-dimensional Fourier transform technique. The same protocol for data acquisition was used. The examinations began with a r,-weighted sagittal multislice scan (spin-echo (SE), time to repeat (TR) 350, time to echo (TE) 20, two excitations) for positioning the prostate (Fig. 1). A r2-weighted transaxial multislice scan (SE, TR 2000, TE 50-100, two excitations) was then obtained with sections of 5 mm with 0.5 mm gaps. In two cases, additional coronal r2-weighted scans were obtained. A 1 h time limit was set for the examination of each volunteer. The appearances of the prostate, urethra, periprostatic fascia and venous plexus were analysed to determine anatomical detail and signal features. Address for correspondence: P. A. Gevenois, MD, Department of Radiology, Hopital Erasme, University of Brussels, Route de Lennik, 808, B-1070 Brussels, Belgium. Vol. 63, No. 746
Figure 1. On a sagittal SE 350/20 image of a young adult, the prostate (P) shows an intermediate homogeneous signal. The bulging of the bladder wall is always present (arrow). The seminal vesicles (SV) appear as a low signal (B = bladder, Pu = pubis).
101
P. A. Gevenois et al
Figure 2. On an axial SE 2000/50 image from the upper half of the prostate, the prostatic zonal differentiation is demonstrated, with the peripheral prostate (pp) being of higher signal intensity than the central prostate (cp). Anterior to the urethra (u) is a zone composed of fibromuscular stroma (f). The prostatic venous plexus (arrow heads) is seen posterolaterally, and the prostatic capsule is visualized (dark arrows) (B = bladder, R = rectum). 102
Figure 3. On an axial SE 2000/50 image from the lower half of the gland, peripheral prostate (pp) is discernible. The urethra (u) is surrounded by a thin low-signal margin (dark arrows). The prostatic venous plexus is seen posterolaterally (arrow heads) (P = pubis, la = levator ani muscle, R = rectum).
The British Journal of Radiology, February 1990
MRI of the normal prostate at 1.5 T
Figure 4. A coronal SE 2000/50 image shows the low-signal intensity of the central prostate (cp), which is lower than the peripheral prostate (pp). The prostatic capsule is discernible (arrow heads). The prostatic venous plexus (PVP) is visualized superolaterally. (la = levator ani muscle, cs = corpus spongiosum.)
separate zones within the gland in all cases. This zonal distinction was well defined on axial images but was also discernible on coronal images (Figs 2,3). McNeal describes four different anatomical regions of substantially different composition (McNeal, 1978, 1980a). One large region, the anterior fibromuscular stroma which is up to one third of the mass of the organ, is entirely non-glandular, consisting mainly of smooth muscle fibres. Another region surrounds the proximal or preprostatic half of the prostatic urethra above the verumontanum. This is a complex transitional region of mixed glandular and non-glandular tissue, which in the normal prostate is very small. The peripheral zone is the largest of the two major glandular regions of the prostate and represents roughly 75% of the total glandular tissue. The central zone is the second component of the functioning glandular prostate and makes up about 25% of its mass. It completes the proximal quadrant of the glandular tissue above and behind the verumontanum (McNeal, 1980a). The four zones visible by MRI were as follows (Fig. 2). a) A very low-intensity anterior region with maximal Vol. 63, No. 746
thickness in the images through the upper portion of the prostate. b) Two peripheral posterior symmetric crescents of high signal intensity. c) An intermediate-intensity region between these two regions in the central portion of the gland. This region is identifiable only on scanning the upper half of the prostate. d) A small circular area with a high signal lying posterior to the dark anterior region and in the anterior third of the gland. This region is bordered by a thin lowsignal margin in the lower half of the gland (Fig. 3). This small circle is thought to correspond to the urethra, surrounded by periurethral glands. The verumontanum was never seen. These four regions were observed in all cases. The T2weighted coronal image through the midportion of the prostate showed a zone of high intensity inferior and lateral to a region of lower intensity (Fig. 4). Between the two peripheral symmetric crescents, a high signal intensity was observed in three cases (Fig. 5). In one case, three points of quite high intensity were 103
P. A. Gevenois et al
(a)
Figure 5. On a transverse SE 2000/50 image from the upper half of the prostate, a very high-intensity signal (*) is observed between the two peripheral symmetric crescents (pp). This signal may represent the ejaculatory ducts or the prostatic utricle. The prostatic venous plexus (light arrows) courses laterally around the gland. The prostatic capsule is discernible (dark arrows) (B = bladder, f =fibromuscularstroma, cp = central prostate, pp = peripheral prostate, u = urethra, R = rectum).
seen, corresponding to the region of the ejaculatory Discussion ducts and prostatic utricle. In 10 cases, a thin rim of low Magnetic resonance imaging provides an ideal anatosignal intensity was poorly seen at the periphery of the mical image of the prostate. Spin-echo r2-weighted gland on r2-weighted scans, which may correspond to images obtained at 1.5 T allow distinction between peripheral and central zones and may reveal very small the prostatic capsule proper (Figs 2, 4-6). The relationships between the prostate gland, the structures such as the urethra or ejaculatory ducts. bladder floor, the rectum, the venous plexus within the Historically, the study of the anatomy of the prostate periprostatic fat, the symphysis pubis and the muscles has been characterized by a proliferation of contradictwere well seen. On the midline sagittal scan, a normal ory findings (McNeal, 1980b). McNeal (1980a) has bulging of the infero-posterior bladder wall was always defined a peripheral and a central zone, the histological present (Fig. 1). On T2- weigh ted images, a periprostatic differentiation of which leads to a zonal distribution of zone with high signal intensity was observed, repre- diseases. Cancer and benign prostatic hyperplasia senting the periprostatic venous plexus (PVP) in fatty (BPH) arise mainly in the peripheral and central zones, tissue (Figs 2-5), seen in the posterolateral and lateral respectively (Edwards et al, 1953; Franks, 1954; periprostatic tissue, but never in the posterior space McNeal, 1969; McNeal, 1978). Magnetic resonance between the prostate and rectum. In the coronal scan, depiction of the zonal anatomy of the prostate corresthe relationship of the prostatic gland to the urogenital ponds to McNeal's description (McNeal, 1972, 1980a). diaphragm was well defined (Fig. 6). McNeal described an anterior fibromuscular stroma, The seminal vesicles were well identified in all cases. which corresponds to the dark anterior signal The normal signal was always symmetrical, and (Figs 2, 5). Leiomyomas arising from this stroma have changed from low intensity on Tx -weighted images been described (Gevenois et al, 1987b). The central zone appears on T2-weighted images as an (Fig. 1) to high intensity on r2-weighted images (Fig. 7). The ampulla of the ductus deferens could not be differ- intermediate-intensity signal and the peripheral zone as a high-intensity signal (Fig. 2). The biochemical reasons entiated from the seminal vesicles. 104
The British Journal of Radiology, February 1990
MRI of the normal prostate at 1.5 T
Figure 6. A coronal SE 2000/50 image shows the prostatic urethra (u) and the relationships between the prostate and the perineum. (B = bladder, la = levator ani muscle, cc = corpora cavernosa, cs = corpora spongiosum, ICM = ischiocavernous muscle, BCM = bulbocavernous muscle, MUD = muscles of the urogenital diaphragm).
for this difference are not known. The peripheral zone should contain more free water than the central zone, and the central zone more than the fibromuscular stroma. The definition of these zones depends on differences in gland architecture. The peripheral zone ducts are long, narrow and straight, with short terminal branches ending in small, simple, round acini. The centra/ zone ducts are /arger with more compfex arborization. They produce large acini of irregular contour, partially compartmentalized by septa. The peripheral zone epithelium consists of pale cells in a simple columnar arrangement with basal, small dark nuclei. The central zone cells have granular, opaque cytoplasm (McNeal, 1980a). This striking histologic difference suggests a great difference in biological functions. The differences in signals by MRI confirm a chemical difference between central and peripheral glandular tissue. The urethral zone appears as a very high signal. This may result from urine in the utethral lumen or liquid secretions in the periurethral glands within the preprostatic sphincter. The thin, low-signal ring surrounding the urethra may represent this sphincter. Vol. 63, No. 746
The PVP is always seen. It courses laterally around the prostate to join anteriorly the plexus of Santorini. The plane directly posterior between the prostate and the rectum is known to be avascular. No PVP is ever seen in this region. The high signal of the PVP results from low venous blood flow. The bulging of the bladder wall is always seen and should not be misinterpreted as tumour infiltration of the inferior wall by prostatic carcinoma. Seminal vesicles appear as very high symmetrical signals, contrasting with the central prostatic zone. McNeal has shown that the architectural and histologic features of the central zone closely resemble those of the seminal vesicles (McNeal, 1980a), leading to the suggestion that the central zone may be of Wolffian duct origin, while the remainder of the glandular prostate arises from the urogenital sinus. Nevertheless, the intensities of the MR signal from these structures are completely different, reflecting biochemical differences between the structures. Recent studies have reported the results of MRI of the normal prostate (Sommer et al, 1986; Philips et al, 105
P. A. Gevenois et al
Figure 7. An axial SE 2000/50 image shows the seminal vesicles (SV). They appear as a symmetric high-signal intensity. (B = bladder, R = rectum).
1987a). These retrospective studies have been made with patients aged from 27 to 75 years (Sommer et al, 1986) or from 7 months to 67 years (Philips et al, 1987a), with no clinical evidence of prostatic disease. Berry et al (1984) have observed that the growth of BPH is probably initiated before the patient is 30 years old. The early phase of BPH growth (between 31 and 50 years old) is characterized by the shortest doubling time for the tumour weight (4.5 years). The prevalence of pathological BPH is only 8% at the fourth decade, but 50% of the male population have pathological BPH by the time they are 51-60 years old (Berry et al, 1984). McNeal has emphasized that BPH nodules originate selectively from a very small region near the cylindrical urethral sphincter above the verumontanum, and most nodules arise from the glands and the stroma of the transitional zone of the prostate (McNeal, 1978). Because of this, all 22 of our volunteers were chosen from adults less than 30 years old. Of the supposedly normal specimens examined by other authors, several were probably adenomatous. Since carcinomas arise frequently in the peripheral zone, any focal disruption of the normal high signal of this zone should arouse suspicion of malignancy. The examination of the prostatic contours and the PVP may 106
be of great interest in the evaluation of extracapsular neoplasic involvement. Although disruption of this high-signal zone can occur in prostatic carcinoma, some authors (Philips et al, 1987b) regard it as an unreliable sign. References BERRY, S. J., COFFEY, D. S., WALSH, P. C. & EWING, L.
L.,
1984. The development of human benign prostatic hyperplasia with age. Journal of Urology, 132, 474-479. BRYAN, P. J., BUTLER, H. E., LIPUMA, J. P., HAAGA, J. R., E L YOOSEF, S. J., RESNICK, M. I., COHEN, A. M., MALVIYA, V. K., NELSON, A. D., CLAMPITT, M., ALFIDI, R. J., COHEN, J. &
MORRISON, S. C , 1983. NMR scanning of the pelvis: initial experience with a 0.3 T system. American Journal of Roentgenology, 141, 1111-1118. EDWARDS, C. N., STEINTHORSSON, E. & NICHOLSON, D.,
1953.
An autopsy study of latent prostatic cancer. Cancer, 6, 531-534. FRANKS, L. M., 1954. Benign nodular hyperplasia of the prostate; a review. Annals of Royal College of Surgery, 14, 92-106. GEVENOIS, P. A., VAN REGEMORTER, G., VAN GANSBEKE, D., DELCOUR, C , CORBUSIER, A. & STRUYVEN, J., 1987a.
Pathologie prostatique en resonance magnetique. Journal de Radiologie, 68, 185-192. The British Journal of Radiology, February 1990
MRI of the normal prostate at 1.5 T GEVENOIS, P. A., GHYSELS, M., CORBUSIER, A., VAN REGEMORTER, G., DEPIERREUX, M. & STRUYVEN, J., 1987b.
MCNEAL, J. E., 1980b. Anatomy of the prostate: an historical survey of divergent views. The Prostate, 1, 3—13.
Leiomyome de la prostate. Aspect en IRM. Journal de Radiologie, 68, 631-634.
PHILIPS, M. E., KRESSEL, H. Y., SPRITZER, C. E., ARGER, P. H., WEIN, A. J., AXEL, L., WARREN, B. G. & POLLACK, H. M.,
HRICAK, H., WILLIAMS, R. D., SPRING, D. B., MOON, K. L., HEDGCOCK, M. W., WATSON, R. A. & CROOKS, L. E., 1983.
1987a. Normal prostate and adjacent structures: MR imaging at 1.5 T. Radiology, 164, 381-385.
Anatomy and pathology of the male pelvis by magnetic resonance imaging. American Journal of Roentgenology, 141, 1101-1110. MCNEAL, J. E., 1969. Origin and development of carcinoma in the prostate. Cancer, 23, 24-34. MCNEAL, J. E., 1972. The prostate and prostatic urethra: a morphologic synthesis. Journal of Urology, 107, 1008-1016. MCNEAL, J. E., 1978. Origin and evolution of benign prostatic enlargement. Investigative Urology, 15, 340-345. MCNEAL, J. E., 1980a. The anatomy heterogeneity of the prostate. In Models for Prostate Cancer. Ed by G. P. Murphy (Alan R. Liss, New York) pp. 149-160.
PHILIPS, M. E., KRESSEL, H. Y., SPRITZER, C. E., ARGER, P. H., WEIN, A. J., MARINELLI, D., ASEL, L., GEFTER, W. B. &
Vol. 63, No. 746
POLLACK, H. M., 1987b. Prostatic disorders: MR imaging at 1.5 T. Radiology, 164, 386-392. POON, P. Y., MCCALLUM, R. W., HENKELMAN, M. M., BRONSKILL, M. J., SUTCLIFFE, S. B., JEWETT, M. A. S., RIDER,
W. D. & BRUCE, A. W., 1985. Magnetic resonance imaging of the prostate. Radiology, 154, 143-149. SOMMER, F. G., MCNEAL, J. E. & CARROL, C. L., 1986.
MR
depiction of zonal anatomy of the prostate at 1.5 T. Journal of Computed Assisted Tomography, 10, 983-989.
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