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Benign prostatic hyperplasia: Appearance on magnetic resonance imaging
URORADIOLOGY
BENIGN PROSTATIC HYPERPLASIA: APPEARANCE ON MAGNETIC RESONANCE IMAGING CYNTHIA JANUS, M.D. MARGUERITE LIPPERT,
M.D.
From the Departments of Radiology and Urology, University of Virginia Medical Center, Charlottesville, Virginia ABSTRACT-Benign prostatic hyperplasia (BPH) bas a uariable appearance on magnetic resonance imaging (MRZ). This study reviews and categorizes the MRZ findings of this entity in a sample of 26 men. Cases where atypical or suspicious changes are incidental findings should be reported to the urologist for further inuestigation. Zn addition, familiarity with both the appearance of the nomnal prostate and the changes caused by BPH is necessary when staging patients with known prostate cancer.
The appearance of the normal prostate gland on magnetic resonance imaging (MRI) bas been described includiing delineation of the characteristic zonal anatomy on T2 weighted sequences . lw6 This study was undertaken to categorize the speatrum of findings in benign prostatic hyperplasia (BPH) on MRI. It is important to become familiar with the appearante of this very common entity.
the seminal vesicles was measured on axial Tl images. The prostate gland has been described anatomically as being comprised of three glandular regions, the transition, central, and peripheral zones, and a nonglandular zone, the anterior fibromuscular stroma. Recently standardized ultrasound terminology defines the central portion of the prostate containing nodules of BPH in the transitional zone as the “inner” gland. In this report, the term “central gland” includes the transitional zone, central glandular region, and fibromuscular structure anterior to the urethra since these areas cannot be reliably distinguished from each other on magnetic resonance imaging. On T2 weighted sequences, the centra1 gland is of variable but for the most part low signal intensity compared with the high signal intensity peripheral zone (Fig. 1). Areas of the centra1 gland and of the entire prostate were obtained from the axial view. The signal characteristics of the centra1 gland and the presence of discrete nodules were also noted (Fig. 2). Each study was evaluated for presence of a detectable capsule and pseudocapsule (Fig. 1).
Material and Methods Patients in this study were considered to have benign prostatie hyperplasia on the basis of having symptoms of bladder outlet obstruction and confirmation of an enlarged prostate on recta1 examination. None had any clinical or laboratory evidente of carcinoma. The population consists of 26 men ranging in years age from fort -six to seventy-eight (average age 6 g .8 years). MRI examinations were performed on a 1.0 Tesla scanner (Siemens). Corona1 Tl weighted (TR 600-800, TE 20-25) and axial TI (TR 600-800, TE 2025) and T2 (TR 2500, TE 20, 70-80) weighted sequences were obtained. Other imaging parameters included a slice thickness of 5 mm, and an interslice gap of 1 mm. The length of the gland was measured in the coronal projection; width and AP dimensions were obtained on the axial projection. Width of
UROLOGY
/ DECEMBER1992
/ VOLUME40.NUMBER
Results The prostate gland ranged from 31 to 83 mm (average 49.8 mm) in length, 43 to 61 mm (average 51.1 mm) in width, and 18 to 57 mm
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539
FIGURE 1. T2 weighted shows high signal intensity heterogeneous lower signal (C). (Single arrow denotes arrows point to capsule.)
axial uiew of prostate peripheral zone (P) and intensity centra1 gland pseudocapsule; double
capsule were visible in 5 men (19 % ). The capsule could not be delineated in 9 patients (35 % ) . The surgical pseudocapsule between the centra1 gland and peripheral zone was displayed as a distinct thin low signal intensity line in 8 patients (31%) and appeared as a low signal intensity zone of variable thickness in 11 (42 % ) . Portions of the pseudocapsule were seen in 5 (19%) and not seen at al1 in 2 (8%). Nodules 1 cm or larger were seen in 2 patients (Fig. 2). In 1 patient the nodules were of high signal intensity while in the other patient, there were nodules of both increased and decreased signal intensity. In 14 patients the central gland region was heterogeneous in signal intensity with nodular foei under 1 cm in size of increased andlor decreased signal intensity. The central gland was of heterogeneous signal intensity without definable nodularity in 10 cases. Incidental findings on MRI (other than pathology related to the lumbosacral spine common in this age group) included bladder diverticulum (l), müllerian duet cyst (1)) colonic diverticula (5), inguinal hernia (l), and hydrocele (2). Comment
FIGURE 2. High s-ignal intensity nodule (n) is seen within markedly enlarged centra1 gland (B = urinary bladder).
(average 34.4 mm) in AP dimension. Width of the central gland ranged from 30 to 64 mm (average 37 mm). AP measurements ranged from 18 to 46 mm (average 30 mm). The central gland comprised 33.5 percent to 99.3 percent (average 55.3%) of the area of the entire prostate. Seminal vesicles ranged from 8.8 to 28 mm (average 15 mm) in thickness. A low signal intensity line on T2 weighted sequences previously described as representing the prostatic capsuIe was identified in its entirety in 12 patients (46 % ) while portions of the
540
The prostate bas been divided into the central, peripheral, and transitional zones. Normally, the peripheral zone (PZ) comprises 75 percent of the volume of the glandular prostate and is the site of approximately 70 percent of cancers. 1,2,8The stroma of the centra1 zone (CZ) consists of compact smooth muscle fibers which display a relatively low signal on T2 weighted sequences. In the peripheral zone, the muscle bundles are loosely interwoven and there are more glandular elements which is believed to explain the higher signal intensity on T2 weighted sequences. g A smal1 transitional zone (T2) normally comprising 5 percent of the gland is found immediately surrounding proximal urethra and within its sphincter. Clinically symptomatic BPH is essentially the result of nodular enlargement of the centrally located transitional zone and to a lesser extent the periurethral tissues.2,7-eThe centra1 and transitional zones are not reliably delineated from each other on MRI. Previous investigators have reported on the inability to reliably demonstrate the prostatic capsule on MRI in normal glands. The low signal peripheral line on T2 sequences believed to represent the capsule was visualized in its entirety in slightly less than half the cases studied
UROLOGY
/ DECEMBER1992
/ VOLUME40,NUMBER6
well-differentiated nodules of prostatic adenocarcinoma. Although it would be inappropriate to consider MRI as a screening modality for prostatic pathology, the findings of BPH are commonly present on MR stans of the pelvis in males over forty years, and it is important to recognize the varied appearances of this entity. The detection of early prostate cancer may be difficult as findings may be subtle as wel1 as nonspecific. Detection or delineation of tumor may be even more challenging when changes of BPH exist. Inability to demonstrate an intact capsule in its entirety, for example, may not be a reliable sign in staging known prostatic cancer. However, the finding of focal signal abnormality in the peripheral zone or a dominant or suspicious area in the centra1 gland should prompt the radiologist to alert the clinician so that appropriate urologie follow-up can take place.
by Phillips et al. l It was either partially seen or not seen at al1 in the remainder. Hricak et d2 found a rim of low signal intensity around the prostate on T2 weighted sequences in 31 percent of patients. Its width, however, was greater than 1 mm which is the thickness of the normal capsule. This group believed that the low signal intensity line may represent a combination of the capsule and periprostatic tissue. Bezzi et al. l” reported that the low signal intensity line representing capsule was not seen in 17 of 37 patients (46 % ) . In 6 patients (16 % ) the line was incompletely seen. The portion most difficult to delineate was most often located posteriorly where the prostate abuts the rectum. In 38 percent (14/37) the capsule was seen and was normal in appearance. Four of the 6 patients in whom the capsule was incompletely delineated had Stage C carcinoma. In evaluating the prostatic capsule it should also be remembered that the chemical shift artifact can account for the apparent presence of a portion of the capsule at a margin of the gland. This imaging artifact results in alternate dark and bright bands at sharp interfaces between predominantly fatty structures and those containing predominantly water. In regard to glandular texture, Bryan et aL4 studied 7 patients with benign nodular hyperplasia. In 2 patients the enlarged prostate had a homogeneous signal intensity on al1 pulse sequences similar to normal prostate. In the other 5 patients signal intensity was inhomogeneous with nodules of relatively low signal intensity on short TR/TE sequences. On long TR/TE sequences, some nadules were of increased and others were of decreased signal intensity. Schiebler et UE.l1 performed high resolution MR stans of twanty-four fresh radical prostatectomy specimens. The MR signal characteristics of BPH seen in ten specimens were variable, Areas of highest signal intensity corresponded to dilated glandular elements while areas containing collagen and fibromuscular stroma displayed low signal intensity. Nodules containing a mixture of glafidular and fibromuscular elements had signal intensities similar to those of
UROLOGY
i
DECEMBER
1992
i
VOLUME
40, NUMBER
Vineland,
ACKNOWLEDGMENT. ante
in the preparation
To Andrew
P.O. Box 2420 New Jersey 08360 (DR. JANUS) Martin
for
his assist-
of this manuscript.
1. Phillips ME, et al: Normal prostate and adjacent structures: MR imagine at 1.5 T. Radioloev 164: 381 119871. 2. HrGac H, et &‘MR ima&g of the piostaie gland: normal anatomy, AJR 148: 51 (1987). 3. Lee JKT, and Rholl KS: MRI of the bladder and prostate, AJR 147: 732 (1986). 4. Bryan PJ, et al: Magnetic resonance imaging of the prostate, AJR 146: 543 (1986). 5. Poon PY: Magnetic resonance imaging of the prostate, Sem Ultrasound, CT MhI 7: 298 (1986). - 6. Frituche Pl. and Wilbur MI: The male nelvis: MRI in the abdomen and pe&, Sem Ultraso*und, CT MfiI 10: 11 (1989). 7. McNeal JE: Regional morphology and pathology of the prostate, Am J Clin Pathol 49: 347 (1968). 8. Carrol CL, Sommer FC, McNeal JE, and Stamey TA: The abnormal prostate: MR imaging at 1.5T with histopathologie correlation, Radiology 163: 521 (1987). 9. Phillips ME, et al: Prostatic disorders: MR imaging at 1.5T, Radiology 164: 386 (1987). 10. B&zi M, et al: Proitate carcinoma: staging with MR imagine at 1.5T. Radioloev 169: 339 (19881. “11. Schiébler MLret al: Prostatic ckinoma and benign prostatic hyperplasia: correlation of high resolution MR and histopathologie findings, Radiology 172: 131 (1989).
6
541
BENIGN PROSTATIC HYPERPLASIA: APPEARANCE ON MAGNETIC RESONANCE IMAGING CYNTHIA JANUS, M.D. MARGUERITE LIPPERT,
M.D.
From the Departments of Radiology and Urology, University of Virginia Medical Center, Charlottesville, Virginia ABSTRACT-Benign prostatic hyperplasia (BPH) bas a uariable appearance on magnetic resonance imaging (MRZ). This study reviews and categorizes the MRZ findings of this entity in a sample of 26 men. Cases where atypical or suspicious changes are incidental findings should be reported to the urologist for further inuestigation. Zn addition, familiarity with both the appearance of the nomnal prostate and the changes caused by BPH is necessary when staging patients with known prostate cancer.
The appearance of the normal prostate gland on magnetic resonance imaging (MRI) bas been described includiing delineation of the characteristic zonal anatomy on T2 weighted sequences . lw6 This study was undertaken to categorize the speatrum of findings in benign prostatic hyperplasia (BPH) on MRI. It is important to become familiar with the appearante of this very common entity.
the seminal vesicles was measured on axial Tl images. The prostate gland has been described anatomically as being comprised of three glandular regions, the transition, central, and peripheral zones, and a nonglandular zone, the anterior fibromuscular stroma. Recently standardized ultrasound terminology defines the central portion of the prostate containing nodules of BPH in the transitional zone as the “inner” gland. In this report, the term “central gland” includes the transitional zone, central glandular region, and fibromuscular structure anterior to the urethra since these areas cannot be reliably distinguished from each other on magnetic resonance imaging. On T2 weighted sequences, the centra1 gland is of variable but for the most part low signal intensity compared with the high signal intensity peripheral zone (Fig. 1). Areas of the centra1 gland and of the entire prostate were obtained from the axial view. The signal characteristics of the centra1 gland and the presence of discrete nodules were also noted (Fig. 2). Each study was evaluated for presence of a detectable capsule and pseudocapsule (Fig. 1).
Material and Methods Patients in this study were considered to have benign prostatie hyperplasia on the basis of having symptoms of bladder outlet obstruction and confirmation of an enlarged prostate on recta1 examination. None had any clinical or laboratory evidente of carcinoma. The population consists of 26 men ranging in years age from fort -six to seventy-eight (average age 6 g .8 years). MRI examinations were performed on a 1.0 Tesla scanner (Siemens). Corona1 Tl weighted (TR 600-800, TE 20-25) and axial TI (TR 600-800, TE 2025) and T2 (TR 2500, TE 20, 70-80) weighted sequences were obtained. Other imaging parameters included a slice thickness of 5 mm, and an interslice gap of 1 mm. The length of the gland was measured in the coronal projection; width and AP dimensions were obtained on the axial projection. Width of
UROLOGY
/ DECEMBER1992
/ VOLUME40.NUMBER
Results The prostate gland ranged from 31 to 83 mm (average 49.8 mm) in length, 43 to 61 mm (average 51.1 mm) in width, and 18 to 57 mm
6
539
FIGURE 1. T2 weighted shows high signal intensity heterogeneous lower signal (C). (Single arrow denotes arrows point to capsule.)
axial uiew of prostate peripheral zone (P) and intensity centra1 gland pseudocapsule; double
capsule were visible in 5 men (19 % ). The capsule could not be delineated in 9 patients (35 % ) . The surgical pseudocapsule between the centra1 gland and peripheral zone was displayed as a distinct thin low signal intensity line in 8 patients (31%) and appeared as a low signal intensity zone of variable thickness in 11 (42 % ) . Portions of the pseudocapsule were seen in 5 (19%) and not seen at al1 in 2 (8%). Nodules 1 cm or larger were seen in 2 patients (Fig. 2). In 1 patient the nodules were of high signal intensity while in the other patient, there were nodules of both increased and decreased signal intensity. In 14 patients the central gland region was heterogeneous in signal intensity with nodular foei under 1 cm in size of increased andlor decreased signal intensity. The central gland was of heterogeneous signal intensity without definable nodularity in 10 cases. Incidental findings on MRI (other than pathology related to the lumbosacral spine common in this age group) included bladder diverticulum (l), müllerian duet cyst (1)) colonic diverticula (5), inguinal hernia (l), and hydrocele (2). Comment
FIGURE 2. High s-ignal intensity nodule (n) is seen within markedly enlarged centra1 gland (B = urinary bladder).
(average 34.4 mm) in AP dimension. Width of the central gland ranged from 30 to 64 mm (average 37 mm). AP measurements ranged from 18 to 46 mm (average 30 mm). The central gland comprised 33.5 percent to 99.3 percent (average 55.3%) of the area of the entire prostate. Seminal vesicles ranged from 8.8 to 28 mm (average 15 mm) in thickness. A low signal intensity line on T2 weighted sequences previously described as representing the prostatic capsuIe was identified in its entirety in 12 patients (46 % ) while portions of the
540
The prostate bas been divided into the central, peripheral, and transitional zones. Normally, the peripheral zone (PZ) comprises 75 percent of the volume of the glandular prostate and is the site of approximately 70 percent of cancers. 1,2,8The stroma of the centra1 zone (CZ) consists of compact smooth muscle fibers which display a relatively low signal on T2 weighted sequences. In the peripheral zone, the muscle bundles are loosely interwoven and there are more glandular elements which is believed to explain the higher signal intensity on T2 weighted sequences. g A smal1 transitional zone (T2) normally comprising 5 percent of the gland is found immediately surrounding proximal urethra and within its sphincter. Clinically symptomatic BPH is essentially the result of nodular enlargement of the centrally located transitional zone and to a lesser extent the periurethral tissues.2,7-eThe centra1 and transitional zones are not reliably delineated from each other on MRI. Previous investigators have reported on the inability to reliably demonstrate the prostatic capsule on MRI in normal glands. The low signal peripheral line on T2 sequences believed to represent the capsule was visualized in its entirety in slightly less than half the cases studied
UROLOGY
/ DECEMBER1992
/ VOLUME40,NUMBER6
well-differentiated nodules of prostatic adenocarcinoma. Although it would be inappropriate to consider MRI as a screening modality for prostatic pathology, the findings of BPH are commonly present on MR stans of the pelvis in males over forty years, and it is important to recognize the varied appearances of this entity. The detection of early prostate cancer may be difficult as findings may be subtle as wel1 as nonspecific. Detection or delineation of tumor may be even more challenging when changes of BPH exist. Inability to demonstrate an intact capsule in its entirety, for example, may not be a reliable sign in staging known prostatic cancer. However, the finding of focal signal abnormality in the peripheral zone or a dominant or suspicious area in the centra1 gland should prompt the radiologist to alert the clinician so that appropriate urologie follow-up can take place.
by Phillips et al. l It was either partially seen or not seen at al1 in the remainder. Hricak et d2 found a rim of low signal intensity around the prostate on T2 weighted sequences in 31 percent of patients. Its width, however, was greater than 1 mm which is the thickness of the normal capsule. This group believed that the low signal intensity line may represent a combination of the capsule and periprostatic tissue. Bezzi et al. l” reported that the low signal intensity line representing capsule was not seen in 17 of 37 patients (46 % ) . In 6 patients (16 % ) the line was incompletely seen. The portion most difficult to delineate was most often located posteriorly where the prostate abuts the rectum. In 38 percent (14/37) the capsule was seen and was normal in appearance. Four of the 6 patients in whom the capsule was incompletely delineated had Stage C carcinoma. In evaluating the prostatic capsule it should also be remembered that the chemical shift artifact can account for the apparent presence of a portion of the capsule at a margin of the gland. This imaging artifact results in alternate dark and bright bands at sharp interfaces between predominantly fatty structures and those containing predominantly water. In regard to glandular texture, Bryan et aL4 studied 7 patients with benign nodular hyperplasia. In 2 patients the enlarged prostate had a homogeneous signal intensity on al1 pulse sequences similar to normal prostate. In the other 5 patients signal intensity was inhomogeneous with nodules of relatively low signal intensity on short TR/TE sequences. On long TR/TE sequences, some nadules were of increased and others were of decreased signal intensity. Schiebler et UE.l1 performed high resolution MR stans of twanty-four fresh radical prostatectomy specimens. The MR signal characteristics of BPH seen in ten specimens were variable, Areas of highest signal intensity corresponded to dilated glandular elements while areas containing collagen and fibromuscular stroma displayed low signal intensity. Nodules containing a mixture of glafidular and fibromuscular elements had signal intensities similar to those of
UROLOGY
i
DECEMBER
1992
i
VOLUME
40, NUMBER
Vineland,
ACKNOWLEDGMENT. ante
in the preparation
To Andrew
P.O. Box 2420 New Jersey 08360 (DR. JANUS) Martin
for
his assist-
of this manuscript.
1. Phillips ME, et al: Normal prostate and adjacent structures: MR imagine at 1.5 T. Radioloev 164: 381 119871. 2. HrGac H, et &‘MR ima&g of the piostaie gland: normal anatomy, AJR 148: 51 (1987). 3. Lee JKT, and Rholl KS: MRI of the bladder and prostate, AJR 147: 732 (1986). 4. Bryan PJ, et al: Magnetic resonance imaging of the prostate, AJR 146: 543 (1986). 5. Poon PY: Magnetic resonance imaging of the prostate, Sem Ultrasound, CT MhI 7: 298 (1986). - 6. Frituche Pl. and Wilbur MI: The male nelvis: MRI in the abdomen and pe&, Sem Ultraso*und, CT MfiI 10: 11 (1989). 7. McNeal JE: Regional morphology and pathology of the prostate, Am J Clin Pathol 49: 347 (1968). 8. Carrol CL, Sommer FC, McNeal JE, and Stamey TA: The abnormal prostate: MR imaging at 1.5T with histopathologie correlation, Radiology 163: 521 (1987). 9. Phillips ME, et al: Prostatic disorders: MR imaging at 1.5T, Radiology 164: 386 (1987). 10. B&zi M, et al: Proitate carcinoma: staging with MR imagine at 1.5T. Radioloev 169: 339 (19881. “11. Schiébler MLret al: Prostatic ckinoma and benign prostatic hyperplasia: correlation of high resolution MR and histopathologie findings, Radiology 172: 131 (1989).
6
541