AJR 2003; 181:1669-1672
© American Roentgen Ray Society
Midline Prostatic Cysts in Healthy Men: Incidence and Transabdominal Sonographic Findings
Masahito Ishikawa1,
Hiroshi Okabe1,
Takaki Oya2,
Mari Hirano2,
Masanori Tanaka2,
Machiko Ono2,
Kenichi Kawamura2,
Nozomu Fujimoto2 and
Keisuke Sakurada2
1 Department of Clinical Laboratory, Sapporo Teishin Hospital, 14-1-5 Kawazoe,
Minami-ku, Sapporo 005-8798, Japan.
2 Department of Health Care, Sapporo Teishin Hospital, Sapporo 005-8798,
Japan.
Received January 27, 2003;
accepted after revision June 10, 2003.
Address correspondence to M. Ishikawa.
Abstract
OJBECTIVE. The purpose of this study was to use transabdominal
sonography to investigate the incidence of midline prostatic cysts in healthy
men.
CONCLUSION. Midline prostatic cysts represent a common variant in
asymptomatic men. In a patient with urologic symptoms, detection of a midline
prostatic cyst requires a focused examination to determine whether the cyst
represents a normal variant or is the cause of symptoms.
Introduction
Cystic lesions in the male pelvis have been considered a relatively rare
disorder. They are classified according to their location as midline or
off-midline, their position relative to the prostate gland, and their
embryologic origin [1]. Moore
[2] reported an approximately
1% incidence of congenital prostatic cysts at autopsy. It has been reported
that medial prostatic cysts may be observed in 5% of outpatients with urologic
symptoms [3]. The incidence in
apparently healthy men is, however, unknown.
During routine health checkups, we examined men with transabdominal
sonography to determine the incidence of midline prostatic cysts in apparently
healthy men and to investigate the size and characteristics of these cysts. We
also observed changes in cyst size during follow-up examinations.
Subjects and Methods
We designed a prospective study of the incidence of cysts in which the
sonographer specifically examined each patient for the presence of midline
prostatic cysts. The study included a total of 1,826 transabdominal
sonographic examinations performed on 1,115 men who visited the health care
department of our hospital for routine health checkups during a 3-year period
(from April 1999 to March 2002). A transabdominal sonographic examination is a
routine component of most health checkups in Japan for patients older than 35
years. Since May 1995, in addition to upper abdominal mass screening, our
hospital has included lower abdominal scans in routine health checkups. All
subjects provided written informed consent for participation in this study.
Because this was a study of healthy patients during a routine health visit, we
chose the noninvasive transabdominal sonography instead of transrectal
sonography. Patient age on the first visit for the health checkup ranged from
35 to 65 years (mean, 51 years). The follow-up examination period ranged from
7 to 26 months (mean, 16 months).
In this study, midline prostatic cysts were defined as hypoechoic to
anechoic cystic lesions located in the midline of the prostate detected during
transabdominal sonographic examination. Midline prostatic cysts were diagnosed
on the basis of transverse scans showing cystic lesions in the midline of the
prostate gland and longitudinal scans revealing cystic lesions within the
prostate gland or between the prostate gland and the seminal vesicles (Fig.
1A,
1B). During the examination,
the sonographer decided whether a cyst was present. A patient was recorded as
having a midline prostatic cyst when the cyst was visible in both transverse
and longitudinal scans. In those cases, the two scans were then printed out as
records, and the attending physician made the final diagnosis. In all cases,
the physician's diagnosis of the presence of a midline prostatic cyst
confirmed the initial observation by the sonographer. In some cases, a
cystlike object was detected but was only visible on either the transverse or
the longitudinal scan. The image was added to the subject's record, but these
patients were not recorded as having a midline prostatic cyst.
Detection of midline prostatic cysts is limited by the resolution of
sonographic systems. In our experience, cysts smaller than 3 mm in diameter
are difficult to detect, and the internal echo characteristics of such small
cysts are difficult to define. Therefore, we have included only cysts with a
diameter equal to or greater than 3 mm in this study (Fig.
2A,
2B). The image quality of each
detected cyst was assessed on the basis of an objective scale ranging from
excellent to suboptimal. We then investigated the midline prostatic cysts for
age distribution, incidence, cyst size and shape, posterior echo enhancement,
and prostate weight. In addition, changes in cyst size and shape were also
observed in 30 cases in which the original patients returned for follow-up
examinations.
All transabdominal sonographic examinations were performed with the
full-bladder technique. When the bladder was not full, the subject was asked
to drink as much water as possible and wait for reexamination. Sonographic
images were obtained with three scanners: U-sonic RT 4600 (General Electric
Medical Systems, Milwaukee, WI), LOGIQ 7 (General Electric Medical Systems),
and HDI 5000 (ATL, Bothell, WA). The scanners were equipped with convex probes
of 3.5, 3.5, and 5-2–MHz, respectively.
Results
Transabdominal sonography revealed midline prostatic cysts in 85 (7.6%) of
1,115 men. Table 1 shows the
age distribution and incidence of midline prostatic cysts. The age of the
subjects with midline prostatic cysts ranged from 35 to 65 years (mean
± SD, 51 ± 7 years). Prostate weight determination was based on
transabdominal sonographic measurements and calculated by using the formula
for a prolate ellipse:
where d1 is the transversal; d2, the
anteroposterior; and d3, the sagittal diameter
[4]. The prostate weights of
subjects with midline prostatic cysts ranged from 11 to 46 g (mean weight, 21
± 6 g). In Japan, prostate gland size of approximately less than 20 g
is considered within the limit for a healthy prostate
[5]; thus, our first weight
group ranged from 11 to 20 g. The incidence in prostate gland weight less than
or equal to 20 g was 5.4% (47/871) and in prostate size from 21 to 58 g was
15.6% (38/244) (chi-square test, p < 0.01).
The midline prostatic cysts detected on transabdominal sonography were all
monolocular and had smooth borders. Morphologically, the cysts were round on
transverse scans and oval or beaklike on longitudinal scans. The cyst size
ranged from a minimum of 3 x 3 x 4 mm to the maximum of 12 x
13 x 17 mm, with a mean diameter of 7 mm transversely, 7 mm anteriorly,
and 9 mm sagittally. Forty-two cysts were clearly shown with excellent image
quality, 41 were fair, and two were suboptimal. Internally, the 85 detected
cysts ranged from hypoechoic to anechoic, of which 56 showed posterior echo
enhancement.
The cysts were either completely intraprostatic in 81 cases (95.3%) or
partially exophytic between the prostate and the seminal vesicles in four
cases (4.7%). We did not observe any exophytic cysts above the prostate.
Although we did not include it in this study, we did find one case of a cyst
in the off-midline position. In addition, there were no off-midline cysts
among those subjects with a midline prostatic cyst.
In 28 (93.3%) of 30 cases, no change in cyst size was observed between the
original presentation and the follow-up examinations. However, two cases
(6.7%) did show a small increase in size. Figure
3A,
3B,
3C,
3D shows cyst increase during a
1-year period; Figure 4A,
4B,
4C,
4D shows cyst increase over an
8-month period.
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Fig. 3A. —Growth of midline prostatic cyst during 12 months in
46-year-old man with urologic symptoms. Hematospermia had been noticed
immediately after initial examination in our study. Transverse sonogram shows
midline prostatic cyst (arrow) in 2001, before complaints of
hematospermia. Cyst size (8 x 8 x 11 mm) had not changed since
original discovery in 1996.
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Fig. 3B. —Growth of midline prostatic cyst during 12 months in
46-year-old man with urologic symptoms. Hematospermia had been noticed
immediately after initial examination in our study. Longitudinal sonogram of
A shows posterior echo enhancement.
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Fig. 3C. —Growth of midline prostatic cyst during 12 months in
46-year-old man with urologic symptoms. Hematospermia had been noticed
immediately after initial examination in our study. Transverse sonogram of
midline prostatic cyst (arrow) obtained in 2002, at follow-up
examination after development of hematospermia, shows cyst growth (10 x
8 x 14 mm) compared with that in 2001.
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Fig. 3D. —Growth of midline prostatic cyst during 12 months in
46-year-old man with urologic symptoms. Hematospermia had been noticed
immediately after initial examination in our study. Longitudinal sonogram of
C shows posterior echo enhancement.
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Fig. 4A. —Growth of midline prostatic cyst during 8 months in
58-year-old asymptomatic man. B, Transverse (A) and longitudinal
(B) sonograms obtained in 2000 show beaklike midline cyst
(arrow, A and B) in prostate (10 x 10
mm).
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Fig. 4B. —Growth of midline prostatic cyst during 8 months in
58-year-old asymptomatic man. Transverse (A) and longitudinal
(B) sonograms obtained in 2000 show beaklike midline cyst
(arrow, A and B) in prostate (10 x 10
mm).
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Discussion
Midline prostatic cysts are more common than previously described and are
found in 7.6% of asymptomatic men. The first major study of the incidence of
congenital prostatic cysts was performed by Moore in 1937
[2]; Moore found cysts at
autopsy in seven of 678 cases. The incidence of approximately 1% continues to
be the standard quoted figure. In 1985 in Japan, Kitahara et al.
[6] performed endorectal
sonography on 660 patients who complained of dysuria, and they found cystic
lesions on the midline in the posterior upper region of the prostate in seven
patients (1.1%). In 1990, Higashi et al.
[7] performed transabdominal
sonography on 624 patients referred to the department of radiology and found
midline cystic lesions in seven patients (1.0%), which is consistent with the
reported values of 1% by Slocum in 1954
[8]. However, in 1996 Dik et
al. [3] examined 704 patients
with symptoms of bladder outlet obstruction or lower urinary tract symptoms
using transrectal sonography and reported 34 (5%) with a medial prostatic
cyst. This incidence of 5% was found in a study of symptomatic patients;
however, to our knowledge, the incidence in healthy men has not been
previously reported.
In our study using transabdominal sonography on 1,115 asymptomatic men, we
found 85 cases (7.6%) of midline prostatic cysts. Compared with the size of
midline prostatic cysts (15–30 mm in diameter) in the study by Kitahara
et al. [6] of a symptomatic
population, the cysts observed in this study were smaller (from 3 x 3
x 4 mm to 12 x 13 x 17 mm; mean, 7 x 7 x 9 mm).
The difference may be associated with whether clinical symptoms exist.
Regarding the relationship between location and size, the cysts found between
the prostate gland and seminal vesicle (mean, 10 x 10 x 13 mm)
were larger than the intraprostatic cysts (mean, 7 x 6 x 9 mm). In
addition, two patients in this study showed a small increase in cyst size over
a period of time (Figs. 3A,
3B,
3C,
3D and
4A,
4B,
4C,
4D). From the observed growth
in one patient (Fig. 4A,
4B,
4C,
4D), we speculate that midline
prostatic cysts might grow toward the seminal vesicle.
We found that the incidence of midline prostatic cysts showed a bimodal
distribution across age groups. The incidence in the youngest age group of
35–40 years was 10.1%, and the incidence in the oldest age group of
61–65 years was 11.6% (Table
1). In the case of prostate size and rate of detection, we found a
statistically significant increasing trend in the incidence of cysts with
increasing prostatic weights. We consider as a factor contributing to our
finding of an overall higher incidence of detection (7.6%) the possibility
that more cysts are found in recent studies because of the improved quality of
sonographic systems and the use of higher frequency wideband probes.
Some cystic lesions in the male pelvis may be discovered by chance with
sonography that is now more widely used; in other cases, however, they may
remain overlooked. Although transabdominal sonography is a common screening
technique, it is difficult to obtain clear images of the pelvic area or detect
cystic lesions when the bladder is not full. To improve the detection ratio of
midline prostatic cysts, radiologists need to be fully aware of the presence
of asymptomatic cysts and use transabdominal sonography with the full-bladder
technique.
A limitation of this study is the lack of pathologic correlation with the
sonographic findings. The actual cause of our cystic lesions could only be
defined with more invasive procedures such as urethrography, seminal
vesiculography, or cyst puncture. However, given the asymptomatic nature of
the patients, such correlation could not be obtained.
In conclusion, midline prostatic cysts represent a more common variant than
has been previously reported. The midline prostatic cyst has rarely been
found, perhaps because of its smaller size and absence of noticeable symptoms
in patients. In our series, cysts were present in 7.6% of asymptomatic men.
Thus, in patients with urologic symptoms, detection of midline cysts will
require a focused examination to determine whether the cysts represent a
normal variant or are the cause of the symptoms. Future studies are needed to
determine which sonographic characteristics may be useful to distinguish the
normal variant cyst from the cyst that is responsible for urologic
symptoms.
Acknowledgments
We thank Shogo Shimamura for valuable advice throughout this
investigation.
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Abstract
Introduction
