Prostate volume measurement by TRUS using heights obtained by transaxial and midsagittal scanning: comparison with specimen volume following radical prostatectomy.

Abstract

The purpose of this study was to determine, when measuring prostate volume by TRUS, whether height is more accurately determined by transaxial or midsagittal scanning.
Sixteen patients who between March 1995 and March 1998 underwent both preoperative TRUS and radical prostatectomy for prostate cancer were included in this study. Using prolate ellipse volume calculation (height x length x width x pi/6), TRUS prostate volume was determined, and was compared with the measured volume of the specimen.
Prostate volume measured by TRUS, regardless of whether height was determined transaxially or midsagittally, correlated closely with real specimen volume. When height was measured in one of these planes, a paired t test revealed no significant difference between TRUS prostate volume and real specimen volume (p =.411 and p =.740, respectively), nor were there significant differences between the findings of transaxial and midsagittal scanning (p =.570). A paired sample test, however, indicated that TRUS prostate volumes determined transaxially showed a higher correlation coefficient (0.833) and a lower standard deviation (9.04) than those determined midsagittally (0.714 and 11.48, respectively).
Prostate volume measured by TRUS closely correlates with real prostate volume. Furthermore, we suggest that when measuring prostate volume in this way, height is more accurately determined by transaxial than by midsagittal scanning.

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110
Korean J Radiol 1(2), June 2000
Prostate Volume Measurement by TRUS Using
Heights Obtained by Transaxial and Midsagittal
Scanning: Comparison with Specimen Volume
Following Radical Prostatectomy
Objective: The purpose of this study was to determine, when measuring
prostate volume by TRUS, whether height is more accurately determined by
transaxial or midsagittal scanning.
Materials and Methods: Sixteen patients who between March 1995 and
March 1998 underwent both preoperative TRUS and radical prostatectomy for
prostate cancer were included in this study. Using prolate ellipse volume calcula-
tion (height
lengthwidth/6), TRUS prostate volume was determined,
and was compared with the measured volume of the specimen .
Results: Prostate volume measured by TRUS, regardless of whether height
was determined transaxially or midsagittally, correlated closely with real speci-
men volume. When height was measured in one of these planes, a paired t test
revealed no significant difference between TRUS prostate volume and real speci-
men volume (p = .411 and p = .740, respectively), nor were there significant dif-
ferences between the findings of transaxial and midsagittal scanning (p = .570). A
paired sample test, however, indicated that TRUS prostate volumes determined
transaxially showed a higher correlation coefficient (0.833) and a lower standard
deviation (9.04) than those determined midsagittally (0.714 and 11.48, respec-
tively).
Conclusion: Prostate volume measured by TRUS closely correlates with real
prostate volume. Furthermore, we suggest that when measuring prostate volume
in this way, height is more accurately determined by transaxial than by midsagittal
scanning.
ince prostate volume may influence the operative approach in patients
with prostatism, its estimation is of concern to urologists. Prostate volume
has been measured by various methods including digital rectal examina-
tion, cystourethrography, urethrocystoscopy, and urethral pressure profile, but all of
these are inaccurate (1 3). For this reason, ultrasound scanning has gained wide popu-
larity in the past few years (4 10). Three different ultrasound approaches are available:
the transrectal, the transurethral, and the transabdominal, though prostate volume
measurement using the transrectal approach appears to be most accurate (4, 10).
Three commonly used prostate volume measurement techniques in transrectal ultra-
sonography (TRUS) are planimetry calculation, prolate ellipse volume calculation, and
an ellipsoid volume measurement technique. Prolate ellipse volume calculation is fast
and precise, and its universal availability makes it practical for routine clinical applica-
tion. It is calculated as follows: prolate ellipse volume (centimeters) = (height
width)/6. Transverse diameter (width) is defined as the maximal transverse di-
ameter at mid-gland level, while longitudinal diameter (length) is defined as the dis-
length
Sung Bin Park, MD
Jae Kyun Kim, MD
Sung Hoon Choi, MD
Han Na Noh, MD
Eun Kyung Ji, MD
Kyoung Sik Cho, MD
Index words:
Prostate, US
Prostate, hypertrophy
Ultrasound (US), technology
Korean J Radiol 2000;1:110-113
Received October 19, 1999; accepted
after revision June 1, 2000.
All authors: Department of Radiology,
University of Ulsan College of Medicine
Address reprint requests to:
Kyoung Sik Cho, MD, Department of
Radiology, University of Ulsan College of
Medicine, 388-1, Poongnap-Dong, Songpa-
Gu, Seoul 138-736, Korea.
Telephone: (822) 2224-4400
Fax: (822) 472-4719
S

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tance from the proximal external sphincter to the urinary
bladder (11).
Anteroposterior diameter (height) may be measured in
two planes-axial and sagittal. Most authors have employed
midsagittal scanning, but some have measured the diame-
ter perpendicular to the transverse diameter seen on
transaxial scans (12). By comparing the findings with real
specimen volume, we aimed to determine whether height
is more accurately determined by transaxial or midsagittal
scanning.
MATERIALS AND METHODS
Sixteen patients aged between 51 and 73 (mean, 62) years
who underwent preoperative TRUS and radical prostatec-
tomy for prostate cancer were included in this study. Using
a HDI 3000 scanner (Advanced Technology Laboratories,
Bothell, Wash) with using a 10MHz transverse sector
probes, and calculating prolate ellipse volume by means of
the (height
lengthwidth
ume was measured and then compared with real specimen
volume (Fig. 1).
The volume of gross pathologic specimens (prostate on-
ly) was calculated using the formula for prolate ellipse vol-
ume calculation, measuring three unequal axes of the
prostatectomy specimen within 1hr of excision. Triaxial
measurements of the prostate were thus obtained. The
transverse diameter was recorded at the point of maximal
transverse diameter perpendicular to the anteroposterior
plane of the prostate. The anterior-posterior diameter was
recorded in the transverse plane at a point perpendicular
/6) formula, prostate vol-
to the greatest transverse diameter, while the longitudinal
diameter was recorded as the distance between the junc-
tion of the bladder neck and the prostate, and the prostatic
apex at the genitourinary diaphragm. Prior to measure-
ment, all specimens were immersed in normal saline to
minimize tissue dessication.
Statistical analysis using a paired t test was used to deter-
mine the difference between the volume measured by
TRUS and real specimen volume. A paired sample test was
used for correlation of these two volume measurements.
RESULTS
Real specimen volume was 16.5 80.6 (average, 31.7
16.1) cc. Prostate volume measured by TRUS using height
determined from transaxial scans was 22.0 78.3 (average
29.8 14.8) cc, and using height determined midsagitally
was 21.4 72.4 (average 32.7
measured either transaxially or midsagittally correlated
closely with real specimen volume. When height was mea-
sured in one of these planes, a paired t test revealed no sig-
nificant difference between prostate volume according to
TRUS and real specimen volume (p = .411 and p = .740,
respectively), nor were there significant differences be-
tween the findings of transaxial and midsagittal scanning (p
= .570). A paired sample test, however, showed that TRUS
prostate volumes determined transaxially showed a higher
correlation coefficient (0.833) and lower standard devia-
tion (9.04) than those determined midsagittally (0.714 and
11.48, respectively) (Table 1) (Fig. 2).
13.6) cc. Prostate volume
Prostate Volume Measurement by TRUS Using Heights Obtained by Transaxial and Midsagittal Scaning
Korean J Radiol 1(2), June 2000
111
Fig. 1. Measurement of prostate volume by TRUS
A. Height (arrow) was measured by transaxial scanning (3.15 cm), and prostate volume was calculated as 36.1 cc.
B. Height (arrow) was measured by midsagittal scanning (3.35 cm), and prostate volume was calculated as 35.0 cc. Specimen volume
was 45.81 cc.
AB

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DISCUSSION
Prostate volume was measured by means of the prolate el-
lipse volume calculation (height
formula used for ellipsoids with three unequal axes. In the
early stages of prostate volume measurement by TRUS,
maximal height and width measurements were obtained by
axial scanning at the mid-gland level which appeared
largest. Length was defined as the distance from the proxi-
mal external sphincter to the bladder base, as seen on mid-
sagittal scans (11).
To avoid the salami effect, however, height measure-
ment was corrected by sagittal projection in a plane per-
pendicular to length measurement: salami can be sliced in
many different ways; to obtain larger slices, some prefer to
cut it obliquely (13). It has been found that height mea-
sured transaxially was accurate, and high correlation with
real volume was found (11), but as far as we know, no pre-
vious study has investigated whether prostate volume
lengthwidth/6), a
measured by TRUS is more accurately calculated using the
height measurement obtained by transaxial scanning or by
midsaggital. Thus, we determined whether, when measur-
ing prostate volume by TRUS, height is more accurately
determined by transaxial or midsagittal scanning, compar-
ing the volume finding thus obtained with real specimen
volume.
Using the height measurement obtained in our study by
transaxial or by midsaggital scanning, a paired t test
demonstrated excellent correlation between TRUS
prostate volume and real specimen volume (p = .411 and p
= .740, respectively).
Nor were there significant differences between the find-
ings of transaxial and midsagittal scanning (p = .570). A
paired sample test, however, showed that TRUS prostate
volume determined transaxially showed a higher correla-
tion coefficient (0.833) and lower standard deviation (9.04)
than that determined midsagittally (0.714 and 11.48, re-
spectively). We therefore suggest that when determining
prostate volume by TRUS, volumes calculated using the
height measurement obtained transaxially are more accu-
rate.
Terris et al. (14) have claimed that since the point of
juncture between the prostate apex and distal urethra is
frequently poorly visualized, prolate ellipse volume calcu-
lation may be technically difficult. Likewise, definition be-
tween the base of the prostate and the seminal vesicle and
bladder neck is often unclear. Accurate height, they be-
lieve, is more difficult to determine by midsagittal scanning
than by transaxial. Using experimental models, Kim et al.
(15) investigated the accuracy of prostate volume calculat-
ed by TRUS using height measurements determined
transaxially and midsagitally. They concluded that the
transaxial mode was more accurate.
Our results are supported by the two studies above.
Because we compared the prostate volume obtained by
TRUS with real specimen volume, we believe that our
study was more physiologic than that of kim et al. (15). In
addition, prostate weight or volume of water displaced
may provide a more precise measure of prostate size; ma-
nipulation of the pathologic specimen (removal of seminal
vesicles; dissection of periprostatic fat, connective tissue,
and residual bladder neck tissue) prior to sectioning may,
however influence the accuracy of the findings. Because
we calculated specimen volume using the formula for pro-
late ellipsoids with three unequal axes (as described for
TRUS prostate volume), our result may be more accurate.
During prostate volume measurement by TRUS and pro-
cessing of the prostate specimen, our study suffered from
several limitations. First, since ultrasound is a dynamic
modality, operator-dependent factors may contribute to
Park et al.
112
Korean J Radiol 1(2), June 2000
Table 1. Correlation between Prostate Volume Measured
by TRUS and Real Prostate Volume Measured
after Radical Prostatectomy
MeanR*
SD*
P value
Vol. (axial)
Vol. (sagittal)
Vol. (specimen)
09.80
32.68
31.71
14.81
13.56
16.13
0.833
0.714
09.04
11.48
.41 (NS)
.74 (NS)
Note.─ *Paired sample test, Paired t test, Vol. (axial): prostate volume
calculated by TRUS, with height in axial plane, Vol. (sagittal): prostate
volume calculated by TRUS, with height in sagittal plane, Vol.
(specimen): specimen volume, R: correla-tion coefficient, SD: standard
deviation, NS: no significant difference in statistical analysis (p > .05)
Fig. 2. Correlation between prostate volume measured by TRUS
and real prostate volume measured after radical prostatectomy.
When height was determined transaxially rather than midsagital-
ly, prostate volumes measured by TRUS showed higher correla-
tion coefficient (0.833 vs 0.714).
Axial Volume
Sagittal Volume
Axial-specimen
Sagittal-specimen

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Prostate Volume Measurement by TRUS Using Heights Obtained by Transaxial and Midsagittal Scaning
Korean J Radiol 1(2), June 2000
113
the differences observed between TRUS-derived prostate
volume estimates and the volume of the corresponding
specimen. Second, after surgical removal of the prostate,
varying amounts of residual tissue are left behind, depend-
ing on the surgeon and the surgical method; a comparison
of the volume of surgically removed tissue with ultrasoni-
cally estimated volume may, therefore, be inaccurate.
Third, prostate tissue looses between 15 and 42% of its
weight after tissue cauterization and due to the effect of ir-
rigating solutions (16, 17).
Henneberry et al. (8), however, who estimated prostate
volume pre-and post-operatively in 29 patients (18 of
whom had undergone transurethral resection, and 11 open
prostectomy), found good correlation in the 11 open
prostatectomy cases, but that almost all of the 18 resected
specimens weighed less than estimated preoperatively (8).
In our study, prostatectomy was performed by open
surgery, and we therefore expected less prostate tissue
shrinkage.
The value of our study is that we measured prostate vol-
ume by TRUS using the height determined by transaxial
and midsagittal scanning, and then comparing our finding
with a real prostatic specimen. Thus, we investigated which
method was most accurate and therefore most useful for
clinical evaluation and determination.
In conclusion, prostate volume measured by TRUS close-
ly correlates with real prostate volume. Furthermore, we
suggest that when measuring prostate volume in this way,
height is more accurately determined by transaxial than by
midsagittal scanning.
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