Indian Journal of Urology
ORIGINAL ARTICLE
Year
: 2006  |  Volume : 22  |  Issue : 4  |  Page : 322--325

Does estimation of prostate volume by abdominal ultrasonography vary with bladder volume: A prospective study with transrectal ultrasonography as a reference


Shivadeo S Bapat, Satyajeet S Purnapatre, Ketan V Pai, Pushkaraj Yadav, Abhijit Padhye, YG Bodhe 
 Department of Urology, Maharashtra Medical Foundation’s, Ratna Memorial Hospital, 986 Senapati Bapat Road, Pune - 411 004, India

Correspondence Address:
Shivadeo S Bapat
Janhavi 797/4, Bhandarkar Institute Road, Pune - 411 004
India

Abstract

Objectives: Ultrasonography (USG) is the commonest modality for ascertaining prostate volume. Urologists commonly encounter a discrepancy between prostate volume on USG and actual volume of prostate, whereas transrectal ultrasonography (TRUS) gives near correct prostate volume. We undertook a prospective study to compare the relationship between changing bladder volumes to the volume of prostate. Materials and Methods: After approval of the Institutional Ethics Committee and informed consent, 25 patients (age group: 52-78 years) with lower urinary tract symptoms were assessed for prostate volume by USG at different bladder volumes and final comparison was done with TRUS in one setting. Each USG and TRUS was done by one urology resident under the guidance of one qualified radiologist with experience of over 15 years in this field. Equipment used was SIEMENS SONNOLINE ADARA with 3.5 MHz probe for USG and 7.5 MHz Endo p-2 (biplaner) probe for TRUS. First, patients were asked to empty their bladder and post void residual urine was measured along with prostate volume. Patients were given oral fluids and USG was repeated serially at three intervals with bladder volume of 100-200 ml, 200-300 ml and > 300 ml. Finally uroflowmetry was carried out followed by TRUS. Results were recorded in a tabulated form on «SQ»Excel spread sheet«SQ». Results: 1. Measurement of prostate volume increases with increase in bladder volume. 2. Calculated prostate volume at minimal bladder capacity (100-200 ml) was found to be the closest to the volume calculated by TRUS. Conclusion: Minimal bladder volume (100-200 ml) is essential for near correct estimation of prostate volume by USG. With increasing bladder volume, the volume of prostate increases disproportionate to its actual volume.



How to cite this article:
Bapat SS, Purnapatre SS, Pai KV, Yadav P, Padhye A, Bodhe Y G. Does estimation of prostate volume by abdominal ultrasonography vary with bladder volume: A prospective study with transrectal ultrasonography as a reference.Indian J Urol 2006;22:322-325


How to cite this URL:
Bapat SS, Purnapatre SS, Pai KV, Yadav P, Padhye A, Bodhe Y G. Does estimation of prostate volume by abdominal ultrasonography vary with bladder volume: A prospective study with transrectal ultrasonography as a reference. Indian J Urol [serial online] 2006 [cited 2020 Dec 4 ];22:322-325
Available from: https://www.indianjurol.com/text.asp?2006/22/4/322/29114


Full Text

Abdominal ultrasonography (USG) is the commonest modality for ascertaining prostate volume. It is commonly observed that there is a discrepancy in the volume of prostate measured by USG and actual volume of prostate. We also encountered discrepancy in the USG report of prostate volume calculated by the same sonologist on the same patient with one machine but performed at two different times.[1] We undertook this study to ascertain whether increasing bladder volume affects measurements of prostate volume since bladder acts as a window through which prostate is visualized. Transrectal ultrasonography (TRUS) gives near correct prostate volume[2],[3] with which we compared our results. A study of a large number of patients is required to come to a definite conclusion. This is an ongoing study and we herewith present our initial data of 25 patients.

 Materials and Methods



After approval of the Institutional Ethics Committee and informed consent, 25 male patients in the age group of 52 to 78 years with lower urinary tract symptoms were assessed for prostate volume at different bladder volumes by USG. These results were compared with TRUS. All the tests were carried out in a single setting. Every USG and TRUS was performed by one urology resident under the guidance on one qualified radiologist with experience of over 15 years in this field. Equipment used was SIEMENS SONNOLINE ADARA with 3.5 MHz probe for USG and 7.5 MHz Endo p-2 (biplaner) probe for TRUS. Patients were first asked to empty the bladder and post void residual urine was measured along with prostate volume. Planimetric technique was used for calculating prostate volume as well as bladder volume. The following formula was used to calculate prostate as well as bladder volume: A-P Length x Cranio Caudal Length x Transverse Length x 0.52 (P/6) in cubic cm. Patients were given oral fluids and USG was repeated serially at three intervals with bladder volume of 100-200 ml, 200-300 ml and > 300 ml. Each time the prostate volume was measured. Finally uroflowmetry was carried out followed by TRUS to measure near correct prostate volume with planimetric technique. Results were recorded in tabulated forms on 'Excel spread sheet'. For each patient a division factor was calculated for all three bladder volumes by dividing USG-calculated prostate volume by TRUS-calculated prostate volume. Finally a mean division factor was calculated for each bladder volume.

 Results



Measurement of prostate volume increases with increase in bladder volume. This type of linear accelerating relationship was found in all patients. In three patients residual urinary volume could not be calculated as they had perurethral catheter passed earlier for retention of urine. Their bladders were filled artificially with normal saline. Prostate volume was underestimated on USG than TRUS in nine cases (36%) at 100-200 ml bladder volume, three cases (12%) at 200-300 ml bladder volume and none (0%) at bladder volume > 300 ml. To know the exact relationship between the volumes calculated by two different modalities (TRUS and USG), a division factor was calculated. By dividing USG prostate volume by TRUS prostate volume, a division factor was calculated for each bladder volume. Finally a mean division factor was calculated for three different bladder volumes [Table 1][Table 2]. Calculated prostate volume by USG at minimal bladder capacity (100-200 ml) was found to be closest to the volume calculated by TRUS since it had lowest division factor.

 Discussion



Digital rectal examination although a standard modality to assess prostate volume is unreliable and subjective especially if performed by different examiners.[4],[5] In an effort to accurately determine prostate volume, radiographic techniques have been utilized. However it has proved extremely difficult to obtain satisfactory images of the prostate gland, owing to its location deep in the pelvis behind the pubis and the inability of the prostate to retain contrast agent.[6],[7] ultrasonography has provided relatively accurate measurements of prostate size.[8],[9] However, visualization of the prostate may be obscured by the pubic bone or by small capacity bladder. It is a well established fact that TRUS provides precise images of the prostate, seminal vesicles and adjacent structures.[10] In TRUS as the distance from the transducer to the prostate is minimal, the internal prostatic echo graphic pattern is superior to that obtained by means of USG.

Currently two techniques are employed to determine prostatic volume by TRUS: ellipsoid and plenimetric.[11],[12] The application of TRUS and the principle of planimetry for volume determination were originally described by Watanabe and coworkers,[13],[14] and are now considered as the gold standard.[15],[16] The specific gravity of the prostate has been calculated to be 1.05 gm /cubic cm; hence, the weight of the prostate is essentially equal to its estimated volume.[6] For USG the ellipsoid formula is used to calculate prostate volume.

Linear accelerating relationship between prostate volume and bladder volume observed in our study was considered for bladder volume up to 400 ml. In the present pilot project we did not investigate any patient with large bladder capacity (>400 ml). Prostate volume was underestimated on USG than TRUS in nine cases (36%) at 100-200 ml bladder volume, three cases (12%) at 200-300 ml bladder volume and none (0%) at bladder volume > 300 ml. Blanc et al[17] have reported similar findings in their study. Yuen et al[18] have noted that with increasing bladder volume the median lobe protrusion decreases. However, the study was restricted only to the visualization of the median lobe. In our study the entire prostate gland was considered and not just median lobe protrusion. No special effort was made to study the transitional zone as it is only visualized on TRUS and not on USG.

After analyzing our results we have suggested a division factor for USG prostate volume at different bladder volumes that can be used in our day-to-day practice. Resultant values are very close to the near correct TRUS prostate volume.

The formula is

Near correct prostate volume = prostate volume on USG for particular bladder volume ÷ division factor for that particular bladder volume. Working example for this is given in [Table 3][Table 4].

In many centers the facility for TRUS is not available. Hence the above-mentioned formula could prove very useful.

The possible explanation for the discrepancy in the estimation of the prostate volume with changing bladder volumes is as follows. Put a coin on the table and over the coin place a transparent glass beaker filled with water. The coin will appear larger when it is viewed through the medium of water. The mass of water will act as a magnifying lens. A similar mechanism may be operating during the visualization of the prostate through water medium within the bladder. Thus, larger the bladder volume, larger will be the volume of prostate as perceived by the USG probe.

Despite the above possible explanation, there is no scientific reasoning to support our hypothesis. But our observations have been supported by similar observations by Blanc et al[17] and Yuen et al .[18]

 Conclusion



Prostate volume measurement on USG does vary with changes in bladder volume. Bladder capacity of 100-200 ml is sufficient to know near correct prostate volume on USG. One can get near correct prostate volume on USG by using a formula as suggested in this study.

 Acknowledgement



Authors wish to express their gratitude to the Trustees of the Maharashtra Medical Foundation's, Ratna Memorial Hospital, 986 Senapati Bapat Road, Pune - 411004, India for the purchase of the expensive TRUS equipment and greatly subsidizing the charges for the patients.

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