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1
Department of Radiology, University of Washington Medical Center, Box 357115,
1959 N.E. Pacific St., Seattle, WA 98195.
2
Present address: Department of Radiology, University of Wisconsin Hospital,
E3/311 CSC, Box 3252, Highland Ave., Madison, WI 53792.
3
Department of Urology, University of Washington Medical Center, Box 356510,
Seattle, WA 98195.
4
Present address: Group Health Cooperative, 2700 152nd Ave., N.E., Redmond, WA
98052.
5
Present address: Department of Radiology, The University of Michigan, 1500 E.
Medical Center Dr., B1D530A, Ann Arbor, MI 48109-0030.
Received November 29, 1999;
accepted after revision March 20, 2000.
Address correspondence to T. C. Winter.
Abstract
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SUBJECTS AND METHODS. Using power Doppler technology, we performed four transrectal sonographic examinations before and immediately, 6 hr, and 24 hr after ejaculation in 10 healthy volunteers. Images were assessed by three independent observers.
RESULTS. Ninety-seven percent of the images ranked as having the least flow were from the baseline examination. There was a significant difference between the rankings when categorized into the four time sets (mean score for the baseline group was 1.1, whereas for the immediate, 6-, and 24-hr postejaculation groups it was 2.5, 2.9, and 2.4, respectively (p < 0.0001). The only statistically significant difference was between the baseline and the three remaining groups. Interobserver agreement was high, with the chance-corrected measure of agreement of 0.78.
CONCLUSION. Transrectal sonography revealed that prostate vascular flow increases dramatically after ejaculation and remains elevated for at least 24 hr. This observation should be considered when power Doppler sonography is used to assess for potential hyperemia in patients suspected of having prostate abnormalities.
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Our department is currently assessing patients with clinical symptoms of prostatitis in an attempt to define an abnormal vascular flow pattern as shown by transrectal power Doppler sonography. During this process we encountered a potential pitfall of this technique: a normal condition (recent ejaculation) that could cause increased blood flow to the prostate. The aim of this study was to ascertain whether ejaculation is indeed a factor in increasing blood flow to the prostate gland and to determine how long this effect may last.
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The protocol included four transrectal sonographic examinations. The first was done as a baseline examination. The second was done immediately after ejaculation. The third and fourth sonographic examinations were done at 6 and 24 hr after ejaculation. Sonographic examinations were performed by a single examiner using a Diasonics Spectra VST unit (General Electric Medical Systems, Milwaukee, WI) with a 7.0-MHz endfire endocavitary transducer. Machine settings were optimized for each patient and remained the same throughout all four examinations on that particular patient.
The patient was placed in the left lateral decubitus position with his knees pulled up toward his chest. After a digital rectal examination, a 10-min transrectal examination of the prostate was performed using standard technique. Representative gray-scale, color, and power Doppler images were recorded through the base, midportion, and apex of the prostate in the transverse plane (the plane was actually oblique between the transverse and coronal planes as is true of all endfire probes used for prostate assessment). These were accompanied by longitudinal images through the right, mid, and left portions of the prostate. Ejaculation was then achieved by masturbation in a separate room. A sperm sample was shown to prove successful ejaculation. Three additional sonographic examinations using the same protocol were performed immediately, 6, and 24 hr after ejaculation.
A representative power Doppler image from each examination was chosen (transverse orientation at the base of the prostate), masked to obscure which of the four examinations it represented, and the resulting set of four images from each of the 10 patients was assessed by three independent observers (the observers did not include the individual who performed the examinations). Images from each volunteer were presented in random order to the observers. Each observer was asked to rank the images from most flow to least flow and to grade flow in each image according to a published scoring system [12]. The Kruskal-Wallis nonparametric one-way analysis of variance test was used to determine statistical significance for the ranked data. Interobserver agreement was statistically assessed using the chance-corrected measure of agreement; the chance-corrected measure of agreement is similar to but more robust than the more familiar kappa value [13].
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2=65.6,p<0.0001). This difference was caused by
hyperemia after the baseline examination, with no significant difference in
rankings between the immediate, 6-, and 24-hr prostejaculation groups
(p = 0.24). Similar results were obtained for the numeric vascular
grades. Using the five-point scale, the mean score for the baseline group was
1.1, whereas for the immediate, 6-, and 24-hr postejaculation groups it was
2.5, 2.9, and 2.4, respectively (p<0.0001, analysis of
variance).
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Using the Tukey honestly significant difference test, we found the only statistically significant difference to be between the baseline and the three remaining groups, with no significant difference between the three postejaculation grades. Interobserver agreement was high, with all three observers assigning identical rank orders in 30 (75%) of 40 cases. Two of the three observers agreed in the remaining 10 cases, and in eight (80%) of these 10 cases, the odd observer was within one rank of the other two. Interobserver statistically measured agreement was similarly high, with the chance-corrected measure of agreement being 0.78.
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The prostate is supplied from the internal iliac arteries by the prostaticovesical arteries [12, 16, 17]. The prostaticovesical artery gives rise to two terminal branches, the prostate artery and the inferior vesical artery. The prostate artery then divides into urethral and capsular arteries. The latter divides into two sets on the surface of the gland, one located anteriorly and the other posterolaterally. Centripetal branches from these vessels perforate the capsule to supply the prostatic parenchyma as they course toward the periurethral zone.
Power Doppler sonography is a newer type of color Doppler sonography in which the integrated power of the Doppler signal is displayed, rather than the mean frequency shift that is used in conventional color Doppler sonography [18]. The three primary advantages of power Doppler sonography are improved sensitivity to slow flow, relative angle independence, and, potentially, a more accurate depiction of tissue perfusion [19, 20]. Tissue perfusion [21] is theoretically a more useful tool than the mean frequency map found in conventional color Doppler imaging in assessing inflammatory and malignant conditions of the prostate. Power Doppler sonography has been shown to be superior to conventional color Doppler sonography in revealing normal renal [22] and prostatic vasculature [12].
This study demonstrated a definite increase in vascular flow to the prostate after ejaculation. Using ranking criteria, we determined that 97% (29/30) of the images ranked as having the least flow were from the baseline examination (p < 0.0001). Using grading criteria (a five-point scale of 0-4, least flow to most flow), we determined that the mean score for the baseline group was 1.1, whereas for the immediate, 6-, and 24-hr postejaculation groups it was 2.5, 2.9, and 2.4, respectively (p < 0.0001). What was surprising to us was the duration of the ejaculation-induced hyperemia. Specifically, we noted no difference in the degree of hyperemia among the studies performed immediately, 6 hr, and 24 hr after ejaculation. Using ranking criteria, we found that there was no significant difference in rankings between the immedaite, 6-, and 24-hr postejaculation groups (p = 0.24). Using grading criteria and the Tukey test, we found that there was no statistically significant difference between the three postejaculation grades (all p values > 0.05). Future studies will have to address the issue of the duration of prostate hyperemia induced by ejaculation; we showed that it persisted to at least 24 hr and it is unknown when it returns to baseline.
Strengths of this study are twofold. First, this is the only study of its kind of which we are aware. Second, there was a high level of agreement between the three observers as detailed in the Results section. Study weaknesses are threefold. First, there is a potential bias in choosing "transverse, base" as our comparison image. We believe that logically this is the most useful single plane in comparing flow patterns across categories. However, three-dimensional volumetric perfusion assessment would likely be more useful in comparisons. Second, we did not find it possible to separate focal versus diffuse increases in flow in these healthy volunteers because of the marked heterogeneity in flow throughout the prostate, particularly given the improved flow detection noted with power Doppler imaging over that of color Doppler imaging. Third, could the insertion of the transrectal probe alone (independently of ejaculation) theoretically account for the hyperemia we observed? Prostate manipulation has been shown to increase the serum prostate-specific antigen level [23]. Ejaculation has also been reported to increase the prostate-specific antigen level [24, 25], although this finding is controversial [23]. We believe that the process of transrectal sonography alone is unlikely to account for the hyperemia given the light probe pressures used.
It may be difficult to recruit subjects for a follow-up study of a similar design. However, if an additional investigation is performed in the future, four enhancements to the protocol are suggested. One: require a longer period of abstinence before the study and continue imaging beyond 24 hr to determine when vascular flow returns to baseline. Two: enroll an older population of volunteers to more closely match the population that is typically afflicted with prostatitis and cancer of the prostate. Three: increase the number of subjects enrolled. Four: enroll a nonejaculatory control group who receive just transrectal sonography to prove that the sonogram alone cannot cause the observed hyperemia. Additional potential topics for investigation are whether sexual stimulation without ejaculation might be associated with prostatic hyperemia and whether longer or shorter periods of time might be required for older men to return to baseline.
In conclusion, prostate vascular flow in healthy volunteers increases dramatically after ejaculation and remains elevated for at least 24 hr. This phenomenon has the potential to dramatically skew results whenever prostate flow is assessed for clinical purposes and should therefore be considered whenever power Doppler sonography is used to assess for potential hyperemia in patients suspected of having prostate abnormalities such as prostatitis or malignancy.
Acknowledgments
We thank Jerry Jarvik for calculation of the chance-corrected measure of
agreement, and Maureen Michaud and Carrie Poole for preparation of this
manuscript.
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