an anatomical configuration of the prostate termed the intravesical prostatic protrusion ( ipp ) can be measured as the vertical distance from the tip of the protruding prostate to the base of the bladder at the base of the prostate gland .
the ipp can be measured noninvasively by transrectal ultrasonography ( trus ) and can predict voiding parameters for determining boo in men who present with luts .
ipp may also be a useful predictor for clinical progression in men with benign prostatic hyperplasia ( bph ) [ 3 - 6 ] .
ipp is insufficient for managing patients with bph / luts ; physicians know only that ipp is a significant predictor for boo , because most elderly people with bph / luts have some degree of ipp . hence , a novel means of gauging ipp is needed .
the goal of this study was therefore to determine noninvasive parameters for predicting boo and defining the degree of ipp causing boo in a large population of korean men by analyzing the receiver operating characteristic ( roc ) curves for ipp , including the cutoff , and correlating ipp and other clinical variables with the results of a pressure - flow study .
we performed a retrospective analysis of clinical outcomes of consecutive male korean patients aged 50 to 90 years with luts / bph who underwent transurethral resection of the prostate ( turp ) from may 2007 to december 2010 .
patients with a known history of prostate or bladder carcinoma , urinary tract infection , renal impairment , bladder calculi , or neurological deficit were excluded .
survey of the international prostate symptom score ( ipss ) and quality of life ( qol ) scores was performed for evaluation of baseline parameters .
a physical examination included a digital rectal examination to screen for prostatic growth suspicious of malignancy and a neurological examination to exclude any neurological deficits or neurologically related bladder dysfunction .
preoperative evaluation included urodynamic studies including pressure - flow studies and serum prostate - specific antigen ( psa ) .
four urodynamic parameters including the postvoiding residual urine ( pvr ) , peak flow rate ( qmax ) , detrusor pressure at the peak flow rate ( pdetqmax ) , and maximal detrusor pressure during voiding ( pdetmax ) were statistical analyzed .
urethral resistance was quantified by using the boo index ( booi ) , according to the formula booi = pdetqmax-2qmax .
patients were classified into two groups by the boo : obstructed ( booi>40 ) and unobstructed ( booi40 ) .
ipp was also measured as the vertical distance from the tip of the protruding prostate to the base of the bladder at the base of the prostate gland ( fig .
roc curve analysis was performed to evaluate the diagnostic performance of ipp for predicting boo .
a multivariate logistic regression was performed to identify strength and association between boo and ipp , compensating for factors such as age , ipss , qol , prostatic volume , and urodynamic parameters .
of the 534 patients , 239 patients were included and 295 patients were excluded because of neurologic deficits , urinary tract carcinoma , or renal impairment . the mean age of the 239 included patients was 69.98.0 years ( meanstandard deviation ) .
the mean ipss was 14.211.6 , the mean qmax was 9.56.8 ml / s , the mean pvr was 35.146.6 ml , and the mean degree of ipp was 3.424.71 mm .
the number of patients in the unobstructed and obstructed groups was 193 and 46 , respectively .
significant boo ( index>40 ) was associated with higher ipp ( 8.086.74 mm , p<0.001 ) compared with equivocal boo ( 1.983.11 mm , p<0.001 ) .
the area under the roc curve ( auc ) for ipp was 0.759 ( 95% confidence interval [ ci ] , 0.657 to 0.861 ) ( fig .
the aucs for total prostate volume , serum psa , qmax , and pvr were 0.746 , 0.572 , 0.384 , and 0.696 , respectively .
boo was positively correlated with ipp , pvr , and prostate volume ( spearman 's rho=0.551 , 0.225 , and 0.391 , respectively ; p<0.001 for each parameter ) and was negative correlated with qmax ( spearman 's rho=-0.159 , p=0.026 ) .
ipss and the qol index had poor predictive significance for boo ( positive predictive value of < 60% , p=0.624 and p=0.138 , respectively ) .
qmax , pvr , prostatic volume , and ipp had significant predictive value for boo ( p=0.026 , p<0.001 , p<0.001 , and p<0.001 , respectively ) .
however , qmax , pvr , and prostatic volume had lower positive predictive values ( 27% to 53% vs. 79% ) than did ipp , and the negative predictive value of qmax , pvr , and prostatic volume were similar to that of ipp ( 87% to 91% vs. 89% ) .
logistic regression analysis revealed that ipp was a significant independent variable when other covariates including age were considered .
the odds ratio of boo for ipp was 3.99 ( 95% ci , 1.46 to 10.8 ) ( table 2 ) .
one of the important pathophysiologies in bph is boo , making evaluation of the severity and presence of boo important .
there is no definite or reference standard for boo , except for pressure - flow study .
however , the latter is too expensive ( especially in developing countries ) , is invasive , and is uncomfortable for patients . to avoid these drawbacks ,
the identification of new accurate methods that could substitute for the gold standard pressure - flow study at lower cost , expanded accessibility , and with relief of patient discomfort has become an important goal .
other noninvasive clinical variables have no significant correlation with boo [ 5,8 - 10 ] .
the ipss is a simple tool in the evaluation of benign prostatic enlargement , and a worsening score may warrant intervention .
pvr may reflect the severity of boo , but the presence of bladder dysfunction confounds its value . in our study , ipss and qol score were not correlated with boo ( p=0.624 and p=0.138 , respectively ) .
this was expected , because symptoms need not be related to obstruction . in addition , the urine flow rate and pvr had lower positive predictive values than did ipp .
clinical data such as ipss , pvr , and flowmetry correlate mostly to lower urinary tract functional status rather than mechanical obstruction itself [ 8 - 10 ] .
ipp aside from pressure - flow studies is a predictor of boo in bph / luts patients .
ipp arises from the enlargement of the median and lateral lobes and causes a ball - valve type of obstruction , which thus disrupts the funneling effect of the bladder neck .
the severity of ipp has been correlated with prostate volume , creating boo in patients with bph / luts . in the present study ,
the boo group displayed a greater ipp than did the equivocal boo group ( p<0.001 ) , and the degree of ipp correlated with boo ( r=0.551 ) . despite this
analysis of the roc curve concerning the relationship between ipp and boo revealed a cutoff of 5.5 mm for ipp ( sensitivity of 66.7% and specificity of 80.5% ) : an ipp exceeding 5.5 mm was significantly associated with boo .
but the finding that ipp exists in bph / luts patients can not completely explain the situation in patients in whom symptoms are intractable to treatment with alpha - blockers or turp . we think that a specific degree of ipp can be applied in the treatment of bph / luts patients .
further studies are needed to define a cutoff of ipp as a causative criterion of boo .
reported that roc curves of ipp yielded an auc of 0.858 and 0.758 , respectively , which are similar or greater than the presently found value .
reported that the best cutoff was 7.5 mm ( sensitivity of 75.5% and specificity of 82.6% ) , which was greater than our cutoff of 5.5 mm .
the patients in our study were korean males who presented with a complaint of luts .
there could be a racial explanation for the difference in cutoff values between the prior and present studies . also
, the study number ( n=239 ) was small ; studies with larger numbers are warranted . yet
, the present study corroborates the findings of prior studies concerning the ipp cutoff for boo .
we analyzed roc curves concerning the relationship between ipp and boo and between boo and other parameters ( prostate volume , psa , qmax , pvr ) .
interestingly , the ipp displayed a greater auc value of 0.759 than did prostate volume ( 0.746 ) .
the prevailing view is that ipp correlates with boo but does not have a significant value compared with prostate volume .
the presently determined auc value for ipp indicates that the measurement of ipp has greater diagnostic value in boo than does prostate volume in evaluating prostate sonographic data .
boo is dynamic and is influenced by the physical obstruction of the bladder and prostate , and we think that ipp measurement is needed in patients when prostate volume is not excessive , and that boo patterns may be useful .
also , ipp measurements besides uroflowmetry , pvr , and psa likely are influential in diagnosing boo , in that in the present study ipp produced a larger auc than did psa , qmax , or pvr .
these data support the view that ipp can predict boo , compared with qmax , pvr , and prostate volume , for bph / luts patients , and may have diagnostic predictive value similar to that of pressure - flow studies
. also , by predicting boo and defining a specific ipp cutoff linked with the occurrence of boo , we suggest that the degree of ipp can be a guideline for further treatment in patients with bph / luts .
 purposethe present study was done to define the degree of intravesical prostatic protrusion ( ipp ) causing bladder outlet obstruction ( boo ) in patients with benign prostatic hyperplasia ( bph)/lower urinary tract symptoms.materials and methodswe retrospectively evaluated 239 patients with bph , analyzing age , ipp , prostate volume , international prostate symptom score ( ipss ) , and the results from a pressure - flow study . 
 urethral resistance was quantified by using the boo index ( booi ) , according to the formula booi = pdetqmax-2qmax ( where pdet is detrusor pressure at the peak flow rate and qmax is peak flow rate ) . 
 boo was defined by a booi above 40 . 
 patients with a booi below 20 were excluded . 
 patients were classified into two groups ( obstructed and unobstructed groups ) by the booi . 
 correlations were determined by logistic regression analysis , and receiver operating characteristic curves were plotted to estimate the optimal cutoff for ipp.resultsthere were significant differences in total prostate volume , postvoiding residual urine ( pvr ) , ipp , and qmax ( p<0.001 , p<0.001 , p<0.001 , and p=0.026 , respectively ) between the obstructed and unobstructed groups , but there were no significant differences in age ( p=0.653 ) , ipss total score ( p=0.624 ) , or quality of life score ( p=0.138 ) . 
 ipp had a significant prognosis ( p<0.001 ) but was weakly correlated with prostate volume ( p=0.026 ) . 
 the correlation coefficients between ipp and qmax , pvr , prostate volume , and boo were 0.551 , -0.159 , 0.225 , and 0.391 , respectively . 
 for ipp , the area under the curve was 0.759 ( 95% confidence interval , 0.657 to 0.861 ) and the cutoff to indicate boo was 5.5 mm with 66.7% sensitivity and 80.5% specificity.conclusionsan ipp exceeding 5.5 mm was significantly associated with boo . 
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS