lower urinary tract symptoms ( luts ) are common in older men . though the guidelines of the american urological association suggest transurethral resection of the prostate ( turp ) as the standard surgical treatment for benign prostate hyperplasia ( bph ) , recent studies introduce holmium laser enucleation of the prostate ( holep ) as the  new gold standard  surgical management . some studies report that holep is preferable due to less blood loss and shorter hospital stay than turp . theoretically , adenoma tissue will be lost during laser enucleation and morcellation , as much as 20% loss of the enucleated adenoma during holep . however , there is no evidence quantifying the postoperative specimen loss of enucleated adenoma in spite of frequent quotation in various studies . most studies report surgical outcomes using specimen weight , and none have assessed volume of the enucleated specimen . however , it seems important to measure the volume of enucleated adenoma , not only because the density of prostate tissue is different for each prostate , but because preoperative ultrasonographic data means volume of adenoma . accordingly , our study was designed to assess the difference between preoperatively estimated adenoma size and postoperatively remnant specimen , and assess the strength of association of preoperative volume of the prostatic adenoma with enucleated weight , the volume and calculated volume of the adenoma by pre- and postoperative transrectal ultrasonography ( trus ) . our study was a prospective , multicenter study and was approved by the institutional review board of seoul national university hospital ( seoul , south korea ) ( approval number : h-1008 - 136 - 330 ) and gachon university gil medical center ( incheon , south korea ) ( approval number : gairb2013 - 82 ) . we prospectively collected data from consecutive patients who underwent holep for management of symptomatic luts / bph between 2010 and 2015 . all operations were performed using a holmium : yttrium - aluminum - garnet laser by two surgeons ( sjo and jko ) . the holmium laser apparatus used in our study were omnipulse ( trimedyne inc . , irvine , ca , usa ) and versapulse powersuite ( lumenis , yokneam , israel ) . the enucleated adenoma tissue was immediately weighed and tissue volume measured after retrieval in the operation room . to estimate volume of the enucleated adenoma a specimen of enucleated adenoma was put into the cylinder . the increased volume in the measuring cylinder was measured by single examiner ( jko ) and recorded as the volume of the enucleated specimen . the calculated enucleated adenoma volume was estimated by the formula : calculated enucleated adenoma volume = preoperative prostate volume the defect volume was determined using the same prostate volume calculation with ellipsoid method ( fig . 1 ) . to compare the difference between preoperative transitional zone volume and postoperative enucleated adenoma , difference ratio was calculated as follows . difference ratio with transitional zone volume ( % ) = ( transitional zone volume  weight or volume of enucleated prostate)/transitional zone volume . to compare the difference between calculated enucleated volume and postoperative enucleated adenoma , difference ratio was calculated as follows . difference ratio with calculated enucleated volume ( % ) = ( calculated enucleated volume  weight or volume of enucleated prostate)/calculated enucleated volume . a descriptive analysis of age , weight and volume of postoperative specimen , ultrasonographic parameters including prostate volume , transitional zone volume , postoperative residual prostate volume , calculated enucleated adenoma volume was performed . to assess the association with preoperative adenoma volume , a multiple linear regression model was used with transitional zone volume as the outcome variable and other postoperative parameters introduced as independent variables . null hypotheses of no difference were rejected if p - values were less than 0.05 . all statistical analyses were conducted using sas 9.3 ( sas institute , cary , nc , usa ) . our study was a prospective , multicenter study and was approved by the institutional review board of seoul national university hospital ( seoul , south korea ) ( approval number : h-1008 - 136 - 330 ) and gachon university gil medical center ( incheon , south korea ) ( approval number : gairb2013 - 82 ) . we prospectively collected data from consecutive patients who underwent holep for management of symptomatic luts / bph between 2010 and 2015 . all operations were performed using a holmium : yttrium - aluminum - garnet laser by two surgeons ( sjo and jko ) . the holmium laser apparatus used in our study were omnipulse ( trimedyne inc . , irvine , ca , usa ) and versapulse powersuite ( lumenis , yokneam , israel ) . the enucleated adenoma tissue was immediately weighed and tissue volume measured after retrieval in the operation room . to estimate volume of the enucleated adenoma a specimen of enucleated adenoma was put into the cylinder . the increased volume in the measuring cylinder was measured by single examiner ( jko ) and recorded as the volume of the enucleated specimen . the calculated enucleated adenoma volume was estimated by the formula : calculated enucleated adenoma volume = preoperative prostate volume the defect volume was determined using the same prostate volume calculation with ellipsoid method ( fig . 1 ) . to compare the difference between preoperative transitional zone volume and postoperative enucleated adenoma , difference ratio was calculated as follows . difference ratio with transitional zone volume ( % ) = ( transitional zone volume  weight or volume of enucleated prostate)/transitional zone volume . to compare the difference between calculated enucleated volume and postoperative enucleated adenoma , difference ratio was calculated as follows . difference ratio with calculated enucleated volume ( % ) = ( calculated enucleated volume  weight or volume of enucleated prostate)/calculated enucleated volume . a descriptive analysis of age , weight and volume of postoperative specimen , ultrasonographic parameters including prostate volume , transitional zone volume , postoperative residual prostate volume , calculated enucleated adenoma volume was performed . to assess the association with preoperative adenoma volume , a multiple linear regression model was used with transitional zone volume as the outcome variable and other postoperative parameters introduced as independent variables . null hypotheses of no difference were rejected if p - values were less than 0.05 . all statistical analyses were conducted using sas 9.3 ( sas institute , cary , nc , usa ) . one hundred forty - two patients with a mean age ( standard deviation ) of 69.8 ( 8.8 ) years were analyzed . the preoperative mean total prostate volume was 60.8 ( 27.0 ) ml and transitional zone volume were 31.7 ( 21.4 ) ml . the mean postoperative residual volume was 31.6 ( 10.7 ) ml , and the calculated enucleated adenoma volume was 29.2 ( 20.1 ) ml . the postoperative parameters of the adenoma specimen are weight , 22.3 ( 17.0 ) g , and volume , 22.3 ( 16.8 ) ml . the difference ratio between preoperative transitional zone volume and the postoperative adenoma was 31.7% for weight and 31.3% for volume . and the difference ratio between postoperatively calculated volume of enucleated adenoma and both of weight and volume of postoperative adenoma were 26.1% . the ratio between weight and volume of enucleated adenoma was 1.0 ( 0.2 ) g / ml ( table 1 ) . the postoperative calculated enucleated volume is strongly associated with preoperative transitional zone volume by multivariate analysis ( p<0.001 ) ( table 2 ) . current research describes the advantages of holep comparing other surgical manipulations in the aspects of preservation of erectile function , operability of concomitant anticoagulation , and acontractile detrusor function . eureka! is from a famous anecdote regarding the ancient greek physicist , archimedes . to our knowledge the first aim of our study was to compare prostatic volume with weight . to investigate these parameters , archimedes ' principle was applied to assess the volume of enucleated tissue using a 200-ml measuring cylinder . we observed a ratio between weight and volume of specimen of 1.00.2 ( g / ml ) . these findings are highly suggestive , not only that the mean prostatic density was about 1.0 g / ml in our study , but also that there is no difference in presenting either weight or volume of specimen to report surgical outcomes . in our results , there was a 26% difference between the calculated enucleated volume and postoperative weight of specimen . inversely , the calculated enucleated volume using trus was 30% more than postoperative weight of enucleated adenoma . there was a significant relationship between preoperative transitional zone volume and postoperative calculated enucleated volume in a multiple linear regression model . to the best of our knowledge , this is the first study to prove the presence of difference between preoperative adenoma volume planned to remove and postoperative enucleated adenoma volume in holep . first , small morcellated adenoma tissue can not be collected easily . in general , enucleated tissue is strained through a sieve using gauze in operation room . different from a turp specimen , the size of enucleated adenoma varies according to the morcellator . furthermore , some tiny morcellated adenoma can freely penetrate holes of a sieve . therefore , loss of some morcellated adenoma is unavoidable during tissue collection . second , some tissue will be vaporized during holep . though the main procedure of holep is enucleation of prostatic adenoma along the adenoma plane , vaporization of some tissue is inevitable using the holmium laser . as a result , third , theoretically tissue volume may decrease due to loss of blood supply after enucleation . according to our above results , it is reasonable to assume that true volume of enucleated adenoma is above 30% more than the weight of the postoperative specimen in holep . in the analysis of the relationship between preoperative transitional zone volume and postoperative variables , calculated enucleated volume showed statistically strong association with preoperative transitional zone volume ( p<0.001 ) . this result may have clinical significance for the need to assess the true amount of enucleated adenoma . this kind of ultrasonographic assessment with defect volume may be useful to examine further follow - up trus of the patients who underwent holep . however , immediately postoperative ultrasonography is not always feasible in clinical practice not only because of bleeding control , but because of the necessity of additional preparation of ultrasonographic device in operation room . therefore , an additional 30% more weight of postoperative specimen should be considered when the surgical outcome is compared between holep and other surgery of bph . otherwise , immediately postoperative trus is recommended more than weight of postoperative specimen for obtaining the true volume of enucleated adenoma in case of considering comparative study about bph surgeries . our next study will focus on the change of prostate size after surgery and long - term observation results of holep . in our study , there was a significant difference between preoperative transitional zone volume and postoperative weight of enucleated adenoma during holep . to assess more accurate volume of enucleated adenoma in holep in case of comparing specimen weight with those of other bph surgery , it is highly recommended to consider 1.3 times of postoperative weight or volume of enucleated prostate tissue as the volume of actually enucleated adenoma .
purposeto analyze postoperative outcomes of prostate surgery , resected specimen weight is commonly used . the difference between the preoperative calculated transitional zone volume and actual enucleated specimen weight following holmium laser enucleation of the prostate ( holep ) 
 is reported at over 20% . 
 the reason for this difference is unclear . 
 we assessed the association of volume of the prostatic adenoma with enucleated weight , the volume and calculated volume of the adenoma by pre- and postoperative ultrasonographic measurement.materials and methodsall patients were prospectively enrolled who underwent holep by two surgeons ( sjo and jko ) between 2010 and 2015 . 
 preoperative and postoperative prostate ultrasonography examinations were performed by a single examiner ( jko ) during surgery , and weight and volume of the enucleated adenoma were measured . 
 we compared preoperative adenoma size with postoperative weight and volume of the enucleated adenoma , calculated enucleated volume using ultrasonography , and calculated the correlation coefficients between preoperative adenoma volume and postoperative parameters.resultsone hundred forty - two patients with a mean age ( standard deviation ) of 69.8 ( 8.8 ) years were analyzed . 
 the mean preoperative ultrasound - measured adenoma volume was 31.7 ( 21.4 ) ml , while postoperatively the mean retrieved weight of the adenoma was 22.3 ( 17.0 ) g and the mean volume was 22.3 ( 16.8 ) ml . 
 postoperatively calculated enucleated volume using ultrasonography was most strongly correlated with preoperative adenoma size ( pearson correlation coefficient 0.965 , p<0.01).conclusionsour study showed a significant difference between preoperative adenoma size and postoperative enucleated weight of adenoma during holep . 
 postoperatively calculated enucleated volume using ultrasonography may be the most reliable parameter to assess surgical outcomes following holep .