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Year : 2006  |  Volume : 22  |  Issue : 3  |  Page : 205-207

Is transition zone index useful in assessing bladder outflow obstruction due to benign prostatic hyperplasia?: A prospective study

1 Department of Urology, Christian Medical College, Vellore, India
2 Department of Radiology, Christian Medical College, Vellore, India

Correspondence Address:
Nitin S Kekre
Department of Urology, Christian Medical College, Vellore - 632 004
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-1591.27625

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BACKGROUND: Benign prostatic enlargement (BPE) is the commonest cause of bladder outlet obstruction in men above 50 years of age. Though pressure-flow study is the gold standard in establishing outlet obstruction, it is associated with definite morbidity. Several noninvasive parameters are described to diagnose outlet obstruction due to BPE and evaluate treatment efficacy. AIM: We studied the role of transitional zone index (TZI) in assessing bladder outlet obstruction (BOO) due to BPE. SETTING AND DESIGN: Prospective hospital-based cross-sectional diagnostic study. MATERIALS AND METHODS: Thirty-five men aged between 50 and 77 years with untreated lower urinary tract symptoms due to BPE were studied. Patients with prostate cancer, prostatitis, active UTI urethral stricture, neurovesical dysfunction and diabetes mellitus were excluded. All patients underwent a standard assessment using the American Urological Association (AUA) symptom score, uroflow, pressure-flow (PF) study and transrectal ultrasound (TRUS) estimation of TZI. Investigators undertaking PF studies and TRUS were blinded to the investigation of others. From the PF studies, Abrams Griffith (AG) number was calculated. Based on this, patients were grouped into obstructed (AG>40) and unobstructed (AG<40) groups. STATISTICAL ANALYSIS: TZI was calculated and compared with PF studies using Mann-Whitney U test, logistic regression analysis and receiver operator characteristic curve (ROC). RESULTS: The mean age was 63.2 years (SD). The mean AUA scores and peak flow rate were 16.7 and 7.5 ml/sec, respectively. Of the 35 men, 21 were obstructed and 14 were unobstructed. TZI was not significantly different between the two groups, while the differences in age, AUA symptom score, prostate volume and TZ volume were statistically significant. Logistic regression model did not show any independent effect of TZI in predicting obstruction. ROC curve showed a poor overall accuracy in diagnosing obstruction due to BPE. CONCLUSION: Age, prostate volume and TZ volume are better indicators than TZI in diagnosis of BOO secondary to BPE.

Keywords: Bladder outflow obstruction, benign prostatic hyperplasia, transition zone index

How to cite this article:
Sailo S L, Viswaroop BS, Shyam Kumar N K, Gopalakrishnan G, Kekre NS. Is transition zone index useful in assessing bladder outflow obstruction due to benign prostatic hyperplasia?: A prospective study. Indian J Urol 2006;22:205-7

How to cite this URL:
Sailo S L, Viswaroop BS, Shyam Kumar N K, Gopalakrishnan G, Kekre NS. Is transition zone index useful in assessing bladder outflow obstruction due to benign prostatic hyperplasia?: A prospective study. Indian J Urol [serial online] 2006 [cited 2021 Oct 25];22:205-7. Available from:

Benign prostatic enlargement (BPE) is probably the commonest benign human neoplasm. It is seen in approximately one half of men at the age of 60 years.[1] It has been documented that only two-thirds to three-fourths of men with BPE actually have bladder outflow obstruction (BOO).[1]

Pressure-flow (PF) study is the most reliable investigative tool in the diagnosis of infravesical obstruction.[2] But because of its invasive nature, along with the attendant complications, it has a limited but definite role in men with lower urinary tract symptoms (LUTS) due to BPE.[3] Several surrogate parameters are used in the diagnosis and evaluation of treatment efficacy. Of them, AUA symptom score, uroflowmetry, post-void residue and prostate volume are most commonly used.[4] Though BPE involves the hypertrophy of all elements of prostate, the total prostate volume is known to have a weak correlation with other parameters of BPE. McNeal described BPE as hyperplasia of the transition zone, with a minor contribution from the hyperplasia of the central zone and peri-urethral glands.[1] The enlargement of the transition zone, with subsequent compression of the surgical capsule, results in symptoms of infravesical obstruction. Kaplan et al[5] reported the transition zone index to be a useful parameter, which correlates significantly with certain parameters of BPE, like AUA symptom score and peak urine flow. They suggested that transition zone index of greater than 0.5 is indicative of significant bladder outlet obstruction due to BPE. Some studies[6],[7] have concurred with the results of Kaplan and some have been reported with contradictory results.[8],[9],[10] This prospective study aims to assess the predictive value of TZI in the diagnosis of BOO due to BPE.

   Materials and methods Top

From January 2000 to July 2000, 45 men aged 50 to 84 years with symptomatic BPE were enrolled into the study. BPE was diagnosed on the basis of symptoms and physical findings. All patients with prostate cancer, active urinary tract infection, prostatitis, neurogenic bladder, urethral stricture, diabetes mellitus and history of drug treatment for BPE were excluded from the study. Ten were excluded and 35 were included. Symptoms were scored using the American Urological Association (AUA) symptom score.

Urodynamic evaluation

Pressure-flow studies were performed with the use of the DANTEC system. Intravesical pressure was obtained through a 5F urethral catheter and the intra-abdominal pressure was recorded via a rectal balloon. A 5 Fr feeding tube was used to fill the bladder. A cystometrogram was done in the sitting position using saline at physiologic temperature at the rate of 50 ml/min. Once the patients complained of strong desire to pass urine, the filling line was removed and they were allowed to void in privacy, in the sitting position. Voided volume and Pdet at maximum flow rate were noted. The Abrams-Griffiths (AG) number was then calculated as Pdet Qmax - (2 x Qmax). Based on the AG number, patients were grouped into obstructed (AG number >40) and unobstructed (AG number <40).[11]

Transition zone index determination

A single radiologist, blinded to the results of pressure-flow studies, performed transrectal ultrasound. Imaging was done in transverse and longitudinal views. Prostate volume was calculated using the formula for an ellipsoid (Volume = width x length x height x 0.52).[5] Width was measured using the transverse view, while length was measured using the longitudinal view. Height was measured in the transverse plane, at right angle to the gland width. Determination of transition zone volume was similarly performed by ellipsoid calculation. The transition zone index was then calculated according to the formula - Transition zone index = transitional zone volume divided by total volume of the prostate.

Statistical analysis

Mann-Whitney U test was used to compare the two groups. Logistic regression analysis was done to study the significance of the transition zone index, after controlling for the effects of other study variables. The Receiver Operator Characteristic curve was drawn. SSPS PC PLUS software was used for the analysis.

   Results Top

There were 35 patients in the study, who had a mean age of 63.2 years at presentation. Mean AUA symptom score and peak flow rate were 16.7 and 7.5 ml/s respectively [Table - 1]. Based on the results of pressure-flow studies with use of AG number, 21 were found to be obstructed and 14 were unobstructed.

Statistical analysis done using [Table - 2] Mann-Whitney U test showed no significant difference in the values of TZI between the obstructed and the unobstructed group. However, age, total prostate volume, transitional zone volume, AUA symptom score and peak flow rate were statistically significant between the two groups. Logistic regression analysis did not show any independent effect of TZI in differentiating the obstructed from the unobstructed group [Table - 3].

Receiver Operator Characteristic curve analysis indicated that TZI has a very poor overall accuracy in the diagnosis of bladder outflow obstruction due to BPE.

   Discussion Top

The pathophysiology of BOO in men with clinical benign prostatic hyperplasia (BPH) has been attributed to the enlargement of the prostate.[12] The advent of TRUS has made it possible to accurately evaluate the size and shape of the prostate, both objectively as well as quantitatively.[13] Garraway et al[14] based on necropsy studies using TRUS, defined BPH as showing a prostate weight more than 20 g. Prostate weight has been shown to correlate with age[15] and in turn, with pressure-flow studies.[16]

Kaplan et al reported TZ volume as a more sensitive marker of BPE and showed TZI >0.5 to be an indicator of significant BOO.[5] Kurita et al[6] reported that men with TZI >0.65 had a higher risk of developing acute urinary retention (AUR). The possible reason for higher cutoff of TZI in this retrospective series could be the selection of men with AUR. On the other hand, Lepor et al[8] did not find significant correlations between TZI and AUA symptom score, although there was weak correlation between TZI and peak flow rate. This could probably be due to a mixed cohort of patients.

Witjes et al[9] in a prospective study on a large number of patients (n = 150), found significant correlation between total prostate volume, transition zone volume and TZI with age but a weak correlation between TZI and pressure-flow studies. The problem with this study is that it consisted of men with a wide range in terms of age (ranging from 30 to 85 years), prostate volume and symptom score (1-33), which could have resulted in the discrepancy in the results. Also, it was a nondescript cohort of patients with LUTS, not specific for BPH. Kojima et al[10] introduced the concept of peripheral circle area ratio (PCAR). They showed that PCAR is a better indicator than TZI in predicting outflow obstruction due to BPE.[10]

Contrary to negative studies reported previously, our study population, though small in sample size, involved only men with BPH. Our study, in consistence with other studies, showed that age, total prostate volume and TZ volume were better markers of BOO due to BPE. The measurement of transition zone is difficult and the way in which it is measured and the race (Indian population) could be the reasons for the negative correlation. Kaplan et al also suggested the impact of race on measurement of TZ volume and TZI.

   Conclusion Top

TZI alone is not able to differentiate between obstruction and no obstruction in men with BPE. Age, prostate volume and TZ volume are better indicators of BOO secondary to BPE.

   References Top

1.McNeal JE. The Prostatic gland: Morphology and pathology. Monogr Urol 1988;9:36.  Back to cited text no. 1  [PUBMED]  
2.Blaivas JG. Multichannel urodynamic studies in men with benign Prostatic hyperplasia: Indications and interpretation. Urol Clin North Am 1990;17:543-52.   Back to cited text no. 2  [PUBMED]  
3.McConnell JD. Why pressure flow studies should be optional and not mandatory studies for evaluating men with benign prostatic hyperplasia. Urology 1994;44:156-8.  Back to cited text no. 3  [PUBMED]  [FULLTEXT]
4.Kuo HC. Clinical prostatic score for diagnosis of bladder outlet obstruction by prostatic measurements and uroflowmetry. Urology 1999;54:90-6.  Back to cited text no. 4  [PUBMED]  [FULLTEXT]
5.Kaplan SA, Te AE, Pressler LB, Olsson CA. Transition zone index as a method of assessing benign prostatic hyperplasia: Correlation with symptoms, urine flow and detrusor pressure. J Urol 1995;154:1764-9.  Back to cited text no. 5  [PUBMED]  
6.Kurita Y, Masuda H, Terada H, Suzuki K, Fujita K. Transition zone index as a risk factor for acute urinary retention in benign Prostatic hyperplasia. Urology 1998;51:595-600.  Back to cited text no. 6  [PUBMED]  [FULLTEXT]
7.Otani T, Fujimato K, Yoshida K, Ozono S, Hirao Y, Okajima E, et al . Transition Zone Index in predicting therapeutic efficacy of benign prostatic Hyperplasia. Nippon Hinyokika Gakkai Zasshi 2002;93:20-7.  Back to cited text no. 7    
8.Lepor H, Nieder A, Feser J, O'Connell C, Dixon C. Total prostate and transition zone volumes and transition zone index are poorly correlated with objective measurement of clinical benign prostatic hyperplasia. J Urol 1997;158:85-8.  Back to cited text no. 8  [PUBMED]  
9.Witjes WP, Aaranik RG, Ezz-el-Din K, Wijkstra H, Debruyne EM, de la Rosette JJ. The correlation between prostate volume, transition zone volume, transition zone index and clinical and urodynamic investigations in patients with lower urinary tract symptoms. Br J Urol 1997;80:84-90.  Back to cited text no. 9    
10.Kojima M, Ochiai A, Naya Y, Ukimura O, Watanabe M, Watanabe H. Correlation of presumed circle area ratio with infravesical obstruction in men with lower urinary tract symptoms. Urology 1997;50:548-55.  Back to cited text no. 10  [PUBMED]  [FULLTEXT]
11.Abrams PH, Griffiths DJ. The assessment of Prostatic obstruction from urodynamic measurements and from residual urine. Br J Urol 1979;51:129-34.   Back to cited text no. 11    
12.Shapiro E, Lepor H. Pathology of clinical benign Prostatic hyperplasia. Urol Clin North Am 1995;22:285-90.  Back to cited text no. 12  [PUBMED]  
13.Watanabe H, Kato H, Kato T, Morita M, Tanaka M. Diagnostic application of the ultrasonography for the prostate. Nippon Hinyokika Gakkai Zasshi 1968;59:273-9.  Back to cited text no. 13  [PUBMED]  
14.Garraway WM, Collins GN, Lee RJ. High prevalence of benign prostatic hypertrophy in the community. Lancet 1991;338:469-71.  Back to cited text no. 14  [PUBMED]  
15.Berry SJ, Coffey DS, Walsh PC, Ewing LL. The development of human benign prostatic hyperplasia with age. J Urol 1984;132:474-9.  Back to cited text no. 15  [PUBMED]  
16.Bosch JL, Kranse R, van Mastright R, Schroder FH. Reasons fort the weak correlation between prostate volume and urethral resistance parameters in patients with prostatism. J Urol 1995;153:686-93.  Back to cited text no. 16    


  [Table - 1], [Table - 2], [Table - 3]


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