Is Primary Bladder Neck Obstruction Underdiagnosed in Women?

Primary bladder neck obstruction (PBNO) is one of the causes of bladder outflow obstruction (BOO) in neurologically intact women. Although it was described more than thirty years ago, there is a lack of accurate epidemiological data, definitions, and treatment pathways. Its etiology remains unknown and prevalence low. Symptomatic diagnosis is challenging and non-specific, and an accurate diagnosis requires understanding female voiding dynamics. Considering all those factors, the possibility of underdiagnosis is almost certain.

PBNO occurs when the bladder neck fails to open adequately during voiding, resulting in obstruction of urinary flow in the absence of increased striated sphincter activity or anatomical obstruction. It was first described in women by Diokno (1984). Recently, a functional theory suggested excess striated muscle with increased muscle tone and sympathetic nervous system activity (Sussman et al 2019).

With an unknown etiology and without fully understanding the entity, it is difficult to suspect it and correctly assess it.

Accurate data on its prevalence are limited as epidemiologic studies focus on symptomatic women rather than the general population (Sussman et al 2019). PBNO in women has been identified as the underlying cause in 4.6% to 16% of BOO cases (King and Goldman 2014; Nitti 2005). Prevalence may be underestimated as PBNO is diagnosed in females receiving videourodynamics, and symptomatic women in the general population outnumber the women receiving the test.

Up to 19% of women with lower urinary tract symptoms (LUTS) may have BOO, with urinary frequency as the most typical symptom in women with BOO of any cause (Malde et al 2015). PBNO symptoms are variable, including storage and voiding LUTS and/or pelvic pain; therefore, an accurate symptomatic diagnosis is not feasible.

Physical examination and cystoscopy findings in PBNO are usually unremarkable. The diagnosis is by videourodynamics, although challenging, as female voiding dynamics vary greatly (Nitti 2005). Many women void with low detrusor pressure or by relaxing pelvic floor muscles. Others, as a habit void by abdominal straining. For that reason, there are no set urodynamic parameters to define BOO in women, although many criteria have been proposed (King and Goldman 2014). In general, a high detrusor pressure with low flow, a closed bladder neck, with no evidence of distal urethral obstruction or abnormal activity at the level of the urinary sphincter is needed for diagnosis (King and Goldman 2014).

Urethral pressure profilometry (UPP) is another urodynamic tool to consider for diagnosing PBNO. Despite the lack of data available, the typical female UPP trace morphology may differ, and increased closure pressure at the bladder neck level may be present.

Without clear urodynamic parameters to diagnose PBNO in women and the scarce availability of videourodynamics, the possibility of underdiagnosis is unmeasurable.

The underdiagnosis of PBNO is very likely as the entity is poorly understood and not clearly defined by any urological society, resulting in limited data on its prevalence and lack of treatment guidelines. A detailed assessment is critical, using videourodynamics to allow a better understanding of the pathophysiology, thus allowing surgeons to select appropriate treatment, albeit limited.

References:

Diokno AC, Hollander JB, Bennett CJ. Bladder Neck Obstruction in Women: A Real Entity. J Urol. 1984 Aug;132(2):294–8.

King AB, Goldman HB. Bladder Outlet Obstruction in Women: Functional Causes. Curr Urol Rep. 2014 Sep;15(9):436.

Malde S, Solomon E, Spilotros M, Mukhtar B, Pakzad M, Hamid R, et al. Female bladder outlet obstruction: Common symptoms masking an uncommon cause. LUTS Low Urin Tract Symptoms. 2019 Jan;11(1):72–7.

Nitti VW. Primary bladder neck obstruction in men and women. Rev Urol. 2005;7 Suppl 8:S12-17.

Sussman RD, Drain A, Brucker BM. Primary Bladder Neck Obstruction. Rev Urol. 2019;21(2–3):53–62.

What proportion of women (approximate number) in your practice with voiding difficulty get the definitive diagnosis of PBNO?

In the last 20 years, I don't recall any women with this diagnosis. As mentioned, it is not a term that has been defined by ICS/IUGA and hence is not used. Voiding dysfunction and BOO are the terms we use.

What treatment modalities do you adopt in women with diagnosed PBNO? Do you perform bladder neck incision?

We use pelvic floor physio relaxation, alpha blockers, self-catheterization or SNM. I don't recall needing to do a BNI on a female due to potential risk of urinary incontinence. What we don't know is if PBNO is a functional or anatomical obstruction. If anatomical, then BNI can work but if functional, then unlikely to work for long term. It may well be why urethral dilation in women only works for short periods of days or a few weeks and has been abandoned by most urologists. Until we understand the pathophysiology, have a definition and more data, it will be difficult to make any definitive treatment plans and a multidisciplinary approach is crucial.