Hypothesis / aims of study
Bladder outlet obstruction (BOO) is a prevalent condition in males over 40, and the incidence rate increases with age. The first line of treatment in these cases is medicine for relieving lower urinary tract symptoms (LUTS). Notwithstanding, surgical intervention is recommended for patients who did not improve from medical treatment or when complications such as, recurring urinary tract infections, acute urinary retention, hematuria, and/or bladder stones are present. The most frequent cause of LUTS in aging men is benign prostate enlargement (BPE). It may be assumed that the specimens from transurethral resection of the prostate (TUR-P) show acinar, stromal or purely stromal nodules. Skeletal muscle fibers are not found in material from TUR-P.
In our study, we had fifteen patients with LUTS who underwent TUR-P that showed skeletal muscle fibers. None of those patients presented hyperplastic nodules. This finding was not from the rhabdosphincter of the urethra because all patients are continent. The only histological finding was hyperplastic smooth muscle consistent with bladder neck histology and sections with prominent skeletal muscle fibers. Hence, these findings may be the explanation of why those patients did not have their symptoms resolved with pharmacological therapy.
This study aims to present a new cause of male BOO, attempting to answer why some patients do not respond to medication treatment for LUTS and is associated with the presence of prominent skeletal muscles fibers in sections of TUR-P without any transition zone nodules.
Study design, materials and methods
We performed a retrospective study with the database from the software “PathoControl7” including patients with LUTS who underwent TUR-P from 1995-2018. Those whose histological diagnosis showed an absence of transition zone nodules, but with the presence of skeletal muscle fibers from the bladder neck were reevaluated. A series of information were analyzed, such as age when the patients were submitted to the TUR-P, previous urological surgeries, ultrasonographic evaluation (prostate volume, post void residual urine volume), urodynamics, and the presence of diverticulum and bladder wall trabeculation observed during the TUR-P.
Pathological study: We revised all TUR-P specimens from 15 patients. Hyperplastic smooth muscle and skeletal muscle fibers were present in all cases, while no BPH nodules were found. The number of sections with skeletal muscle fibers as well as the percentage of positive sections from the entire sections of the TUR-P for each case were recorded. The extent of skeletal fibers in each positive section was evaluated along with the area occupied: + (<25%), ++ (>25-<50%), +++ (>50%-<75%), and ++++ (>75%). As a control group for presence of skeletal muscle fibers, we analyzed the bladder neck sections from surgical specimens of 50 patients submitted to radical prostatectomy.
Fifteen patients fulfilled the selection criteria. All of them could void spontaneously without the need of a indwelling urinary catheter. The mean age of the patients when submitted to TUR-P was 59.8 years (range from 40 - 77). Only 11 patients had their prostatic volume measured by ultrasonography, nine of whom presented a prostatic volume lower than 40 cc.
Before the TUR-P, seven patients underwent urodynamics in which five of them were diagnosed with BOO. In the surgical findings, seven patients presented large median lobe of the prostate, three had bladder diverticulum, and seven showed trabeculated bladder wall. When asked about previous urological surgeries, six patients had undergone renal transplantation. Five of these six had undergone urodynamics in which three had diagnostic of BOO and two underactive detrusor.
After surgical treatment, 11 patients were still able to void spontaneously, and four needed to perform clean intermittent catheterization.
Pathology findings: Hyperplastic muscle fibers and skeletal muscle fibers were found in 15/15 (100%) patients submitted to TUR-P; the percentage of sections showing skeletal muscle fibers for each case varied from 8.3% to 50% (median 25%), and the extent in each section + (32.4%), ++ (29.6%), +++ (18.3%), and ++++ (19.7%). In the controls, 10/50 (20%) patients showed skeletal muscle fibers in the bladder neck; the percentage of sections showing skeletal muscle fibers varied from 0% to 25% (median 3.3%), and the maximum extent in each section in all cases was + (100%).
Interpretation of results
The findings of our study favor that BOO of the patients was due to bladder neck obstruction rather than to BPH. Primary bladder neck obstruction in men was first described by Marion in 1933. To date, the etiopathogenesis of this condition is still unclear. One of the theories attributes the bladder neck dysfunction to abnormalities of the striated urethral sphincter.
In 1966, Manley  confirmed a previous study by Kalischer  that, in children, the skeletal urethral sphincter forms a distinctly marked muscle cap on the prostate, whereas in adults, the muscle fibers are partially atrophied and irregularly dispersed among the smooth muscles of the prostate. Thus, the muscle cap appears much less distinct except in the apex of the prostate where it is part of the urogenital diaphragm.
We speculate that in primary bladder neck obstruction there is a persistence of the cranial part of the skeletal urethral sphincter, which may interfere in the complex process of voiding. The presence of frequent and prominent skeletal muscle fibers in our cases is striking in comparison with the lack of these fibers that were present only in a few patients of the control group.
It is noteworthy that six patients were previously submitted to kidney transplantation and 11 patients (73%) had small prostate size. Voiding dysfunction is frequently seen in the early post transplant period, mainly due to the atrophic changes to the bladder due to the reduction of the urinary volume. It is expected that this bladder dysfunction will be resolved a few months after the transplantation. If there is no improvement, other etiologies such as, anatomic, functional and secondary causes must be taken into consideration . The diagnosis and subsequent treatment of this condition must take place soon, sense there is a significant impact to the patient's quality of life and there is the risk of bladder damage and subsequently, impaired kidney function.