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Prostate Enlargement Demystified

Understanding the Process That May Lead to Chronic Urinary Retention

January 4, 2022

Unlike most body parts, the prostate gland—along with the nose and ears–are organs that enlarge over time. Because the prostate envelops the urinary channel (urethra) similar to a hand wrapped around and squeezing a garden hose, this growth may affect urination, and not for the better! The condition of prostate enlargement is known as BPH—benign prostate hyperplasia—one of the most common plagues of men above 40 years of age. 

What does the prostate do?

The prostate is a reproductive organ that produces a milky liquid that functions as a nutrient and energy vehicle for sperm. Like the breast in so many respects, the prostate consists of numerous glands (70% of the prostate is glands) that produce this fluid, ducts that convey the fluid, and muscle (30% of the prostate is muscle) that contracts to push the fluid through the ducts. At the time of sexual climax, this prostate fluid is released into the urethra where it mixes with the other reproductive secretions—fluid from the seminal vesicles (constituting the bulk of the volume of semen), as well as with sperm from the testes—to form semen.

Reproductive/urinary crossroads

The urethra conducts urine and semen from the bladder and reproductive glands, respectively. The prostate is situated at the crossroads of the urinary and reproductive tracts and completely surrounds the urethra, enabling its many ducts to drain into the urethra. However, this necessary anatomical relationship can potentially be the source of issues for the aging male since the growth of the reproductive organ (prostate) may profoundly affect the function of the urinary organ (urethra).

Prostate enlargement: As inevitable as death and taxes

A young man’s prostate is about the size of a walnut. Under the influence of aging, genetics and the male sex hormone testosterone, the prostate ever so gradually increases in size. As it does so, it may compress and mechanically obstruct the urethra. Remember that the prostate is 30% muscle; excessive prostate muscle tone, often stress-related, can give rise to the same bothersome urinary symptoms that are caused by benign enlargement of the prostate. Many men experience urinary symptoms on the basis of both mechanical obstruction from the compressing prostate tissue as well as a functional obstruction from excessive prostate muscle tone.

Prostate growth varies a great deal from man to man. Some prostates may even grow to the size of a large Florida grapefruit! As the prostate enlarges, it often—but not always—squeezes the sector of the urethra that runs through it, making urination difficult and resulting in a number of annoying symptoms and sleep disturbance. The symptoms that occur may range from a tolerable nuisance to a situation that has a huge negative impact on daily activities and quality of life.

Although larger prostates tend to cause more crimping of urine flow than smaller prostates, the relationship is imprecise and a small prostate can, in fact, cause more symptoms than a large prostate, much as a small hand squeezing a garden hose tightly may affect flow more than a larger hand squeezing gently. A complicating factor is prostate muscle tone that can vary from moment to moment depending upon one’s adrenaline (stress hormone) levels.

Symptoms of BPH can be classified into “obstructive” and “irritative.” Obstructive symptoms are due to the prostate “welded shut like a lug nut,” in the words of one of my patients. These symptoms include a weak stream that is slow to start (hesitant), stops and starts (intermittency), prolonged emptying time, and at times, a stream that is virtually a forceless gravity drip. Another one of my patients described urinary intermittency as “peeing in chapters.” Many men have to urinate a second or third time to empty (double and triple voiding). It is not uncommon to experience after-dribbling of urine (post-void dribbling). Irritative symptoms include a strong desire to urinate requiring hustling to the bathroom (urgency) that gives rise to urinary frequency day and night (nocturia) and at times urinary leakage before arriving to the bathroom (urgency incontinence).


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BPH - Symptoms

BPH - Symptoms

As a result of these symptoms, some men plan their daily routine based upon the availability of bathrooms, sit in an aisle seat on airplanes and avoid engaging in activities that provide no bathroom access. Nighttime urination is particularly bothersome because it is sleep-disruptive and the resultant fatigue can make for a very unpleasant existence. 

Not all men with BPH need to be treated; in fact, many can be observed if the symptoms are livable. There are effective medications for BPH, and surgery is used when appropriate. Three types of medications are used to manage BPH: those that relax the muscle tone of the prostate; others that actually shrink the enlarged prostate gland; and the PDE5 inhibitors that can treat erectile dysfunction as well as BPH. There are numerous surgical means of alleviating obstruction and currently the most popular procedure uses laser energy to vaporize a channel through the obstructed prostate gland.

Prostate enlargement deconstructed

Initial enlargement phase: The prostate naturally enlarges, starting age 40 or so under the influence of genetics, aging, and testosterone. The prostate gradually starts crimping the urethra.

Compensation: As the resistance to flow of urine increases, the bladder muscle compensates by increasing its muscle mass, seen on cystoscopy as trabeculation (thick, interlacing bundles of bladder muscle). Any muscle in the body that works out against resistance will respond by getting thicker and more muscular and the bladder is no exception. By generating higher pressures, the bladder can overcome the increased urethral resistance. This process occurs silently, without creating many symptoms and explains why many men with BPH do not experience symptoms initially.

Compensation continues: As the prostate continues to grow larger and resistance to flow increases, the bladder thickens even more, becoming increasingly muscular. The patient may start to notice obstructive as well as irritative symptoms as the increased muscle mass restricts bladder capacity and the excessive muscle tissue can become “irritable,” contracting on its own without its owner’s permission.

Compensation maxes out: Prostate growth is sustained unabated and may continue indefinitely. However, the bladder muscle can only hypertrophy to a finite extent and there comes a point when the bladder muscle hypertrophy peaks out. As this process progresses, the bladder–despite generating high pressures–is no longer able to empty completely because resistance pressures exceed bladder pressures and the bladder starts retaining urine.

Decompensation: The bladder muscle can no longer fully overcome the urethral resistance and the volume of urine voided diminishes and the volume of urine remaining in the bladder after voiding increases. Bladder contractile pressures slowly decrease and urinary flow rates weaken. Over time, the bladder retains more and more urine until the urine volume that remains after urinating becomes significant. The bladder gradually overstretches and loses tone. This often manifests with urinary urgency, frequency and possibly urinary leakage and bed wetting as the bladder never empties completely and tends to overflow. At times, the patient can get to this point without having experienced any significant prior symptoms, explained by the compensation process.

Decompensation continues: Decompensation is a slowly progressive problem and as the bladder muscle continues to weaken, lose tone and become flabbier, flow rates get slower, voided volumes less, residual volumes remaining in the bladder more, and eventually the patient gets to the point where he cannot urinate at all. This is a full-fledged case of chronic urinary retention, the inability to empty the bladder based upon a protracted course of obstruction, compensation and decompensation. At this point it is possible that kidney function may be compromised by the over-distended bladder backing up the plumbing. This painless condition is as opposed to acute urinary retention, which is a sudden, acutely painful inability to urinate often precipitated by situations such as surgery, anesthesia, constipation, etc.

Image of bladder trabeculation within the urinary bladder via cystoscopy. If this was your abdomen, it would be called a 6-pack!

The graph that follows helps explain the process of BPH. Graph is from an article by Steve Kaplan et al entitled: Noninvasive Pressure Flow Study in the Evaluation of Men with Lower Urinary Tract Symptoms Secondary to Benign Prostate Hyperplasia: A Review of 50,000 Patients from Journal of Urology, Vol 204, 1296-1304, Dec 2020.

The top graph illustrates gradually increasing bladder pressures that occur with aging (bladder compensation process) followed by declining bladder pressures (decompensation process).

The second graph illustrates the declining urinary flow rates that occur with aging, manifesting as a weaker and weaker urinary stream.

The third graph illustrates declining voided volumes of urine that occur with the aging process.

Ignore the fourth graph. 

The fifth graph illustrates increasing post-void residual volumes (amount of urine left in the bladder after voiding) that occurs with the aging process.

Management of chronic urinary retention

Bladder decompensation clearly is not a good thing since it indicates that the BPH process is advanced and possibly irreversible, with a likelihood that bladder function may be permanently impaired and spontaneous voiding will never resume. Fortunately, this is not always the case. The goal of BPH management is to arrest the process before bladder decompensation occurs. This can be achieved with medications or surgical intervention to alleviate the obstruction when the patient is in the compensation stage.

Initial management of chronic urinary retention involves placement of a urinary catheter to decompress the bladder. It is possible to have several liters of urine in the bladder and after catheter placement, the kidneys may produce copious volumes of urine in response to the relief of this chronic obstruction. Medications to relax/shrink the prostate are typically started. The patient is taught the technique of self-intermittent catheterization in which he learns to pass a catheter at least four times daily in order to enable emptying of the urinary bladder. This serves to empty the bladder completely, facilitate the return of bladder tone and contractility, provide an opportunity to urinate spontaneously prior to each catheterization, and enable measuring the voided and residual volumes that will indicative of improvement/resolution of the problem.

Subsequent management includes cystoscopy and urodynamics to evaluate the lower urinary tract anatomy and bladder function, respectively. Based upon these tests, surgical interventions to reduce outlet resistance may be in order. 

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