An enlarged bladder, also known as bladder hypertrophy, occurs when the bladder becomes larger than its typical size. This condition often results in incomplete emptying, where the bladder cannot fully expel the urine it holds. When the bladder walls are overstretched, they can thicken and expand over time.
Obstruction of Urine Flow
A common reason for an enlarged bladder is a physical blockage that obstructs urine outflow. When urine cannot leave the bladder freely, it accumulates, causing the bladder to stretch. This continuous strain can lead to a loss of elasticity in the bladder walls.
One frequent cause of obstruction, particularly in men, is Benign Prostatic Hyperplasia (BPH), an age-related non-cancerous enlargement of the prostate gland. As the prostate grows, it can compress the urethra, the tube that carries urine from the bladder, impeding urine flow. This compression makes it difficult for the bladder to empty completely, leading to urine retention.
Urethral stricture also causes obstruction, involving a narrowing of the urethra due to scar tissue, inflammation, or injury. This narrowing restricts urine flow, forcing the bladder to work harder to empty. Bladder stones can also block the bladder outlet, forming from mineral salts in the urine and growing large enough to create a physical barrier.
Growths in or near the bladder, whether benign or malignant, can cause a physical obstruction. Tumors can directly block the bladder outlet or compress the urethra, preventing complete bladder emptying. Management of these obstructions can prevent further bladder enlargement and potential kidney damage.
Nerve Signal Disruption
Proper bladder function relies on communication between the bladder and the brain through nerve signals. These signals orchestrate the bladder’s ability to store urine and then contract to empty it, while ensuring the urinary sphincter relaxes. When these nerve pathways are damaged or disrupted, the bladder may not receive the necessary messages to contract effectively, or the sphincter might not relax as it should, leading to incomplete emptying.
Conditions that damage the nervous system can impact bladder control. Spinal cord injuries, for instance, can interrupt nerve signals between the brain and the bladder, resulting in a loss of coordinated bladder function. This neurological damage can prevent the bladder from sensing fullness or contracting to expel urine, causing it to retain large volumes.
Various neurological diseases also impair nerve function. Multiple sclerosis, Parkinson’s disease, and stroke can all affect the nerves responsible for bladder control. These conditions can lead to an overactive bladder that contracts involuntarily or an underactive bladder that struggles to empty, both resulting in chronic urine retention.
Diabetes is another condition that can cause nerve damage, known as diabetic neuropathy. High blood sugar levels can harm nerves throughout the body, including those that supply the bladder. This damage can reduce the bladder’s sensitivity and its ability to contract, leading to incomplete emptying.
Bladder Muscle Weakness
The bladder’s ability to empty effectively depends on the strength and coordinated action of its muscular wall, primarily the detrusor muscle. This muscle contracts to push urine out of the bladder. If the detrusor muscle becomes weak or underactive, it may not generate sufficient force to expel all the urine, leading to residual urine after urination.
When the bladder consistently retains urine, it becomes chronically overstretched, which can further damage muscle fibers. This prolonged distension can diminish the muscle’s elasticity and ability to contract, exacerbating incomplete emptying.
Aging is a common factor contributing to detrusor muscle weakness. As individuals age, there can be a natural decline in muscle strength throughout the body, including the bladder. This age-related weakening can reduce the bladder’s efficiency in emptying, leading to increased residual urine volumes.
Beyond aging, chronic overdistension, resulting from any cause of prolonged urine retention, directly impacts the detrusor muscle. The constant stretching can lead to structural changes in the muscle tissue, making it less effective at contracting. Some systemic medical conditions can also impact overall muscle health, potentially contributing to bladder muscle weakness.
Additional Factors
Certain medications can interfere with the bladder’s normal function. Drugs such as anticholinergics, often used for conditions like overactive bladder or irritable bowel syndrome, can relax the bladder muscle too much or prevent the sphincter from relaxing, leading to urine retention. Antihistamines and some antidepressants can also have similar effects, impairing the bladder’s ability to empty.
Habitually delaying urination or “holding it in” for extended periods can also contribute to bladder issues. Regularly overstretching the bladder by delaying emptying can weaken its muscle fibers and reduce its elasticity. This behavior can eventually lead to chronic incomplete emptying.
In some rarer instances, an enlarged bladder can be linked to congenital abnormalities. These are structural issues present from birth within the bladder or urinary tract. Such abnormalities might include malformations that impede urine flow or affect the bladder’s natural development, predisposing an individual to bladder enlargement from an early age.