Urology: Bladder path

Anatomy of the Urethra and Bladder Support

• Urethral Structure: The urethra is described as a circular membrane that conveys urine from the bladder to the external environment.

• Sphincter Control:

  • Internal Sphincter: Controlled by the autonomic nervous system. It is involuntary, meaning humans do not have conscious control over its function.

  • External Sphincter: This sphincter allows for voluntary control, enabling a person to decide when to initiate voiding.

• Medial Umbilical Ligament:

  • Embryological Origin: This ligament represents a superior component that is a remnant of the urachus.

  • Urachus Function: In utero, the urachus functions as an excretory organ for the fetus.

  • Clinical Significance: If the urachus ligament reopens (becomes patent), fluid or urine can leak from the bladder and tracks out through the umbilicus. This path is also a site where cysts and other pathologies, including cancers or small cell pathologies, can form. Patients may present with pain or liquid drainage in the umbilical region.

Bladder Physiology and the Micturition Cycle

• The Two Phases of Bladder Function:

  1. Filling Phase: The bladder accumulates urine coming from the ureters.

  2. Voiding Phase: The process of emptying the bladder.

• Filling Dynamics and Continence:

  • Continence (the ability to hold urine) depends on the sphincters holding urine in place and the physiological expansion of the bladder, which keeps internal pressure low.

• Stretch Receptors: Located within the detrusor muscle, these sensors detect distension and signal the brain.

  • Type A Receptors: These sense low-volume urine.

  • Type C Receptors: These detect high-volume urine and are specifically associated with painful sensations when the bladder is overextended.

• Neural Pathways of Voiding:

  • Once a certain distension threshold is met (typically starting around $400\,ml$), receptors send a message to the spinal cord, which then relays the signal to the Pons Micturition Center in the brain.

  • The Pons Micturition Center sends motor signals back down to:

    1. The Detrusor Muscle: Instruction to contract.

    2. The Sphincters: Instruction to relax and open (applies to both internal and external sphincters).

• The Role of the Prefrontal Cortex:

  • The prefrontal cortex has executive control over the Pons Micturition Center. It can suppress the voiding signal (e.g., preventing one from wetting the bed at $2:00\,AM$ or $3:00\,AM$).

  • Pathological Changes: Neuromuscular pathologies like strokes, dementia, or Alzheimer’s disease affect the prefrontal cortex, leading to voiding dysfunction. If the signal to the pons is lost, the patient may urinate constantly; if the pons is damaged, the patient may be unable to void.

Developmental Differences in Physiology

• Infants: Babies lack high-level cortical maturation. Their voiding is governed by the Micturition Reflex. The signal travels from the bladder to the spinal cord and directly back to the detrusor and sphincters, causing spontaneous voiding without brain intervention.

• Adults: As toilet training occurs and the brain develops, these signals are regulated by the higher centers of the brain (prefrontal cortex).

Overactive Bladder (OAB) Syndrome

• Definition: A clinical syndrome characterized by a sudden and compelling need to urinate. It is more common in females.

• Hallmark Symptoms:

  • Urgency: The defining symptom (‘I’ve got to go’).

  • Urge Incontinence: Leaking if the bathroom is not reached in time.

  • Frequency: Needing to void very often (e.g., every $10$ to $15$ minutes).

• Workup and Diagnosis:

  • History and objective assessment (voiding diaries).

  • Physical exam and Urinalysis/Culture to rule out Urinary Tract Infection (UTI).

  • Post Void Residual (PVR): Assessed via sonogram to ensure the patient is not in retention.

  • Urodynamic Studies: Measuring contractility and capacity using instruments inside the bladder.

  • Urine Cytology: Used primarily if there is a risk of cancer or hematuria.

• Treatment Options:

  1. Behavioral Therapy: Bladder training and timed voiding (e.g., voiding every $45$ minutes regardless of urge).

  2. Pharmacologic Management: Anticholinergics.

     • Side Effects: Dry mouth and constipation are most common; others include blurred vision and dizziness.

     • Insurance Note: Documentation of medical need is often required for more expensive brand-name versions.

  3. Vaginal Sensors: Used to stimulate and strengthen pelvic floor muscles.

  4. Interstim: Implanted electrical devices to stimulate the nerves.

  5. Botox: Injections every few months to relax the bladder.

  6. Surgical Options: Cystoplasty (bladder augmentation) using a piece of intestine to expand the bladder size.

Urinary Incontinence and Retention Types

• Stress Urinary Incontinence: Loss of urine during physical exertion. Can be treated with a pessary in the vagina to support pelvic musculature, transurethral bulking agents, or a sling (two-bone vesical sling) to lift the urethra.

• Overflow Incontinence:

  • Mechanism: The bladder is obstructed (e.g., by the prostate) or the detrusor muscle fails (e.g., in long-term diabetes). The bladder fills until pressure exceeds the sphincter resistance, causing continuous leaking.

  • Symptom Masking: Patients might report they are peeing ‘normally,’ but they are actually only passing ‘dribbles’ of overflow. They often suffer from nocturia and frequency without pain, as they have adjusted to the volume over time.

• Neurogenic Bladder: Nerve damage (from accidents, diabetes, or vitamin $B_{12}$ deficiency) disrupts communication.

  • Spastic/Hyperreflexic: Constant contraction.

  • Underactive/Hypotonoplast: Failure to contract leading to massive distension.

Urinary Tract Infections (UTI) and Cystitis

• Common Organisms: E. coli (most common), Enterobacteria, Klebsiella, Staph, and Enterobacter.

• Risk Factors: Sexual intercourse, history of UTI, diabetes, and menopause.

• Clinical Pearl: In postmenopausal women, dysuria may be caused by vaginal mucosal dryness due to estrogen absence rather than infection; steroid or estrogen creams are effective treatments.

• Mandatory Protocol: Always perform a pregnancy test for any female of childbearing age before procedures like CAT scans to avoid fetal exposure.

• Diagnostic Criteria:

  • Urinalysis: Positive leukocyte esterase and positive nitrites.

  • Culture: Significant if there are more than $100,000\,CFU/ml$ (colony forming units).

  • Note on Colonization: A Foley catheter will always eventually show bacteria colonization; do not treat based on colonization alone if the patient is asymptomatic.

• Post-Obstructive Diuresis: If a patient passes more than $200\,ml/hr$ for at least two consecutive hours after catheterization to relieve an obstruction, they must be monitored for electrolyte imbalances and potentially admitted.

Specialized Diagnostic Findings

• Urine Color and Clarity:

  • Clear/Pale Yellow: Good hydration.

  • Dark Yellow: Dehydration.

  • Brown/Red: Possible liver disease or hematuria.

  • Cloudy: Associated with infection or sediments, but not definitive of infection without symptoms/culture.

• Specific Markers:

  • pH: High or low values influence the type of kidney stones formed.

  • Protein/Glucose: Leaking indicates kidney disease or diabetes. Proteinuria should be confirmed with a $24$-hour urine collection.

  • Occult Blood: Often misleading due to dietary factors; red blood cell (RBC) count under a microscope is the true marker for hematuria.

• Antibiotic Sensitivity (MIC): The Minimum Inhibitory Concentration is the lowest amount of medicine needed to kill the organism. In outpatient settings, oral agents (like nitrofurantoin) are preferred over IV (like amikacin).

Emphysematous Cystitis and Bladder Cancer

• Emphysematous Cystitis: A potentially fatal condition where gas forms in the bladder wall, commonly caused by E. coli. Visible on ultrasound or KUB/images as black gas pockets in the bladder wall.

  • Case Lesson: A $72$-year-old diabetic patient was undertreated (only $1$ day of IV antibiotics instead of the standard $5$ to $7$ days). Clinicians must treat the patient’s symptoms and empirical data (culture results) rather than just imaging. If a patient is afebrile and asymptomatic, home treatment with a culture-specific antibiotic may be appropriate.

• Bladder Neoplasms:

  • Risk Factors: Smoking (primary), Schistosomiasis (common in China, Africa, and the Middle East), occupational chemical exposure.

  • Presentation: Hematuria (gross hematuria is more concerning than microscopic).

  • Diagnosis: Cystoscopy is the test of choice.

  • Treatment: Muscle-invasive cancer requires a radical cystectomy. Non-invasive cases may be managed with intravesical treatments.

  • Prognosis: Very high for early-stage/in situ disease ($97\%$ five-year survival), but decreases significantly as stage advances.

Questions & Discussion

• Q: Does the signal in babies skip the brain?

  • A: Yes, in babies, it goes from the bladder to the spinal cord and right back. This is the micturition reflex.

• Q: Is BPH (Benign Prostatic Hyperplasia) mediated by nerves?

  • A: No, BPH is an obstructive mechanism where the prostate physically blocks the pathway; it is not nerve-mediated like the neurogenic models discussed.

• Q: Should you use a Coude catheter first?

  • A: No, use a regular catheter first. If it cannot pass the prostate, then use the Coude, which has a curved tip to rise over the obstruction.

• Q: If you see blood when inserting a catheter, what should you do?

  • A: Stop immediately. You may create a false passage in the urethra.

• Q: What is the first response to a non-draining catheter?

  • A: First, try to irrigate the catheter to check for obstruction. If that fails, change the Foley. If it still doesn't drain, check for bladder distension via palpation or bedside ultrasound. If the bladder is empty, provide a fluid challenge before calling nephrology.