Many patients are initially reluctant to seek treatment for pelvic organ prolapse and will later cite that it was a change in their bladder function, including difficulty emptying, suprapubic pressure, nocturia, new-onset urgency, or urinary incontinence, that prompted them to consult a specialist. Although pelvic floor disorders can cause these symptoms, there are other pathologies, such as pelvic or bladder wall carcinoma, that may present with similar symptoms. In this chapter, we will briefly review the pertinent anatomy, physiology, and diagnostic tools that are utilized when evaluating bladder function. Our discussion will focus primarily on the lower urinary tract.

Anatomy

The genitourinary system is divided into upper and lower tracts. The upper urinary tract (UUT) consists of the renal parenchyma and the collecting system components (renal pelvis and ureters). The bladder and urethra compose the lower urinary tract (LUT). The kidneys lie in the retroperitoneum and weigh approximately 135 g in women. The superior margin of the left kidney is located at the level of the 12th thoracic vertebral body and the right kidney is 1 to 2 cm lower due to displacement by the liver.¹

The ureters are also located in the retroperitoneum. They vary in length from 22 to 26 cm and travel from the renal pelvis located at the level of the 1st to 2nd lumbar vertebral body to the posterior bladder base.¹ There are three distinct regions where the ureteral lumen narrows: the ureteropelvic junction, where the ureter crosses over the iliac vessels and also upon entering the bladder, or ureterovesical junction. The distal ureter traverses obliquely through the muscular layers of the bladder base and terminates at the ureteral orifice on the trigone. This results in distal ureter constriction when the bladder contracts. For this reason, ectopic ureteral orifices that are positioned lateral to the trigone are at risk for urinary reflux. Ureteral orifices that are medial to the normal placement on the trigone traverse thicker muscular layers that surround the bladder neck and proximal urethra and are more susceptable to ureteral obstruction.²

The bladder is located in the lower pelvis and the superior surface of the bladder (located at the level of the pubic bone) has an apex where a fibrous remnant of the allantois, the urachus, once drained the fetal bladder. The posterior-inferior surface of the bladder including the trigone is called the base. The remaining two bladder surfaces on the left and right are described as being positioned inferior-lateral.

The internal surface of the bladder, ureters, and renal pelvis are lined with transitional epithelium called the “urothelium.” This layer is usually six to seven cells thick and rests on the lamina propria, a supporting structure (Figure 7-1).¹ The urothelium is smooth when the bladder is full and contracts into folds when the bladder empties. The lamina propria is composed of fibroelastic connective tissue that allows distension and contains numerous blood vessels and smooth muscle fibers called the muscularis mucosae. The lamina propria is an anatomic landmark that is critical for the staging and prognosis of bladder cancers. Bladder tumors confined to the urothelium are considered superficial. Once a tumor has invaded the lamina propria it is called an “invasive” bladder cancer and carries the risk of hematogenous spread.

Lateral to the lamina propria lays the branching and interlacing smooth muscles of the bladder wall. The 3 muscle types are inner longitudinal, middle circular, and outer longitudinal. In the upper part of the bladder near the urachus these layers are not very pronounced or distinct. Near the bladder base and bladder neck the detrusor muscle is clearly layered² and funnels to the internal urethral meatus.

On magnetic resonance imaging (MRI), the female urethra measures approximately 2.65 cm in length, extending from the bladder neck to the urethral meatus.³ The sphincter muscle is composed of both striated and smooth muscle layers. The striated urogenital sphincter muscle is intimately associated with the distal two-thirds of the urethra.³ Urethral function is less well studied than bladder function; however, Rud et al. attempted to determine the factors responsible for continence by measuring urethral pressure awake and under general anesthesia. By comparing pressures between awake and anesthetized patients, they determined that one-third of the resting pressure of the urethra is derived from the striated urethral sphincter, one-third from the smooth urethral sphincter, and final third from mucosal coaptation from urethral intravascular blood pressure.⁴

Radiographic and histologic studies have shown that over time there is loss of the striated urethral sphincter muscle that corresponds to the increasing incidence of urinary incontinence with aging.⁵ Perucchi et al. used histologic sectioning of female cadaveric urethras to estimate that approximately 2% of sphincter muscle fibers are lost per year as a woman ages. The overall decrease in urethral sphincter muscle density with age is also correlated with a shorter urogenital sphincter and longer vesical neck, all of which more commonly associated with stress urinary incontinence and poorer pelvic floor muscle function.³

Function

Innervation

Sensory impulses from the bladder relay information about distension, inflammation, and other stimuli along afferent nerves that accompany primarily the (efferent) parasympathetic (pelvic, S2–S4) and the sympathetic (hypogastric, T10-L2) nerves. The afferents terminate on interneurons mainly in the posterior horn of the spinal cord. Targets of the interneurons include the periaqueductal gray matter of the midbrain and eventually the pontine micturition center.⁶

Bladder afferents include δ fibers and C fibers. δ fibers are myelinated mechanoreceptors that increase their firing with increases in bladder wall tension, whereas C fibers are unmyelinated nocioceptors thought to be primarily involved in sensations of urinary urgency and bladder pain. They fire when in contact with noxious chemical irritants, increased urinary potassium, and decreased pH or cold temperatures. During normal bladder filling, δ fibers are active and C fibers are silent.⁶ During noxious filling, for example, during acute urinary tract infection (UTI), C fibers become more active and generate the sensation of discomfort.

Motor innervation of the LUT occurs through the autonomic and somatic nervous systems. The hypogastric nerve carries preganglionic sympathetic nerve fibers that originated in the T11 to L2 segments in the spinal cord, to the bladder and urethra.⁷ Stimulation of these fibers results in activation of the β-adrenergic inhibitory receptors in the bladder wall resulting in detrusor relaxation and the α-adrenergic excitatory receptors in the urethral smooth muscle resulting in urethral contraction (Figure 7-2). This promotes urinary storage easily remembered with the mneumonic “sympathetic = storage.” The pelvic nerve carries preganglionic parasympathetic nerve fibers that originated from spinal segments S2 to S4. Their stimulation results in excitation of muscarinic receptors in the bladder wall with an end result of bladder contraction and release of nitrous oxide at the proximal urethra causing relaxation of the urethral smooth muscle (Figure 7-3). These actions promote bladder emptying “parasympathetic = pee.” The pudendal nerve is a somatic motor nerve that activates the striated urethral sphincter. It arises in S2–S4 motor neurons in Onuf nucleus and when stimulated results in striated sphincter contraction.

Normal Storage and Emptying

Normal bladder filling and storage require the bladder to accommodate increasing volumes of urine, with appropriate sensation and minimal increases in intravesical pressure. To maintain continence, the urethral sphincter has to remain closed at rest and remain closed with increases in intravesical pressure. As bladder filling increases, the forces at the bladder neck increase and the intraluminal pressure of the urethra increases. This is known as the “guarding reflex.” As the bladder continues to fill, the afferent activity increases and alerts higher brain centers. Once voiding is appropriate, the storage phase is then switched to the voiding phase by the activation of the pontine micturition center and inhibition of the pontine continence center. For the bladder to empty effectively, the smooth and striated urethral sphincters and the pelvic floor need to relax to allow the outflow of urine. This is followed by a coordinated contraction of the bladder smooth muscle.

Functional Classification

The function of the LUT is to store urine between voids and to empty the bladder when appropriate. When patients present with LUT symptoms related to urine storage or voiding, the dysfunction can usually be categorized as being a failure to store or a failure to empty and can be attributed to either the bladder or the urethra. For example, a woman who presents with urinary incontinence may have a bladder etiology such as overactive bladder or a urethral etiology such as stress urinary incontinence. This “Functional Classification System” was introduced by Alan Wein (Table 7-1). It provides a logical framework for understanding the possible etiologies of patient symptoms.

Terminology

Confusion surrounding the description of patient symptoms, prolapse quantification, LUT syndromes, and urodynamic diagnoses has been significantly reduced due to the collaborative work of the International Urogynecologic Association (IUGA) and International Continence Society (ICS). Both of these organizations have standardized the terminology used to describe female pelvic floor function and dysfunction.⁸ Table 7-2 lists terminology used to describe patient storage and voiding symptoms. According to IUGA/ICS Terminology, symptoms are any departure from normal structure, function, or sensation, experienced by a woman and indicative of disease or a health problem. Symptoms can be described by the patient or the caregiver.⁸ Signs are any abnormality indicative of disease or a health problem that can be seen by the examiner. Examples of signs are stress or urgency urinary incontinence, extraurethral incontinence (fistula), or stress incontinence with prolapse reduction (occult or latent incontinence). Lastly, diagnoses are made based on the correlation between symptoms, signs, and any relevant diagnostic investigations.

Diagnosis of bladder dysfunction is highly reliant on patient history. A detailed history of the patient’s urinary storage and voiding habits should be obtained. The best way to elicit patient symptoms is to simply ask. Each symptom can be explored by inquiring when the symptom started, what it is associated with, how long it lasts, and what makes it better or worse. It is also important to ask specifically about how much the symptom bothers the patient. Some symptoms may occur infrequently but because of their unpredictability be the most bothersome (ie, urgency incontinence).

Many diseases of the central nervous system may result in lower urinary tract dysfunction (LUTD). Lesions may be located at or above the brainstem, within the spinal cord, or locally within the bladder itself. To elicit these symptoms, women should be asked about any changes in their overall health before or at the time their LUT symptoms started. Additional questions to explore LUT changes should include questions about changes in gait, balance, sensory, or motor function of the lower extremities, and bowel function.

Women who have recently undergone surgery and present with new LUT symptoms may have a surgical complication. Complaints of continuous urinary leakage at rest and activity herald the development of a genitourinary fistula. Women who have undergone radical resections of the colon or uterus for cancer can present with injuries of the pelvic plexus that manifest as urinary incontinence due to incomplete emptying of the bladder. The increasing use of surgical mesh in surgeries for pelvic floor reconstruction requires a low threshold for suspecting that the LUT symptoms may be due to “foreign-body” in either the bladder or urethra.