Loyalist College Module 3: Comprehensive Study Guide to Urinary System Pathology

Urinary System Anatomy, Physiology, and Terminology

• System Components: Often referred to as the Excretory System, it consists of the following structures:
  • Two kidneys.
  • Two ureters.
  • One urinary bladder.
  • One urethra.
• Functional Unit: The nephron is the functional unit of the kidney, responsible for:
  • Filtration: Processing waste products from the blood.
  • Resorption: Balancing levels of water and essential nutrients.
  • Secretion: Eliminating excess substances out of the body as urine.
• Essential Terminology:
  • Bacteriuria: The presence of bacteria in the urine.
  • Blood Urea Nitrogen (BUN): A clinical laboratory test used to assess kidney function.
  • Dysuria: Painful or difficult urination.
  • Glomerular Filtration Rate (GFR): A primary assessment metric for kidney function.
  • Hematuria: The presence of blood in the urine.
  • Incontinence: The involuntary emptying of the urinary bladder.
  • Intravenous Pyelogram (IVP) / Intravenous Urogram (IVU): Specific radiographic procedures using contrast to visualize the urinary tract.
  • Micturition: The physiological process of bladder emptying or urination.
  • Oliguria: A significantly reduced output of urine.
  • Proteinuria: The presence of protein in the urine.
  • Pyuria: The presence of pus in the urine.
  • Retroperitoneum: The anatomical cavity located behind the peritoneum; it contains the kidneys and the pancreas.
  • Serum Creatinine (SCr) level: A blood test used for the assessment of kidney function.
  • Ureteropelvic Junction (UPJ): The point where the renal pelvis connects to the ureter.
  • Ureterovesical Junction (UVJ): The point where the ureter enters the urinary bladder.
  • Voiding Cystourethrogram (VCUG): A functional study of the bladder and urethra performed during micturition.

Anatomical and Physiological Characteristics of Urinary Organs

• Kidneys:
  • Shape: Bean-shaped with medially concave and laterally convex borders.
  • Structure: Divided into upper and lower poles.
  • Location: Retroperitoneal organs generally situated between levels $T12$ and $L3$. They lie in an oblique plane with the hilum rotated approximately $30$ degrees anteromedially toward the aorta.
  • Positioning Varaiations: The right kidney is typically lower (caudal) than the left due to the liver. In sthenic individuals, the superior border is at $T12$. Hypersthenic individuals have higher kidneys, while asthenic individuals have lower ones.
• Ureters:
  • Length: Approximately $10-12\,inches$.
  • Function: Transport urine from the renal pelvis to the bladder through slow, rhythmic peristaltic contractions.
  • Attachment: Connect from the UPJ of the kidney to the posterolateral surface of the bladder at the UVJ.
• Urinary Bladder:
  • Structure: A musculomembranous sac acting as a urine reservoir, located posterior and superior to the pubic symphysis.
  • Capacity: An adult bladder holds roughly $500\,mL$ of fluid. The urge to urinate typically occurs when the bladder contains approximately $250\,mL$.
  • Movement: When empty, it sits in the pelvic cavity; as it fills, it expands superiorly and anteriorly into the abdominal cavity.
• Urethra:
  • Definition: A musculomembranous tube with a sphincter at the bladder neck.
  • Female/Internal Reproductive Organs: Length is approximately $4\,cm$.
  • Male/External Reproductive Organs: Length is approximately $17.5-20\,cm$. It also functions as the excretory canal for the reproductive system.
  • Prostate: A small glandular body surrounding the proximal urethra in males; it is part of the reproductive system but anatomically critical to urinary function.

Imaging Modalities and Technical Considerations

• Imaging Modalities:
  • Ultrasound (US): Used for identifying cysts, abscesses, and hydronephrosis without ionizing radiation.
  • Computed Tomography (CT): Highly effective for detecting calculi (CT KUB protocols) and staging tumors.
  • Plain Radiography: Includes Urograms, Cystograms, and VCUGs.
  • Magnetic Resonance Imaging (MRI): Superior for staging bladder carcinoma and assessing the prostate.
• Contrast Media: Water-soluble, non-ionic iodinated contrast, known as Low-Osmolar Contrast Media (LOCM), is the standard for urinary imaging to maximize patient safety and comfort.
• Radiographic Technique:
  • Positioning: Images must include the superior borders of both kidneys down to the superior portion of the pubic bones to ensure the bladder is visible. For KUB projections, the pelvis must be symmetric, and spinous processes must be centered over vertebral bodies.
  • Respiration: Images should be captured on FULL expiration to allow the diaphragm to move superiorly, preventing abdominal compression. The kidneys can move up to $1\,inch$ with respiration and may drop up to $2\,inches$ when moving from supine to an upright position.
  • Density/Contrast: Proper imaging should clearly demonstrate the kidney shadows, psoas major muscle, and the lumbar transverse processes.
  • Sterile Technique: A cystogram is a minor sterile procedure. While it does not require sterile gowning, strict hygiene is necessary to prevent nosocomial urinary tract infections.

Congenital and Hereditary Pathologies

• Unilateral Renal Agenesis (Solitary Kidney):
  • Description: Absence of one kidney due to the failure of the embryonic renal bud or vascular system.
  • Diagnostics: Uses US or CT to confirm the absence of tissue and the ipsilateral renal artery.
  • Imaging Sign: The "Lying down adrenal" sign (elongated appearance of the adrenal gland when not molded by a kidney).
• Supernumerary Kidney: A rare anomaly featuring one or more extra (accessory) kidneys. These are usually small, rudimentary, and possess their own pelvis, ureter, and blood supply. They function normally but can lead to secondary infections.
• Renal Hypoplasia: A small kidney that is a miniature replica of a normal kidney, maintaining a normal meat-to-collecting system ratio. It must be differentiated from atrophic kidneys.
• Compensatory Hypertrophy: The enlargement of a kidney to handle increased functional demand when the other kidney is absent, hypoplastic, or removed via nephrectomy.
• Malrotation: Abnormal rotation that creates a bizarre appearance of the renal parenchyma and calyces on imaging, though function usually remains normal.
• Ectopic Kidneys: Kidneys located outside the normal renal fossa. Common sites include the pelvic cavity (Pelvic Kidney) or above the diaphragm (Intrathoracic Kidney).
• Horseshoe Kidney: The most common fusion anomaly; the kidneys are malrotated and fused at the lower poles by a band of tissue. This often leads to obstruction at the UPJ.
• Complete Fusion Anomalies: Rare anomalies resulting in a single irregular mass; names include pancake, cake, disc, lump, or doughnut kidney.
• Duplication (Duplex Kidney): The most common congenital ureteral abnormality.
  • Incomplete: Bifid Pelvis (two systems unite proximally) or Bifid Ureters (unite distally).
  • Complete: Two separate pelves and ureters that enter the bladder at separate orifices.
• Ureterocele: Cystic dilatation of the distal ureter near its insertion into the bladder.
  • Imaging Sign: The "Cobra head sign" (a round density with a thin radiolucent halo in a filled bladder).

Inflammatory Pathologies

• Pyelonephritis: Suppurative inflammation of the kidney and renal pelvis caused by pyogenic bacteria. It typically ascends from the bladder.
  • Symptoms: High fever, chills, back pain, dysuria, and pyuria.
  • Acute Imaging: Generalized kidney enlargement and delayed calyceal opacification.
  • Chronic Imaging: Patchy calyceal clubbing and parenchymal scarring.
• Cystitis: Inflammation of the urinary bladder, highly common in women due to the shorter urethra. Chronic cystitis results in decreased bladder size and wall irregularity.

Urinary Calculi and Obstructions

• Urinary Calculi (Kidney Stones): Solid masses of crystals, usually forming in the kidneys due to hypercalcemia or urinary stasis.
  • Radiopacity: Over $80\%$ contain enough calcium to be seen on plain film. Radiolucent stones consist of oxalates or uric acid.
  • Staghorn Calculi: Large stones that conform to and fill the entire renal pelvis and calyces.
  • Treatment: Includes fluid intake, Lithotripsy (shock waves), and Chemolysis.
• Hydronephrosis: Dilation of the renal pelvis and calyces due to fluid buildup caused by obstruction.
• Hydroureter: Dilation of the ureter greater than $3\,mm$ due to blockage. Common obstruction sites include the UPJ and UVJ.

Renal Cysts, PKD, and Neoplasms

• Simple Renal Cysts: Very common fluid-filled, unilocular masses. Imaging shows the "beak or claw sign" (smooth radiopaque rim).
• Polycystic Kidney Disease (PKD): An inherited disorder causing multiple cysts that progressively impair renal function.
  • Complications: Associated with liver cysts ($33\% \text{ of cases}$) and cerebral (saccular) aneurysms ($10\% \text{ of cases}$).
  • Imaging Sign: "Swiss cheese" nephrogram pattern on IVU.
• Renal Cell Carcinoma (RCC): Also known as Hypernephroma, it is the most common kidney cancer (usually in patients over $40$).
  • Symptoms (Classic Triad): Hematuria, flank pain, and a palpable abdominal mass.
• Bladder Carcinoma: Known as Urothelial Carcinoma; primary risk factors are cigarette smoking and exposure to industrial chemical dyes. CT shows finger-like projections or wall thickening.

Renal Failure and Systemic Conditions

• Acute Renal Failure (ARF/AKI): Rapid decline in function characterized by oliguria ($<400\,mL/24\,h$).
  • Causes: Prerenal (blood flow issues), Postrenal (obstructions), or Nephrotoxic agents (contrast or antibiotics).
• Chronic Renal Failure (CRF/CKD): Gradual loss of function over time leading to uremia. Imaging shows small, echogenic kidneys on ultrasound.
• Benign Prostatic Hyperplasia (BPH): Non-cancerous enlargement of the prostate, affecting up to $90\%$ of men over $80$. It causes a "fishhook appearance" of the distal ureters on IVU. Surgical treatment includes TURP (Transurethral Resection of the Prostate).
• Renal Hypertension: High blood pressure caused by narrowing of renal arteries. CT Angiography can show a "beaded appearance" if caused by fibromuscular dysplasia.

Questions & Discussion

• Scenario/Prompt: "What other pathology is noted? Think back to our GI Module…" (referring to a case study of an 80-year-old with weight loss and rectal bleeding).
• Instructor Note: "Think back to CV modules in Pathology 1" when discussing the beaded appearance of renal arteries in fibromuscular dysplasia.
• Final Reminder: The next lesson will transition to pathologies and conditions of the Reproductive System.