A 62-year-old man comes to the physician because of increased frequency of urination. He also says that he needs to urinate 4 to 5 times nightly and has difficulty initiating a urinary stream. He has had several episodes of acute cystitis treated with ciprofloxacin during the past year. Digital rectal examination shows a firm, symmetrically enlarged, non-tender prostate. This patient is most likely to develop which of the following complications?

Irreversible decrease in renal function

Inflammation of the renal interstitium

Abscess formation in the prostate

Impaired intracavernosal blood flow

A 70-year-old woman comes to the physician for the evaluation of loss of urine for the last several months. She loses small amounts of urine without warning after coughing or sneezing. She also sometimes forgets the names of her relatives. She is retired and lives at an assisted-living facility. She has type 2 diabetes mellitus and hypertension. Her older sister recently received a ventriculoperitoneal shunt. She does not smoke or drink alcohol. Medications include metformin and enalapril. Vital signs are within normal limits. She walks without any problems. Sensation to pinprick and light touch is normal. Which of the following is the most likely underlying cause of this patient's symptoms?

Decreased cerebrospinal fluid absorption

Bacterial infection of the urinary tract

A 37-year-old woman presents to the Emergency Department after 8 hours of left sided flank pain that radiates to her groin and pelvic pain while urinating. Her medical history is relevant for multiple episodes of urinary tract infections, some requiring hospitalization, and intravenous antibiotics. In the hospital, her blood pressure is 125/83 mm Hg, pulse of 88/min, a respiratory rate of 28/min, and a body temperature of 36.5°C (97.7°F). On physical examination, she has left costovertebral tenderness and lower abdominal pain. Laboratory studies include a negative pregnancy test, mild azotemia, and a urinary dipstick that is positive for blood. Which of the following initial tests would be most useful in the diagnosis of this case?

Fractional excretion of sodium (FeNa+)

Contrast abdominal computed tomography

Blood urea nitrogen (BUN): serum creatinine (SCr) ratio

A 32-year-old female presents with acute onset abdominal pain accompanied by nausea, vomiting, and hematuria. She is currently taking glipizide for type 2 diabetes mellitus. Past medical history is also significant for lactose intolerance. She has just started training for a marathon, and she drinks large amounts of sports drinks to replenish her electrolytes and eats a high-protein diet to assist in muscle recovery. She admits to using laxatives sporadically to help her manage her weight. On physical exam, the patient appears distressed and has difficulty getting comfortable. Her temperature is 36.8°C (98.2°F), heart rate is 103/min, respiratory rate is 15/min, blood pressure is 105/85 mm Hg, and oxygen saturation is 100% on room air. Her BMI is 21 kg/m2. CBC, CMP, and urinalysis are ordered. Renal ultrasound demonstrates an obstruction at the ureteropelvic junction (see image). Which of the following would most likely be seen in this patient?

Flank pain that does not radiate to the groin

Rebound tenderness, pain exacerbated by coughing

Colicky pain radiating to the groin

A 58-year-old man presents to the Emergency Department after 3 hours of intense suprapubic pain associated with inability to urinate for the past day or two. His medical history is relevant for benign prostatic hyperplasia (BPH) that has been under treatment with prazosin and tadalafil. Upon admission, he is found to have a blood pressure of 180/100 mm Hg, a pulse of 80/min, a respiratory rate of 23/min, and a temperature of 36.5°C (97.7°F). He weighs 84 kg (185.1 lb) and is 175 cm (5 ft 7 in) tall. Physical exam, he has suprapubic tenderness. A bladder scan reveals 700 ml of urine. A Foley catheter is inserted and the urine is drained. Initial laboratory tests and their follow up 8 hours after admission are shown below. Admission 8 hours after admission Serum potassium 4.2 mmol/L Serum potassium 4.0 mmol/L Serum sodium 140 mmol/L Serum sodium 142 mmol/L Serum chloride 102 mmol/L Serum chloride 110 mmol/L Serum creatinine 1.4 mg/dL Serum creatinine 1.6 mg/dL Serum blood urea nitrogen 64 mg/dL Serum blood urea nitrogen 62 mg/dL Urine output 250 mL Urine output 260 mL A senior attending suggests a consultation with Nephrology. Which of the following best justifies this suggestion?

Estimated glomerular filtration rate (eGFR)

Serum blood urea nitrogen (BUN)

A 43-year-old man presents with acute-onset left flank pain for the past 6 hours. He describes the pain as severe, intermittent, colicky, and “coming in waves”, and he points to the area of the left costovertebral angle (CVA). He says he recently has been restricting oral liquid intake to only 2 glasses of water per day based on the advice of his healer. He also reports nausea and vomiting. The patient has a history of hypertension, gout, and type 2 diabetes mellitus. He is afebrile, and his vital signs are within normal limits. On physical examination, he is writhing in pain and moaning. There is exquisite left CVA tenderness. A urinalysis shows gross hematuria. Which of the following is the next best step in the management of this patient?

Non-contrast CT of the abdomen and pelvis

Contrast CT of the abdomen and pelvis

Obstructive uropathies for USMLE Step 1: High-Yield Pathology Lessons

Etiology & Types - Plumbing Problems

Causes of Urinary Tract Obstruction by Age and Type

Location-Based Causes:
- Intrinsic (within tract): Calculi, tumors (TCC), strictures, sloughed papillae.
- Extrinsic (compression): Tumors (prostate, cervical), retroperitoneal fibrosis, pregnancy, aortic aneurysm.
- Bladder Outlet Obstruction (BOO): Benign Prostatic Hyperplasia (BPH), prostate cancer, urethral valves (children).

⭐ In adult males, Benign Prostatic Hyperplasia (BPH) is the most common cause of urinary tract obstruction.

Pathophysiology - Pressure Cooker Kidney

The "pressure cooker" effect: Relentless back-pressure from obstructed urine flow progressively damages the renal parenchyma.
Unilateral obstruction may remain clinically silent as the contralateral kidney compensates, masking the decline in function.

⭐ With complete obstruction, GFR ceases in ~24 hours. Significant functional recovery is possible if relieved within 1-2 weeks; after 12 weeks, damage is largely irreversible.

Clinical & Diagnosis - Spotting the Stop

Presentation Varies: Acute (sudden, severe flank pain) vs. Chronic (insidious, silent).
Symptoms:
- Pain: Flank pain, often radiating to the groin (renal colic).
- Urinary Changes: Anuria (bilateral obstruction), oliguria, or paradoxical polyuria (impaired concentrating ability).
- Lower Tract (LUTS): Hesitancy, weak stream, dribbling, nocturia (e.g., BPH).
Physical Exam:
- Costovertebral angle (CVA) tenderness.
- Palpable, distended bladder.
- Hypertension (due to ↑ renin).

SFU Hydronephrosis Grading

Initial Labs:
- ↑ Serum BUN and Creatinine (Postrenal Azotemia).
- BUN:Cr ratio > 15.
- Urinalysis: Hematuria, pyuria, crystals.
Imaging:
- Ultrasound: Best initial test; detects hydronephrosis & hydroureter.
- Non-contrast CT: Gold standard for stones.
- VCUG: For vesicoureteral reflux (VUR) or posterior urethral valves in children.

⭐ Post-Obstructive Diuresis: After relief, expect massive diuresis (> 200 mL/hr). This can lead to volume depletion and severe electrolyte loss (↓Na⁺, ↓K⁺).

High‑Yield Points - ⚡ Biggest Takeaways

Hydronephrosis is the hallmark, resulting from urinary outflow obstruction.

Key causes include BPH, nephrolithiasis, tumors, and congenital anomalies (e.g., posterior urethral valves).

Pathophysiology involves ↑ intratubular pressure, leading to ↓ GFR and progressive parenchymal atrophy with fibrosis.

Bilateral obstruction presents with features of acute kidney injury or chronic kidney disease.

Ultrasound is the initial imaging of choice to confirm hydronephrosis.

Watch for post-obstructive diuresis after relieving the obstruction.

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