10.3 Nephrolithiasis, Urinary Tract Infections & Prostate Pathology
Key Takeaways
- Calcium oxalate stones account for 75-80% of kidney stones, appear radiopaque on non-contrast CT, and are treated acutely with hydration, analgesia, and alpha-1 blockers (tamsulosin) for stones <10 mm.
- Struvite (magnesium ammonium phosphate) stones form in alkaline urine (pH >7.0) due to urease-positive organisms (Proteus mirabilis, Klebsiella), presenting as radiopaque staghorn calculi requiring surgical removal.
- Uncomplicated cystitis in non-pregnant women is treated empirically with nitrofurantoin (100 mg BID for 5 days), trimethoprim-sulfamethoxazole (160/800 mg BID for 3 days), or fosfomycin (3 g single dose).
- Acute pyelonephritis requires outpatient oral fluoroquinolones (ciprofloxacin) or inpatient IV ceftriaxone, with renal ultrasound indicated if fever persists past 48-72 hours to evaluate for perinephric abscess.
- Prostate cancer screening involves shared decision-making for men aged 55-69; digital rectal exam showing a hard, nodular prostate or elevated PSA (>4.0 ng/mL) warrants transrectal ultrasound-guided (TRUS) needle biopsy.
Nephrolithiasis: Diagnosis & Management
Nephrolithiasis (kidney stone disease) presents acutely with paroxysmal, severe colicky flank pain radiating anteroinferiorly to the groin or labia/scrotum, frequently accompanied by nausea, vomiting, dysuria, and microscopic hematuria. On USMLE Step 2 CK, management depends on stone composition, size, location, and the presence of surgical emergencies like infection or complete obstruction.
Stone Characteristics & Prevention
| Stone Composition | Frequency | Radiodensity (CT / X-Ray) | Urinary pH Associations | Crystal Morphology | Long-Term Prevention |
|---|---|---|---|---|---|
| Calcium Oxalate | 75-80% | Radiopaque / Radiopaque | Envelope or dumbbell shaped | Thiazide diuretics (reduce urinary Ca²⁺), low Na⁺ diet, citrate | |
| Calcium Phosphate | 10-15% | Radiopaque / Radiopaque | Alkaline (pH >6.5) | Wedge-shaped prisms / rosettes | Address hyperparathyroidism or distal RTA (Type 1) |
| Struvite (Mg-NH₄-PO₄) | 10-15% | Radiopaque / Radiopaque | Highly Alkaline (pH >7.0) | Coffin-lid crystals | Surgical extraction; treat urease(+) bacteria (Proteus) |
| Uric Acid | 5-10% | Radiopaque / Radiolucent | Acidic (pH <5.5) | Diamond or rhomboid crystals | Potassium citrate (alkalinize urine pH >6.5), Allopurinol |
| Cystine | 1-2% | Radiopaque / Faintly Radiopaque | Acidic (pH <6.0) | Hexagonal crystals | Urinary alkalinization, penicillamine, tiopronin |
Clinical Management Workflow for Ureteral Stones
[ Acute Flank Pain + Microhematuria ]
|
[ Gold Standard: Non-contrast Helical CT ]
|
+------------------------------+------------------------------+
| |
[ Stone Size <5 mm ] [ Stone Size 5-10 mm ]
| |
Spontaneous passage (>90%) Medical Expulsive Therapy
-> Hydration, NSAIDs, -> Tamsulosin (Alpha-1 blocker)
Strain urine at home plus hydration & NSAIDs
|
(If >10 mm or fails MET)
|
Ureteroscopy or Shock
Wave Lithotripsy (ESWL)
- Emergent Surgical Decompression: Indicated immediately if a kidney stone presents with concurrent infection (fever, purulent urine, urosepsis) or in a patient with a solitary kidney or complete renal failure. Emergency nephrostomy tube placement or retrograde ureteral stenting is mandatory.
- Staghorn Calculi: Large branching struvite stones occupying the renal pelvis and calyces require percutaneous nephrolithotomy (PCNL) for complete surgical eradication.
Urinary Tract Infections (UTIs)
Urinary tract infections are divided into lower tract infection (cystitis) and upper tract infection (pyelonephritis).
Uncomplicated vs. Complicated Cystitis
- Uncomplicated Cystitis: Occurs in healthy, non-pregnant, immunocompetent adult women. First-line empirical treatments:
- Nitrofurantoin: 100 mg BID for 5 days (contraindicated if CrCl <30 mL/min).
- Trimethoprim-Sulfamethoxazole (TMP-SMX): 160/800 mg (DS) BID for 3 days (avoid if local resistance >20%).
- Fosfomycin: 3 g single oral dose.
- Complicated Cystitis: Occurs in men, pregnant women, patients with diabetes, indwelling catheters, anatomical abnormalities, or renal insufficiency. Regimens require 7 to 14 days of broad-spectrum therapy (oral fluoroquinolones like ciprofloxacin, or beta-lactams).
UTI in Pregnancy
Pregnant women must undergo routine screening for asymptomatic bacteriuria at 12–16 weeks gestation. Untreated bacteriuria causes acute pyelonephritis in up to 40% of pregnancies, predisposing to preterm delivery and low birth weight. Safe oral options include cephalexin, amoxicillin-clavulanate, or nitrofurantoin (avoid nitrofurantoin during 1st trimester and past 36 weeks gestation). TMP-SMX and fluoroquinolones are contraindicated.
Acute Pyelonephritis & Complications
Acute pyelonephritis presents with fever, chills, flank pain, costovertebral angle (CVA) tenderness, and systemic toxicity. Urinalysis demonstrates WBCs and WBC casts.
- Outpatient Management: Oral ciprofloxacin or levofloxacin for 7 days in stable patients.
- Inpatient Management: Intravenous ceftriaxone, ampicillin-sulbactam, or piperacillin-tazobactam.
- Perinephric Abscess: Suspected when a patient with pyelonephritis exhibits persistent fever and leukocytosis past 48 to 72 hours of appropriate IV antibiotic therapy. Diagnosis is confirmed by CT scan or ultrasound; treatment requires percutaneous drainage and tailored antibiotics.
Prostate & Male Reproductive Pathology
| Condition | Anatomical Zone / Pathophysiology | Key Clinical Presentation | Diagnostic Workup | First-Line Management |
|---|---|---|---|---|
| Benign Prostatic Hyperplasia (BPH) | Transition Zone periurethral hyperplasia (DHT-driven) | Lower urinary tract symptoms (LUTS): hesitance, weak stream, nocturia, post-void dribbling | DRE (smooth, firm, enlarged prostate); urinalysis; serum PSA | Tamsulosin (Alpha-1 blocker, rapid relief); Finasteride (5-alpha reductase inhibitor, reduces volume) |
| Acute Bacterial Prostatitis | Ascending infection (E. coli, Proteus) into prostate gland | Fever, dysuria, perineal pain, pelvic tenderness | DRE reveals exquisitely tender, boggy prostate; urine culture | Ciprofloxacin or TMP-SMX for 4-6 weeks; Do NOT perform vigorous prostate massage |
| Prostate Adenocarcinoma | Peripheral Zone posterior lobe malignancy | Often asymptomatic early; firm, hard nodule on DRE | PSA >4.0 ng/mL; TRUS-guided needle biopsy (Gleason score) | Active surveillance, radical prostatectomy, radiation, Androgen Deprivation Therapy |
| Testicular Torsion | Incomplete fixation of testis to tunica vaginalis ("bell-clapper") | Acute severe testicular pain, high-riding horizontal testis | Absent cremasteric reflex; negative Prehn sign | Emergency surgical detorsion & bilateral orchidopexy within 6 hours |
| Acute Epididymitis | Infections (C. trachomatis / N. gonorrhoeae in young; E. coli in older) | Gradual onset posterior testicular pain and swelling | Intact cremasteric reflex; Positive Prehn sign (pain relief with scrotal elevation) | Ceftriaxone + Doxycycline (<35 yo); Levofloxacin (>35 yo) |
A 35-year-old male accountant presents to the emergency department with sudden-onset, agonizing right-sided flank pain that radiates to his right groin. He also reports severe nausea and one episode of non-bloody vomiting. Vital signs are within normal limits. Physical examination reveals marked right costovertebral angle tenderness. Urinalysis demonstrates microscopic hematuria (25-30 RBCs/hpf) without leukocytes or bacteria. A non-contrast helical CT scan of the abdomen and pelvis reveals a 4 mm stone in the right distal ureter without hydronephrosis. Which of the following is the most appropriate management approach?
A 26-year-old primigravida at 14 weeks gestation presents to the clinic for her initial prenatal visit. She has no dysuria, urinary frequency, urgency, fever, or pelvic pain. Her past medical history is unremarkable. As part of routine prenatal screening, a clean-catch urine specimen is sent for urinalysis and culture. The urine culture yields >100,000 colony-forming units/mL of Escherichia coli sensitive to multiple agents. Physical examination is unremarkable. Which of the following is the best next step in management?
A 19-year-old college student presents to the emergency department with sudden, severe left scrotal pain that awoke him from sleep 2 hours ago. The pain is accompanied by lower abdominal nausea. On physical examination, the left testicle is diffusely tender, swollen, and positioned high in the scrotum with a horizontal lie. Stroking the left inner thigh fails to elicit testicular elevation. Light elevation of the left scrotum does not alleviate his pain. Which of the following is the most appropriate next step in management?