First, Understand the Urinary Tract Urine is made in the kidneys and travels down through this path: Kidney →
Urinary Tract Obstruction & Renal Neoplasms --- First, Understand the Urinary Tract Urine is made in the kidneys and travels down through this path: Kidney → Renal pelvis → Ureter → Bladder → Urethra → Outside Obstruction can happen at any point along this path. When urine cannot flow freely, it backs up — and that backed-up pressure damages the kidney over time. --- What is Obstructive Uropathy? When something blocks urine flow, three things happen: Urine backs up and increases pressure inside the kidney That pressure destroys kidney tissue over time Stagnant urine becomes a breeding ground for bacteria and stones The end result of unrelieved obstruction is a shrunken, scarred, non-functional kidney — this is called hydronephrosis. --- Causes of Obstruction Think of causes as coming from inside the urinary tract or from outside pressing on it. Congenital (born with it) Posterior urethral valves — abnormal flaps of tissue in the urethra blocking urine flow Urethral strictures — narrowing of the urethra Ureteropelvic junction obstruction — narrowing where the ureter meets the kidney Severe vesicoureteral reflux — urine flows backwards from bladder to kidney Stones Kidney stones lodging anywhere along the urinary tract Enlarged prostate Benign prostatic hypertrophy — the prostate grows around the urethra and squeezes it shut Prostate cancer — same effect but malignant Tumors Bladder tumors blocking the ureter openings Cervical or uterine cancer pressing on the ureters from outside Retroperitoneal lymphoma pressing on the ureters Inflammation and scarring Prostatitis, urethritis, retroperitoneal fibrosis Other causes Pregnancy — the growing uterus presses on the ureters Uterine prolapse Blood clots or sloughed renal papillae blocking the ureter Neurogenic bladder — spinal cord damage or diabetic neuropathy stops the bladder from emptying properly --- What Happens Inside the Kidney — Hydronephrosis Hydronephrosis means dilation of the renal pelvis and calyces due to backed-up urine, combined with progressive destruction of kidney tissue. Here is how it develops step by step: Obstruction occurs → urine cannot drain → builds up in the renal pelvis and calyces The kidney does not immediately stop making urine — glomerular filtration continues for a while The filtrate that cannot drain seeps back into the kidney tissue and eventually into lymphatics and veins The pelvis and calyces dilate — sometimes massively The backed-up pressure travels inward through the collecting ducts into the cortex → cortical atrophy It also compresses blood vessels in the medulla → reduced medullary blood flow What fails first — tubules or glomeruli? Tubules fail first. The medullary vessels are compressed early, and tubules depend on medullary blood flow for concentrating urine. So the first functional sign is inability to concentrate urine. Later, GFR falls as the cortex atrophies. Eventually, interstitial inflammation develops → interstitial fibrosis → permanent scarring. --- What Does the Kidney Look Like — Morphology Sudden complete obstruction — mild dilation of pelvis and calyces; some parenchymal atrophy Partial or intermittent obstruction — progressive dilation; true hydronephrosis develops Early — dilated pelvis and calyces; interstitial inflammation even without infection Chronic — cortical tubular atrophy; diffuse interstitial fibrosis; blunting of pyramid apices (the tips of the pyramids become rounded and cupped instead of pointed) Far advanced — the entire kidney becomes a thin-walled cyst up to 15–20 cm; no pyramids left; paper-thin cortex; completely non-functional --- Clinical Features Acute obstruction Pain — from distension of the collecting system or renal capsule If a stone is the cause → severe colicky flank pain (renal colic) radiating to the groin Unilateral obstruction Can be completely silent for a long time The other kidney compensates and maintains normal renal function Often found incidentally on imaging Bilateral partial obstruction First sign: inability to concentrate urine → polyuria and nocturia Later: distal tubular acidosis, salt wasting, secondary stones, chronic tubulointerstitial nephritis Hypertension is common Bilateral complete obstruction Oliguria or anuria — little or no urine output Incompatible with survival unless obstruction is relieved urgently After relief of obstruction Post-obstructive diuresis occurs — the kidney suddenly floods out large volumes of sodium-rich urine Can be massive and cause electrolyte imbalances Investigation of choice: Ultrasonography — non-invasive, shows dilated pelvis and calyces --- Urolithiasis — Kidney Stones Urolithiasis simply means stones anywhere in the urinary tract. Most form in the kidney. Affects 5–10% of people in their lifetime More common in men than women Peak age: 20–30 years Familial and hereditary predisposition exists The core mechanism of all stone formation: Stones form when the concentration of stone-forming substances in urine exceeds their