# Clinical Cases: Renal Anatomy and Histology ## Case 1: Polycystic Kidney Disease ### Patient Presentation A 38-year-old male presents to his primary care physician for evaluation of flank pain and hypertension. He reports intermittent dull aching in both flanks for the past 6 months. His father died at age 52 from kidney failure requiring dialysis, and his paternal aunt is currently on dialysis. ### History of Present Illness - Bilateral flank discomfort, worse on the left - Recent onset of headaches - Occasional blood in urine (gross hematuria) - No dysuria or urinary frequency ### Physical Examination - Blood pressure: 156/98 mmHg - Bilateral palpable abdominal masses in the flanks - No lower extremity edema - Cardiac exam: Normal S1/S2, no murmurs ### Workup **Laboratory Studies:** - Serum creatinine: 1.4 mg/dL (elevated) - eGFR: 58 mL/min/1.73m2 (CKD Stage 3a) - Urinalysis: 2+ blood, trace protein - BUN: 24 mg/dL **Imaging:** - Renal ultrasound: Bilateral enlarged kidneys (right 16 cm, left 17 cm) with multiple cysts of varying sizes throughout the cortex and medulla - Total kidney volume: >1500 mL ### Diagnosis **Autosomal Dominant Polycystic Kidney Disease (ADPKD)** ### Discussion This case illustrates key anatomical concepts from the lecture: - **Cortex and Medulla**: The cysts in ADPKD arise from tubular epithelium and can develop in both cortical nephrons (85% of nephrons) and juxtamedullary nephrons (15%) - **Nephron Structure**: Cysts develop from all segments of the nephron, including proximal tubules, loops of Henle, and collecting ducts - **Renal Size**: Normal kidney length is approximately 11 cm; the bilateral enlargement to 16-17 cm reflects progressive cyst expansion ### Treatment - Blood pressure control with ACE inhibitor (target <130/80 mmHg) - Tolvaptan (vasopressin V2 receptor antagonist) for rapidly progressive disease - Genetic counseling for family members - Monitoring for complications: hepatic cysts, intracranial aneurysms ### Clinical Pearl The anatomical location of cysts determines clinical manifestations: cortical cysts cause flank pain and hematuria from capsular stretching, while collecting duct cysts contribute to concentrating defects and polyuria. --- ## Case 2: Renal Artery Stenosis ### Patient Presentation A 62-year-old female with a history of smoking presents with difficult-to-control hypertension despite being on three antihypertensive medications including an ACE inhibitor, calcium channel blocker, and thiazide diuretic. ### History of Present Illness - Hypertension diagnosed 3 years ago - Blood pressure readings consistently >160/95 despite medication adherence - Recent creatinine increase from 1.0 to 1.6 mg/dL after starting lisinopril - No symptoms of heart failure ### Physical Examination - Blood pressure: 168/102 mmHg in both arms - Abdominal bruit heard in the left paraumbilical region - Peripheral pulses diminished bilaterally - Evidence of peripheral vascular disease ### Workup **Laboratory Studies:** - Serum creatinine: 1.6 mg/dL - Potassium: 3.2 mEq/L (low) - Plasma renin activity: Elevated - Aldosterone: Elevated **Imaging:** - CT angiography: 80% stenosis of the left renal artery at its origin - Right kidney: 11 cm, normal appearance - Left kidney: 9 cm (atrophic) ### Diagnosis **Atherosclerotic Renal Artery Stenosis** ### Discussion This case highlights the unique renal vasculature discussed in the lecture: - **Segmental Arteries**: The renal artery divides into five segmental arteries, each supplying a distinct renal segment without collateral circulation - making these end arteries where occlusion leads to infarction - **Two Capillary Beds**: The glomerular capillaries (high-pressure filtration) and peritubular capillaries (low-pressure reabsorption) explain why GFR drops when renal perfusion is compromised - **Afferent/Efferent Arterioles**: In renal artery stenosis, the kidney depends on angiotensin II-mediated efferent arteriolar constriction to maintain GFR; ACE inhibitors remove this compensation, causing acute creatinine rise ### Treatment - Discontinue ACE inhibitor (creatinine rose >30%) - Percutaneous angioplasty with stenting considered for refractory hypertension - Risk factor modification: smoking cessation, statin therapy - Blood pressure management with calcium channel blockers ### Clinical Pearl The rise in creatinine after ACE inhibitor initiation in this patient is a clue to bilateral renal artery stenosis (or stenosis of a solitary kidney). The normal compensatory response to reduced renal perfusion involves angiotensin II-mediated efferent constriction to maintain glomerular capillary pressure. --- ## Case 3: Ureteropelvic Junction Obstruction ### Patient Presentation A 24-year-old male presents to the emergency department with sudden onset of severe left flank pain that began 2 hours ago after drinking a large amount of water during a marathon. ### History of Present Illness - Severe, colicky left flank pain - Nausea and one episode of vomiting - No hematuria noted - Similar but milder episodes in the past that resolved spontaneously ### Physical Examination - Blood pressure: 142/88 mmHg - Heart rate: 96 bpm - Left costovertebral angle tenderness - Abdomen soft but tender in left upper quadrant - No palpable masses ### Workup **Laboratory Studies:** - Serum creatinine: 1.0 mg/dL (normal) - Urinalysis: 1+ blood, no WBCs, no bacteria - CBC: WBC 9,500/mcL (normal) **Imaging:** - CT abdomen/pelvis without contrast: Severe left hydronephrosis with dilated renal pelvis; no ureteral stones identified; ureter appears normal caliber below the ureteropelvic junction ### Diagnosis **Ureteropelvic Junction (UPJ) Obstruction** ### Discussion This case demonstrates the clinical relevance of urinary tract anatomy: - **Three Physiological Narrowings**: The lecture describes three sites where kidney stones commonly lodge: the ureteropelvic junction (UPJ), the pelvic brim, and the ureterovesical junction (UVJ). Congenital UPJ obstruction occurs at the first narrowing. - **Renal Pelvis**: The funnel-shaped renal pelvis collects urine from the major calyces and continues as the ureter - **Transitional Epithelium**: The urothelium lining the renal pelvis can stretch but obstruction causes back-pressure transmitted to the nephrons ### Treatment - Pain management with ketorolac and opioids - Urology consultation for definitive management - Pyeloplasty (surgical repair of UPJ obstruction) - Follow-up imaging to assess resolution of hydronephrosis ### Clinical Pearl UPJ obstruction often presents intermittently, particularly during periods of high urine output (after large fluid intake) when the fixed narrowing cannot accommodate increased flow. This "Dietl's crisis" is characteristic of the condition. --- ## Image Reference For visual reference of kidney anatomy and histology relevant to these cases, see: - Wikimedia Commons: [Category:Histology of kidney](https://commons.wikimedia.org/wiki/Category:Histology_of_kidney) - Public domain images of nephron structure - Radiopaedia: [Hydronephrosis](https://radiopaedia.org/articles/hydronephrosis) - Ultrasound images of dilated collecting system - Wikimedia Commons: [Category:Nephron](https://commons.wikimedia.org/wiki/Category:Nephron) - Diagrams of nephron components --- ## Learning Points 1. **Cortical vs. Juxtamedullary Nephrons**: The two nephron populations have different loop lengths, explaining why diseases affecting concentrating ability may spare some nephrons. 2. **End Arteries**: The segmental arteries are end arteries without collateral circulation, making renal infarction possible with vascular occlusion. 3. **Urinary Tract Narrowings**: The three anatomical narrowings (UPJ, pelvic brim, UVJ) are critical for understanding stone impaction and congenital obstructions. 4. **Two Capillary Beds**: The unique arrangement of glomerular and peritubular capillaries allows independent regulation of filtration and reabsorption.