Kidney Benign Tumours Overview

Kidney Benign Tumours

• Xanthogranulomatous Pyelonephritis (XGP):
  • Rare form of chronic granulomatous pyelonephritis
  • Macroscopically: Enlarged kidney with yellow nodules
  • Microscopically: Aggregates of foamy macrophages, loss of functional parenchyma (medulla + cortex)
• Angiomyolipoma:
  • Hamartoma (disorderly mixed tissue)
  • Macroscopically: Single or multiple masses
  • Microscopically: Vessels (angio-), smooth muscle (myo-), fat (lipo-)
  • Etiology: Sporadic (most common) or tuberous sclerosis (genetic syndrome)
  • Tuberous sclerosis is a multisystem hamartoma with a triad of mental retardation (MR), seizures, and skin lesions
  • Genetic basis: Mutations in TSC1 & TSC2 genes (TSG): hamartin and tuberin
• Renal Papillary Adenoma:
  • Asymptomatic, often incidental findings
  • Macroscopically: Single or multiple nodules of ≤1cm at the cortex
  • Microscopically: Papillary/tubular pattern
  • Considered a precursor to carcinoma if size ≥1.5cm or high grade
• Oncocytoma:
  • Difficult to distinguish from renal cell carcinoma (RCC) even with biopsy
  • Macroscopically: Dark brown, with a pseudo-capsule compressing normal parenchyma
  • Microscopically: Eosinophilic cells with abundant mitochondria (oncocytes)
  • Determined only by evidence of metastasis or aggressive infiltration into adjacent structures
• Medullary Fibroma:
  • Within the cortex

Urinary Tract Benign Tumours

• Malakoplakia:
  • Rare form of chronic granulomatous cystitis
  • Macroscopically: “Soft plaque”
  • Microscopically: Michaelis-Gutmann bodies (defective macrophages with intracellular deposition of calcium and iron)
  • Most commonly found in the bladder as a result of bacterial infection
  • Pathogenesis: Macrophages partially digest bacteria, leading to glandular changes with cystic formation
  • Glandular changes: Chronic cystitis can progress to cystitis glandularis cystica with repeated UTIs

Metaplasia

• Replacement of urothelium by another type of epithelium.
• Glandular metaplasia: increased risk of adenocarcinoma.
• Squamous: schistosomiasis, urinary calculi, chronic irritation.
• Chronic inflammation of urothelium.

Benign neoplasms

• Urothelial papilloma: exophytic, nipple-like projection, fibrovacular core, visible on cystoscopy.
• Inverted Papilloma: endophytic.

Malignant neoplasms: Kidney

Renal cell carcinoma

• Triad: hematuria, palpable renal mass, flank pain.

• Left-sided varicocele.

• Paraneoplastic syndromes: polycythemia, hypercalcemia, hypertension.

• Metastasis: lung (MC), bone.

• Risk factors (RF): smoking, obesity, hypertension, chronic kidney disease (CKD).

• Sporadic: most common

• Hereditary (5%): von Hippel-Lindau disease (VHL).

• Pathological characteristics:

  • Macro: heterogeneous tumor with areas of hemorrhage, yellowish tissue, and cystic areas.
  • Micro:
    • Clear cell carcinoma (most common): contain lipid and glycogen in renal tubular epithelium.
    • Papillary cell carcinoma: intercalated cells of the renal tubule.
    • Chromophobe carcinoma.
    • Collecting duct carcinoma.

• Prognosis:

  • Fuhrman grading: nuclear size.
  • TNM staging:
    • T1: tumor < 7cm, within kidney.
    • T2: tumor > 7cm, within kidney.
    • T3: tumor extends into perinephric tissues or major veins.
    • T4: tumor extends beyond Gerota's capsule.

• Treatment:

  • Surgery
  • Growth factor inhibitors: sorafenib, bevacizumab, interferon.
  • Cytokine: immune response.
  • Targeted therapy.

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Malignant neoplasms: Urinary Tracts

Urothelial carcinoma (TCC)

• More common in men > 50 years old.
• Painless hematuria.
• Recurrent UTIs
• Risk factors (RF): smoking, alkylating agents used in chemotherapy (cyclophosphamide), industrial carcinogens, Schistosoma haematobium infection.
• Genetics: FGFR3, p53, HRAS.
• Field effect: common malignant stem cell; inevitable recurrence.
• Pathological characteristics:

  • Staging (TNM):

    • Ta: non-invasive papillary carcinoma.
    • Tis: non-invasive flat carcinoma in situ.
    • T1: invades lamina propria.
    • T2: invades muscle.
    • T3: invades perivesical fat.
    • T4: invades adjacent organs or fixed to pelvic side wall.
    • N ≥1 or M1: stage IV.

  • Grading:

    • Low grade (grade I/II): well-differentiated.
    • High grade (grade III): poorly differentiated.

Squamous cell carcinoma (SCC)

• 5% of urinary tract cancers.
• Risk factor: Schistosomiasis (MC).
• Schistosomiasis leads to squamous metaplasia, which can lead to SCC.

Wilms tumor

• Most common renal tumor in children (5% childhood cancers)
• Nephrogenic cysts: of nephrogenic mesoderm (embryonic remnant).
• Pathological characteristics:
  • Macro: very large, pale-grey tumor.
  • Micro: triphasic (blastemal, epithelial, stromal, primitive connective tissue), may contain bone.
• Risk factors (RF):
  • Sporadic: most common
  • Genetics: suppressor gene WT1 inactivation:
    • WAGR syndrome (Wilms tumor, aniridia, genitourinary anomaly, mental retardation)
    • Denys-Drash syndrome (DDS)
    • Beckwith-Wiedemann syndrome (BWS)
• Prognosis:
  • Staging, size, anaplasia.
  • Undifferentiated (mitosis #)
  • Loss of differentiation.
  • Hyperchromatic nuclei (high ratio)
• Treatment:
  • Surgery.
  • Chemotherapy.
  • Radiation.
  • With treatment: 90% cure rate.

This quiz explores various benign tumours of the kidney, including Xanthogranulomatous Pyelonephritis, Angiomyolipoma, and Renal Papillary Adenoma. Each condition is described with its macroscopic and microscopic features, etiology, and genetic implications. Test your knowledge on the characteristics and differences of these kidney disorders.