Kidneys, Ureters, and Urinary Bladder

Kidneys, Ureters, and Urinary Bladder

The organ system examined in this chapter is the site of numerous diverse conditions, including congenital and hereditary diseases of the kidney, primary disease of the kidney, systemic diseases affecting the kidney, and diseases of the urinary system.

The kidneys are the primary regulators of the internal environment, particularly the volume, tonicity, and compartmental distribution of body fluids. They perform this function by exchanging and excreting water, minerals, and nonmetabolized solutes from the daily diet and end products of nitrogen metabolism (urea and creatinine). To accomplish this task, the kidneys produce an ultrafiltrate of plasma amounting to 180 L per day, reabsorbing more than 99% of it to produce an average of 1.5 L urine per day. Normal kidney function requires well-regulated blood flow through the kidneys, amounting to approximately 20% of the cardiac output, even though both kidneys comprise only approximately 1% of total body weight. Thus, even minor changes in renal structure can cause major functional disturbances and diseases. Consequently, microscopic investigations of the kidneys (e.g., by biopsy) are valuable for the diagnosis and classification of renal diseases.

Primary Diseases of the Kidney

Acute renal failure (ARF), which occurs in approximately 5% of hospitalized patients, is defined as an increase in serum creatinine of 0.5 to 1.0 mg/dL. Chronic renal failure (CRF) is a long-standing and usually irreversible impairment of renal function with reduction of the filtration rate, azotemia, and uremia. Common causes of ARF and CRF, as discussed in this chapter, are diverse, and both renal and extrarenal diseases must be considered in differential diagnosis.

The etiopathogenesis of glomerular and tubuloglomerular diseases (e.g., glomerulonephritis and nephrotic syndrome) is also highly diverse, as reflected in the difficulty in their classification. Many cases follow an autoimmune disorder; therefore, it is necessary to supplement the usual biopsy histology for staging and grading of the disease with immunohistologic procedures, occasionally including serology. Consequently, although the primary manifestation of an autoimmune renal disease may be the kidney, virtually all these conditions should be considered systemic processes (as in postinfectious autoimmune glomerulonephritis). Some, such as anaphylactoid purpura, lupus nephritis, and Wegener syndrome (see below), show systemic organ involvement from the beginning.

The Kidney and Systemic Diseases

Many primary systemic diseases affect the kidney, including diabetes mellitus (DM), essential hypertension, various renovascular diseases, and several toxic and metabolic disorders. Progressive renal disease (diabetic nephrosclerosis, Kimmelstiel-Wilson disease) is a common complication of DM (see chapter 12) and is responsible for renal failure in 30% to 40% of patients with insulin-dependent DM and 20% of those with non–insulin-dependent DM. Benign and malignant nephrosclerosis are the renal manifestations of essential hypertension and must be distinguished from renovascular hypertension, the consequence of renal artery stenosis. Hypertensive vascular diseases affect approximately 20% of the population and, with the complications of myocardial infarction, renal failure, and stroke, constitute a major health hazard. (The cause and pathogenesis of hypertension are discussed in chapter 2.) Systemic vasculitis syndromes frequently affect renal vessels or glomeruli or both (Table 6-1). Toxic nephropathy encompasses a large variety of diseases of different origins causing pathologic changes including cortical necrosis, tubular necrosis, focal hemorrhage, interstitial nephritis, and papillary necrosis. Causative toxins may be exogenous (e.g., drugs, plant toxins, allergens) or endogenic (e.g., toxemia of pregnancy), and the pathogenesis may include immune mechanisms (e.g., Shwartzman-Sanarelli syndrome). Metabolic disturbances such as amyloidosis and hypokalemic and calcium nephropathy also are associated with renal pathology.

Diseases of the Urinary System

Common diseases of the urinary system include pyelonephritis, obstructive uropathy, infections (e.g., tuberculosis, parasitic infections, cystitis) nephrolithiasis, some malformations (cystic disease, diverticula), neurogenic bladder, and neoplastic diseases. Obstructive nephropathy and hydronephrosis result from mechanical impediment of urine flow with renal dysfunction, dilatation of the collecting system, and frequent infections. Causes include intraluminal calculi (urolithiasis) and tumors (papilloma), compression (prostatic hypertrophy, pregnancy, retroperitoneal fibromatosis or tumors) and ureteral dysfunctions (amyloidosis, malformations, neurogenic conditions). Infections resulting from such functional disturbances are frequent causes of pyelonephritis, a bacterial infection of the renal parenchyma calyces and pelvis.

Other frequent and important diseases discussed in this chapter are malignant tumors such as adenocarcinoma and nephroblastoma of the kidney and transitional carcinoma of the urinary tract and bladder. Adenocarcinoma (renal cell carcinoma [RCC]) constitutes approximately 90% of renal malignancies; it occurs in more than 10,000 persons per year in the United States, and its annual incidence is increasing. A few cases occur as hereditary tumors and may be part of a cancer syndrome (e.g., von Hippel-Lindau syndrome). Clinical features are hematuria, pain, and an abdominal mass, which may lead to diagnosis and treatment by surgical resection. The 5-year survival rate of RCC is 40%. Urothelial cell (transitional cell) carcinoma (UCC) of the renal pelvis represents 5% to 10% of all kidney tumors. UCCs are more frequent in the urinary tract and account for 80% of neoplasms in the bladder. As long as the disease is confined to the bladder, as it is in approximately 85% of cases at initial presentation, survival after surgery amounts to 57% and 35% for low-grade and high-grade malignancy tumors, respectively. Nephroblastoma (Wilms tumor [WT]) constitutes the most frequent solid abdominal tumor in children. WTs may develop bilaterally and may accompany various congenital syndromes (e.g., Beckwith-Wiedemann syndrome). Karyotypic analysis reveals characteristic chromosomal changes in sporadic and congenital WTs such as alterations of the tumor suppressor gene WT1 or the susceptibility gene WT2. These changes apparently support the unrestricted growth of the nephrogenic blastoma, resulting in a tumor composed of blastemal, stromal, and epithelial elements. Early diagnosis before the age of 2 years with surgical removal of the tumor, radiation therapy, and chemotherapy may result in long-term survival of up to 90%.

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Jun 28, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Kidneys, Ureters, and Urinary Bladder

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