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Each kidney weighs approximately 150 g in adults, with ranges of 125 to 175 g for men and 115 to 155 g for women; both together represent 0.4% of the total body weight. Each kidney is supplied by a single renal artery originating from the abdominal aorta; the main renal artery branches to form anterior and posterior divisions at the hilus and divides further, its branches penetrating the renal substance proper as interlobar arteries , which course between lobes. Interlobar arteries extend to the corticomedullary junction and give rise to arcuate arteries , which arch between cortex and medulla and course roughly perpendicular to interlobar arteries. Interlobular arteries , branches of arcuate arteries, run perpendicular to the arcuate arteries and extend through the cortex toward the capsule (Fig. 1.1). Afferent arterioles branch from the interlobular arteries and give rise to glomerular capillaries (Fig. 1.2). A glomerulus represents a spherical bag of capillary loops arranged in several lobules (Fig. 1.3); the capillaries merge to exit the glomerulus as efferent arterioles , which, in most nephrons, branch to form another vascular bed, peritubular or interstitial capillaries , which surround tubules. Efferent arterioles from juxtamedullary glomeruli extend into the medulla as vasa recta, which supply the outer and inner medulla. The vasa recta and peritubular capillaries collect, forming into interlobular veins ; the veins follow the arteries in distribution, size, and course, and leave the kidneys as renal veins , which empty into the inferior vena cava.

Membranous glomerulopathy is a major cause of the nephrotic syndrome in adults (1,2). Only in the past decades has it been surpassed by focal and segmental glomerulosclerosis as the main cause of the nephrotic syndrome (3–5). Membranous glomerulopathy develops mostly idiopathically, but can also be seen in relation with and possibly secondary to, among others, hepatitis B, Sjögren’s syndrome, transplantation, lupus erythematosus, diabetes mellitus, sarcoidosis, syphilis, exposure to certain drugs and heavy metals (penicillamine, bucillamine, gold, mercuric chloride), and malignancies (10%), including carcinomas, carcinoids, sarcomas, lymphoma’s, and leukemias (2,6–10). The possibility of a malignancy must be considered especially in older patients with membranous glomerulopathy. In these patients it is also imperative to perform urinary immunoelectrophoresis routinely to rule out myeloma and renal primary amyloidosis (AL) (2). Finally, idiopathic membranous glomerulopathy, of which an autoimmune origin has not been established, must be distinguished from membranous lupus glomerulonephritis (11), as discussed in Chapter 8. Synonyms for membranous glomerulopathy are membranous nephritis, (epi)membranous nephropathy, extramembranous glomerulopathy, and perimembranous nephropathy (7,12).

Membranoproliferative glomerulonephritis (MPGN) refers to a pattern of injury characterized by diffuse mesangial expansion due to endocapillary proliferation and increased mesangial matrix, and thickened capillary walls, often with a split “tram-track” appearance (1,2). The immune complexes may be undefined in terms of the inciting antigen (“idiopathic”) or secondary to chronic infections (3). Of note, basement membrane splitting may be seen in other non-immune complex injuries, such as the late phase of thrombotic microangiopathy (3). Although light microscopy may appear similar to MPGN, immunofluorescence findings and electron microscopy readily allow recognition of the immune complexes in MPGN. We and others prefer to use the term membranoproliferative glomerulonephritis only for immune complex glomerulonephritides with this pattern (1). Membranoproliferative glomerulonephritis type I typically presents as combined nephritic/nephrotic syndrome with hypocomplementemia. Patients typically have progressive renal disease, with about 50% renal survival at 10 years in children, and similar rates of progression in adults. Idiopathic MPGN is more common in children and young adults, whereas MPGN-type lesions are more commonly secondary to chronic infections in adults. New insights into the role of complement regulation in renal injury are adding to our understanding of the etiology of injury in cases previously classified as idiopathic.

Minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) are both common causes of the nephrotic syndrome. Minimal change disease accounts for greater than 90% of cases of nephrotic syndrome in children, vs. 10% to 15% of adults with nephrotic syndrome (1). Focal segmental glomerulosclerosis has been increasing in incidence in the United States in both African Americans and in Hispanics, in both adult and pediatric populations (2–4). It is now the most common cause of nephrotic syndrome in adults in the U.S. Patients with FSGS may have hypertension and hematuria. Serologic studies, including complement levels, are typically within normal limits in both MCD and FSGS.

Acute postinfectious glomerulonephritis is a kidney disease that follows after an infection. The most common and best understood form of acute postinfectious glomerulonephritis is poststreptococcal glomerulonephritis. Less is known about the other forms of postinfectious glomerulonephritis. In addition, there are glomerulonephritides that occur during persistent bacterial infections such as bacterial endocarditis, deep abscesses, and infected atrioventricular shunts in hydrocephalus (1).

Immunoglobulin A (IgA) nephropathy was first described by the pathologist Jean Berger (1,2) and thus is sometimes called Berger’s disease. Immunoglobulin A nephropathy is defined by the presence of IgA-dominant or co-dominant mesangial immunoglobulin deposits (Fig. 6.1) (3). Lupus glomerulonephritis, which may have IgA dominant or co-dominant deposits, is excluded from this diagnostic category. Immunoglobulin A nephropathy occurs as a primary (idiopathic) disease, as a component of Henoch- Schönlein purpura small-vessel vasculitis, secondary to liver disease (especially alcoholic cirrhosis), and associated with a variety of inflammatory diseases including ankylosing spondylitis, psoriasis, Reiter’s disease, uveitis, enteritis (e.g., Yersinia enterocolitica infection), inflammatory bowel disease, celiac disease, dermatitis herpetiformis, and HIV infection (4–6).

Classical Alport’s syndrome is an X-linked disease and is the most common form of Alport’s syndrome (90% of patients), with an overall incidence of Alport’s syndrome in the United States of 1 : 5000 to 1 : 10,000 (1–4). Patients show hematuria in childhood with progressive hearing loss in one third, and ocular defects and progression to renal failure in 30% to 40% by early adulthood. Anterior lenticonus is the most common eye defect.

Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown cause that can occur at almost any age, although it affects mostly women in their 20s. The annual incidence of SLE is 50 to 70 people per million of the population, and prevalence is 500 per million (1). Epidemiologic data show that the incidence of new cases and the survival of patients with SLE are both increasing (2). The disease is characterized by a large variety of organ disorders involving many different immune mechanisms. This is reflected in particular by the spectrum of glomerular lesions, resulting in a strong variation of the clinical symptoms of the renal disease. Clinical or morphologic involvement of the kidney in SLE occurs in 50% to 80% of lupus patients at any moment during the course of their disease. Moreover, renal alterations are found in almost 90% of lupus patients at autopsy. The lowest 5-year survival has been reported for patients with central nervous system and renal involvement (1).

Crescentic glomerulonephritis is not a specific disease but rather is a manifestation of severe glomerular injury that can be caused by many different etiologies and pathogenic mechanisms. The major immunopathologic categories of crescentic glomerulonephritis are immune complex-mediated, anti-glomerular basement membrane (anti-GBM) antibody-mediated, and pauci-immune, which usually is antineutrophil cytoplasmic autoantibody (ANCA)-mediated (1). Table 9.1 shows the relative frequency of these immunopathologic categories of crescentic glomerulonephritis. Crescentic glomerulonephritis can occur as a renal limited process or as a component of systemic small vessel vasculitis, such as Henoch-Schönlein purpura, Goodpasture’s syndrome, or ANCA vasculitis (2,3). In addition to smallvessel vasculitis, the kidneys also are a frequent site of involvement by other forms of vasculitis, such as polyarteritis nodosa, Kawasaki disease, giant cell arteritis, and Takayasu arteritis (3).

Approximately 60 million people in the United States have hypertension. Many are undiagnosed or untreated. Different populations have different risks and different consequences of hypertension. Increased hypertension is seen with aging, positive family history, African-American race, and exogenous factors such as smoking. Although African Americans make up only 12% of the U.S. population, they are fivefold overrepresented among patients with end-stage renal disease (ESRD) presumed due to hypertension (1,2). Hypertension is associated with significant morbidity and mortality due both to cardiovascular and renal diseases (1–5).