C h a p t e r 2 5
Disorders of Renal Function
621
polydipsia, and enuresis (bed-wetting), which reflect
impaired ability of the kidneys to concentrate urine.
Other manifestations of the disorders include salt wast-
ing, growth retardation, anemia, and progressive renal
insufficiency.
Simple and Acquired Renal Cysts
Simple cysts are a common acquired disorder of the kid-
ney. The cysts may be single or multiple, unilateral or
bilateral, and they are commonly 1 to 5 cm in diameter,
but may reach 10 cm or more. The cysts usually are
confined to the cortex. In rare instances, massive cysts
as large as 10 cm in diameter are encountered.
4,5
Most
simple cysts do not produce signs or symptoms or com-
promise renal function. When symptomatic, they may
cause flank pain, hematuria, infection, and hypertension
related to ischemia-produced stimulation of the renin-
angiotensin system. They are most common in persons
older than 50 years. Although the cysts are benign, the
main concern is to differentiate them from renal cell
carcinoma. Ultrasound and CT scanning are the recom-
mended procedures for evaluating these masses.
4,5
An acquired form of renal cystic disease occurs in per-
sons with chronic kidney disease who have undergone
prolonged dialysis treatment.
4
Although the condition
is largely asymptomatic, the cysts may bleed, causing
hematuria. Tumors, usually adenomas but occasionally
adenosarcomas, may develop in the walls of these cysts.
Disorders of Glomerular
Function
Glomerular disorders are one of the most common
forms of kidney disease. The glomeruli may be the major
site of disease (primary glomerular disease) or part of
a disease affecting other organs (secondary glomerular
disease). Hereditary glomerular diseases such as Alport
syndrome, although relatively rare, are an important
category of glomerular disease because of their associa-
tion with progressive loss of renal function and trans-
mission to future generations.
Etiology and Pathogenesis of
Glomerular Injury
Many of the clinical manifestations of glomerular dis-
orders result from dysfunction of specific components
of the glomeruli, which consist of a network of capillar-
ies, lined with a fenestrated endothelium invested in two
layers of epithelium (Fig. 25-4A). The visceral epithe-
lium is incorporated into and becomes an intricate part
of the capillary wall, separated from the endothelium
by a basement membrane.
4,5
The parietal epithelium,
which lines Bowman space within which urine collects,
is attached to the basement membrane by long, footlike
processes (
podocyte
s) that encircle the outer surface of
the capillaries. The glomerular capillary membrane is
selectively permeable, allowing water and small particles
(e.g., electrolytes and dissolved particles, such as glu-
cose and amino acids) to leave the blood and enter the
Bowman space while preventing larger particles (e.g.,
plasma proteins and blood cells) from leaving the blood.
SUMMARY CONCEPTS
■■
Congenital abnormalities of the kidney include
agenesis or failure of the kidneys to develop,
which is incompatible with life if both kidneys are
affected; hypogenesis or failure of the kidneys
to develop to normal size, which usually causes
no problems unless both kidneys are affected;
and renal dysplasia, which is characterized by
disorganized and maldifferentiated development
of kidney tissue, usually accompanied by cyst
formation. Other developmental kidney defects
can result in kidneys that lie outside their normal
position or are fused to form horseshoe-shaped
kidneys.
■■
Cystic diseases of the kidney are hereditary and
nonhereditary disorders in which there is dilation
of tubular structures with cyst formation.
■■
There are two forms of polycystic kidney disease:
autosomal dominant (ADPKD) and autosomal
recessive (ARPKD). Autosomal dominant (adult)
polycystic kidney disease results in the formation
of numerous fluid-filled cysts in the tubular
structures of both kidneys with the threat of
progression to chronic kidney disease. ARPKD,
which is rare compared with ADPKD and usually
presents as severe renal dysfunction during
infancy, is characterized by cystic transformation
of the collecting ducts.
■■
Nephronophthisis and adult-onset medullary
cystic kidney disease are characterized by the
presence of similar progressive medullary cystic
disease, but with different genetic causes and
inheritance. Nephronophthisis is an autosomal
recessive disorder, with onset in infancy,
childhood, or adolescence; whereas adult-
onset medullary cystic disease is an autosomal
dominant disorder with onset in adolescence and
renal failure in adulthood.
■■
Simple cysts are an acquired disorder of the
kidney.They may be single or multiple, unilateral
or bilateral, and are commonly 1 to 5 cm in
diameter. Although the cysts are benign, the
main concern is to differentiate them from
malignancies.
