Diagnostic ultrasound ( PDFDrive )

370 PART II Abdominal and Pelvic Sonography
A
B
FIG. 9.86 Renal Vein Thrombosis. (A) Color Doppler image shows an echogenic right kidney and nonocclusive right renal vein thrombus
extending into inferior vena cava. (B) Corresponding contrast-enhanced CT shows an enlarged right kidney, a delayed right nephrogram, and a right
renal vein thrombus. (Courtesy of Shweta Bhatt, MD.)
obstruction is not found, this oten indicates a renal parenchymal
abnormality—thus the terms medical renal disease or renal
parenchymal disease. he acutely injured kidney may be hyperechoic,
echogenic, or normal appearing at ultrasound; a thin
rim of perirenal luid is oten shown in the acute setting. 289,290
he chronically diseased kidney is small and echogenic (Fig.
9.87). Unfortunately, it is usually impossible to distinguish between
the numerous causes of intrinsic renal disease based on the
appearance of the kidney at ultrasound, although renal size is a
clinically relevant parameter used to distinguish between acute
and chronic processes. hus percutaneous biopsy is oten necessary
when clinical features and history are inconclusive.
Acute Tubular Necrosis
Acute tubular necrosis (ATN) is the most common cause of
acute reversible renal failure and is related to deposition of cellular
debris within the renal collecting tubules. Both ischemic and
toxic insults will cause tubular damage. Initiating factors include
hypotension, dehydration, drugs, heavy metals, and solvent
exposure. he sonographic appearance of ATN depends on the
underlying cause. With ATN caused by hypotension, kidneys
may appear normal, whereas drugs, metals, and solvents will
cause enlarged, echogenic kidneys. Prerenal disease and ATN
account for 75% of all patients presenting with acute renal failure.
Acute Cortical Necrosis
Acute cortical necrosis (ACN) is a rare cause of acute renal
failure resulting from ischemic necrosis of the cortex with sparing
of the medullary pyramids. he outermost aspect of cortex remains
viable as a result of capsular blood supply. ACN occurs in association
with sepsis, burns, severe dehydration, snakebite, and
pregnancy complicated by placental abruption or septic abortion.
he exact cause is uncertain, although it is likely related to a
transient episode of intrarenal vasospasm, intravascular thrombosis,
or glomerular capillary endothelial damage. At sonography,
the renal cortex is initially hypoechoic 291 (Fig. 9.88). With time
(mean, 2 months), both kidneys atrophy and the cortex may
calcify.
Glomerulonephritis
Necrosis and mesangial proliferation of the glomerulus are the
hallmarks of acute glomerulonephritis. Systemic diseases that
also have acute glomerulonephritis as a feature include polyarteritis
nodosa, systemic lupus erythematosus, Wegener
granulomatosis, Goodpasture syndrome, thrombocytopenic
purpura, and hemolytic uremic syndrome. Patients oten present
with hematuria, hypertension, and azotemia. At sonography,
both kidneys are afected; the size of the kidneys may be normal,
but renomegaly is oten encountered. he echo pattern of the
cortex is altered; renal cortex may be normal, echogenic, or
hypoechoic, but the medulla is spared (see Fig. 9.87). With
treatment, the kidneys may revert to a normal size and echogenicity.
Chronic glomerulonephritis occurs with unabated
acute disease over weeks to months following an acute episode.
Profound, global, symmetrical parenchymal loss occurs. he
calices and papillae are normal, and the amount of peripelvic
fat increases. Small, smooth, echogenic kidneys are seen, with
prominence of the central echo complex.
Acute Interstitial Nephritis
Acute interstitial nephritis is an acute hypersensitivity reaction
of the kidney most oten related to drugs. Penicillin, methicillin,
rifampin, sulfa drugs, nonsteroidal antiinlammatory drugs,
cimetidine, furosemide, and thiazides have been implicated.
Usually, renal failure will resolve with cessation of drug therapy.
At sonography, enlarged echogenic kidneys are noted.