2. Acute Renal Failure
• Rapid deterioration in renal function
characterized by :
- azotemia with
- decline in glomerular filtration rate
(GFR)
- which may or may not be accompanied
by Oliguria (urine output <400 ml/d)
Chronic Renal Failure
• Kidney damage or decreased renal
function for ≥ 3months duration
resulting in GFR of less than 60
mL/min/1.17m2
4. 1. Enlarged kidneys in the setting of AKI
2. increased renal cortical echogenicity and loss
of the normal corticomedullary differentiation
3. Increased cortical thickness
1. Small or atrophic kidneys are often seen with
CKD
2. Markedly increased renal cortical echogenicity
is seen in CKD
3. Decreased cortical thickness
reduced renal cortical thickness <6 mm
Ultrasonography
Acute RF Chronic RF
5. • Preserved interpapillary line is a useful landmark for evaluating
loss of renal parenchyma.
• Interpapillary line is drawn through the tips of papilla (base of
the calyces) the distance from this line to lateral surface of
kidney is the renal parenchymal thickness which averages to
2.5–3 cm.
• Distances less than 2 cm are suggestive of parenchymal loss
while those greater than 3.5 cm indicate mass lesion or
infiltration.
INTERPAPPILARY LINE
8. Renal Vein Thrombosis
• USG
Enlargement and unilateral hypoechoic parenchyma
• Doppler findings include:
1. reversal of arterial diastolic flow
2. absent venous flow
3. visualization of thrombus within the lumen
4. high resistance in the renal artery with elevated RI
reversal of arterial diastolic flow
9. the thrombosis is observed as a
filling defect during venous
phase imaging following
intravenous contrast
Long linear filling defect in the left renal vein.
CT findings
10. Renal infarction
Renal infarction results from interruption of the normal blood supply to part of,
or to the whole kidney.
• Causes of renal infarction include
1. Thromboembolism
2. Aortic dissection
3. Renal artery stenosis
11. Power doppler Colour doppler
Ultrasound
• Hyperechoic
• Absence of flow in the renal artery
• Infarcts will appear as wedge-shaped regions of nonperfusion
12. contrast-enhanced CT demonstrate hypoattenuation of the posteroinferior part of the
kidney with surrounding stranding.
There is preservation of the very outer layer of parenchyma (cortical rim sign).
cortical rim sign
14. Without dilated PCS
Unilateral smooth enlarged kidney
Progressively dense Nephrogram
Obstructive uropathy
With dilated PCS
Absent nephrogram + Echogenic collection in PCS
Dilated calyces with contracted pelvis containing calculus
s/o xanthogranulomatous pyelonephritis
Acute venous
thrombosis
Renal infarct
• Cortical rim
enhancement
• Angiography
Thrombus/ Embolus
•Filling defect in
renal vein with a/w
renal enlargement
Acute pyelonephritis
Clinical diagnosis
• Bacteremia
• Pyuria
• Flank pain
15. Acute urinary obstruction causes a large,
smooth left kidney with delayed contrast excretion
and prolonged nephrogram. Acute pyelonephritis. Generalized enlargement
of the left kidney with decreased density of
contrast material in the collecting system
17. - Renal cause of AKI characterized by tubular epithelial cell damage from toxins or ischemia
- Most common Reversible cause of renal failure
• Etiology
1. Ischemia: Hypotension (most common cause),
hypovolemia, renal vasoconstriction, DIC
2. Toxins
– Exogenous: Iodinated contrast media, antibiotics, chemotherapeutic drugs, organic solvents, heavy metals
– Endogenous: Hemolysis, rhabdomyolysis, uric acid, oxalate
Acute Tubular Necrosis
18. Ultrasonographic Findings
Morphology
- Enlarged
- Smooth outline
Echogenicity
1. Ischemic ATN- Normal cortical and medullary
echogenicity
2. Drug related ATN- increased cortical echogenicity
and maintained corticomedullary differentiation
○ Perirenal hypoechoic rim ("kidney sweat")
Color Doppler
- Resistive index: ↑ (> 0.7)
IMAGING
"kidney sweat“ sign
20. Characterized by ischemic necrosis of renal cortex with sparing of renal medulla and thin
rim of subcapsular cortex.
• Etiology
○ Obstetrical complication (> 50% of cases)
– Abruptio placentae, septic abortion, eclampsia
○ Hemolytic uremic syndrome, disseminated intravascular coagulopathy, shock, sickle cell anemia, renal
allograft rejection
Renal Cortical Necrosis
21. Plain Radiography
• Cortical calcification: Dual linear opacities paralleling
corticomedullary line ("tram line" sign), which is
usually seen after 4 weeks
Imaging
22. Ultrasonographic Findings
• Diffusely enlarged kidneys
• Loss of corticomedullary differentiation
• ↓ cortical echogenicity
• acoustic shadow due to cortical calcification
24. B/L smooth enlarged kidneys
Neonatal/Juvenile
age group
Associated with
striated
nephrogram
Periportal fibrosis
Dilated bile ducts
F/O PH
ARPCKD
Dilated PCS
Delayed contrast excretion
B/L obst
Uropathy
- Increase serum urea level
- Nephrogram- progressively
dense
Intense hyperechoic
cortex with
hypoechoic medulla
HUS
Elderly pt.
Osteopenia
vert. body &
Mandibular
involvement
Mult. Myeloma
Child with
abnormal
peripheral smear
increase WBC
count
Changes in bone
Leukemia
Absent cortical
nephrogram
with selective
enhancement
of medulla +
Tram line
calcification
Acute cortical necrosis
Renal
involvement
following
History of drug
exposure
Clinical features-
• Rash
• Eosinophila
• Proteinuria
• Hematuria
• Azotemia
Acute interstitial nephritis
Acute urate nephropathy
25. UNILATERAL SMALL SMOOTH KIDNEYS
1. Ischemia due to renal artery stenosis
2. Post-obstructive atrophy
3. End result of renal infarction
4. Congenital hypoplasia
5.Reflux atrophy
26. Renal artery stenosis
Renal artery stenosis (RAS) refers to a narrowing of a renal artery with reduction of internal
diameter by at least 60%
Etiology
1. Atherosclerosis
2. Polyarteritis nodosa
3. Fibromuscular dysplasia
4. Compression of RA by mass
27. Ultrasound
1. Increased peak systolic velocity (PSV): some advocate 180 cm/s 4
2. Increased renal-aortic ratio (RAR), i.e. PSVrenal/PSVaorta: usually taken as
>3.5 turbulent flow in a post-stenotic area
3. Decreased (interlobar) renal arterial resistive index (RI): <0.55 in severe stenosis
4. Resistive index difference between kidneys >5%
28. Left intrarenal Doppler examination shows a normal
arterial curve with sharp systolic peak and resistance
index <0.70
29. Pulsed Doppler sampling reveals elevated peak systolic
velocities (PSV) 366 cm/sec at the site of color aliasing.
31. CT angiography shows atherosclerotic calcifications of the right
renal artery ostium and a moderate to severe stenosis.
32. CE-MRA shows a high-grade stenosis of the proximal right renal artery.
The right kidney was markedly smaller but smoothly marginated.
Parenchymal enhancement of the right kidney was delayed.
33. Small smooth kidneys
Unilateral Bilateral
With small PC system With<5 calyces With dilated PC system
Cong. hypoplasia
H/o radiation
therapy
Radiation nephritis
Abnormal renal
Vessels (Art)
Dense Faint/Nil
Acute ischemia
Signs of obstruction
Post obstructive atrophy
Reflux
Reflux atrophy
Chr. infarction
Nephrogram
35. Definitions:
• Necrosis of renal papilla within medulla secondary to interstitial nephritis or ischemia
Renal Papillary Necrosis
Causes:
Analgesic nephropathy (M/C cause)
Diabetes
Infant in shock
Pyelonephritis
Obstruction,
Sickle cell disease
Ethanol
(Pneumonic to remember causes of renal papillary necrosis—ADIPOSE)
36. IMAGING
Ultrasonographic Findings
○ Early stage – Necrotic renal papillae: Seen as echogenic foci
○ Advanced stage – Single or multiple cystic cavities in medullary pyramids continuous with calyces ±
calcification
41. Reflux nephropathy
• Renal scarring and shrinkage secondary to multiple episodes of acute pyelonephritis
during early childhood
• Most cases secondary to vesicoureteral reflux (VUR)
first-choice imaging modality for the kidneys in the context of AKI is US
Doppler findings
higher RI is associated with intrarenal causes of AKI
RI greater than 0.70 (segmental and interlobular arteries)
Schematic diagram of normal interpapillary line: This line is
drawn by joining the tips of renal papillae; smooth uninterrupted
interpapillary line is seen in normal kidney
Morphological criteria are useful to categorize the wide spectrum of renal parenchymal diseases.
Evaluation is done based on renal size, contour and laterality of involvement
Renal vein thrombosis
The kidney is greatly enlarged with a hazy, irregular hypoechoic structure.
• Nephrotic syndrome and underlying malignancy (usually RCC) are the most common etiologies in adults
• Dehydration and sepsis are the most common etiologies in children
Axial C+ portal venous phase CT
Long linear filling defect in the left renal vein
Power Doppler: avascular area of the upper pole of the right kidney depicting the infarction.
Color Doppler: the wedge-shaped avascular region confirms the infarct.
On Color Doppler :
Complete absence of perfusion when the entire kidney is affected, or patchy if segmental arteries are involved
Absence of flow in the renal artery
Over time the regions of infarctions shrink, becoming hyperechoic scars
Infarcts will appear as wedge-shaped regions of nonperfusion
absence of contrast enhancement in the cortex and relatively hyperdense medulla and subcapsular cortex, the characteristic ‘cortical rim sign’
Preserved enhancement of thin rim of subcapsular cortical tissue due to separate capsular blood supply
CT scan demonstrates
low density rounded parenchymal collections throughout the right kidney, without hydronephrosis, with a central large (presumably staghorn) calculus.
Also note the enlarged periaortic and pericaval lymph nodes.
The bear paw sign refers to the cross-sectional appearance of the kidney affected by xanthogranulomatous pyelonephritis.
There is a radial arrangement of multiple, low attenuation rounded spaces representing dilated calyces, surrounded by thin renal parenchyma that has higher attenuation or contrast enhancement, mimicking the appearance of the dark toe pads on a polar bear's paw.
*Nephrogram=IVP
Obstructive uropathy- ivu progressively becomes dense
Xanthogranulomatous pyelonephritis- ivu fails to fill in presence of good thickness of renal substance (parenchymal inflammation due to foamy histiocytes)
Acute venous thrombosis- ivu varies from absent to normal
Renal infarct- ivu absent to diminished density
USG- The kidney sweat sign refers to the presence of thin, hypoechoic, extracapsular fluid collections around kidneys in renal failure patients.
This fluid is thought to represent perirenal edema. It can be appreciated on ultrasound, CT and MRI.
T2W MRI- demonstrating kidney sweat sign
Striated nephrogram is a descriptive term indicating an appearance of alternating linear bands of high and low attenuation in a radial pattern
extending through the corticomedullary layers of the kidney on iodine-based intravenous contrast enhanced imaging.
Fig: Right kidney- There is punctate calcification in right kidney
Left kidney- And a peripheral rim of calcification surrounding left kidney
USG- Right kidney ultrasonography showed a hypoechoic renal cortex.
Axial post-contrast CT scan (corticomedullary phase)
absence of contrast enhancement in the cortex and relatively hyperdense medulla and subcapsular cortex, the characteristic ‘cortical rim sign’
Preserved enhancement of thin rim of subcapsular cortical tissue due to separate capsular blood supply
a bilateral hypoattenuating renal cortex compared with intact medullary enhancement, which is called “reverse rim sign” (white arrowhead),
and In contrast enhanced ct
In arterial phase the ct scan shows senhancement of inter lobular and arcuate arteries adjacent to the non enchancing cortex.
In the portovenous phase the CT shows enchnacement of the renal medulla with a hypoantttenuating non enchanging cortex ,this is called the reverse rim sign
B. Ball-on-tee/egg in cup appearance: Contrast material filling central excavations in the papilla of the interpolar region gives ball-on-tee appearance.
D. Lobster claw sign: Excavation extending from the caliceal fornices produces the lobster claw deformity.
F. Club shaped saccular calyx: Due to sloughed papilla
E. Signet ring sign: The necrotic papillary tip may remain within the excavated calyx, producing the signet ring sign when the calyx is filled with contrast material.
Coronal CECT urography in a 33-yearold man with history of IV drug use -
shows loss of the normal renal pyramids in the upper pole of the right kidney
with blunted, rounded calyces ſt.
Compare these with the cupped, normal calyces on the left and the pyramids, with
their rays of contrast-opacified tubules.
Generalized arteriosclerosis involving most of the interlobar and arcuate arteries causes uniform shrinkage of both kidneys.
Benign nephrosclerosis :Thickening and subendothelial hyalinization of afferent arterioles associated with hypertension.
Atheroembolic renal disease:Caused by the dislodgment from the aorta of multiple atheromatous emboli that occlude intrarenal arteries.
USG img-
(a) First grade of hydronephrosis with mild dilatation of the intrarenal urinary tract (arrow).
(b) Second grade of hydronephrosis with pyelocaliectasis and normal morphology of the renal calyx.
(c) Third grade of hydronephrosis with pyelocaliectasis and renal calyces with a balloon shape.
(d) Fourth grade of hydronephrosis with a progressive thinning of the renal parenchyma (arrow)