Urinary: Infection

Question 1

Classic appearance of pyelonephritis on CT

Answer 1

• Striated nephrogram (best seen on excretory phase)
• Vague, focally reduced areas of enhancement with associated perinephric stranding

Question 2

How can you differentiate between pyelonephritis and renal infarction on imaging?

Answer 2

Cortical rim sign:

Pyelonephritis classically involves a complete wedge of kidney extending through the cortex

Infarct classically involved a central wedge where there is a cortical rim of normally enhancing cortex peripherally

Question 3

Pyelonephrosis

Answer 3

Pyelonephritis with obstruction

Note: A fluid-fluid level is often seen on ultrasound.

Question 4

Differential for striated nephrogram

Answer 4

Things that cause hypoperfusion or edema:

• Acute ureteral obstruction
• Acute pyelonephritis
• Acute renal vein thrombosis
• Radiation nephritis
• Acutely following renal contusion
• Hypotension (would be bilateral)
• Infantile polycystic kidney (would be bilateral)

Question 5

Treatment for pyelonephrosis

Answer 5

Urgent decompression with percutaneous nephrostomy

Question 6

Treatment for renal abscess

Answer 6

IR-guided drainage (if >3 cm)

Question 7

Spectrum of pyelonephritis

Answer 7

• Pyelonephritis (striated nephrogram)
• Lobar nephronia (phlegmon: ill-defined focal low density but not yet cystic, more common in pediatrics)
• Renal abscess (well-defined cystic core, usually with a thick enhancing rim)

Question 8

CT appearance of chronic pyelonephritis

Answer 8

Renal scarring with atrophy/cortical thinning and hypertrophied residual tissue

Question 9

Answer 9

Emphysematous pyelonephritis

Note: Perinephric echogenic line with dirty shadowing.

Question 10

Emphysematous pyelonephritis is most common in what pt population?

Answer 10

Diabetics

Question 11

Emphysematous pyelitis

Answer 11

When gas is limited to the collecting system (not as bad as emphysematous pyelonephritis)

Question 12

Answer 12

Emphysematous pyelitis

Note: Gas limited to collecting system.

Question 13

Common causes of papillary necrosis

Answer 13

• Diabetes (most common)
• Pyelonephritis
• Sickle cell disease
• Tuberculosis
• Analgesic use
• Cirrhosis

Question 14

Answer 14

Renal papillary necrosis

Note: “Lobster claw sign” of the renal calyx.

Question 15

Answer 15

Renal papillary necrosis

Note: Linear streaks/filling defects in renal calyces.

Question 16

What percentage of pts with sickle cell disease develop renal papillary necrosis?

Answer 16

50%

Question 17

Answer 17

Xanthogranulomatous pyelonephritis (in the setting of stag horn calculus)

Note: Characteristic “bear paw” appearance. This kidney is not functional.

Question 18

Xanthogranulomatous pyelonephritis

Answer 18

A chronic destructive granulomatous process involving the kidney (virtually always seen in the setting of a stag horn calculus), giving a characteristic “bear paw” appearance on CT. The affected kidney is not function and sometimes treated with nephrectomy.

Question 19

Pts with xanthogranulomatous pyelonephritis are at high risk for…

Answer 19

Psoas abscess

Question 20

AIDS pt with nephrotic syndrome (massive proteinuria)…

Answer 20

HIV nephropathy

Note: Bilateral hyperdense kidneys (more dense than liver) in an AIDS pt with nephropathy.

Question 21

Diagnosis of HIV nephropathy

Answer 21

Biopsy

Question 22

Most common cause of renal impairment in AIDS pts

Answer 22

HIV nephropathy

Question 23

HIV pt

Answer 23

Disseminated PCP infection

Note: Punctate cortical calcifications, appears the same as cortical nephrocalcinosis.

Question 24

What is the most common extra-pulmonary site of tuberculosis?

Answer 24

Urinary tract

Question 25

What is the earliest finding of renal tuberculosis?

Answer 25

Calyceal blunting (“most eaten calyces”)

Note: This is nonspecific and can be seen with ischemia, diabetes, etc.

Question 26

Answer 26

Renal tuberculosis

Note: Dilated calyces with “cavity” formation and calcifications.

Question 27

Answer 27

Renal tuberculosis

Note: Distorted calyces with dilatation and papillary necrosis and classic “Kerr Kink” at the renal pelviureteral junction.

Question 28

Answer 28

Renal tuberculosis

Note: Complete replacement of the kidney with calcifications (“putty kidney”).

Question 29

What peritoneal sign might help you identify renal abnormalities as renal tuberculosis?

Answer 29

The presence of multiple calcified mesenteric lymph nodes

Question 30

Risk factors for contrast-induced nephropathy

Answer 30

• Renal insufficiency
• Diabetes
• Heart failure
• Dehydration
• Myeloma

Question 31

What can be done to minimize contrast induced nephropathy in high risk pts?

Answer 31

IV 0.9% normal saline 6-12 hours before the study and continuing 4-12 hours after

Note: Oral hydration does not work as well.