Kidney

Xanthogranulomatous Pyelonephritis

Lithium Nephrotoxicity

• Basically multiple bilateral renal cysts

• Duration of lithium therapy increases the risk of ESRD

Medullary Sponge Kidney

• Dilatation of medullary and papillary ducts

  • Commonly from tiny stones

• Presents as recurrent renal colic/flank pain

• In image below you see dilated ducts that the arrows point to and i guess normally you should not see them

Retroperitoneal Fibrosis

• Literally fibrotic changes in the retroperitoneum typically for unknown cause/trigger although can be related to radiation, drugs, malignancy or pretty much anything else but vast majority of cases are idiopathic

• Fibrotic changes results in compression of ureters and vasculature -

  • If there is displacement of the Aorta, IVC there should be concern for malignant etiology

  • Classically there should be encasement but no invasion of these structures

• Maiden waist sign - medial deviation of the middle 1/3 of both ureters

Hypertrophy of Column of Bertin

• Refers to enlarged piece of renal cortex that protrudes through the medulla

• Commonly mistaken for a renal mass

• Isoechoic/Isointense/Isodense to renal cortex

• Will show communication with the regular peripheral renal cortex

• Usually unilateral and on the left

Hematoma

• Immediate to 1 week

• Look for echogenic debris

• Blood can be hypo, iso or hyper echogenic depending on acuity

Renal Doppler

Ureterocele

You need to check and make sure the “t” markers (as seen on first sequence in this photo) are at the top (red arrow) and bottom (green arrow) otherwise you will get wrong values.

The yellow line is the acceleration velocity and should be almost a straight line normally.

Renal Artery Stenosis US

• Normal Values

  • PSV < 180 cm/s

  • Proximal renal artery to aorta velocity ration < 3.5:1

  • AT < 0.07

  • RI < 0.08 and <5% difference between the two kidneys

Waveform seen in arterial stenosis, including RAS.

There is a stenosis so it takes longer to reach the peak velocity as there is a huge roadblock.

It also takes longer to get back to baseline values simply because there is less flow overall.

Renal Transplant US

• 3 major categories in pathology of the transplanted kidney

  • Vascular pathology

  • Urinary tract pathology

  • Post-op fluid collections, in the order they occur

    • Hematoma

    • Urinoma

    • Abscess

    • Lymphocele

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Immediate post-op Complications

• Renal allograft compartment syndrome

  • Typically presents 2 hours after surgery

  • The transplanted kidney is commonly in the extra-peritoneal space which is bound by the anterior and lateral abdominal walls and the peritoneum posteriorly

  • If there is direct compression on the organ or its blood supply it can result in HTN and organ ischemia

    • May be because the organ is large and not a lot of space, hematoma compression, etc.

  • So why not just place it in the peritoneum? —> too mobile —> high risk of torsion

• AVF

  • Look for aliasing + feeding artery with high velocity

  • Typically clinically insignificant because they are small

• Pseudo-aneurysm

  • Need intervention if >2 cm

  • May look like a cyst when doppler is not on

  • To and fro pattern of doppler flow = ying-yang sign

Post-Renal transplant Fluid collections

• In order occur as hematoma —> urinoma —> abscess —> lymphocele

• Need to evaluate for mass effect

Metabolic Disorders

Nutcracker Syndrome

• Compression of the left renal vein between aorta and SMA

• Can cause thrombosis, hematuria

Acquired Cystic Renal Disease

• 3+ cysts per kidney in patient with CKD

• Typically in long term dialysis patients

• Mildly increased risk of RCC - however the RCC that occurs tends to be less aggressive

Metastatic Disease

• Bronchogenic carcinoma is one of the most common causes of metastatic disease to the kidney

Renal Masses

Oncocytoma

• Benign mass

• Central scar

• No invasion of adjacent structures

• No hemorrhage or necrosis (is seen in RCC)

• Cannot definitively differentiate from RCC on imaging alone

• Note that just because a biopsy shows oncocytes does not mean it is benign, malignant masses can have oncocytes too, don’t assume presence of oncocytes means it is an oncocytoma

References:

• Case courtesy of Tom Foster, Radiopaedia.org, rID: 151112 (lithium renal disease)

• Case courtesy of Pablo Lorenzzoni, Radiopaedia.org, rID: 70005 (lithium renal disease)

• https://link.springer.com/article/10.1007/s00261-018-01890-4 (maiden waist sign)

• Case courtesy of Bruno Di Muzio, Radiopaedia.org, rID: 27754 (column of bertin)

• Case courtesy of Dennis Odhiambo Agolah, Radiopaedia.org, rID: 99867 (Renal Doppler)

• Case courtesy of Osamah A. A. Alwalid, Radiopaedia.org, rID: 61414