Rapid review: Renal pathology


Below are 26 interactive, unknown DICOM cases covering a wide variety of renal pathology, with the intention of helping you to grow your case experience and diagnostic comfort with common and uncommon renal pathology. This is primarily geared toward residents, fellows, and practicing radiologist, though advanced medical students will also find this interesting.

You will notice that histories are omitted from the cases, which I felt would be too leading in many cases, and quite frankly, can unfortunately be misleading in real life. So the images will have to speak for themselves, and of course in real life you will have a clinical history and laboratory values to help confirm your diagnoses. Ultimately radiology is not about being right, but being responsible, and offering careful recommendations for management or futher workup to reach a diagnoses in unknown or challenging cases.

Quick tip: it is helpful to window/level manually for several cases to approximate a more aggressive "liver" window, which is not programmed into the DICOM viewer.

After jotting down your answers for each case, click on the text below to expand a detailed information including the history, peritient positives, negatives, differential diagnosis and teaching points for each case. Don't forget to check out the recommended reading at the end. Please help me by providing feedback!

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Warm up!

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Case 1: Pyelonephritis

History: Fever, flank pain

Pertinent positive: Symmetric renal enlargement, perinephric stranding, striated nephrogram, urothelial/ureteral thickening and enhancement, ?bladder wall thickening

Pertinent negative: No abscess or obstruction.

DDX: Recently passed stone or relieved obstruction; if hypoenhancement was more pronounced could consider embolic infarcts.

TP: Enhancement pattern is due to tubular obstruction with inflammatory debris, edema, and vasospasm. These same hypoenhancing areas often have persistent nephrograms on delayed images due to prolonged accumulation

Looking at the kidneys on coronal reforms with liver windows can help identify the striated nephrogram.

Case 2: Pyelonephritis complicated by abscess

History: Flank pain and fever

Pertinent positive: Right renal cortical hypoenhancement with coalescing small intrarenal collections. Right urothelial thickening and enhancement. Subtle hypoenhancement left upper renal pole.

Pertinent negative: no obstruction

DDX: urothelial carcinoma

TP: Take a moment and review the noncontrast exam with and without liver windows - would you have suspected pyelonephritis or abscess? Notice how much easier this is with contrast, and why it might be reasonable to recommend a repeated study with contrast in this setting. Notice how intrarenal abscesses can start small and coalesce, and often do not have the typical “rim-capsular enhancement” that you think of with abscesses.

Case 3: Urothelial carcinoma

History: Left lower quadrant pain, mild leukocytosis, normal urinalysis no fever or chills.

Pertinent positive: Enhancing soft tissue filling the left renal pelvis and proximal ureter. Infiltrative strandy soft tissue about the renal pelvis, proximal ureter, and vascular pedicle resulting in vascular narrowing. Dilated calyces, worse in the upper pole.

Pertinent negative: No significant bladder wall thickening, normal right kidney, no solid organ mets, no adenopathy

DDX: ECD, RPF, infection, lymphoma

TP: This case highlights an unusual appearance of a more invasive and infiltrative urothelial carcinoma involving the renal pelvis, resulting in obstruction of the upper pole calyces. The final pathology confirmed “invasive high-grade urothelial carcinoma with positive arterial margin involving the adventitia”. It is important to take the clinical picture into consideration here - the urine was not infected and there is no fever. Additionally, the infiltrative nature in the renal pelvis is unexpected and when you look carefully, it is enhancing and narrowing the vasculature, indicating a neoplastic or infiltrative process rather than infection.

Case 4: Pyelonephritis complicated by abscess

History: Flank pain and fever.

Pertinent positive: Striated right nephrogram. Severe left pyelonephritis with coalescensing abscesses and small areas of hemorrhage (high density on noncontrast).

Pertinent negative: Patent vessels. No obstruction.

DDX: urothelial carcinoma

TP: Again take some time to review the noncontrast exam - what features would have made you concerned about abscess? Would you recommend a contrast-CT based on that appearance? Did you notice the hemorrhage (high density)? Does liver windows help?

Case 5: Lithium-related nephrotoxicity with abscess


History: Flank pain, fever; long-term lithium use for bipolar disorder

Pertinent positive: normal sized kidneys with numerous uniformly distributed microcysts; larger, enhancing left renal cyst with subtle surrounding stranding

Pertinent negative: n/a

DDX: ADPKD, GCKD, medullary cystic kidney disease, and acquired cystic kidney disease; differentiated based on small size and distribution of cysts with relevant clinical history

TP: This is a typical look for microcystic disease associated with long term lithium use. The left renal abscess (treated with percutaneous drainage and abx) helps to highlight the differences in abscess versus sterile cystic change

Case 6: Pyelonephritis with abscess and obstructing proximal ureteric stone

History: Flank pain.

Pertinent positive: Obstructive right proximal ureteral stone, mild/moderate hydronephrosis, complex anterior cortical abscess, diffuse cortical hypoenhancement

Pertinent negative: Normal left kidney

DDX: focal XGP, chronic pyelonephritis

TP: This is a spectrum of severe pyelonephritis with obstructive proximal ureteric stone, complicated by a large abscess formation. It does not have typical features of XGP (cortical thinning, diffuse enlargement), but that is not worth getting caught up on - what is most important to remember here is that an infected, obstructed kidney needs urgent attention for decompression due to risk of sepsis, loss of kidney and death (i.e. call IR to evaluate for percutaneous nephrostomy tube placement).

Game time!

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Case 1: Massive hydronephrosis due to chronic UPJ obstruction, superimposed chronic infection + likely hemorrhage from MVC (history not provided)

History: Motor vehicle collision

Pertinent positive: Massive and abnormal right kidney: central stone, calyces blown out with layering calcifications, dense material in upper/posterior calyx which does not definitely enhance pre/post contrast. Small amount of retroperitoneal/peripancreatic fluid. Mild thickening/hyperenhancement of the right ureter with surrounding fluid.

Pertinent negative: No rupture into the retroperitoneum.

DDX: XGP, retroperitoneal mass, cystic RCC

TP: This is an extremely abnormal kidney. The dense material in the upper pole is initially concerning for urothelial tumor, but does not enhance and may be blood products related to the trauma. In terms of the distinction between severe hydronephrosis and xanthogranulomatous pyelonephritis (XGP), a few comments can be made: First, this is a chronically obstructed kidney due to a central staghorn stone with areas of thickening/fibrosis. Several of the calyces appear isolated due to fibrosis. There is likely some component of chronic inflection and inflammation here. The distinction of this being xanthogranulomatous or not (filled with lipid laden macrophages) probably doesn't matter. XGP often will rupture/decompress into the retroperitoneum, and does not usually reach this size. This is a surgical case either way.

Case 2: Localized cystic renal disease

History: 55 y/o male with incidental renal mass; stable for 3 years

Pertinent positive: Cysts replacing the left upper through interpolar cortex

Pertinent negative: no thickened septations, nodules, solid enhancing component

DDX: MEST, ADPKD, MCDK, cystic nephroma, cystic RCC;

TP: lack of capsule helps to differentiate from nephroma or cystic RCC. “Localized cystic renal disease is a rare condition in which a cluster of tightly spaced, variably sized cysts replaces a portion of or the entire renal parenchyma of one kidney” (Ref: 10.1148/rg.351130016)

Case 3: Chronic ureteropelvic junction obstruction

History: Left flank pain. Negative UA.

Pertinent positive: Severely dilated left renal pelvis and calyces with cortical thinning. Abrupt transition at the proximal ureteropelvic junction. Proximal ureteral enhancement.

Pertinent negative: No stone, rupture, discrete mass.


TP: This is a spectrum of the chronically obstructed kidneys (in this case due to a benign stricture), but in this setting there is no infection. It was managed with percutaneous nephrostomy and stent placement, with negative cultures, cytology and brushing indicating a benign process.

Case 4: Emphysematous pyelonephritis

History: Diabetes, flank pain.

Pertinent positive: Right renal parenchyma largely replaced by gas, with a small amount in the collecting system. Retroperitoneal gas extends to the left and mediastinum.

Pertinent negative: No extra-renal fluid collections. Patent vasculature. Normal left kidney.

DDX: Emphysematous pyelitis.

TP: Life-threatening necrotizing infection most common in diabetics. Requires aggressive medical management and often nephrectomy. E coli, Klebsiella pneumoniae, and Proteus mirabilis are most common organisms. A less severe subtype has nephric/perinephric collections with gas rather than such extensive parenchymal destruction with gas as in this case.

Case 5: Xanthogranulomatous pyelonephritis

History: Evaluate renal abnormality.

Pertinent positive: Enlarged left kidney with dilated calyces filled with low-attenuation material and a few small calcifications. Central staghorn calculus. Perinephric fluid/stranding with a small collection along the anterior upper pole. Ureteral thickening leading into an ill defined area of soft tissue stranding in the pelvis adjacent to a large cystic pelvic mass.

Pertinent negative:

DDX: urothelial carcinoma

TP: Typical appearance of XGP which was treated with nephrectomy. During surgery, there were dense inflammatory adhesions surrounding the kidney and ureter, resulting in a very challenging surgery. The distal ureteral thickening was related to chronic inflammation and infection (and not the pelvic cyst).

Case 6: Renal cell carcinoma


History: 50 y/o female with left renal mass.

Pertinent positive: Diffuse enlargement and replacement of the left kidney by infiltrative tumor, with an exophytic heterogeneous component along the posterior aspect. Tumor thrombus in the retroaortic vein terminating just before the IVC. Borderline adjacent lymph nodes. RP varices.

Pertinent negative: No collecting system dilation. Normal right kidney.

DDX: urothelial carcinoma, lymphoma

TP: This case helps to illustrate the appearance of a more diffuse/infiltrative RCC and the importance of identifying tumor thrombus for surgical planning. Making the distinction between urothelial neoplasm and RCC is not necessary as this need to proceed to biopsy either way for definitive diagnosis. However there are several aspects favoring RCC. Urothelial carcinoma rarely causes tumor thrombus as does RCC, offering a hint. There is more focal rounded mass indicating the tumor started there and infiltrated the rest of the kidney. There is no collecting system dilation often seen with urothelial tumor.


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Case 1: Perirenal lymphoma

History: Mantel cell lymphoma restaging

Pertinent positive: perirenal soft tissue infiltration, bladder wall thickening, RP and pelvic adenopathy, splenomegaly with small infarcts, pleural effusions

Pertinent negative: no obstruction, symmetric enhancement


TP: Unusual appearance of lymphomatous infiltration around the kidneys with a relatively symmetric appearance. It is helpful to be aware of the different renal/perinephric and retroperitoneal manifestations of lymphoma.

Case 2: Splenosis


History: Left perirenal mass. History of gunshot wound and splenectomy.

Pertinent positive: Retroperitoneal round enhancing mass along the posteromedial border of the left kidney distorting its contour. Smaller crescentic mass slightly lateral and superior. Few fine metallic bullet fragments in the overlying body wall. Splenectomy. Left lower quadrant colostomy.

Pertinent negative: No claw sign. No hydronephrosis.

DDX: RCC, primary retroperitoneal mass.

TP: The rounded mass may initially be concerning for renal cell carcinoma. However, notice that it distorts the contour of the kidney rather than arising from it (no "claw sign"), and thus other diagnoses should be considered. Also there is another smaller mass adjacent to it along the superior/lateral aspect (best seen on coronal images). The history of splenectomy due to gunshot wound (and overlying soft tissue metallic fragments) indicate that the retroperitoneum was likely violated at the time of injury and thus could be seeded with splenic tissue. This benign diagnosis was confirmed with sulfur colloid SPECT.

Case 3: Left peririenal/retroperitoneal leiomyosarcoma; right RCC

History: Renal mass evaluation.

Pertinent positive: Large, lobulated homogeneous left retroperitoneal mass displacing the left renal vein anteriorly and kidney inferiorly. Closely associated with the renal pelvis. Renal artery appears to run through it. Approximates the psoas with ? invasion. Partially calcified heterogeneous exophytic mass right renal pole. Pericardial effusion.

Pertinent negative: No tumor thrombus. No distant disease.

DDX: Lymphoma, exophytic RCC, other primary RP sarcomas.

TP: The most important thing to communicate in this case is that the masses are different processes and need to be addressed separately. The right renal mass looks like a typical RCC, and left mass is indeterminant for a primary renal versus retroperitoneal process (although the latter is favored given the unconvincing renal cortical involvement and displacement of the kidney inferiorly). The leiomyosarcoma was resected first due to greater risk for concern.

Case 4: Left perirenal/hilar lymphoma

History: Asymptomatic microscopic hematuria.

Pertinent positive: Infiltrative mass in the left renal pelvis with adjacent retroperitoneal adenopathy. Surrounds renal vessels and may involve renal vein. Upper pole calyceal dilation with excretion in the lower poles.

Pertinent negative: Normal right kidney. No distant sites of disease.

DDX: urothelial carcinoma, primary retroperitoneal tumor

TP: Lymphoma can have a variety of manifestations involving the kidneys. Symmetric renal involvement may be most memorable, but I have personally seen more cases of perinephric masses of various sizes. This one is challenging but perhaps the fact that it seems centered on the hilum rather than within the collecting system, the bulky conglomerate RP adenopathy, and lack of lower pole obstruction might tip you toward an alternative diagnosis from urothelial carcinoma. Either way, this needs to be biopsied, which was performed with CT. The patient also had testicular involvement of lymphoma.

Case 5: Perirenal plasmacytoma; history of multiple myeloma. Notice right RP, pelvic, and muscular plasmacytomas indicating widespread disease

History: Multiple myeloma restaging

Pertinent positive: Left hilar soft tissue without obstruction. Bilateral RP/perirenal masses. Presacral and extraperitoneal pelvic/space of Retzius masses. Subcutaneous and muscular (right paraspinal) masses. Multiple bone lesions.

Pertinent negative: No obstruction. No adenopathy.

DDX: Lymphoma, melanoma, aggressive neoplasm.

TP: As multiple myeloma progresses, keep this diagnosis in mind, realizing that it can affect all organ systems. Expand your search pattern to carefully look for muscular and subcutaneous sites of disease, which might be targeted for radiation therapy for palliative intent.

Case 6: Erdheim Chester disease

History: Vague abdominal pain.

Pertinent positive: Infiltrative bilateral hilar/perihilar soft tissue with some perinephric component. Moderate left hydronephrosis. Periaortic soft tissue infiltration which involves the SMA and focally obstructs.

Pertinent negative: No solid organ masses. No adenopathy. Ureters not medialized.

DDX: RPF, lymphoma, igg4.

TP: Biopsy-proven case of Erdheim-Chester disease (ECD).

ECD is a non-Langerhan-cell histiocytosis of unclear etiology. It is characterized by abnormal proinflammatory cytokine response resulting in systemic proliferation and infiltration of histiocytes, and can involve any organ system. Bone pain most common presentation. Diagnosis made on the basis of imaging features and the presence of foamy histiocytes (CD68+ and CD1a-).

The major presenting feature on this case was the perirenal and renal hilar soft tissue infiltration. The differential for that finding alone includes:

-Erdheim-Chester disease ("hairy kidney")


-igG4-related sclerosing disease

-retroperiteonal fibrosis


-extramedullary hematopoesis


However, taking into account the additional findings of right atrial soft tissue thickening (only partially seen on the first few images, but a common feature of ECD), coating of the aorta/SMA, and absence of findings typical of the other diagnoses (e.g. no adenopathy for lymphoma, no auto-immune pancreatitis for igG4, RPF usually starts at the aortic bifurcation and ascends, no history of multiple myeloma, no hepatosplenomegaly for EMH or amyloidosis), ECD is the leading diagnosis.

After reading the CT, it would be reasonable to recommend the following:

-hematology or rheumatology consultation

-check igG4 levels (even though less likely, if they are elevated, this patient can be treated with steroids and avoid risk of biopsy)

extremity long bone radiographs to look for medullary sclerotic lesions typical of ECD

-depending on those results, PET/CT and bone scan can also play a role in evaluating the extent of disease and identifying the safest biopsy target. In this case, a first attempt was made at CT-guided biopsy of the left perirenal soft tissue thickening (not shown), but was unsuccessful. The bone scan was essential for identifying a target in the left tibia, which was occult on radiographs


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Case 1: Mucinous metastasis invading the left renal hilum; notice colectomy and right retroperitoneal implants

History: History of mucinous colorectal carcinoma and right hemicolectomy.

Pertinent positive: Soft tissue nodules in the right paracolic gutter/retroperitoneum likely invading body wall. Infiltrative soft tissue left renal hilum with thrombus in the left renal vein. Numerous surrounding varices.

Pertinent negative: No obstruction.

DDX: Lymphoma, primary retroperitoneal mass, urothelial carcinoma

TP: This is a tough case without the history. The major teaching point here is to remember that metastases can occur in the renal hilum and result in a confusing appearance that could be mistaken for primary urothelial tumor. The patient had a mucinous-type adenocarcinoma which can tend to cause atypical metastasis compared to non-mucinous adenocarcinoma.

Case 2: Complicated pyelonephritis with abscess

History: Flank pain, fever

Pertinent positive: Right striated nephrogram with minimal hydro and urothelial thickening and enhancement. More severe left involvement with coalescing abscesses with rupture along the lower pole. Mild to moderate left hydronephrosis. Bladder wall thickening.

Pertinent negative: No stones.

DDX: urothelial carcinoma.

TP: Familiarize yourself with uncomplicated pyelo on the right and complicated left pyelo with rupture of abscess into the retroperitoneum. This patient was treated with percutaneous drainage and antibiotics.

Case 3: Renal cell carcinoma with tumor thrombus

History: Flank pain.

Pertinent positive: Large hetergenously enhancing right lower pole mass with tumor thrombus extending into both renal veins (lower to the junction with the IVC, upper within the hilum only).

Pertinent negative: No obstruction. No mets.

DDX: urothelial neoplasm

TP: Typical case of a large RCC with enhancing tumor thrombus.

Case 4: Urothelial carcinoma

History: Hematuria; no fever.

Pertinent positive: Infiltrative mass replacing and expanding the left upper half of the kidney. Extends into left adrenal gland. Small surrounding lymph nodes. Ureteral thickening and enhancement.

Pertinent negative: No tumor thrombus. No obstruction.

DDX: pyelonephritis, RCC, lymphoma

TP: This case was unfortunately misinterpreted as pyelonephritis, but fortunately the astute ordering provider recommended urology follow-up because of the lack of infectious symptoms which resulted in a quick diagnosis.

Case 5: Emphysematous pyelonephritis

History: Diabetes, flank pain.

Pertinent positive: Replacement of much of the right kidney with gas. RP and collecting system gas. Surround fluid/stranding. Small ascites. Less severe involvement of the left kidney perinephric collections containing gas.

Pertinent negative: N/A.


TP: Bilateral involvement demonstrating the variety of severity with diffuse cortical destruction on the right and more minor involvement on the left centered on perinephric collections.

Case 6: Lithium related nephrotoxicity, left RCC, nonexclusive ischemic colitis descending colon

History: Left lower quadrant pain.

Pertinent positive: Normal-sized kidneys with diffuse cortical microcysts. Left upper pole mass. Descending colitis.

Pertinent negative: No obstruction.

DDX: Acquired cystic kidney disease.

TP: There’s a lot to look at here! Don’t miss the suspected left RCC which should undergo biopsy. The pattern of descending colitis is typical of nonocclusive ischemic colitis.

Case 7: Retroperitoneal fibrosis

History: Evaluate stent position, right renal mass.

Pertinent positive: Periaortic soft tissue infiltration extending from the bifurcation to slightly above the IMA. Medialization of the ureters with stenting of the left ureter, mild to moderate hydronephrosis, and delayed nephrogram.

Pertinent negative: No adenopathy. Aorta is not “lifted” by the soft tissue.

DDX: lymphoma, erdheim chester disease

TP: Typical case of retroperitoneal fibrosis. This was confirmed with CT-guided biopsy (notice the approach taken) which demonstrated “Fibroadipose tissue with fibroblasic/myofibroblasic proliferation, fibrosis and mixed chronic inflammation including plasma cells consistent with RPF; not sufficient for igG4-related.” RPF usually starts around L4-L5 at the bifurcation and ascends (this has been a very helpful principle for me), medializing and obstructing the aorta. While retroperitoneal lymphoma is a consideration, it typical “lifts” the aorta and displaces the ureters, NOT medializes them toward the mass.

Case 8: Renal infarct

History: Abdominal pain

Pertinent positive: Heavy atherosclerosis of the abdominal aorta with aneurysm and occlusion of the SMA and left common iliac artery. Occlusion of the left renal artery. Hypo-absent enhancement of the majority of the kidney without volume loss. Perhaps a tiny amount of capsular enhancement. Small amount of perinephric fluid.

Pertinent negative: No hydronephrosis.

DDX: Pyelonephritis.

TP: Occlusion of the left renal artery resulting in acute infarction in this vasculopathic patient, with absent enhancement of the majority of the left kidney. The preserved volume of the kidney with surrounding fluid indicates an acute presentation rather than chronic finding. A few areas of enhancement in the left kidney may be due to a tiny amount of flow preserved in the renal artery. Note is made of the common collateral pathway following SMA occlusion, which is likely reconstituted by the pancreaticoduodenal arcade from the celiac artery. See this case of mine for a better example of rim capsular enhancement: https://radiopaedia.org/cases/acute-renal-infarction-rim-capsular-enhancement?lang=us

Featured at RSNA 2020!

RSNA 2020 rapid review renal.pdf