Thickening of the renal pelvis: spectrum of CT findings · Please note: Links to movies, ppt...

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Thickening of the renal pelvis: spectrum of CT findings

Poster No.: C-1708

Congress: ECR 2014

Type: Educational Exhibit

Authors: D. Coll, C. Yanguas, M. J. Diaz-Ruiz, R. Monmany, O. Valencoso,J. Trullas; Manresa/ES

Keywords: Abdomen, Kidney, Urinary Tract / Bladder, CT, Education,Calcifications / Calculi, Cancer, Edema

DOI: 10.1594/ecr2014/C-1708

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Learning objectives

To describe the CT findings of renal pelvic wall thickening and to correlate them withtheir etiology.

Background

The renal sinus is a spacious central cavity formed by the extension of the perinephricspace into the deep recess located at the medial border of the kidney, and is surroundedby the renal parenchyma. It is occupied by the major branches of the renal artery andvein, the major and minor calyces and the renal pelvis, the kidney's collecting system. Theremainder of the sinus contains adipose tissue, lymphatic channels, nerve fibers of theautonomic nervous system, and varying quantities of fibrous tissue Fig. 1 on page 3 .

The renal pelvis is thin-walled. The tissue composition of the renal pelvis, ureters,bladder and urethra is comparatively simple. Each of these elements has a wall lined bytransitional epithelium (urothelium) containing smooth muscle.

Usually the renal pelvis is non-dilated and may be ectatic and extrarenal.

Various imaging techniques can be used to evaluate pathological conditions affecting therenal pelvis, including US, CT and MR imaging.

US is the initial screening technique for noninvasive imaging of the kidney. The normalrenal sinus appears as an area of increased echoes with variable contours due to the fat-parenchyma interface. A collapsed renal pelvis may be indistinguishable from echogenicrenal sinus fat. Though in general US obtains good results, it has limitations, especiallyin the case of small lesions, when the renal sinus lesion is poorly defined, or if the echopattern is similar (or identical) to that of the adjacent renal sinus fat or adjacent renalparenchyma.

CT is the most sensitive, efficient, and comprehensive imaging technique for evaluatingthe kidney and is the technique of choice for a wide variety of renal sinus lesions.

A typical CT urography protocol has three phases which allow complete evaluationof the most common urologic causes of hematuria: that is, calculi, renal masses, andurothelial tumors. After an initial unenhanced acquisition, nephrographic phase imagesare acquired 90-100 seconds after administration of a nonionic contrast agent (100-150mL of 300 mg I/mL at 2-4 mL/s). Pyelographic phase images are acquired 5-15 minutes

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after contrast administration to evaluate the urothelium from the kidneys to the bladderFig. 2 on page 4. Sometimes, an arterial phase acquired 20-25 seconds afteradministration of a nonionic contrast agent is obtained.

MR imaging is an alternative to CT for evaluation of renal sinus lesions. It can also beused in patients with renal failure or contrast material allergies.

The clinical presentation of the thickening of the renal pelvis varies widely: it may beasymptomatic, cause colicky pain and hematuria, or present clinical and analytical signsof sepsis.

Treatment options vary depending on the etiology, which may be inflammatory (pyelitisor pyeloureteritis related to lithiasis), catheter-related or idiopathic, infectious (relatedto tuberculosis or bacterial infection), or neoplastic (related to urothelial carcinoma orlymphoma).

Knowledge of the various radiological manifestations of the etiologies of thickening of therenal pelvis is the key to correct diagnosis and the selection of optimal treatment.

Images for this section:

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Fig. 1: Diagram showing the normal anatomy of the renal sinus and its major constituents

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Fig. 2: Normal uro-CT. A. Unenhanced acquisition. B. Nephrographic phase. C axialand D and coronal view of pyelographic phase. Normal renal pelvis (white arrow) in thedifferent phase images.

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Findings and procedure details

The renal pelvis may present a variety of abnormalities, which either arise primarily fromsinus structures or extend into it secondarily from the adjacent cortex or retroperitoneum.

Thickening of the renal pelvis may have an inflammatory/infectious or neoplastic etiologyand may be mucosal or submucosal. The identification of additional radiological featuresbesides wall thickening - lithiasis, pyelonephritis, alterations in renal parenchyma,segmental or diffuse thickening or the presence of air, retroperitoneal adenopathies orthe association with clinical and analytical findings - facilitate accurate diagnosis.

In this study, we describe patients with radiological alterations of the renal pelvis on CTand correlate these abnormalities with the clinical and pathological evolution.

FALSE THICKNESS OF THE RENAL PELVIC WALL

1.- Vascular attachment to renal pelvic wall

Vascular structures in the renal pelvis such as an artery or a vein may occasionallysimulate a false increase in renal pelvic wall thickness. Fig. 3 on page 11

PRIMARY ABNORMALITIES OF THE RENAL PELVIS

1.- INFLAMMATORY ETIOLOGY

Lithiasis

Impaction of kidney stones in the renal pelvic wall may cause inflammatory changes inthe urothelial epithelium. These CT images show a thick renal pelvic wall and radiodensestones. Fig. 4 on page 11

Pyeloureteritis

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Pyeloureteritis is a rare entity that may simulate a urothelial neoplasm. Diagnosis is basedon clinical symptoms and laboratory findings. In this case, symptoms disappeared withantibiotic treatment. Fig. 5 on page 12 and Fig. 6 on page 12

2.- INFECTIOUS ETIOLOGY

Bacterial pyelonephritis

In acute pyelonephritis, the use of CT is usually reserved for patients whose clinicaldiagnosis is unclear, patients who fail to respond to conventional medical treatment,diabetics, and other immunocompromised patients. Bacterial renal infections, exceptthose caused by Gram-positive organisms, occur via the ascending route and spana continuum of varying severity from uncomplicated acute pyelonephritis throughprogressively worsening stages of interstitial inflammation to frank abscess formation.

Wedge-shaped areas of hypoattenuating cortex and poor corticomedullary differentiationon a nephrographic CT scan is typical of acute pyelonephritis. CT commonlydemonstrates other signs of renal infection, including soft-tissue stranding and thickeningof the Gerota fascia, obliteration of the renal sinus and calyceal effacement due toadjacent affected renal parenchyma, thickening of the walls of the pelvis and calycesandmild dilatation of the renal pelvis Fig. 7 on page 13 and ureter.

TBC pyelonephritis

The genitourinary tract accounts for 4-17% of extrapulmonary infections. Urinaryfrequency, pain, hematuria, and sterile pyuria may occur. The upper renal tract is the mostfrequently affected part of the genitourinary tract, and the renal parenchyma and uppercollecting system are often simultaneously involved. Renal parenchymal involvement canappear as focal nephritis, nodular mass (tuberculoma), or parenchymal scar formation.Focal nephritis appears in the form of wedge-shaped areas of reduced enhancement thatis identical in appearance to nephritis caused by other organisms. Nodular mass is anuncommon finding that may be mistaken for a tumor. Parenchymal scars and calcificationcan develop following healing by fibrosis. The earliest change in the upper collectingsystem is papillary necrosis, which may appear as small poorly defined areas of reducedenhancement at the tip of the medullary pyramids, or as calyceal clefts and cavities.Late changes in the upper collecting system changes include wall thickening and fibrosisFig. 8 on page 13 . Infundibular strictures can cause focal or uneven caliectasis.Renal pelvis involvement may appear as a smooth, angulated kink (Kerr's kink) withgeneralized hydronephrosis or diffuse pelvic contraction. Irregular ureteral thickeningcan show contrast enhancement and cause proximal hydro-ureteronephrosis. End-stagetuberculosis can result in autonephrectomy, in the form of a shrunken, poorly functioning

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kidney with parenchymal thinning, severe hydronephrosis, and lobar calcification. Lobarcalcification occurs as a result of dystrophic calcification within caseous debris, and itcan form a cast of the kidney (putty kidney) when it is diffuse. Advanced ureteral fibrosiscauses a pipe-stem, corkscrew, or beaded appearance of the ureter owing to multiplestrictures, and mural calcification may occur.

Emphysematous pyelitis

Emphysematous pyelitis (EP) is a gas-forming urinary tract infection associated withgas localized exclusively in the renal collecting system. This entity is cited in radiologytextbooks and is associated with diabetes mellitus and obstruction of the collectingsystem. However, to our knowledge, only two isolated cases have been described ascase reports in the literature.

The diagnosis of EP is often delayed because clinical manifestation may be nonspecificand resemble that of uncomplicated acute pyelonephritis. On radiographs, themanifestation of this disorder is similar to findings on gas pyelograms, with gas inside thepelvocalyceal system. The gas may be present in the ureters and on rare occasions maybe associated with emphysematous cystitis. Although abdominal radiography usuallyallows easy detection of air, the sensitivity reported with radiography is low (33%). Thisis due to difficulty in differentiating renal gas from air in overlying loops of bowel.

In patients with diabetes and febrile urinary tract infection, US is recommended fordetecting urinary tract obstruction. The typical US appearance of gas-producing renalinfections comprises high-amplitude flat anterior margin echoes within the renal sinusor calyces, which are associated with distal shadowing containing low-level echoes andreverberations. In theory, this dirty shadowing can be differentiated from the more distinctecho-free clean acoustic shadowing that occurs distally to renal calculi. US providesless specific information about gas-producing renal infection because of the potentialconfusion with either air or renal calculi or calcifications within the kidney. In practice,confusion is possible and US images may be difficult to interpret. CT is the most reliablediagnostic imaging technique currently available for this purpose. Ureteral stones canbe accurately evaluated and differentiated from intracalyceal, intrapelvic, or perinephricgas collections. CT is a sensitive technique that is able to demonstrate and accuratelylocate air within the calyceal system, thus allowing its elimination from/within the kidneyparenchyma and/or pararenal spaces. CT allows both accurate diagnosis and stagingFig. 9 on page 13 .

Indeed, EP should be differentiated from the reflux of air or gas from the bladder orfrom ileal ureterosigmoidostomy. The spontaneous appearance of gas within the upperurinary tract has three main origins: iatrogenic manipulation (i.e, ureteral instrumentation,

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surgical or interventional radiologic procedure), fistulous connection with a hollow viscus,or bacteria caused by reflux from the bladder.

The overall mortality rate of EP is low. If gas is localized in the collecting system and noobstruction is present, antibiotic therapy alone appears to be sufficient. CT can indicatethe complete resolution of air and dilatation of cavities.

3.- NEOPLASTIC ETIOLOGY

Urothelial neoplasms

Transitional cell carcinoma (TCC) is commonly encountered in the urinary bladder andis usually diagnosed at cystoscopy. Five per cent of urothelial tumors arise from theureter or the renal pelvis or calyces, accounting for approximately 10% of upper tractneoplasms. Patients with TCC typically present with hematuria, which may be frank ormicroscopic. Up to one-third of patients present with flank pain or acute renal colic,symptoms more typically associated with calculi. Occasionally, tumors may manifest withdistant metastases or be discovered incidentally on radiologic examination.

Renal TCC most frequently arises in the extrarenal part of the pelvis, followed by thethe infundibulocalyceal region. It is distributed equally between the left and right kidneys,with 2%-4% of cases occurring bilaterally. Twenty-five per cent of upper tract tumorsoccur in the ureter, whereas 60%-75% of cases are found in the lower third, with no sidepredominance. Tumor spread occurs by mucosal extension or by local, hematogenous,or lymphatic invasion. The most common sites for metastases are the liver, bone, andlungs. The tumor stage at diagnosis influences the development of local recurrence andmetastases and hence overall survival. Multicentric TCC is common and is associatedwith poor survival. Synchronous or metachronous tumor of the ipsilateral or contralateralcollecting system is also common, necessitating careful urologic and radiologic follow-up.

Upper tract TCC typically occurs in the sixth and seventh decades of life, affectingmales three times more often than females. Besides increasing age and male gender,the most important risk factor is smoking, with smokers being two to three times morelikely to develop TCC than nonsmokers. Chemical carcinogens (aniline, benzidine,aromatic amine, azo dyes), cyclo-phosphamide therapy, and heavy caffeine consumptionare also associated with TCC, and all predispose to synchronous and metachronoustumor development. These substances are metabolized and excreted in the urine ascarcinogenic substances which act locally on the urothelium. Stasis of urine and structuralabnormalities such as horseshoe kidney are also associated with increased prevalence.

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These tumors are usually small at diagnosis, grow slowly, and follow a relatively benigncourse. Pedunculated or diffusely infiltrating tumor is less common, accounting forapproximately 15% of upper tract TCCs, but tends to behave more aggressively andbe more advanced at diagnosis. Infiltrating tumors are characterized by thickening andinduration of the ureteral or renal pelvic wall. If the renal pelvis is involved, there is ofteninvasion into the renal parenchyma Fig. 10 on page 14 . However, this infiltrativegrowth pattern preserves the renal contour and differs from renal cell carcinoma, whichis typically expansile.

SECONDARY ABNORMALITIES OF THE RENAL PELVIS

1.- Renal neoplasms

Although renal collecting system invasion is not considered in the current TNM stagingsystem of renal cell carcinoma, this finding may be relevant in terms of treatment planningand prognosis.

Collecting system invasion exclusively in renal cell carcinoma with excretory phase CTimages presenting a filling defect within the collecting system account for 5.4% of cases.Fig. 11 on page 15

2.- Lymphoma

Renal lymphoma appears in a wide variety of forms on CT. In many cases, diagnosisis not difficult because patients present with a known lymphoma at the time of imaging.Lymphoma typically involves the kidney, in one of several recognizable patterns includingmultiple renal masses, solitary masses, renal invasion due to contiguous retroperitonealdisease, perirenal disease, renal sinus involvement and diffuse renal infiltration. Nospecific correlation has been found between the exact type of lymphomatous involvementand the pattern or prevalence of renal involvement.

Direct renal invasion from contiguous retroperitoneal disease is another common patternof involvement in renal lymphoma, and is seen in approximately 25%-30% of patients withdocumented disease. These patients typically present with a large, bulky retroperitonealmass that envelops the renal vasculature and invades the renal hilum. Lymphoma mayaffect the renal sinus, although this is uncommon. In most patients, the renal arteriesand veins remain patent despite tumor encasement. However, contiguous extension ofretroperitoneal involvement in the renal collecting system can often cause obstruction,and affected patients will commonly present with hydronephrosis Fig. 12 on page 16. Transitional cell carcinoma is usually associated with a greater degree of obstruction

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of the collecting system Fig. 13 on page 16 . Displacement of the kidney can also beseen. Following treatment of larger masses, residual fibrosis is often seen and can bemistaken for recurrent or residual disease.

Images for this section:

Fig. 3: Normal uro-CT with a left renal sinus artery (black arrow) simulating an increasein renal pelvic wall thickness. A. Axial nephrographic phase. B. Coronal nephrographicphase.

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Fig. 4: Pyelouretheral junction impaction of stones (white arrow) increasing the thicknessof the renal pelvic wall (black arrow). A and B. Axial nephrographic phase.

Fig. 5: 57-year old male with left colic pain, fever and leukocytosis. A Axial unenhancedCT. B Axial nephrographic phase CT. C Axial pyelographic phase CT, demonstratingrenal pelvic wall thickness (white arrow). One month after medical treatment, renal pelvicwall had returned to normal (black arrow). D Axial nephrographic phase, and E Axialpyelographic phase.

Fig. 6: Ureteral wall thickness (white arrow) was also present in the same case asfigure 5. A Coronal unenhanced CT, B Coronal pyelographic phase CT, demonstrating

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ureteral wall thickness with periureteral fat stranding. C Coronal pyelographic CT showingresolution after one month of medical treatment.

Fig. 7: Acute pyelonephritis in a 27-year-old woman with fever that did not remit with oralmedical treatment. A and B, Axial nephrographic CT showing wedge-shaped areas ofhypoattenuating cortex (black arrow) and thickness of the renal pelvic wall (white arrow).

Fig. 8: Tuberculous pyelonephritis in a 50-year-old man. Axial unenhanced images dueto renal failure, A and B, show mild dilatation and thickness of the renal pelvic wall (blackarrow) and of the ureteral wall (white arrow). Right kidney is slightly smaller than the leftkidney. Mycobacterium tuberculosis was cultured from urine.

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Fig. 9: 72-year-old man referred for low abdominal pain. A axial nephrographic CT, andB coronal nephrographic CT demonstrating gas and stones inside the renal pelvis (whitearrow) and thickness of the renal pelvic wall (black arrow).

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Fig. 10: 43-year-old man with left flank pain. A axial unenhanced CT, B axialnephrographic CT and C axial pyelographic demonstrating marked thickness of the renalpelvic wall (white arrow) suggestive of urothelial neoplasm. D coronal nephrographic CTshowing parenchymal extension of neoplasm in the mid left kidney (white asterisk).

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Fig. 11: 60-year-old man with left renal solid neoplasm. A axial nephrographic CT showsa large mass in the left kidney suggestive of renal cell carcinoma (white asterisk) invadingthe renal pelvis (white arrow); B coronal nephographic CT; other excretory structures arenot infiltrated (black arrow).

Fig. 12: 80-year-old woman with right colic pain. A axial unenhanced CT, B axialnephographic CT, and C axial pyelographic CT demonstrates marked thickness of therenal pelvic wall, associated with a retroperitoneal bulky mass; right renal function ispreserved, with correct uptake and elimination of the endovenous contrast agent. Thediagnosis was made by CT-guided percutaneous core needle biopsy, and the diagnosiswas non-Hodgkin lymphoma type B.

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Fig. 13: The same patient as figure 12. A axial pyelographic CT, and B coronalnephrographic CT demonstrating the invasion of the ureter (white arrow) by a bulkyretroperitoneal mass, without collapsed ureter lumen and preserved elimination ofintravenous contrast agent.

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Conclusion

Thickening of the renal pelvis on CT should be correlated with additional radiological andanalytical findings in order to establish the correct diagnosis.

Personal information

David Coll Gimenez

Fundació Althaia. Xarxa Assistencial Universitària de Manresa.

Barcelona. Spain.

[email protected]

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