Calyceal Diverticulum

Calyceal diverticula are outpouchings of renal calyces or even renal pelvis (pelvi-calyceal diverticula) into the renal cortex connected by narrow neck. These are lined by non-secreting urothelium (transitional cell epithelium).

Incidence: 0.2-0.6% of patients undergoing renal imaging.

Usually these are incidental findings and are mostly asymptomatic. Due to stagnation of urine within the diverticulum, these are prone for stone formation. Stones can be found in upto 50% of the calyceal diverticula.

Exact etiology of the formation of calyceal diverticula are not known, may be congenital or acquired due to infections, VUR, or rupture of a cortical cyst.

These are subdivided into two types:¹
Type 1 communicating with a calyx, usually found in upper pole.
Type 2 communicating with renal pelvis, larger, usually found in mid-pole (also called pyelo-calyceal diverticula). Radiopaedia adopts a slightly varied types, with type 1 from minor calyx and type 2 from major calyx or renal pelvis.²

There may be internal calcifications, either in the form of stones or of milk of calcium. In one small ultrasound series, 7 of 11 cases of calyceal diverticula demonstrated mobile echogenic material. It is suggested that the presence of mobile hyperechogenic material within a cystic structure is diagnostic of a calyceal diverticulum. ³

Differential considerations of a calyceal diverticulum would include complex cyst, dilated calyx, cystic renal neoplasm and abscess. Unless an excretory (or urogram) phase is acquired diagnosis of calyceal diverticulum is not possible. Dilated calyx can be due to obstructing stone, tumor or due to infundibular stenosis in TB.



The following plain and contrast CT images are of a 40 year old male patient who was evaluated for left lumbar pain and tenderness.

Plain CT Axial sections showing calcific focus within a subtle hypodense area in the bilateral renal parenchyma. 

Type I Bosniak cyst is noted medially (not marked).

The above three images shows the Plain CT, venous phase and excretory phase axial sections of both kidneys, which shows contrast filling of the cystic appearing area in the venous phase - consistent with the diagnosis of Calyceal Diverticulum of both kidneys. Calculus formation is noted in both these calyceal diverticulum. 

Oblique coronal MIP image showing the contrast filled bilateral calyceal diverticulum (Green arrows). The yellow arrow points to the pathology for which the patient underwent the CT examination (colitis). As in most cases, this case of bilateral calyceal diverticulum was also asymptomatic.  

3D VRT image demonstrating the calyceal diverticula. 

References
1. Mullett, Rebecca et al. “Calyceal diverticulum - a mimic of different pathologies on multiple imaging modalities.” Journal of radiology case reports vol. 6,9 (2012): 10-7. doi:10.3941/jrcr.v6i9.1123

2. Stunell, H et al. “The imaging appearances of calyceal diverticula complicated by uroliathasis.” The British journal of radiology vol. 83,994 (2010): 888-94. doi:10.1259/bjr/22591022

3. Reynard J, Brewster S, Biers S. Oxford Handbook of Urology. Oxford: Oxford University Press; 2006. p. 328.

4. Leveillee RJ, Bird VG. Treatment of Caliceal Diverticula and Infundibular Stenosis. In: Smith AD, Badlani G, Bagley D, et al., editors. Smith’s Textbook of Endourology. 2nd ed. Ontario: BC Decker; 2007. pp. 171–185.

RARE : Extreme case of bilateral massive renal replacement lipomatosis

Renal Replacement Lipomatosis (RRL) a.k.a Replacement fibrolipomatosis, an extremely rare condition, considered as an advanced form of renal sinus lipomatosis.The latter one is a milder form of the spectrum where the normally present renal sinus fat becomes prominent with ageing, obesity or exogenous steroids. Then again, how extreme can it go?

Renal Replacement Lipomatosis (RRL) is usually associated with infection, long term hydronephrosis, calculi and severe renal parenchymal atrophy. Renal calculous disease along with inflammatory changes are present in ~70% of the cases, and these produced symptoms of flank pain and fever.

The patient is a 60 yr old female patient with non-specific abdominal symptoms.

The above image is the non-contrast (plain) CT images which shows diffuse heterogeneous fatty tissue, filling almost the entire abdomen. On further inspection, we can see the fatty tissue is replacing the normal renal parenchyma (orange arrows), and are displacing the retroperitoneal structures like pancreas and duodenum anteriorly. Both kidneys are markedly enlarged, with near complete fatty replacement of the left kidney. Right kidney shows residual parenchyma (green arrow) in lower pole and in the interpolar region (mid-third). A few discrete fatty lesions (blue arrow) are also seen in the residual right renal parenchyma.

Above image shows the mass effect of the enlarged kidneys.

MIP (31mm) image on left shows the bilateral inferiorly oriented renal arteries, residual enhancing parenchyma of right kidney with fatty lesions. On the right, the axial post contrast images show the marked anterior displacement of the ascending colon (blue arrow) and descending colon (orange arrow).

3D VRT right lateral, frontal and left lateral views again shows the mass effect on colon which are seen markedly displaced anteriorly, against the anterior abdominal wall. Contrast filled small bowel loops are seen in RIF region.

3D VRT image showing the orientation of bilateral main renal arteries.

Delayed MIP images showing contrast excretion into the pelvicalyceal system of both kidneys. Right proximal ureter is marked by the orange arrow.

Delayed MIP axial and coronal images showing the right proximal ureter (orange arrow) and green arrows point to the opacification of pelvicalyceal system. No significant delay in contrast excretion was noted in this patient.

3D VRT of delayed excretory phase showing contrast within the pelvicalyceal system of both kidneys.

As expected renal veins showed moderate dilatation, with left renal vein measuring up to 17mm in diameter.





REFERENCES :

Indian J Nephrol. 2010 Apr; 20(2): 92–93. doi:  10.4103/0971-4065.65303, PMCID: PMC2931141, Renal replacement lipomatosis: A rare type of renal pseudotumor, N. A. Choh, M Jehangir, and S. A. Choh. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2931141/

Setty N, Uma K, Narvekar V N, Desai R S. Bilateral idiopathic replacement lipomatosis of the kidney with posterior mediastinal lipomatosis. Indian J Radiol Imaging [serial online] 2002 [cited 2017 Jun 21];12:251-2. Available from: http://www.ijri.org/text.asp?2002/12/2/251/28457

CASE OF BILATERAL PYELONEPHRITIS

Case : Bilateral Pyelonephritis.

Discussion on : 

1. Appearance of Pyelonephritis on USG and CECT.

2. Acute Pyelonephritis Vs Renal Infarct.

Patient is a 35year old diabetic female, who presented with fever with chills, right upper quadrant and loin pain, with Urine examination showing plenty of pus cells, RBCs and Bacteria.

Clinical diagnosis was of acute right pyelonephritis.

USG showed only hypoechoic mildy enlarged kidneys bilaterally. No urolithiasis / hydroureteronephrosis was seen.

CECT was done, which showed areas with relative lack of enhancement in lower and posterior interpolar region of right kidney and upper pole of left kidney. Only  minimal perinephric fat stranding was seen. Minimal pararenal fascial thickening was seen on right side only.

No urolithiasis / hydroureteronephrosis was seen in CT.

Click on the images to view full size.

ACUTE PYELONEPHRITIS Vs SEGMENTAL RENAL INFARCTS

In segmental renal arterial infarcts, the peripheral most cortical supply gets derived from the capsular arteries, which shows an enhancing rim around the infarct - which is called as the Cortical Rim Sign. This is not seen in Pyelonephritis, in which case the entire thickness is involved. Rim sign is however only seen in approximately 50% cases of renal infarcts.

ACUTE PYELONEPHRITIS

Image courtesy of Dr Frank Gaillard From the case Acute pyelonephritis

Cortical Rim Sign : SEGMENTAL RENAL INFARCTS

Image courtesy of Dr Frank Gaillard, Radiopaedia.org. From the case Renal infarction

CECT findings of Acute Pyelonephritis (abnormal in 65-90%):

1. Perinephric fat stranding and pararenal fascial thickening.
2. Hypoattenuating (80-90 HU) wedge-shaped area of cortex extending from papilla to renal capsule
3. During nephrographic phase(= lobar segments of hypoperfusion +edema)
4. Striated nephrogram
5. Poor corticomedullary differentiation
6. Dense parenchymal staining on scan delayed 3-6 hr in area of earlier diminished enhancement(= functioning renal parenchyma)
7. Soft-tissue filling defect in collecting system (=papillary necrosis, inflammatory debris, blood clot) calyceal effacement.

CT is best for detecting presence of calculi, level of obstruction and complications.

 

 US findings in Acute Pyelonephritis (abnormal in <50%):

1. Swollen kidney of decreased echogenicity – (kidney becomes more globular, with increased AP dimension. The parenchymal thickness sometimes appears to be increased because of parenchymal edema.)
2. Loss of central sinus complex (Sometimes described as effacement of renal sinus fat)
3. Wedge-shaped hypo to isoechoic zones, rarely hyperechoic (due to hemorrhage)
4. Thickened sonolucent corticomedullary bands
5. Blurred corticomedullary junctions
6. Localized increase in size + echogenicity of perinephric fat ± fat within renal sinus
7. Localized perinephric exudate
8. Thickening of wall of renal pelvis
9. Focally decreased blood flow on power Doppler.

Ultrasound is often the first imaging study, and it is difficult to diagnose Pyelonephritis by USG.

Differentiating between Ascending and Hematogenous infection may not be possible, however these points might be of some help -

            'In acute bacterial nephritis, the alternating bands of hypo- and hyperattenuation, which correspond to differential enhancement of infected and noninfected parenchyma, are sharply defined. Over time, the differential enhancement becomes less distinct and ultimately will either completely normalize or evolve to scar, as evidenced by loss of parenchymal volume. When round, peripheral hypoattenuation renal lesions are seen in the clinical setting of pyelonephritis, hematogenous seeding should be considered'. [3]



References : 

• [1] Dahnert, Radiology Review Manual 7th Edition.
• [2] Radiopedia.org article on Cortical Rim Sign.
• [3]  Pyelonephritis: Radiologic-Pathologic Review, Radiographics.

XGP Vs Replacement Lipomatosis of Kidney

Xanthogranulomatous pyelonephritis is characterized by microscopic fat infiltration of the renal parenchyma. Fat cells remain outside the atrophied renal parenchyma in replacement lipomatosis.


Reniform shape of the kidney is maintained in both replacement lipomatosis and xanthogranulomatous pyelonephritis.


Both xanthogranulomatous pyelonephritis and replacement lipomatosis are usually unilateral.

DDs for Replacement Lipomatosis 


1.Xanthogranulomatous pyelonephritis (XGP)


Enlarged kidney with preserved shape and decreased function that occurs in the presence of long-standing inflammation and calculi (typically staghorn)


Lipid-laden macrophages actually infiltrate renal parenchyma in contrast to replacement lipomatosis in which fat cells remain outside of the atrophied renal parenchyma


Characterized by renal tissue destruction and replacement with hard, yellow, xanthogranulomatous material


Ultrasound shows hypoechoic areas representing purulent material, as well as medium-amplitude echoes corresponding to the fibrofatty and/or necrotic debris


CT shows hydronephrosis or pyonephrosis along with xanthogranulomatous tissue, which typically has attenuation values close to that of water


XGP and replacement lipomatosis may coexist


2. Lipoma


3. Angiomyolipoma


4. Liposarcoma