Urinary tract infections are the most common acquired cause of Vesicouteric Reflux (VR) in children. VR can lead to Reflux Nephropathy, which is characterized by chronic tubulointerstitial inflammation with fibrosis and scarring, leading to renal failure.

Is this saying there is vesicoureteral reflux? I could have sworm this same image was on form 20 or 21 and the answer was Wilms tumor

Why is this Intersitial Inflammation? I understand this is a VUR causing hydronephrosis.

I HATED this picture, just like everyone else, lol, so I did some more digging. Everyone below is correct, that the presentation is suggesting an infectious process. UTIs can cause acute pyelonephritis, and if chronic, progresses to chronic. Pyelonephritis is a tubulointerstitial disease. I found this information regarding it, and in the last part, it describes the gross pathology of chronic pyelonephritis. From my interpretation, it sounds like what the picture is showing, but I wasn't able to find a better/just as good one online yet, so I don't know for sure.

Acute Tubulointerstitial Nephritis: Acute inflammation of tubules and interstitium can cause ARF, and if the inflammatory process persists this can evolve into chronic tubulointerstitial nephritis and chronic interstitial fibrosis and tubular atrophy with risk of progression to end-stage kidney disease. Two major categories of acute tubulointerstitial nephritis are acute pyelonephritis and acute hypersensitivity tubulointerstitial nephritis.

Acute pyelonephritis: Caused by bacterial infection most commonly E. coli infection. Hypersensitivity tubulointerstitial nephritis: Caused by an allergic response, for example, to a drug or other substances that are ingested, such as herbal remedies.

By far the most common route of infection in acute pyelonephritis is an ascending infection in the urinary tract, for example, derived from a bacterial bladder infection. Acute pyelonephritis = extensive influx of PMNs within the interstitium, tubules (tubulitis), and lumens of tubules (WBC casts) (http://bit.ly/2JiPyBD).

With persistence or recurrence of acute pyelonephritis, the disease process evolves into chronic pyelonephritis, which usually is accompanied by marked erosion of the papillary tip resulting in dilation of the adjacent calyx (caliectasis).

The most characteristic pathologic features of chronic pyelonephritis are the gross changes in the kidney with broad-based scars in the parenchyma overlying areas of cortical and medullary atrophy with adjacent caliectasis. Also, the presentation suggests hydronephrosis, and from my research, hydronephrosis, when chronic/sever, can contribute to the marked loss of cortex and scars/fibrosis of the medulla (https://webpath.med.utah.edu/RENAHTML/RENAL007.html) and caliectasis (which I think is present on this picture). This is the closest picture with description I could find that matches the stem presentation (i.e. hydroureter and hydronephrosis, suggesting vesicoureteral reflux leading to infection from "a long standing obstruction (probably congenital)" so likely from a child) https://webpath.med.utah.edu/RENAHTML/RENAL008.html.

Also, to mention on the other comments expressing frustration that the same picture was used for tumors and tubular atrophy, from what I read, that gross pathology, is the general appearance of hydroureter due to obstructive uropathy (i.e. tubular atrophy, fibrosis/scarring, caliectasis/calyx dilation, and thin cortical rim due to atrophy. Pathologyonline.com says that the caliectasis is exaggerated in less severe cases/partial obstruction since GFR is not suppressed https://www.pathologyoutlines.com/topic/kidneyobstructive.html).

Hope this helps everyone! It sure helped me, but took WAY too long to understand, lol.

Picture shows dilated ureter and renal pelvis.

Picture shows dilated ureter and renal pelvis