I think @beastaran1 has the correct explanation but I just want to say his kidney is "abnormally small and nonfunctional" which means that it is not being used. When the body doesn't use something (like a muscle) it atrophies. So tubular atrophy makes sense.
Atrophy = gradual decline in effectiveness or vigor due to underuse or neglect.
When a question seems wildly complicated and you have no idea what's going on, take a deep breath and explain it to yourself like you're five.
Believe this one is tubulointerstitial fibrosis of the kidney:
medullary cystic disease is characterized by autosomal dominant inheritance pattern progressive and slow impairment in renal function that ultimately results in end-stage renal disease no or minimal proteinuria with a bland urine sediment medullary cysts on renal ultrasound in most cases medullary cysts are not present can see shrunken kidneys on ultrasound
I think that this is a ureteric stricture or ureteropelvic junction obstruction (not sure if they are the same thing) but according to sketchy, it is the most common cause of unilateral fetal/congenital hydronephrosis and most commonly happens in those who Saturdays are for.. ;)
Hydronephrosis causes tubular atrophy from compression of the tubules by urine. Two common causes of hydronephrosis in infants and young children include pelvic-urethral obstruction and vesicourethral reflux.
AD tubulointerstitial kidney disease: Also called medullary cystic kidney disease. Causes tubulointerstitial fibrosis and progressive renal insufficiency with inability to concentrate urine. Medullary cysts usually not visualized; smaller kidneys on ultrasound. Poor prognosis. FA2020 page 602
submitted by โanechakfspb(77)
Just a rant - i hate this f*cking picture it's been on 3 NBMEs now and every time I've gotten it wrong.