Urinary tract congnital anomalies, cystic disease, urolithiasis, and obstructive disease

List the major types of congenital malformations affecting the kidney
Describe the anatomical and renal functional defects of the major types of congenital malformations affecting the kidney

The major types of congenital malformations affecting the kidney are agenesis of the kidney, kidney hypoplasia, ectopic kidneys, and horseshoe kidneys.

Agenesis

Agenesis involves the absence of one or both kidneys. Bilateral renal agenesis, also known as Potter's syndrome, is incompatible with life, as not only does it result in oligohydramnios (decreased urine output), it also results in hypoplastic lungs (small lungs that haven't formed properly). Fetuses with Potter's disease tend to have very "squashed" faces. Unilateral agenesis, on the other hand, is usually asymptomatic, partly because the remaining kidney may undergo compensatory hypertrophy. Patients with unilateral renal agenesis may also be other abnormalities of the genitourinary tract.

Hypoplasia

Hypoplastic kidneys have developed normally, but are small. Usually only one kidney is affected.

Ectopic kidneys

Ectopic kidneys are kidneys that aren't where they're supposed to be (between around T12 and L3). Usually ectopic kidneys are found in the pelvis due to failure to ascend, but rarely you might get a kidney that has managed to ascend all the way into the thorax. Most ectopic kidneys are either normal sized or slightly smaller.

Horseshoe kidneys

Horseshoe kidneys are formed from fusion of the upper or lower poles of the kidneys. They are usually located quite low down as their ascension is obstructed by the inferior mesenteric artery. Usually horseshoe kidneys have numerous renal arteries supplying them.

Outline the major types of cystic disease of the kidney in terms of aetiology, pathogenesis, clinical features and complications

Cystic diseases are, well, diseases in which there are cysts. There are a range of cystic kidney diseases, but in this post we will only focus on some of the main ones.

Simple renal cysts

Simple, or localised, renal cysts are incredibly common, especially in patients over the age of 50. However, simple cysts are usually asymptomatic. There is a risk of rupture, causing haematuria, pain, and so on, but usually the biggest problem with simple renal cysts is that a malignant tumour might be mistaken as a simple renal cyst. There are some clues, however, that might help in differentiating a malignancy from a simple cyst: multiple septa, thickened cyst walls, and solid areas within or around cysts are all clues to malignancy.

Cystic renal dysplasia

Cystic renal dysplasia is malformation of the kidney (or kidneys- it can be either unilateral or bilateral) with cysts of various sizes. It is a common cause of abdominal mass in infants. Under the microscope, kidneys look abnormal and have many immature structures.

Polycystic kidney disease

Polycystic kidney disease is characterised by fluid-filled cysts in the kidney. It comes in two flavours: autosomal dominant (ADPKD) and autosomal recessive (ARPKD).

ADPKD is the most common type of polycystic kidney disease. The three main genes identified are PKD-1, PKD-2, and PKD-3. Cyst formation begins in utero but progresses very slowly, so patients usually don't present until they are in their 30s or even in their 50s. Due to the formation of cysts, the kidneys can become quite large and the cysts can compress surrounding renal tissue. The resulting damage can cause symptoms such as pain and haematuria.

ARPKD is rare and involves the PKHD1 gene. The kidneys appear smooth and have small cysts. ARPKD, unlike ADPKD, presents quite early on (in childhood or even in infancy).

Classify the different forms of urinary tract obstruction according to aetiology, pathogenesis, morphology, clinical features and complications.
Explain how urinary tract obstruction can lead to kidney injury

Obstructive uropathy is a fancy term that refers to obstruction anywhere in the urinary tract. There are many causes of obstructive uropathy, but they tend to lead to dilation of the renal pelvis and calyces and eventual enlargement of the kidney. The bladder may also have a thick wall. Hydronephrosis may occur as a result of obstructive uropathy. In hydronephrosis, the urine backs up, causing distension and dilation of the renal pelvis and calyces. Eventually, this can lead to atrophy of the kidney, because while kidneys can dish out urine like it's nobody's business, they can't take it.

Urolithiasis, or kidney stones, is a common cause of obstructive uropathy. There are many types of kidney stones, all formed by various solutes precipitating out of solution. Dehydration, hypercalciuria, and several other conditions can all conspire to increase the risk of kidney stones. Certain bacteria (Proteus and Klebsiella) may even be responsible for stones that are made out of struvite (magnesium ammonium phosphate). Such stones are quite large and are sometimes known as "staghorn calculi" because they are shaped somewhat like the horns of a stag.

Kidney stones might be painless if they are small, but if they are larger, they can cause pain and other symptoms related to obstructive uropathy. If they cause damage, they may also result in haematuria and/or infection. If the kidney stones are large, one type of pain that might be experienced is "renal colic," which is an excruciating pain that radiates from the flank to the groin. Renal colic might also be accompanied with other symptoms, from haematuria to vomiting. I have discussed treatment of kidney stones here.