ADH primarily acts on the collecting ducts.Other options:- The juxtaglomerular apparatus is the site of renin production.- The proximal tubule conducts isosmotic reabsorption of about 60% of sodium chloride and volume. Most of the glucose, amino acids, potassium and phosphate are absorbed here.- The loop of Henle is the site of 25% of sodium reabsorption. Active Chloride transport provides the basis for the counter current multiplier aiding urinary concentration.- The distal convoluted tubule is impermeable to water and acts via active sodium chloride absorption to dilute urine.

The child most likely has nephritic syndrome which is characterised by a reduced renal function, proteinuria of non-nephrotic range, haematuria, erythrocyte casts, and oedema. Polyarteritis nodosa usually occurs in middle-aged men but can also be seen in young children. It is accompanied by severe systemic manifestations such as fever, malaise, weight loss and myalgia.Renal cell carcinoma usually presents around 55 years with the classic triad of haematuria, loin pain and a unilateral mass in the flank.Polycystic kidney disease usually presents in adult life with acute loin pain and palpation of masses in the flanks.

The child has nephrotic syndrome which is most commonly caused by minimal change nephropathy in this age group. The condition presents with fusion of foot processes of the glomerular epithelial cells under the microscope.

Distal renal tubular acidosis (dRTA) is characterised by a decreased hydrogen ion excretion from the alpha intercalated cells of the collecting duct of the distal nephron. The resultant acidosis causes calcium and phosphates to be released from bones to buffer the acidosis causing hypercalciuria. This precipitates calcium compounds in the kidney, predisposing it to renal stone formation. On the other hand, proximal renal tubular acidosis is characterised by an impairment in bicarbonate resorption. Both types lead to metabolic acidosis and electrolyte imbalances including potassium depletion. Children often present with failure to thrive. One way to differentiate between the two conditions is with an acid challenge test. In proximal RTA (type 2) administering an ammonium chloride load will decrease the urinary pH whereas in distal disease (type 1), the urine pH will not decrease below 5.3.

The mesonephric duct is one of the paired embryogenic tubules that drain the primitive kidney (mesonephros) to the cloaca. It also gives off a lateral branch forming the ureteric bud. In both the male and the female the Wolffian duct develops into the trigone of the urinary bladder. When the ducts are exposed to testosterone during embryogenesis, male sexual differentiation occurs: the mesonephric duct develops into the rete testis, the ejaculatory ducts, the epididymis, the ductus deferens and the seminal vesicles.

Fanconi tubular syndrome is characterised by malabsorption of various electrolytes and substances commonly absorbed by the proximal tubule. Hypokalaemia, hypophosphatemia, and hyperchloremic metabolic acidosis is usually present. Also, urinalysis reveals an increased fractional excretion of glucose.

Haemolytic-uremic syndrome (HUS) is a clinical syndrome characterized by progressive renal failure that is associated with microangiopathic (nonimmune, Coombs-negative) haemolytic anaemia and thrombocytopenia. HUS is the most common cause of acute kidney injury in children. It predominantly occurs in infants and children after prodromal diarrhoea. In summer epidemics, the disease may be related to infectious causes.Bacterial infections may include the following:S dysenteriaeE ColiSalmonella typhiCampylobacter jejuniYersinia pseudotuberculosisNeisseria meningitidisS pneumoniaLegionella pneumophilaMycoplasma speciesRickettsial infections may include Rocky Mountain spotted fever and microtatobiotesViral infections may include the following:Human immunodeficiency virus (HIV)CoxsackievirusEchovirusInfluenza virusEpstein-Barr virusHerpes simplex virusFungal infections can include Aspergillus fumigatus.Vaccinations may include the following:Influenza triple-antigen vaccineTyphoid-paratyphoid A and B (TAB) vaccinePolio vaccinePregnancy-associated HUS occasionally develops as a complication of preeclampsia. Patients may progress to full-blown haemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome. Postpartum HUS usually occurs within 3 months of delivery. The prognosis is poor, with a 50-60% mortality rate, and residual renal dysfunction and hypertension occur in most patients.

Hyperkalaemia is not to evaluate or detect AKI but rather the result of it. If one of the rest of the options is present, then AKI would be suspected.

Constipation is often associated with nocturnal enuresis in children. The palpable mass is the impacted stool. The decreased appetite is common in those with constipation.

Minimal change glomerulonephritis presents with mild or benign urinalysis findings. However, proteinuria together with the presence of oval fat bodies are typical.Minimal change glomerulonephritis (nephropathy) accounts for most cases of childhood nephrotic syndrome and 20–25% of adult nephrotic syndrome.

Coverings of the spermatic cord:Spermatic cord is covered by three concentric layers of fasciae, derived from the layers the of anterior abdominal wall. Developmentally, each covering is acquired as the processus vaginalis descends into the scrotum through the layers of the abdominal wall. The layers are:External spermatic fascia: It is derived from the external oblique muscle. It attaches to the margins of superficial inguinal ring.Cremasteric fascia: It is derived from the internal oblique muscle. It covers the cremaster muscle.Internal spermatic fascia: It is derived from the fascia transversalis (fascia covering the transversus abdominis muscle). It is attached to the margins of the deep inguinal ring.

The child has a history of pharyngitis followed 10 days later by signs of glomerulonephritis. In this particular case, it is most probably a post-streptococcus glomerulonephritis which accounts for 80% of paediatric cases of glomerulonephritis.

Tuberous sclerosis presents with the growth of numerous noncancerous (benign) tumours in many parts of the body. They may appear in the brain, kidneys, skin or various other organs.

Allergy: A history of a prior allergic-like reaction to contrast media is associated with an up to a 5-fold increase in the likelihood of experiencing a subsequent reaction. Also, any patient with a predilection to allergic reactions may predispose them to a reaction after the administration of contrast media. Given the increased risk of severe life-threatening anaphylaxis related to the administration of contrast media in the setting of the history of atopy, the risk versus benefits should be discussed before following through with the procedure. A premedication regimen may be used to reduce the risk of anaphylaxis.Asthma: A history of asthma may be indicative of a higher likelihood of developing a contrast reaction. Cardiac status: Attention must be turned to patients with significant cardiac disease (congestive heart failure, aortic stenosis, severe cardiomyopathy, and/or pulmonary hypertension), as higher volumes and osmolality of contrast material may result in an increased risk for a contrast reaction.Renal insufficiency: Contrast nephrotoxicity is defined as the rapid deterioration of renal function after the administration of contrast media when no other aetiology can be determined from the clinical records. The major predisposing risk factors include pre-existing renal insufficiency (defined as serum creatinine level >1.5 mg/dL) and diabetes. Other risk factors include dehydration, cardiovascular disease, the use of diuretics, advanced age (>70 years old), hypertension, and hyperuricemia. Obtaining multiple contrast-enhanced studies within 24 hours is also thought to increase the risk for contrast-induced nephrotoxicity. Miscellaneous: Relative contraindications to the use of high osmolality iodinated contrast media (HOCM) in patients with pheochromocytoma, sickle cell disease, and multiple myeloma have been reported. Although the administration of low osmolality or iso-osmotic contrast media may be beneficial in patients with pheochromocytoma and sickle cell disease, little evidence suggests that these agents mitigate the risks associated with multiple myeloma.

Vesicoureteral reflux is a common disorder in children but can result in kidney scarring following acute pyelonephritis. The gold standard diagnostic test to detect renal scars in children is 99mTc-dimercaptosuccinic acid (DMSA) scintigraphy

Among the options provided, the most characteristic finding that can be expected in his patient’s urine microscopy is RBC casts. Red cell casts are a characteristic feature of acute nephrotic syndrome. Other options:- Hyaline casts may be seen in normal urine, particularly after exercise. – Coarse granular casts occur in glomerular and tubular disease. – Tubular cell casts may be seen in patients with acute tubular necrosis. – The presence of 10 or more white blood cells/mm3 is abnormal and indicates an inflammatory reaction, most commonly due to infection.

Based on the presented clinical scenario, the most probable diagnosis for the patient would be testicular torsion.Rationale:The gubernaculum is the structure responsible for aiding the descent of the testicles from the abdomen into the scrotum. The processus vaginalis precedes the descent of the testes and then undergoes closure. Abnormalities such as the persistence of a patent processus vaginalis, known as bell clapper deformity, predispose to testicular torsion.Other options:- Varicocele: Nutcracker syndrome occurs where the left renal vein becomes compressed in between the superior mesenteric artery and the aorta. Since the left gonadal vein drains into the left renal vein, this results in a varicocele. – Epididymitis and mumps orchitis are differentials for acute testicular pain but are not due to a defect in the processus vaginalis. – An incarcerated inguinal hernia presents mainly with signs of bowel obstruction which are not mentioned in the clinical scenario.The descent of testes:- Until the end of foetal life, the testicles are located within the abdominal cavity. – They are initially located on the posterior abdominal wall on a level with the upper lumbar vertebrae (L2). – Attached to the inferior aspect of the testis is the gubernaculum testis which extends caudally to the inguinal region, through the canal and down to the superficial skin. – It is interesting to note that both the testis and the gubernaculum are extra-peritoneal.- As the foetus grows, the gubernaculum becomes progressively shorter. It carries the peritoneum of the anterior abdominal wall (the processus vaginalis). As the processus vaginalis descends the testis is guided by the gubernaculum down the posterior abdominal wall and the back of the processus vaginalis into the scrotum.- By the third month of foetal life the testes are located in the iliac fossae, by the seventh they lie at the level of the deep inguinal ring.Usually, the processus vaginalis closes after birth but may persist predisposing to indirect hernias. On the other hand, a partial closure may result in the development of cysts on the cord.

E. coli accounts for the majority of UTI’s in children. If this child responds well to treatment and has no recurrence of his symptoms, then no form of imaging is required, as per NICE advice for children aged 6 months to 3 years. Had the child been less than 6 months of age, then a USS at 6 weeks would be necessary.Other options:- Pseudomonas causes atypical UTI. This warrants ultrasonography within the acute illness phase as it may reflect an underlying pathology and DMSA at 4-6 months.- Recurrent UTI is defined as two or more episodes of pyelonephritis OR 1 pyelonephritis and one cystitis OR 3 or more cystitis. It requires USS at six weeks and DMSA at 4-6 months.- Septicaemia is a sign of an atypical UTI. This requires USS within the acute illness as it may reflect an underlying pathology and DMSA at 4-6 months.- Unwell 48hrs post antibiotics is a sign of an atypical UTI. This requires USS within the acute illness as may reflect underlying pathology and DMSA at 4-6 months.

The patient shows features of neurofibromatosis. The most likely cause for hypertension in this patient would be renal artery stenosis.Note:Neurofibromatosis is an inherited autosomal dominant disorder which could have affected this girl’s father, and she appears to have the classic skin lesions. A renal bruit might be heard in these patients. Polycystic kidney disease can occur in association with tuberous sclerosis, which also has skin lesions associated (different from those described in this patient). Most causes of hypertension in childhood have underlying renal causes, and a renal ultrasound with doppler is the first-line investigation of choice. Even if this is normal, further imaging would be indicated here, for example, isotope renal scans and angiography.

Alport syndrome is a genetic condition characterized by kidney disease, hearing loss, and eye abnormalities. Alport syndrome can have different inheritance patterns. About 80 percent of cases are caused by mutations in type IV collagen genes (COL4A5) and are inherited in an X-linked autosomal recessive pattern, although other inheritance patterns exist. Alport syndrome has autosomal dominant inheritance in about 5 percent of cases.

People with Alport syndrome experience progressive loss of kidney function. Almost all affected individuals have blood in their urine (haematuria), which indicates abnormal functioning of the kidneys. Many people with Alport syndrome also develop high levels of protein in their urine (proteinuria). The kidneys become less able to function as this condition progresses, resulting in end-stage renal disease (ESRD).

People with Alport syndrome frequently develop sensorineural hearing loss, which is caused by abnormalities of the inner ear, during late childhood or early adolescence. Affected individuals may also have misshapen lenses in the eyes (anterior lenticonus) and abnormal coloration of the light-sensitive tissue at the back of the eye (retina). These eye abnormalities seldom lead to vision loss.

Significant hearing loss, eye abnormalities, and progressive kidney disease are more common in males with Alport syndrome than in affected females.