Urinary stones, tumours and cystic disease

Not every concentrated urine produces a stone, because crystallisation depends on three variables that the nurse can influence. The first is supersaturation: the product of the concentrations of the two ions that will pair, classically calcium with oxalate or calcium with phosphate. The higher that product, the greater the chance that a crystal nucleus forms. The second is the balance between promoters and inhibitors. Normal urine is not pure water; it contains substances that keep crystals small and moving, including citrate, magnesium, nephrocalcin and uropontin. A shortage of any of them, and a low urinary citrate is the commonest example, allows a nucleus to grow instead of redissolving. The third is pH, because some salts are far less soluble at one pH than another. Uric acid precipitates in acid urine, which is why a low-purine diet and alkalinisation help, while struvite needs alkaline urine. Urease, the enzyme made by urea-splitting organisms such as Proteus, Klebsiella, Pseudomonas and some staphylococci, hydrolyses urea into ammonia and raises the pH until magnesium ammonium phosphate crystallises around an infected nidus. That mechanism explains two facts that are easy to confuse. Calcium oxalate, not struvite, is the most common stone in the urinary tract, while struvite is the stone that signals infection and tends to grow rapidly into a branching staghorn calculus filling the renal pelvis. Cystine stones, sometimes miscalled cysteine stones, are the exception that proves the point that stones have causes: they come from cystinuria, an inherited defect of tubular reabsorption of the amino acid cystine, and they are managed with a low-protein diet, alkalinisation and a high fluid intake. For all these reasons the metabolic workup — serum calcium, uric acid and creatinine with a 24-hour urine collection for calcium, uric acid, creatinine, sodium, citrate and pH — is not an academic exercise; it is what turns a stone from an accident into a diagnosis.

A stone that obstructs the ureter sets off a sequence that can end in a destroyed kidney, and every step of it is something the nurse observes. Urine continues to be produced above the blockage, so pressure rises inside the renal pelvis and the proximal ureter, which distend. Ureteric peristalsis increases against the obstacle, and that spasmodic contraction, not the stone itself, is the colicky pain. If the obstruction persists, the raised pressure is transmitted back into the renal parenchyma, the collecting system dilates and hydronephrosis develops; over weeks or months the compressed tissue atrophies and is replaced by fibrosis, so function is lost even though the kidney was never infected. The stagnant urine above the stone is an ideal culture medium, and there the second half of the cycle begins. Bacteria ascend, colonise the stagnant urine and provoke pyelonephritis; if the urine is infected and the obstruction is not relieved, the collecting system can fill with pus, a pyonephrosis, and organisms can escape into the bloodstream, producing bacteraemia and urosepsis, which is a genuine emergency and not a complication to be watched overnight. The organisms themselves make matters worse: urea-splitting species raise the pH and deposit struvite, so the stone grows, and a larger stone obstructs more completely, closing the cycle. The nursing implications follow directly. A patient with renal colic who develops fever, rigors, a rising pulse, loin tenderness, cloudy or foul urine, or a falling urine output no longer has simple colic; the obstruction must be decompressed urgently, often with a ureteric stent or a percutaneous nephrostomy, and systemic antibiotics given, because draining the infected urine is what saves the kidney and sometimes the patient. Preventive measures are equally concrete: early treatment of urinary infection, avoiding prolonged immobility, and maintaining a high fluid intake all reduce the risk that a susceptible patient will ever begin the cycle.

Two conditions complete the picture, and both are recognised by a pattern rather than by a single sign. Autosomal dominant polycystic kidney disease, the form that accounts for most cases, is caused by a mutation in one allele, so an affected parent passes the disease to each child with a probability of one in two; signs usually appear between the ages of 30 and 40, although children can be affected. Autosomal recessive polycystic kidney disease requires a mutation from both parents, carries a one in four risk for each pregnancy, and shows itself shortly after birth or later in childhood. In both forms, fluid-filled cysts enlarge the kidneys and compress the remaining parenchyma. Nearly half of all patients reach kidney failure by the age of 60, and the course is influenced strongly by blood pressure, which is why the nurse treats hypertension control as kidney protection rather than as a separate problem. Because the disease is systemic, the kidneys are not the only organs at risk: liver cysts are common and become more likely with age, cerebral aneurysms are more frequent and can bleed, as many as one adult in four develops mitral valve prolapse, diverticulosis of the colon occurs, and some pregnancies are complicated by pre-eclampsia. A family history of aneurysm or of dialysis therefore changes surveillance, and genetic counselling is part of care because the patient may be planning children.

Wilms tumour is a different story: a nephroblastoma of early childhood, usually found because a parent or a nurse feels an abdominal mass in a three- or four-year-old. Staging runs from a tumour confined to one kidney and completely removable, through spread to surrounding tissues, to distant metastases in lungs, liver, bone or brain, and finally to involvement of both kidneys. Some children have a recognisable syndrome — WAGR, Denys-Drash or Beckwith-Wiedemann — or an associated anomaly such as aniridia, hemihypertrophy, macrosomia or macroglossia. Two nursing points matter here. First, blood pressure is measured in any child with an abdominal mass, because this tumour can raise it. Second, the abdomen is palpated gently and repeatedly avoided, because a firm examination can rupture the tumour and spill cells, changing the stage and the treatment.