Urinary tract stones

Definition

These are the Rolling Stones who are not the same as Renal Stones. Both are medically interesting. The former is unlikely to come up in your exams. (Unless you're studying The Rolling Stones).

Stone in the urinary tract. Anywhere. Even the willy.

Epidemiology

Has a prevalence of 3% in the UK but a staggering, a shocking, a mind-blowing like you just found your Mum is a real life Jack Bauer, 12% in the USA. I'm probably labouring the point a bit. M:F, 2.5:1 and has a bi-modal peak distribution with peaks at mid-20s and mid-50s though the later peak is mostly due to infections in women. 40% pass spontaneously though incidence of upper tract stones is increasing. Upper tract is more common in the developed world. 80% are unilateral.

Awesome.

Pathophysiology

Stones can be made out of lots of stuff. They are created when there's a high amount of said stuff in the urine. So if the stone is made of calcium, that is more likely in somebody who has a large amount of calcium in the urine. It's called supersaturation. However, sometimes stones just form and nobody's sure why.

Calcium (80%), phosphate (10%) and uric acid (5-10%) are the most common constituents of stone.

Risk Factors

There three category of risk factor with specific ones within each category:

• Excess normal constituents in urine
  • increased serum calcium in hypoparathyroidism
  • increased uric acid
  • decreased urinary volume in hot climates
• impaired drainage
  • chronic urinary tract obstruction in enlarged prostate
  • hydronephrosis
• abnormal constituents
  • infection (causes epithelial sloughs which form stones)
  • foreign bodies (e.g. catheter)

Clinical Features

The clincal features depend very much on whereabouts the stone is. It's worth remembering that about 80% of stones are asymptomatic. Stones can present in any number of extremes from an incidental finding on an X-ray to bilateral hydronephosis and renal failure.

Kidney stones

The primary symptoms are: flank pain which spreads round the abdomen as the stone moves down; haematuria which is common and can be both microscopic and macroscopic; and infection which will cause loin tenderness, pyrexia and sepsis.

Ureteric stones

Generally, colic (from flank through to scrotum/labia minorum), haematuria and infection. Tenderness along the renal angle or along the line of the ureter.

Bladder stones

The main symptoms are: pain in the suprapubic area, perineum and the tip of the penis/labium majorum exacerbated by an upright postue, jolting movements and the end of micturition; urgency and frequency usually during the day with sensation of incomplete micturition; strangury, the feeling of painful, frequent, small-volume micturition with severe urgency and feeling of incomplete emptying; haematuria at the end of micturition; and urinary obstruction.

Men may also have prostatic enlargement whilst women may have a palpable stone on bimanual examination.

Investigations

The initial tests are to confirm the presence of a stone (or calculus) and the later tests inform more about management and what exactly you're going to do. Obviously, if the initial tests rule out stones, then don't start chopping them open to get them out.

Initial tests

• Bloods - U+Es and creatinine
• Urine dipstick - for microscopic haematuria
• Urine microscopy, sensitivity and culture - blood, pus cells and infection
• AXR - 90% of stones are radio-opaque
• IVU - to confirm position of obstruction
• Noncontrast helical CT - this is only done if you have the facilities (most DGHs won't) but it is very good at not only assessing the position of the stone but it's composition as well. It also picks up some radio-translucent (can't see on X-ray) stones
• Cystoscopy - supsected bladder stones only

Further tests

• tests for metabolic problems
  • bloods - calcium, phosphate, uric acid and alkaline phosphatase
  • urine - cysteine, pH (>7.5 points to infective, <5.5 to urate)
  • 24h urine - calcium, phosphate, uric acid, creatinine (should be done on a normal diet)
• renography - clever kidney X-ray
• analysis of stone - you want to know what they're made of as it can point to a cause