Staghorn Calculus

A staghorn calculus is a branching stone that fills the renal pelvis and extends into two or more calyces, taking the shape of the collecting system. A complete staghorn fills the entire pelvis and all calyces. A partial staghorn fills the pelvis and at least one calyx.

Most (about 75 percent) are struvite (magnesium ammonium phosphate with carbonate apatite) stones. They form in infected alkaline urine from urease producing organisms (Proteus mirabilis, Klebsiella, Pseudomonas, Providencia, Morganella, Staphylococcus saprophyticus, Ureaplasma, and Corynebacterium urealyticum).

About 25 percent are metabolic (cystine, uric acid, calcium oxalate or calcium phosphate, and brushite) and may become infected.

Urease splits urea to ammonia, which raises urinary pH above 7.2 and produces carbonate, driving crystallisation. Women are affected more than men (about 2:1).

Risk factors:

• Recurrent urinary tract infection.
• Urinary stasis (neurogenic bladder, spinal cord injury, ureteropelvic junction obstruction, urinary diversion).
• Indwelling catheters.
• Previous stone surgery.

Left untreated, the natural history is poor. 30 to 50 percent lose the kidney, and about 25 percent die of sepsis or renal failure within 10 years. Mortality is several fold higher than that of treated patients.

• Recurrent febrile urinary tract infection, flank pain (often a dull ache rather than colic, as the stone is non-obstructing), haematuria, and malaise.
• Chronic pyelonephritis with weight loss, fatigue and anaemia.
• Systemic sepsis from pyonephrosis (fever, rigors, hypotension) and, rarely, xanthogranulomatous pyelonephritis.
• Renal impairment (progressive), proteinuria and hypertension.
• Foul smelling alkaline urine, and passage of stone fragments.
• Many are asymptomatic and found on imaging.

• Non-contrast CT (the standard): the stone filling the collecting system, with density measurement (struvite 600 to 900 Hounsfield units), and assessment of cortical thickness, hydronephrosis and perinephric inflammation.
• Plain radiograph: a branched radio dense stone ("staghorn", struvite is moderately radiopaque, cystine less, and uric acid is radiolucent).
• Ultrasound: strong echogenic mass with acoustic shadow in the renal pelvis with hydronephrosis.
• Nuclear renography (DMSA or MAG3) to measure split renal function before deciding on nephrectomy.
• Urinalysis: alkaline pH (above 7), pyuria, bacteriuria, struvite crystals ("coffin lid"); urine culture with sensitivity (include stone culture and renal pelvis urine culture, which are more accurate than bladder urine).
• Metabolic evaluation: serum calcium, uric acid, parathyroid hormone, 24-hour urine collection, stone analysis.
• Blood: creatinine, eGFR, complete blood count, and C-reactive protein.

The principle is complete removal of all stone material, as any residual fragment harbours bacteria and leads to recurrence in 80 to 90 percent.

• Treat and sterilise urine before surgery: culture directed antibiotics for 7 to 14 days (for example ciprofloxacin 500 mg twice daily, trimethoprim-sulfamethoxazole 160/800 mg twice daily, or amoxicillin clavulanate 625 mg three times daily). Give intravenous cover (ceftriaxone 1 to 2 g or gentamicin 5 mg/kg) at induction and perioperatively.
• In an obstructed infected system, decompress first with a nephrostomy tube or ureteral stent, and defer definitive surgery until sepsis resolves.
• Percutaneous nephrolithotomy (first line): prone or supine access through a posterior calyx under fluoroscopy or ultrasound, with a 24 to 30 Fr tract (or mini percutaneous 12 to 18 Fr).
• Use ultrasonic or pneumatic lithotripsy or holmium laser, and a flexible nephroscope for residual fragments. Multiple access tracts may be needed.
• Stone free rate is 70 to 80 percent for a single session, over 90 percent with a second look. Tranexamic acid 1 g intravenous before surgery reduces bleeding.
• Postoperative nephrostomy tube for 24 to 48 hours with a nephrostogram and a follow up CT for residual stone.
• Combination (sandwich) therapy for large stone burden: percutaneous nephrolithotomy, then shock wave lithotripsy, then repeat percutaneous nephrolithotomy.
• Shock wave lithotripsy alone should not be used as monotherapy, since stone free rates are low (about 30 to 50 percent) and the risks of obstructive steinstrasse and infection are high.
• Retrograde intrarenal surgery with flexible ureteroscopy and laser lithotripsy: acceptable for small partial staghorns or when percutaneous surgery is contraindicated, often in multiple stages.
• Anatrophic nephrolithotomy (open surgery, with nephrotomy through an avascular plane) and laparoscopic or robotic pyelolithotomy: for large complex stones in selected cases, or in the presence of anatomical abnormalities.
• Nephrectomy for a non-functioning (function below 10 to 15 percent), severely infected or xanthogranulomatous kidney, with the opposite kidney normal.
• Adjuvant medical therapy: acetohydroxamic acid (a urease inhibitor) 250 mg three times a day (maximum 15 mg/kg per day) in patients with persistent struvite stones and recurrent infection who are not surgical candidates.
• Side effects of acetohydroxamic acid include haemolytic anaemia, thrombophlebitis, tremor, headache, and teratogenicity (contraindicated in pregnancy and in creatinine clearance below 30 mL/min).
• Urinary acidification (L-methionine 500 to 1,000 mg three times daily or ascorbic acid) is a minor adjunct.
• Chronic suppressive antibiotic therapy (nitrofurantoin 50 to 100 mg at night, or trimethoprim 100 mg at night) in patients with residual fragments. Follow up urine cultures every 1 to 3 months for the first year after treatment.
• Metabolic evaluation and prevention for non-struvite stones: high fluid intake (urine over 2.5 L daily), dietary modification, potassium citrate for uric acid or calcium stones, tiopronin or alkalinisation for cystine.
• Follow up: CT or ultrasound at 3 months after the last procedure and annual imaging, with monitoring for residual and recurrent stones, renal function and urine culture.