they evolve from simple calculi , which grow rapidly over months to form complex renal stones , filling the renal pelvis and branching outwards to occupy one or more renal calyces , characteristically resembling the horns of a stag . patients classically present with recurrent pyelonephritis , cystitis - like urinary symptoms , persistent flank pain , renal colic or haematuria . perforated staghorn calculi have been known to present as subcutaneous abscesses or with leg emphysema mimicking gas gangrene , following secondary urinary infection with gas - forming bacteria [ 2 , 3 ] . below is a description of what is believed to be the first recorded case of a silent perforated staghorn calculus presenting as large bowel obstruction a 63-year - old woman self - presented to the emergency department with a week 's history of worsening abdominal pain , distension , faeculent vomiting and two days of absolute constipation . examination revealed a soft distended abdomen , which was generally tender but more so in the left upper quadrant , with no palpable masses . routine bloods were all within normal parameters , including white cells of 8.9 , except for a marginally raised crp of 28 . abdominal x - ray confirmed large bowel obstruction with a cut - off point in the proximal descending colon . a large staghorn calculus was evident in the left kidney with a second smaller well - defined area of calcification just lateral to the renal parenchyma . 1 ) 
 figure  1:x - ray showing large left - sided stag horn calculus , with a second adjacent fragment outside the renal parenchyma with evidence of bowel obstruction . x - ray showing large left - sided stag horn calculus , with a second adjacent fragment outside the renal parenchyma with evidence of bowel obstruction . conservative management of bowel obstruction was initiated , a nasogastric tube was inserted and the patient was made nil by mouth while intravenous fluids were started . a subsequent ct scan confirmed the presence of xanthogranulomatous pyelonephritis and established that the second area of calcification was a 1.5  1.0  2.5 cm perforated extra - renal fragment of calculus positioned adjacent to the proximal descending colon . this stimulated a diffuse inflammatory response in the left upper quadrant , resulting in a prominent thick - walled proximal descending colon with an abrupt calibre change in the mid descending colon , mesenteric fat stranding , a thickened ileo - psoas muscle with fragments of calculi in the left iliac fossa , gross lymphadenopathy and inflammatory changes around the spleen . 2 ) 
 figure  2:ct scan showing ( a ) extra - renal fragment of calculus adjacent to transition point in thickened descending colon . ct scan showing ( a ) extra - renal fragment of calculus adjacent to transition point in thickened descending colon . the patient 's symptoms did not settle with conservative management , and as a result , she underwent an emergency left hemi - colectomy , left nephrectomy and extraction of the fragmented calculi . the parenchyma had been replaced with extensive fibro - fatty tissue and chronic inflammatory cell infiltrate with small areas of calcification . it contained thick - walled blood vessels and a few atrophic completely hyalinized renal glomeruli and various - size tubules with cast - like esosinophilic amorphous material . many non - caseating granulomas were present in the hilar area with most containing a central calcification . staghorn calculi are more common in women with peak age at presentation being the fifth decade of life . as with this case , most are unilateral at the time of diagnosis . they can be subcategorized into two groups based on composition ; infective and metabolic stones . infective stones account for 80% of cases and formation correlates with urinary tract infection with urease - producing bacteria : proteus , staphylococcus and klebsiella species . the elevated ammonia concentration causes a rise in the ph resulting in alkaline urine ( ph 7.2 ) . in the presence of magnesium and phosphate , this creates an ideal environment for inducing the crystallization of struvite ( magnesium - ammonium - phosphate ) and carbonate - apatite , encapsulating large numbers of bacteria within the stone 's matrix during the process . predisposing factors include vesico - ureteric reflux , indwelling catheters and anatomical abnormalities such as horseshoe kidney [ 1 , 4 ] . metabolic syndromes generate increased solute levels within urine , which when supersaturated precipitate giving rise to metabolic stones . hypercalcaemia , hyperparathyroidism and hypercalciuria can create calcium oxalate calculi , the most prevalent stone , closely followed by uric acid stones ( the product of hyperuricaemia ) . rarer stones include calcium phosphate stones resulting from renal tubular acidosis , while cystinuria , an autosomal recessive condition , produces cysteine stones . interestingly , this case highlights how a staghorn calculus can form in the absence of a metabolic syndrome or any prior noted history of urinary tract infections . the calculus in question had obviously been present for a long time because the kidney was completely atrophic with no parenchyma and was thus non - functioning . throughout that time , the patient remained asymptomatic despite the fact that the calculus continued to enlarge at such a rate that extravasation of multiple calculi fragments occurred , resulting in irritation and inflammation to the surrounding structure . yet , the patient sought help only when the consequential inflammation resulted in such severe colonic muscle hypertrophy that a benign stricture had been generated ; completely occluding the bowel lumen causing large bowel obstruction . once diagnosed , staghorn calculi should be actively treated in order to prevent the development of life - threatening urosepsis or end - stage renal failure . the aim of treatment is to entirely eliminate the stone and preserve renal function [ 1 , 4 ] . due to the introduction of less invasive treatment modalities extracorporeal shockwave lithotripsy and percutaneous nephrolithotomy , open nephrectomy is now rarely used . it is only indicated for persistently symptomatic patients with atrophic kidneys contributing > 10% towards the full renal function . in this case , a nephrectomy seemed the obvious treatment option , preventing the development of future inflammatory strictures and eliminating urosepsis risk . performing a synchronous left hemi - colectomy was required to treat the irreversible stricture , allowing resolution of her bowel obstruction . stag horn calculi account for 11% of renal calculi , yet this report presents what is believed to be the first documented case of large bowel obstruction presenting secondary to extravasation as a consequence of a previously undiagnosed stag horn calculus .
in europe up to nine per cent of people suffer from renal calculi during their lifetime . 
 staghorn calculi are common and account for 11% of cases . 
 classic presentations include persistent loin pain , recurrent pyelonephritis or cystitis - like symptoms , renal colic or occasional haematuria . 
 we present what we believe to be the first documented case of large bowel obstruction caused by a benign colonic stricture formed secondary to extravasation of a staghorn calculus .