the terms pseudoaneurysm , false aneurysm and pulsating haematoma all describe the same phenomenon , that is a defect in the vascular wall leading to an extra - vascular haematoma that freely communicates with the intravascular space . once in its fully developed state , it may have a cavity with an endothelial lining in continuity with that of the artery . isolated internal iliac aneurysms are an uncommon entity  and isolated pseudoaneurysms of the internal iliac artery even more so . here we present an unusual aetiology of massive per - rectal bleeding attributable to pseudoaneurysm of the internal iliac artery , leading to arterio - colic fistula . an 83-year - old male presented to the emergency department with a history of passing a cupful of bright red blood with his morning bowel motion . his past medical history was significant for diverticular disease , which had resulted in a perforated sigmoid colon 23 years before , requiring hartmann 's procedure which was subsequently reversed . he arrived with a blood pressure of 130/75 mmhg and a tachycardia of 104 beats per minute . rigid sigmoidoscopy in the emergency department revealed an empty rectum with copious amounts of stool and blood up to 10 cm . the patient was presumptively diagnosed with a diverticular bleed and admitted to the general surgical unit for observation . the following day a further significant per - rectal bleed occurred on the ward , associated with chest pain and ecg changes . blood tests revealed a haemoglobin drop to 11.3 g / l and an elevated serum troponin level of 0.19 g / l . myocardial infarction was diagnosed and he was placed on telemetry in a cardiac monitoring unit . a further massive per - rectal bleed was reported on the ward that evening , with a subsequent drop in haemoglobin to 7.7 resuscitation was commenced with three units of packed red blood cells and a mesenteric ct angiogram arranged . this revealed a contrast blush within the descending colon closely associated with an aneurysm of the internal iliac artery . the possibility of an arterial fistula to the colon was raised , and a vascular surgery consult was sought . angiography confirmed a false aneurysm arising from the proximal aspect of the left internal iliac artery along its medial and inferior wall . endovascular coil embolization was performed with occlusion of the vessel at the level of the aneurysm . no further episodes of per - rectal bleeding have been reported in 3 months following embolization . follow - up colonoscopy revealed multiple diverticulae in the descending colon , but the site of the previous bleed was not evident . this patient had an isolated pseudoaneurysm of the internal iliac artery resulting in an arterio - colic fistula ( fig .  1 ) . isolated aneurysms of the internal iliac artery themselves are a rare phenomenon , estimated to account for only 0.30.4% of all intra - abdominal aneurysms . forty per cent of patients with isolated internal iliac aneurysms will present with a rupture , with mortality estimated to exceed 50% in such patient groups . figure  1:ct angiogram : a saggital view showing pseudoaneurysm of the left internal iliac artery ( white arrow ) . ct angiogram : a saggital view showing pseudoaneurysm of the left internal iliac artery ( white arrow ) . they have also been reported as a rare complication of pelvic surgery . over the last few decades there has been an increase in the incidence of pseudoaneurysms in general , due to an increase in interventional vascular access . infections , connective tissue disorders , vasculitis and erosion secondary to malignancy may also be implicated in the formation of pseudoaneurysms . in a review of the literature on isolated internal iliac aneurysms , dix et al . cases described have included iliac - rectal fistula following coil occlusion of an iliac aneurysm and fistulous connection between aneurysm and caecal carcinoma . diverticulitis in and of itself is not known as a cause for pseudoaneurysm formation ; however , pelvic infections have been implicated . this patient had an episode of diverticular disease 23 years previously which required a hartman 's procedure , this was reversed 6months later . whether the cause of the pseudoaneurysm was mycotic or traumatic ( secondary to either the first or second stage procedure ) is a matter of conjecture . anastamotic leak post - colostomy reversal could have been implicated , however , on imaging the pseudoaneurysm communicates with a large bowel 5 cm proximal to the anastamotic suture line . regardless of the aetiology , if the pseudoaneurysm occurred around the time of his original operation , it remained quiescent for 23 years before causing symptoms . the reported mortality rate for ruptured internal iliac aneurysms is 50%fortunately in this case the diagnosis was made rapidly with imaging and immediate treatment led to a good outcome . the efficacy of expedient angiography in per - rectal bleeding has been shown previously , with mesenteric embolization clinically successful in 76% of cases of lower gastrointestinal bleeding with active bleeding on angiography . aggressive management of internal iliac aneurysms , regardless of the mode of presentation , is required to avoid the high morbidity and mortality associated with rupture . they can be managed with open or endovascular techniques , with a tendency towards the latter over the previous years . occlusion of the internal iliac artery can result in multiple sequelae , including lumbosacral plexus ischaemia , buttock necrosis , colorectal infarction , impotence and buttock claudication . buttock claudication , the most common of these complications , is estimated to occur in 2840% of patients , with severe debilitating claudication in 9% . at follow - up , no symptomology suggestive of claudication was elicited in our patient . per - rectal bleeding is a common presentation with most cases of massive bleeding caused by diverticular disease and angiodysplasia . the above case will hopefully serve as a reminder that per - rectal bleeding can have a less common aetiology . identification of an iliac aneurysm on imaging for rectal bleeding should alert the clinician to the possibility of an arterial fistula to the colon .
rectal bleeding is a common reason for presentation to hospital , with large bleeds most commonly caused by diverticular disease and angiodysplasia . here 
 we present an unusual aetiology of massive per - rectal bleeding attributable to pseudoaneurysm of the internal iliac artery leading to an arterial fistula to the distal large bowel . 
 it is hoped the case will serve as a reminder that rectal bleeding can have a less common aetiology .