mycotic aortic aneurysms are rare and often masquerade as other acute abdominal pathology , delaying diagnosis . we present a case where serial imaging made the diagnosis of mycotic aneurysm . to our knowledge , this case is the first in the literature to describe serial scanning with the same imaging modality . a 71-year - old man presented to the emergency department after a 2-week history of cramping peri - umbilical pain and rigours . pre - admission computed tomography ( ct ) demonstrated irregular thickening of the infrarenal aorta , which measured 3.3 cm in its maximal diameter . his background was significant for ischaemic heart disease , hypertension , gout , hypercholesterolaemia and an admission for small bowel obstruction which was treated conservatively . there was no history of diabetes , intravenous drug use , or recent medical or dental procedure . the abdomen was centrally tender , without palpable or pulsatile mass , and all lower limb pulses were normal . investigations revealed new atrial fibrillation , a ph of 7.44 , mildly derranged liver enzymes ( aspartate transaminase 51 u / l , alanine transaminase 58 u / l , alkaline phosphatase 136 u / l , gamma - glutamyl transpeptidase 271 u / l and bilirubin 14 mol / l ) , haemoglobin of 131  10/l and white cell count of 11.6  10/l with neutrophilic change ( 8.1  10/l ) . a single dose of prednisolone was administered in the emergency department based on the esr . hepatobiliary iminidiacetic acid scan with cholecystokinin and abdominal ultrasound were suggestive of chronic acalculous cholecystitis . as such , intravenous ampicillin and gentamicin blood cultures remained negative and the white cell count reached 13.6  10/l on the fourth admission day . a repeat ct scan demonstrated a more inflamed and aneurysmal aorta involving the origin of the left renal artery with intraluminal thrombus ulceration . the patient underwent a left axillo - uni - femoral bypass with a rifampicin - soaked dacron graft and debridement of mycotic aneurysm the following day . peri- and postoperative vancomycin and meropenem were provided as advised by the infectious diseases team . from the debrided tissues , polymerase chain reaction showed a 100% match for streptococcus and postoperatively , recovery included a 13-day intensive care admission with renal impairment , gastroparesis and pneumonia . blood cultures remained negative and repeat ct revealed a patent graft with no collection or phlegmon . the patient was discharged on the 49th postoperative day on warfarin , intravenous meropenem and vancomycin for 6 weeks . there are four types , in order of increasing mortality , including post - traumatic infected false aneurysms , mycotic aneurysms , microbial arteritis and infection of an existing aneurysm . this patient presented with abdominal pain and mild leucocytosis , present in 92 and 69% of infected aortoiliac aneurysms , respectively , and later pyrexia . other features may include positive blood cultures and palpable abdominal mass . the absence of clinical features and the presence of distracting signs made for a challenging diagnosis in this case . neither the rate of growth , nor a change of morphology ( new thrombus ulceration ) of mycotic aneurysms , has been discussed in the literature ; the consensus is that all infected aneurysms should be treated as surgical emergencies , regardless of size and shape . rapid expansion of mycotic aneurysm has been described ; however , there are no published cases with serial scanning using a single imaging modality available for reference . the expansion of a mycotic thoracic aortic aneurysm over 3 weeks has been described . another group describes a sudden 4-cm growth of a long - standing aaa over 10 days in a patient with community - acquired pneumonia . while ultrasound accurately determines the size and character of an aaa , it can not reliably comment on infection as an aetiology . soft tissue inflammation , para - aortic mass , eccentrically shaped aneurysms and narrow aneurysm neck may suggest an infective cause . when rapid expansion on serial ct is observed , a mycotic aneurysm has to be considered . radio - labelled white cell scans may demonstrate para - aortic inflammation , but have also been negative in cases of proven abdominal aortitis . treatment options for mycotic infrarenal aaas include extra - anatomic bypass with ligation , resection and debridement or in situ graft placement following extensive debridement . implanted antibiotic releasing carriers have been used in conjunction with open surgery in the past . endovascular repair for mycotic aaas has been reported again with a mortality rate of 42% . long - term antibiotics are always indicated ; however , their use and duration postoperatively has not been extensively studied . often , 6 weeks of intravenous followed by 6 weeks of oral antibiotics with appropriate sensitivities is advised . in summary , we present a case of a 71-year - old gentleman with a peculiar clinical picture of a mycotic aortic aneurysm masquerading as acute acalculous cholecystitis . the most significant clue in his work - up was rapid change in the character of the aneurysm . despite extensive investigation and seeking expert opinion
mycotic infrarenal aortic aneurysms are rare and often masquerade as other abdominal pathology . 
 we present a case where serial imaging made the diagnosis and provided an insight into the pathophysiology of mycotic aneurysm . 
 a 71-year - old man presents with abdominal pain , rigours and dysuria . 
 computed tomography reveals an irregular , thickened ectatic abdominal aorta , but cholescintigraphy suggests acalculous cholecystitis . 
 deterioration prompts repeat radiographical assessment , which demonstrates an increase in the size of the aorta over 10 days . 
 the patient was treated emergently with an open aortic ligation , debridement and extra - anatomical bypass . 
 infections account for up to 2% of abdominal aortic aneurysms . 
 the rate of growth of mycotic aneurysms is sparsely discussed in the literature and to our knowledge , there are no reports with serial single - modality imaging . 
 the most significant finding was rapid expansion in aneurysm size . 
 while mycotic aneurysm requires urgent treatment , diagnosis can be delayed and difficult .