Pancreatic Pseudo aneurysm: An Unusual Cause of Gastrointestinal Bleeding and it’s Radiologically guided Management.  A Case Report and Review of the Literature.

S Mirza, SS.Panesar

Corresponding Author: Saqeb Mirza 16 Catherine’s Gate, Haverfordwest, PEMBS, SA61 1NB United Kingdom 

Email: saqeb_mirza@yahoo.com

SMJ 2008 53(1): 60

 

Key Words:  Pancreatic pseudo aneurysm, Massive Haematemesis, Thrombin Injection

Abbreviations: 

CT       Computerised tomography

SMA    Superior mesenteric artery

GDA    Gastroduodenal artery

GIT      Gastrointestinal tract

ERCP  Endoscopic retrograde cholangiopancreatography

EUS     Endoscopic ultrasound guided

 

Introduction

Pseudo aneurysms are reported to be a rare1 but potentially lethal complication associated with chronic pancreatitis.  The incidence ranges from 6-9.5% of patients with chronic pancreatitis2, 3, 4 although in one series a pseudo aneurysm was found in 17% of all patients operated on for chronic pancreatitis5 thus suggesting a higher incidence.  A very high mortality is reported for this condition6, 7 with some approaching 90% without some form of therapy8 and ranging from 12.5-40% in patients having some form of intervention.2, 5, 9, 10.

 

Case Report

We present a case of a 31-year-old male admitted to hospital with a history of three episodes of acute haematemesis and malaena stool.  The haematemesis was massive accompanied by three episodes of black tarry stool over the preceding four days.  His past medical history included two previous admissions for upper gastrointestinal bleeding in which no specific source of bleeding was identified on endoscopy and he was transfused.  He had a fifteen-year history of heavy and regular alcohol intake.  He did not have any previous history of documented acute or chronic pancreatitis.

 

Examination revealed a pale, tachycardic and hypotensive gentleman with a blood pressure of 90/50 mmHg. He did not have any abdominal tenderness.  His haemoglobin on admission was 7.2 gm/dl, his clotting screen, urea and electrolytes and liver function tests were normal and he had an amylase of 84 iu/l on this admission.  Chest and abdominal x-rays were normal with no calcification visible in the pancreatic area and no free air under the diaphragm.  He was resuscitated with intravenous fluids and blood and stabilised.  Endoscopy carried out the next day failed to identify any specific source of bleeding.  An abdominal ultrasound was normal with no features of portal hypertension.  CT scan showed atrophy of the body and head of the pancreas and dilatation of the main pancreatic duct with a large soft tissue mass with a central area containing contrast intimately related to the third part of the duodenum and this raised the possibility of active bleeding into a pancreatic pseudo aneurysm (Figs: 1 and 2).  A nuclear red-cell scan was negative for bleeding into the alimentary tract.  He had been transfused 23 units of blood in total during this admission and persistent intermittent bleeding necessitated transfer to a specialist centre where a mesenteric arteriogram demonstrated filling of a false aneurysm from a small posterior branch of the SMA on selective SMA catheterisation (Fig: 3).  Selective coeliac and GDA angiography showed that these vessels were normal.  Despite several attempts, sub-selective catheterisation of the feeding vessel to the aneurysm proved impossible and hence constituted a failed attempt at embolisation.  He then underwent an endoscopic ultrasound guided transduodenal injection of the SMA with thrombin after which he stabilised.  A follow-up CT scan three months later showed that the aneurysm had disappeared (Fig: 4) and the patient remains well.

 

Discussion

Most reported cases in the literature appear to be associated with chronic pancreatitis secondary to alcohol abuse.  Posttraumatic pancreatitis11 and cholelithiasis12 however have also been reported as aetiological factors and duration of pancreatic disease is closely related to pseudo aneurysm formation, as is splenic vein thrombosis.13  Repeated episodes of pancreatic inflammation or chronic ongoing low-grade inflammation of the gland and disruption of the duct and ductule system causes fluid exudation into the surrounding structures and spaces.  The enzymes in this fluid exudate begin to digest and erode the walls of the adjacent peripancreatic vessels, thus weakening their walls14 and leading to aneurismal dilatation and necrosis eventually leads to rupture of this aneurysm.  Rupture can occur into a pre-existing pseudo cyst.  Alternatively necrosis of adjacent structures can cause haemorrhage into the retro peritoneum, abdominal cavity, gastrointestinal tract or into the pancreatic duct system itself causing haemosuccus pancreaticus8, 15 or into the biliary tree causing haemobilia.  Erosion of the adjacent bowel may cause bleeding from the bowel mucosa itself.16, 17

 

The splenic artery, the gastroduodenal and the inferior pancreaticoduodenal arteries are the most frequently involved vessels while the SMA, hepatic, dorsal pancreatic and gastric arteries are involved less commonly.18

 

Most cases of pancreatic pseudo aneurysms are associated with known previous pancreatitis and a large proportion have pseudo cysts associated with the condition.2, 5, 9, 10  This is in contrast to our patient who had no previous documented history of pancreatitis although his CT scan was suggestive of the disease. 

 

Given the high associated mortality if not treated in time, a high index of suspicion is necessary for prompt diagnosis and thence management of pancreatic pseudo aneurysms.  A history of previous pancreatitis or chronic alcohol abuse with GI bleeding and right upper quadrant or epigastric pain should prompt the consideration of a pancreatic pseudo aneurysm in the differential diagnosis19.  Previous authors have postulated that rupture into a pseudo cyst with bleeding into the pancreatic duct and hence into the alimentary system are probably the most common pattern of bleeding.15  This presents with intermittent bleeding which may be massive and have devastating consequences.  It is thought that the bleeding is intermittent because increased pancreatic duct pressure leads to thrombosis of its communication with the pseudo aneurysm and thereafter the duct decompresses and the clot lyses thus leading to a repetition of the cycle20.  Haemorrhage may occur over a period of months to years or quite frequently with short periods between bleeds.11  Haemobilia, causing biliary colic and jaundice has also been described.21  Less commonly bleeding may occur through the bowel mucosa itself due to necrosis of bowel wall and fistulation of the aneurysm into the GIT.  Pancreatic duct distension probably causes pain20 which is characteristically described as crescendo-decrescendo type.22  A sudden fall in haematocrit and an increase in size of a pre-existing pseudo cyst due to bleeding into it, without overt external bleeding23 and positive guaiac stools with iron deficiency anemia24 are also occult manifestations of bleeding pancreatic pseudo aneurysms. 

 

Endoscopy is often negative but helps in excluding other sources of bleeding which may be important in those with a history of alcohol abuse.  These include oesophageal varices and ulcers.  Occasionally bleeding from the mucosa may be visible if the pseudo aneurysm communicates with the bowel mucosa.  Visualized bleeding from the papilla is reported to be a rare event15 and careful and sometimes prolonged endoscopy with a side–viewing duodenoscope25 may help identify the problem.

 

Visceral arteriography currently remains the gold standard according to the literature3, 9, 17, 19, 22 and is especially important in identifying the 20% of pseudo aneurysms that are too small to be seen by other kinds of imaging.26  It also allows preoperative diagnosis of pseudo aneurysms, their therapeutic embolisation and serves to identify unusual arterial anatomy27 which may have implications for those requiring major surgical intervention.

 

Dynamic bolus CT scanning has become a widely utilised non-invasive modality of investigation with an 80-100% diagnostic accuracy13, 15 and is also used to follow up pseudo aneurysms that have been embolised.  Rapid contrast injection is said to be necessary especially if cystic lesions are identified in the pancreas or peripancreatic area12 as it is important to distinguish between pseudo cysts and pseudo aneurysms that contain thrombus.  This is because an attempt at drainage of a lesion suspected to be a pseudo cyst that eventually turns out to be a pseudo aneurysm could be devastating.28  Thus this technique is helpful in identifying pseudo aneurysms in asymptomatic patients who have no evidence of bleeding.12

 

Ultrasound is a less well-evaluated imaging modality for pseudo aneurysms.  Doppler ultrasound identifies turbulent arterial flow within a peri-pancreatic swelling, thus confirming a pseudoaneurysm29 while simultaneously observing neighbouring vessels30 and in some centres is used as a monitoring tool for successful embolisation.31

 

ERCP may demonstrate disruption in the ductal system and can be used to define the anatomy of the duct system, may be used therapeutically in pseudo cyst treatment and may also identify a clot in the pancreatic duct confirming the diagnosis of a haemosuccus pancreaticus.11

 

The guidelines for the treatment of pancreatic pseudo aneurysms are not well defined probably because of the rarity of the condition and the lack of enough material for large studies.  Surgical treatment is a well established form of treatment and has been the traditional treatment up until the era of endoscopic and endovascular techniques.  It is reported that 7-17% of patients with the condition will require operative intervention.5, 16  These include people in whom other modalities of treatment have failed and those who are good operative candidates where it offers a definitive treatment for the cause of the pseudo cyst and pseudo aneurysm and also include patients who are haemodynamically unstable and require exploration.  But surgical therapy is not without its complications with a mortality ranging from 20-30%9, 16 with a higher mortality if resection involves the head of the pancreas.11, 13  Most frequently performed, are operations that resect the pseudo aneurysm with the involved pancreatic area.11, 15, 18, 32  Some studies show results similar to radical surgery by proximal and distal ligation of the pseudo aneurysms with internal drainage.5, 16

Visceral artery embolization is considered by some to be the first line treatment for bleeding pseudoaneurysms17, 26, 33, 34 and has been used alone for the definitive treatment of uncomplicated pseudoaneurysms.24, 29,35  This is done most often with metallic coils on either side of the arterial defect36 and success rates of 79% have been reported with this treatment.37  This is also used as an emergency measure to stop massive bleeding and buy time so that elective definitive surgery under controlled conditions can be planned.  However, as in our patient, it is not always possible to sub selectively catheterise the vessel concerned.

 

Ultrasound guided injection of thrombin is a well-recognised technique for the treatment of peripheral pseudoaneurysms.38, 39, 40  However to our knowledge there are only two previous cases in which thrombin has been used for pancreatic pseudo aneurysms and in both these cases ultrasound guidance was external, with thrombin injection being percutaneous.41, 42  One of the complications of this technique is that recanalisation may occur and hence this method requires regular subsequent surveillance.42

 

Our case demonstrates that EUS guided thrombin injection can be used successfully to treat pancreatic pseudo aneurysms especially if endovascular embolisation has failed.  We suggest that this method can also be used as a method of controlling haemorrhage from a pseudo aneurysm and thus conversion of a potential emergency operation with an associated high mortality, to an elective procedure under controlled conditions thereby potentially reducing the patient’s risk of mortality.  There is not enough data to indicate that this method can be used as definitive treatment for bleeding pseudo aneurysms and regular follow-up is needed for these patients.

 

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