Splenic Artery Aneurysm

Etiology

Modifiable risk factors include atherosclerosis, portal hypertension, liver transplantation, pregnancy, and connective tissue disorders such as Marfan or Ehler-Danlos syndrome. Recent studies demonstrate splenic pseudoaneurysms occur in up to 21% of patients diagnosed with chronic pancreatitis. Non-modifiable risk factors include advanced age and female gender. Splenic artery pseudoaneurysms have been associated with blunt and penetrating trauma as well as iatrogenic trauma during instrumentation.[4]

Epidemiology

The prevalence of SAA in general population is reportedto be less than 1%, as most of the SAAs remain asymptomatic and therefore go undetected. A recent retrospective study found that 78% of SAAs occur in women. Mortality because of splenic aneurysm rupture in non-pregnant patients ranges from 25% to 40%. However, maternal mortality due to SAA rupture increases up to 75%, and fetal mortality increases as high as 95%.[5][6] 

Pathophysiology

The exact etiology of visceral aneurysms is not established. Recent literature has suggested that true aneurysms develop secondary to arterial wall weakness due to several causes. These include atherosclerosis (32%), medial degeneration or dysplasia (24%), abdominal trauma (10%), hypertension, connective tissue diseases, and necrotizing vasculitides such as polyarteritis nodosa or Wegner granulomatosis. Pseudoaneurysms are periarterial hematomas that develop as a consequence of iatrogenic trauma or inflammatory processes such as chronic pancreatitis. Pseudoaneurysms lack a true wall hence they are more prone to rupture.

Toxicokinetics

The splenic artery is one of the major branches of the celiac axis.  It courses along the superior aspect of the body, and the tail of the pancreas towards the splenic hilum arises, but its course can be variable. The artery is commonly tortuous, dividing into separate branches that provide a segmental blood supply to the spleen. Aneurysms arise in the middle or distal third of the splenic artery near its bifurcation. SAAs are usually saccular as opposed to fusiform.

History and Physical

The most common presenting symptom is vague epigastric or left upper quadrant abdominal pain that may radiate toward the left shoulder. Other symptoms include gastrointestinal hemorrhage with subsequent hematemesis or hematochezia, or hemorrhage into the pancreatic duct with subsequent hemobilia.True aneurysms can be silent and asymptomatic; however, pseudoaneurysms are always symptomatic. Rupture is a rare but serious complication of SAA which may manifest by acute diffuse abdominal pain and hypovolemic shock with signs and symptoms of an acute surgical abdomen. Rupture incidence increases in multiparous women and patients with portal hypertension due to increased portal blood flow. The reported risk of SAA rupture is 2% to 10%, which is increased to 76% to 83% in symptomatic patients.

Evaluation

Multi-slice abdominal computerized tomography (CT scan) with IV contrast is the ideal diagnostic imaging modality to diagnose SAA and other visceral aneurysms. CT is useful in detecting small SAAs and assessing anatomy for operative planning. Magnetic resonance imaging (MRI) is an alternative to CT, especially in patients with chronic renal insufficiency. Contrast angiography (CA) is the most specific imaging test to identify SAAs and may also be therapeutic. Endoscopic ultrasound can reliably distinguish SAAs from other extrinsic lesions such as pancreatic pseudocysts. [7][8]

Treatment / Management

Due to the increased risk of aneurysmal rupture, intervention rather than a watchful waiting is advised for aneurysms greater than 2 cm in diameter. Other indications for intervention include: symptomatic patients, women of childbearing years, concomitant pregnancy, and cirrhotic patients planning to undergo orthotopic liver transplantation or Porto venous shunting procedures.[9][10](B3)

Open surgical approach: Open surgical intervention is considered the gold standard approach for SAA repair. Techniques involving resection of an aneurysm with interposition bypass are ideal for aneurysms located in the proximal to the mid-splenic artery. Resection of an aneurysm can be combined with splenectomy in cases of a hostile abdomen or distal aneurysms located near the splenic hilum. Patients with ruptured splenic aneurysms should undergo urgent laparotomy and control of hemorrhage with ligation of an aneurysm. Preservation of the spleen is encouraged when possible, but splenectomy should be performed if adequate hemostasis is impossible to achieve otherwise.

Endovascular approach: Endovascular intervention has gained a lot of popularity recently in managing aneurysms. Techniques vary according to the type of an aneurysm, location, whether preserving the splenic artery will be preserved, and the condition of collaterals. Fusiform true aneurysms are better treated with a stent graft (covered stent), while tortuous, saccular aneurysms are treated with aneurysmal coiling techniques. Pseudoaneurysms can be treated with embolization using liquid embolic agents to thrombose the inflow and outflow arteries or filling the sac itself. Distal splenic embolization should be avoided.

Minimally invasive laparoscopic approach:  The laparoscopic approach is a safe therapeutic alternative for cases of elective splenic aneurysm repair. Different techniques have been employed including ligation of the mid-splenic artery via stapling or clipping to splenectomy alone for distal SAAs near the hilum. Splenectomy with distal pancreatectomy may be necessary when the aneurysmal wall is severely inflamed and adherent to the tail of the pancreas. The laparoscopic approach carries the advantage of the rapid recovery, shorter hospital stay, and less postoperative pain compared with the open approach. The laparoscopic approach is also suitable and safe in pregnant SAA patients. Compared with the open approach, laparoscopic splenic aneurysm repair has a lower risk of preterm labor in these patients due to minimal manipulation of intra-abdominal contents.

Differential Diagnosis

• Congenital Antitrypsin Deficiency

• Cystic Medial Necrosis

• Ehlers-Danlos Syndrome

• Marfan Syndrome

• Neurofibromatosis

• Polyarteritis Nodosa

• Systemic Lupus Erythematosus

• Takayasu Arteritis