The splenic artery is defined as aneurysmal when a focal dilation is observed in its diameter of greater than 50% compared to the normal vessel diameter. The normal diameter of the splenic artery varies and ranges from 0.43 cm to 0.49 cm. True splenic artery aneurysms (SAAs) involve all layers of the wall, each of which is intact and thinning. Pseudoaneurysms are the result of a tear in the vessel wall intima with subsequent blood dissection into a false lumen and periarterial hematoma formation. They develop secondary to trauma or inflammation of the splenic artery, such as in cases of pancreatitis. The SAA is the most common visceral artery aneurysm reported. SAA represents 60% to 70% of patients diagnosed with visceral artery aneurysms (VAAs). Hepatic artery aneurysms have been reported in 20%, while celiac or mesenteric artery aneurysms represent 10% of all reported cases of VAAs.
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.
The prevalence of SAA in general population is reported to 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%.
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.
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.
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.
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.
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.
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.
SAA in Pregnancy
SAAs occur predominantly in multiparous women. The true prevalence of SAA in pregnancy is unknown. Fifty percent of SAAs that occur in pregnancy eventually rupture during pregnancy. Two-thirds of SAA rupture in the third trimester and typically in the last two weeks of pregnancy. Multiple factors have been linked to increased SAA incidence particularly in pregnant women. One hypothesis suggests that the increased blood flow and cardiac output in pregnancy may result in increased force against the vessel wall. Another hormonal hypothesis suggests that increased estrogen and progesterone presumably result in medial degeneration of the vessel wall. Elevated levels of relaxin during pregnancy may enhance the elasticity of splenic artery leading to aneurysmal dilation. Additionally, increased frequency of SAAs rupturing in late pregnancy is presumably linked to an increased mechanical pressure of the enlarging gravid uterus.