Splenic artery aneurysm was first described by Baussier in 1770, and St. Leger Brockman described one of the first surgical cases in 1930. Although mycotic aneurysm can be seen in the splenic artery, the majority are idiopathic. The splenic artery is the most common visceral artery aneurysm and the second most common site of intra-abdominal aneurysms, second to the abdominal aorta. The incidence in autopsy series ranges between 0.02 and 0.16%, with a female predominance (4:1). The incidence of splenic aneurysm can increase in certain patient groups, including those with cirrhosis and portal hypertension. In fact, splenic artery aneurysms have been reported in 14% of patients awaiting liver transplant, which can lead to major hemorrhage after transplant.14 Splenic artery aneurysm may also develop in patients with history of pancreatitis and should be suspected in a patient with pancreatitis who develops gastrointestinal (GI) bleeding without an obvious source.
In a contemporary review of 217 splenic aneurysms seen at the Mayo clinic, the mean age at presentation was 62 years, with 79% of the patients being female. Over 90% of the patients were asymptomatic, with only 5% of patients presenting with a rupture, with a mean size of 3.1 cm. While over 10% of men presented with a rupture, this rate was less than 3% in women, in large part due to larger aneurysm sizes in men. The mean size for nonruptured cases was 2.2 cm, and the smallest-diameter aneurysm to rupture was 2.2 cm.15
Risk of rupture of splenic aneurysms is believed to be higher in pregnant women, where rupture of aneurysms less than 2 cm has been reported. Such ruptures have been associated with maternal and fetal death rates of 22 and 15%, respectively.16 Ruptures occur in the third-trimester of pregnancy in 69% of cases.17
Diagnosis in asymptomatic patients is often made as an incidental finding on a CT scan, although occasionally a calcified lesion is noted on plain film of the abdomen (Fig. 62-9).
Rupture of the aneurysm is manifested by sudden abdominal pain. In 12.5% a warning hemorrhage occurs, with temporary cessation of bleeding. Rupture into the colon, stomach, and intestine may take place, but intraperitoneal rupture is by far the most common presentation. When rupture occurs in the nonpregnant woman, it is usually contained in the lesser sac, resulting in a patient mortality rate of less than 5%.
A CT scan of a large splenic artery aneurysm with calcified wall. This calcified wall can also be seen on plain abdominal roentgenogram.
Surgical resection in all symptomatic aneurysms is recommended; however, criteria for elective repair of asymptomatic aneurysms are not firm. In general, asymptomatic aneurysms greater than 2 cm should be removed if the patient is a reasonable operative risk.15 Aneurysms of any size detected in pregnancy should be considered for resection as many of the ruptured aneurysms during pregnancy are less than 2 cm in size.16 These resections should be done before the third trimester, when the risk of rupture is at its peak.
Lesions proximal to the hilus of the spleen can be managed by resection and primary end-to-end anastomosis or proximal and distal ligation with resection of the involved segment.18 Proximal ligation is reasonable because the spleen will not become ischemic following central ligation of the main splenic artery.
Distal lesions generally require laparoscopic splenectomy with resection of the involved splenic artery (Fig. 62-10).
A 3D CT reconstruction of a partially thrombosed large splenic artery aneurysm with a smaller aneurysm more distal. Both aneurysms were treated by a laparoscopic splenectomy.
Although there has been significant recent progress in treating such aneurysms by endovascular means, with a less than 90% success rate the disadvantages of the endovascular procedures include treatment failures, postprocedural pain, and abscess formation, as well as pancreatitis due to occlusion of the pancreatica magna vessel.19
Splenic cysts are generally classified as primary or secondary (pseudocysts). Some of the splenic tumors may also have a large cystic component to them and are discussed separately in the following text (Fig. 62-11). Primary cysts have an epithelial lining and can be nonparasitic or parasitic (echinococcal).
A. A large splenic cyst seen on CT. B. A large splenic cyst that, on careful review, had septations and calcifications. Patient underwent a splenectomy, and pathology confirmed an 8-cm lymphangioma.
Worldwide, Echinococcus infection (hydatid disease) is the most common cause of a splenic cyst. Echinococcus granulosis, the most commonly implicated species, usually results in a unilocular cyst composed of an inner germinal layer (endocyst) and an outer laminated layer (ectocyst) surrounded by a fibrous capsule. Unlike the nonparasitic cysts, these are filled with fluid under positive pressure, and also contain daughter cysts and infective scolices. Echinococcal cysts are usually asymptomatic unless they reach a size causing pressure symptoms or become secondarily infected or rupture.
For diagnostic purposes, the older Casoni skin test is now replaced with serologic testing, which provides reliable diagnostic specificity and sensitivity. Ultrasound, CT, and MRI studies demonstrate a cystic mass that is septated and contains daughter cysts.
Splenectomy is the treatment of choice because there is no effective medical therapy. Care should be taken to avoid spilling the contents of the cyst. Intraoperatively, the lesions can be sterilized by instilling a 3% sodium chloride solution. If intraperitoneal spillage occurs during the dissection, anaphylactic hypotension may occur and require epinephrine to treat the shock. Laparoscopic and percutaneous treatment has not been widely accepted in treating hydatid cysts because of a traditional fear of spillage and anaphylaxis.20
Nonparasitic Primary Cysts
This group of cysts includes simple cysts, epidermoid cysts, and dermoid cysts. Various classifications have been proposed based on whether they are lined with mesothelial, transitional, or epidermoid linings and also whether they are neoplastic, traumatic, or degenerative.21 Simple congenital cysts are lined by flattened or cuboidal cells originating from infolding of peritoneal mesothelioma during splenic development. These lesions are usually small and asymptomatic and do not require excision. When these cysts are large and symptomatic, they can be removed by laparoscopic or open total or partial splenectomy.
About 10% of cysts are lined by squamous epithelium and are rare. These cysts are usually round and unilocular and may be very large. They are filled with yellow or brown turbid fluid. The cyst is dense, and the diagnosis is established by microscopic definition of the stratified squamous lining. Examination of multiple cuts may be required to demonstrate the pathology.
Epidermoid cysts of the spleen occur in children and in young adults in 75% of the cases. About two-thirds of the patients have been female. The clinical manifestations are dependent on the size and are similar to those of the pseudocysts, as are the imaging findings. Laparoscopic or open splenectomy or partial splenectomy is recommended for large or symptomatic cysts.
True dermoid cysts of the spleen are exceedingly rare; fewer than 10 cases have met the pathologic criteria of a squamous epithelium with dermal appendages such as hair follicles and sweat glands. Splenectomy is indicated.
It can be difficult to differentiate these cysts from one another based on imaging only, and usually the differential diagnosis is made when symptomatic cysts, usually greater than 5 cm, are excised and analyzed histologically.22 Asymptomatic cysts, which are often smaller, are observed with no need for surgical resection.
These cysts do not have an epithelial lining and comprise 70–80% of splenic cysts in the Western countries. They are usually a result of trauma and represent resolution of a subcapsular or intraparenchymal hematoma. In over 80% of the cases the lesion is unilocular, and the cyst wall is dense and smooth. Microscopically, the wall consists of fibrous tissue without an internal epithelial lining.
Pseudocysts occur more frequently in women, children, and young adults. One-third of the patients are asymptomatic, and in others the most frequent complaint is left upper quadrant pain radiating to the left shoulder or chest. Symptoms related to pressure on the stomach occur less frequently. Ultrasonography, CT, MRI, and magnetic resonance arteriography will define the cystic nature of the lesion. Although splenectomy is the definitive therapy, these cysts are increasingly managed by laparoscopic unroofing and drainage. Such simple approach is, however, associated with a recurrence rate of 20–40%, and recommendations would be to marsupialize the cyst or decapsulate the cyst when possible, which has been associated with very low recurrence rates.23,24
Splenic abscesses tend to be rare, due to the spleen's ability at fighting infections and bacteria. They are more frequently seen in the tropics, where there is a higher incidence of sickle cell anemia, with associated thrombosis of parenchymal vessels and subsequent superimposed infarction.
The major risk factors for such abscesses in the Western world are intravenous drug use, human immunodeficiency virus disease, other hematogenous spread (endocarditis), splenic trauma, and contiguous spread. Endocarditis can be complicated with splenic abscesses in 5% of cases. They are often multiple splenic abscesses associated with similar findings in other organs; spleen is just a part of overwhelming sepsis.25
Most infections are polymicrobial and include such organisms as Staphylococcus, Salmonella, and Escherichia coli, Proteus mirabilis, Streptococcus group D, Klebsiella pneumoniae, Peptostreptococcus species, Bacteroides species, Fusobacterium species, Clostridium species, Candida albicans, and Mycobacterium.
The symptoms are usually nonspecific such as malaise, weight loss, left upper quadrant pain, and fever. Most patients have a leucocytosis and an ultrasound, CT or magnetic resonance study establishes the diagnosis of a splenic abscess. Treatment consists of broad-spectrum antibiotics and percutaneous drainage, which, if fails, will require laparoscopic or open splenectomy. Many patients have multiple other abscesses, and the spleen is just a part of overwhelming sepsis. Antibiotic treatment should continue until the drains or percutaneous catheters have been removed. If the spleen has multiple abscesses, splenectomy may be required.
Splenic masses may be identified during workup of symptoms, or often incidentally during other imaging (Fig. 62-12). Some of these masses, can have a large cystic component (see Fig. 62-11B). Management of such lesions can be difficult as imaging alone does not always help with a definitive diagnosis. Often, these lesions may need to be followed serially or, if concerning, splenectomy should be considered. In a series of 44 such cases, half of whom were symptomatic and treated surgically, 75% of lesions were benign while the remainder were malignant.26 In a similar study of 28 patients, the risk of a malignant diagnosis was significantly higher at 72%, although 25% of these patients had had a previous history of lymphoproliferative disorder.27 There are increasing data on the use of fine-needle aspiration of the spleen in differentiating such masses, with low complication rates.28 Sensitivity and specificity of such aspiration have been reported as 94 and 79%, respectively.29
Multiple splenic masses were seen during a right upper quadrant ultrasound for symptomatic gallstones and were further evaluated by a CT scan as shown. The lesions were negative on PET scan. Patient did not wish to have a splenectomy or percutaneous biopsy and is therefore followed by regular imaging. Lesions have remained unchanged, and patient is asymptomatic.
Benign splenic neoplasms generally arise from the lymphoid or vascular elements of the spleen. The most common primary neoplasm of the spleen is hemangioma.30 The lesion can be single or multiple.
Hemangiomas vary from well-circumscribed to irregular vascular proliferations. The majority are cavernous in nature. The potential for malignant transformation to angiosarcoma is not known but appears to be low and associated with large hemangiomas. Many splenic hemangiomas are now diagnosed incidentally during the course of imaging for other pathology. On CT scan, hemangiomas appear as homogeneous, hypodense, or multicystic lesions with variable calcification, and peripheral enhancement. Angiography may also be employed to confirm the diagnosis, although this is much more invasive. On angiography, the splenic hemangioma resembles a hepatic hemangioma with fine vascularity and “laking” effect in the capillary phase, which may be accompanied by early filling of the splenic vein.
The majority of splenic hemangiomas do not require surgical intervention. Splenectomy is reserved for large and symptomatic lesions. Most splenic hemangiomas are asymptomatic, with symptoms being associated with enlargement of the tumor and mass effect or rupture. Although there has traditionally been concern about risk of spontaneous rupture of these hemangiomas, a contemporary series from the Mayo Clinic reported no spontaneous rupture among 32 patients with splenic hemangioma, 80% of whom were entirely asymptomatic.30
Littoral cell angioma has been recently described as an endothelial cell neoplasm arising from the cells lining the sinus channels of the splenic red pulp. These rare lesions express vascular and histiocyte-associated antigens. Patients often present with splenomegaly and multiple hypoattenuating masses seen on CT.31 While littoral cell angioma has been described as a benign neoplasm cured with splenectomy, there have been reports of associated malignant lymphomas, other visceral organ cancers, and recurrent disease identified as malignant littoral cell hemangioendothelioma. Splenectomy and close observation are thus warranted.32
Lymphangioma of the spleen is composed of a malformation of lymphatics (see Fig. 62-11B). Microscopically, these endothelium-lined spaces are filled with lymph and blood elements. The lesion may be focal or multiple, a small or large cystic mass, or may diffusely involve the spleen and account for splenomegaly. The diagnosis is made by ultrasound, CT scan, or MR imaging, which reveals water-density cystic lesion(s) of the spleen. The lymphangioma may be isolated to the spleen or occur as a generalized lymphangiomatosis with multivisceral involvement and a poor prognosis. Symptoms, when present, are related to the size and mass effect of the lesion. Splenectomy is indicated for symptomatic lesions. Partial splenectomy is reserved for small, focal symptomatic lesions.
Other benign lesions of the spleen are uncommon. Inflammatory pseudotumor of the spleen is a reactive lesion characterized by a mixture of inflammatory cells and disorganized spindle cells.33 This tumor is typically found incidentally and is generally asymptomatic but may present with systemic symptoms such as fever, malaise, and weight loss. Inflammatory pseudotumor is infiltrative in nature and may mimic malignant lymphoproliferative disease. Splenic hamartomas are composed of irregular vascular channels lined by splenic sinus endothelium with a disorganized reticulin stroma. Splenic hamartomas are uncommon with autopsy series noting an incidence of 0.024–0.13%. Peliosis is not a true neoplastic lesion but a blood-filled cystic lesion without an endothelial lining that may be associated with focal, patchy, or diffuse involvement of the spleen. This lesion is likely reactive as it has been associated with steroids, oral contraceptives, immunosuppression medications, tuberculosis, renal disease, and malignancy. Other benign splenic tumors, such as angiomyolipoma, lipoma, hemangiopericytoma, and fibroma are rare.
Primary, nonlymphoid, malignant tumors of the spleen are exceedingly rare. These include angiosarcomas, malignant fibrous histiocytomas, and plasmacytomas. Angiosarcoma is the most common nonlymphoid primary malignant neoplasm of the spleen. The clinical presentation may include abdominal pain, left upper quadrant abdominal mass, and constitutional symptoms. Metastasis is frequent and often involves the liver. Spontaneous rupture has been reported and is associated with a dismal outcome. Normocytic anemia is present in the majority of cases. Splenomegaly with hypersplenism is also seen. CT imaging often identifies a splenic lesion with central necrosis. The primary treatment is splenectomy. Cisplatin-based chemotherapy has also been used. However, even without rupture, splenic angiosarcoma holds a poor prognosis. Recent studies have reported respective 1-, 3- and 5-year survival rates of 60, 40, and 40%.34
Splenic metastasis of nonhematologic malignancies is rarely seen clinically and usually represents widespread dissemination of disease. In a review of a German oncological database, only 0.002% of those with a malignancy developed reported splenic metastasis, with isolated splenic metastasis being extremely rare.35 Despite lack of clinically evident splenic metastasis, postmortem evidence of splenic metastasis is reported to be higher, although the exact prevalence of this is debated, with older literature reporting rates as high as 34%, while contemporary reports put this rate at approximately 3%.36
The diagnosis of malignancy can be confirmed by positron emission tomography (PET) scanning, although percutaneous biopsies for isolated lesions can also be performed (Fig. 62-13).28
The patient was found to have a splenic lesion on CT which was active on PET scan. She subsequently underwent a splenectomy to obtain a tissue diagnosis.