CHAPTER 22SPLEEN

Canas Genevieve

Introduction

Anatomy

1. Developmental considerations– The spleen develops from mesenchymal tissue in

the dorsal mesogastrium.

– This tissue rotates to the left as development progresses.

– By the end of the third gestational month, the organ is formed. The point at which the spleen remains attached to the dorsal mesogastriumbecomes the gastrosplenic ligament.

– The organ itself consists of an outer capsule and trabeculae, which enclose the pulp. The pulp consists of three zones:• The white pulp is essentially a lymph node. It contains

lymphocytes, macrophages, and plasma cells in a reticular network.

• The red pulp consists of cords of reticular cells with sinuses in between.

• The marginal zone is a poorly defined vascular space between the pulps.

– The adult spleen weighs between 100 g and 150 g and measures 12 — 7 — 4 cm.

2. Location. The spleen is located in the left upper quadrant of the abdomen and is protected by the eighth to the eleventh ribs. It is bordered by the left kidney posteriorly, the diaphragm superiorly, and the fundus of the stomach and the splenic flexure of the colon anteriorly.

3. Vasculature– The main blood supply is the splenic artery, which is a branch of

the celiac axis. It travels along the superior border of the pancreas. At the hilus, it branches into trabecular arteries, which terminate in small vessels to the splenic pulp.

– The splenic vein crosses behind or at the lower border of the pancreas. It joins the superior mesenteric vein to form the portal vein

Physiology

• The spleen has multiple functions, some of which remain poorly understood. Its most important functions are its ability to act as a blood filter and its role in the immunologic process of the body.

1. Filtering functions. Splenic blood flow is approximately 350 L/day of blood. Most blood elements pass through rapidly and uneventfully.

a. Removal of old or abnormal red blood cells

• The spleen removes about 20 mL/day of aged or abnormal red blood cells.

• Cells that have immunoglobulin G (IgG) on their surfaces are removed by monocytes in the spleen. This removal of cells may be the mechanism of increased cell destruction in some diseases, such as idiopathic thrombocytopenic purpura and autoimmune hemolytic anemia.

b. Removal of abnormal white blood cells, normal and abnormal platelets, and cellular debris

2. Immunologic functions

– Opsonin production. The entire reticuloendothelial system is capable of removing well-opsonized bacteria from the circulation, but the spleen, with its highly efficient filtering mechanism, is particularly suited to removing poorly opsonized or encapsulated pathogens.

– Antibody synthesis. This synthesis occurs mainly in the white pulp, where soluble antigens stimulate the production of immunoglobulin M (IgM).

– Protection from infection. It is well established that splenectomy leaves some patients more susceptible to infection.

3. Storage functions. Approximately one third of the body's platelets are stored in the spleen. In some pathologic states, the percentage is increased.

Hypersplenism

• Hypersplenism refers to the exaggerated destruction or sequestration of circulating red blood cells, white blood cells, or platelets by the spleen. The term should not be confused with splenomegaly, which refers only to physical enlargement of the spleen.

A . Primary hypersplenism is uncommon.

B. Secondary hypersplenism is caused by an identifiable underlying disease, such as:

• Disorders of splenic blood flow

• Hematopoietic disorders leading to increased red blood cell turnover

• Immune disorders

• Infiltrative disorders

• Infectious diseases

• Neoplastic diseases

c. Presentation1. Anemia, leukopenia, or thrombocytopenia may be

noted on a routine laboratory workup.– Anemia may lead to pallor, fatigue, and dyspnea.– Leukopenia may lead to increased susceptibility to

infection.– Thrombocytopenia is characterized by easy bruising and

epistaxis.

2. Splenomegaly may be found incidentally during the physical examination or in a radiologic imaging study.

3. The patient may present with pain secondary to splenicenlargement or rupture.

D. Evaluation1. Peripheral blood smears may demonstrate a decreased

number of red blood cells, white blood cells, or platelets.– Reticulocytosis is frequently observed if the hypersplenism is

causing an increased turnover of red blood cells.– Abnormal red blood cell morphology is sometimes diagnostic

for the underlying hematologic disorder (e.g., spherocytosis).

2. Bone marrow aspirate– A compensatory increase in megakaryocytes should be

observed if there is sequestration of platelets in the spleen.– Abnormalities of hematopoiesis may be identified as well.

3. Radiologic imaging– An ultrasound or a computed tomography (CT) scan

can accurately document the size of the spleen as well as determine any structural abnormalities.

– Radioisotope scans may demonstrate a shortened half-life for circulating blood elements and their sequestration in the spleen.

4. Immunologic tests using specific antibodies may be diagnostic for certain diseases, particularly those with an autoimmune basis.

Pathologic Conditions Affecting the Spleen

A. Primary splenic disorders

Primary hypersplenism is essentially a diagnosis of exclusion; it is made only after possible causes of secondary hypersplenismhave been ruled out.

– It is rare, and it affects mainly women.

– There is an exaggerated destruction or sequestration of circulating blood elements.• Any one or all of the formed blood elements may be involved.

• The hematologic findings may be accompanied by recurrent fevers and infections.

– Splenomegaly is almost always present.

– It may, in some cases, actually be an early manifestation of lymphoma or leukemia.

– The treatment is splenectomy. Steroids do not improve the condition.

2. Splenic cysts may be idiopathic or, more commonly, may result from previous trauma. Surgery is indicated if the cysts become large enough to cause pain or torsion or if they exert a significant mass effect on surrounding structures.

B. Disorders of splenic blood flow

1. Portal hypertension may cause passive spleniccongestion.– It is the most common mechanism of secondary

hypersplenism.

– Causes of portal hypertension include alcoholic cirrhosis, viral hepatitis, Budd-Chiari syndrome, and congestive heart failure.

– Hypersplenism associated with portal hypertension is usually mild and clinically insignificant. Only 15% of patients develop significant hypersplenism; therefore, isolated splenectomy is generally not indicated.

2. Splenic vein thrombosis can cause secondary hypersplenism with massive splenomegaly.– Cause. Pancreatitis is the usual cause of the

thrombosis.

– Presentation. The patient may present with bleeding from esophageal or, more characteristically, proximal gastric varices.

– Treatment. The hypersplenism and bleeding varices are cured by splenectomy.

3. Splenic artery aneurysm

C. Hematopoietic disorders

1. Hereditary spherocytosis is one of a group of hereditary hemolytic anemias that cause the most severe symptoms.

a. Characteristics

• Hereditary spherocytosis is characterized by a defect of the red blood cell membrane that results in loss of red blood cell surface area, which causes the cell to be spherical ,small, and more susceptible to lysis than normal red blood cells.

• The cell membrane is thick and rigid, which causes the cells to be held in the splenic pulp.

• It is transmitted as an autosomal dominant trait.

b. Symptoms

• Symptoms of hereditary spherocytosis include malaise, abdominal discomfort, jaundice, anemia, and splenomegaly.

• The disease may be complicated by gallstones (which are rare in patients younger than 10 years of age) and by chronic leg ulcers that heal only after splenectomy.

c. Diagnosis is based on the preceding clinical findings and the results of laboratory studies, which include a demonstration of the following:

• Spherocytes and an elevated reticulocyte count on a Wright-stained blood smear

• Increased osmotic fragility of the red blood cells

• Chromium 51 (51Cr)-tagged red blood cells, which have a greatly shortened half-life and are sequestered in the spleen

d. Treatment is splenectomy.

• This procedure cures the anemia and jaundice in all patients. Failure of splenectomy to cure the patient is normally caused by an accessory spleen that has been overlooked during the operation.

• The operation should be delayed until 4 years of age, if possible, to decrease the chance of postsplenectomysepsis

• The gallbladder should be removed at the time of splenectomy if gallstones are present.

2. Other congenital hemolytic anemias– Enzyme deficiencies, such as glucose-6-phosphate

dehydrogenase (G6PD) deficiency and pyruvate kinasedeficiency

– Hereditary elliptocytosis, in which most of the patient's erythrocytes are misshapen (i.e., they are elliptical) and there are varying degrees of anemia and red blood cell destruction

– Thalassemia major, which is transmitted as a dominant trait and is characterized by defective hemoglobin synthesis that causes homozygotes to have severe anemia and hepatosplenomegaly

• 3. Sickle cell anemia

– Most patients with sickle cell anemiaautosplenectomize because of multiple infarcts caused by stagnation and stasis of the abnormal red blood cells.

– These patients may require splenectomy in rare cases in which excessive splenic sequestration of red blood cells is documented or when areas of infarction develop an abscess.

4. Congenital erythropoietic porphyria is a rare autosomal recessive defect of pyrrolemetabolism that leads to deposition of porphyrins in the skin and other tissues.

– Patients have photosensitivity, bullous dermatitis, and hemolytic anemia.

– Splenectomy improves the hemolytic anemia and decreases tissue levels of porphyrins.

D. Immune disorders

1. Idiopathic autoimmune hemolytic anemiaoccurs most commonly in persons older than 50 years of age and occurs twice as often in women than in men.a. Clinical presentation

• In this disorder, both warm and cold hemolyticantibodies have been described. These antibodies presumably shorten the life of the red blood cells.

• The anemia is accompanied by reticulocytosis. There is splenomegaly in 50% of the patients, and there may be mild jaundice.

2. Diagnosis. The direct Coombs' test result is positive. 51Cr-tagged red blood cells may demonstrate sequestration in the spleen.

3. Treatment. The disease may run a self-limited course that requires no treatment.• Steroids and azathioprine are administered in more

persistent cases.

• Splenectomy is helpful in some patients, especially if they have demonstrated excessive splenicsequestration of 51Cr-tagged red blood cells, and if steroids are ineffective or contraindicated.

2. Idiopathic thrombocytopenic purpura (ITP)

a. The etiology is unknown but is presumed to be immunologic because most patients with chronic disease have platelet-agglutinating antibodies that rapidly destroy transfused platelets.

• The acute form is more common in children younger than 16 years.

• The chronic form is most common in adults, and women predominate in a ratio of 3:1.

b. Clinical presentation• This disease is characterized by a decreased platelet count

accompanied by increased megakaryocytes in the bone marrow. The spleen is usually not enlarged.

• The disease presents as unexplained ecchymoses or petechiae, often accompanied by bleeding from the gums or hematuria.

c. Treatment• Steroids induce remission in 75% of patients; approximately

20% of these patients have a sustained response.• Splenectomy is commonly indicated in individuals who do

not respond to steroids or in those who have a relapse after steroids are tapered off. It is also indicated if central nervous system bleeding occurs.

3. Thrombotic thrombocytopenic purpura (TTP) is a rapidly progressive and usually fatal disease. It is also thought to have an immunologic basis.

a. Clinical presentation includes fever, thrombocytopenic purpura, hemolytic anemia, neurologic disturbances, and renal failure.

b. Diagnosis is confirmed only by biopsy of a purpuriclesion. This characteristic vascular lesion consists of occlusion of arterioles and capillaries by a hyaline membrane.

c. Treatment. The most effective treatments are splenectomy and steroid therapy. Plasmapheresis, antiplatelet agents (e.g., dextran), or exchange transfusions with fresh blood have resulted in survival in a few patients.

d. Prognosis. The long-term survival rate is less than 10%, even with optimal therapy.

4. Felty's syndromea. Clinical presentation

• Felty's syndrome is a triad consisting of chronic rheumatoid arthritis, splenomegaly, and granulocytopenia.

• Spontaneous serious infections can occur due to neutropenia, and splenectomy is helpful in this group of patients.

b. Treatment. Splenectomy may also be indicated for management of intractable leg ulcers, severe thrombocytopenia, and anemia.

E. Infiltrative diseases

1. Myeloid metaplasia is thought to be related to polycythemia vera and myelogenousleukemia.a. Clinical presentation

• It is characterized by connective tissue proliferation in the bone marrow, liver, spleen, and lymph nodes and is accompanied by proliferation of the hematopoietic tissue of the liver, spleen, and long bones.

• The usual symptoms are anemia and splenomegaly, which usually appear in middle-aged or older adults. Secondary hypersplenism may develop.

b. Treatment

• Primary treatment consists of alkylating agents to reduce the size of the spleen and male hormones to stimulate failing bone marrow and to treat anemia.

• Splenectomy does not change the course of the disease, but it may help to control the hypersplenism.

2. Sarcoidosis

– Patients typically have diffuse lymphadenopathy, skin lesions, and pulmonary abnormalities. Approximately 25% of patients develop hypersplenism.

– There is no specific treatment, but patients with significant hypersplenism may experience resolution of their hematologic abnormalities after splenectomy.

3. Gaucher's disease is an inborn error of metabolism characterized by deposition of glucosylceramide lipids throughout the reticuloendothelial system, which causes hepatosplenomegaly and bone pain.– Significant hypersplenism is an indication for

splenectomy.

– Because the diagnosis is often made in childhood, partial splenectomy may be indicated to preserve some immunologic function.

F. Infectious diseases

• may cause splenomegaly and hypersplenism. Treatment is generally medical, although surgery may be indicated for abscess or disease localized to the spleen.

1. Bacterial infections may cause abscess formation or transient splenic enlargement. Splenic abscess is uncommon but has a high mortality rate when it occurs.

a. Causes include the following:

• Infection of a pre-existing lesion, such as a hematoma or an infarct

• Direct spread from adjacent structures, such as the pancreas or colon

• Hematogenous seeding from a remote size (especially in users of intravenous drugs) or during overwhelming bacteremia (e.g., in endocarditis)

• Most common organisms causing infection are Staphylococcus aureus or streptococcus. Less common pathogens include Salmonella or anarobes.

b. Diagnosis should be suspected if signs of abscess, such as fever and an elevated white blood cell count, occur in association with left upper quadrant fullness or tenderness. It can be confirmed by CT scan and scanning with technetium-99m

b. Treatment is broad spectrum antibiotics and splenectomy. Percutaneous drainage may be considered in select cases, but hemorrhage is a potential complication.

2. Viral infections including mononucleosis, human immunodeficiency virus, and hepatitis may cause transient splenomegaly and hypersplenism.

3. Parasitic infections including malaria, leishmaniasis, or trypanosomiasis affect blood cells and may cause splenomegaly. An echinococcal cyst may develop in the spleen. Partial or total splenectomy is curative.

4. Fungal infection with histoplasmosis produces characteristic areas of calcification within the spleen.

G. Neoplastic diseases

1. Primary splenic tumors are rare.

– They include lymphoma, sarcoma, hemangioma, and hamartoma.

– Symptoms are caused by the enlarged spleen, and there may be associated hypersplenism.

– Treatment is splenectomy.

2. Metastatic disease from solid tumors is uncommon, probably owing to its efficient immune mechanism.

3. Hodgkin's disease. Treatment may include radiation therapy alone, chemotherapy alone, or a combination of both.

a. Types of staging

b. Staging laparotomy consists of liver biopsy, splenectomy, complete abdominal exploration, and sampling of lymph nodes from multiple areas but is now performed only rarely.

c. Laparotomy is clearly not indicated in patients with stage IIIB or IV disease. Chemotherapy is the treatment of choice.

4. Non-Hodgkin's lymphoma– Staging for non-Hodgkin's lymphoma uses the same

classification as for Hodgkin's disease. Careful evaluation reveals stage III or IV disease in most patients.

– Laparotomy is not frequently used in non-Hodgkin's lymphoma. Percutaneous liver biopsy, laparoscopy, or bone marrow biopsy frequently reveals diffuse disease.

– Splenectomy may be useful in some of these patients to treat hypersplenism or to relieve symptoms of massive splenomegaly.

5. Leukemias

– Patients with chronic lymphocytic leukemia (CLL) or chronic myelogenous leukemia (CML) may develop thrombocytopenia and massive splenomegaly. Splenectomy is indicated for symptomatic relief.

– Patients with hairy cell leukemia and hypersplenism may benefit from splenectomy.

H. Miscellaneous lesions

1. Rupture of the spleen may follow either penetrating or nonpenetrating trauma as well as iatrogenic injury, or rupture may occur spontaneously.a. Traumatic rupture

b. Iatrogenic (intraoperative) trauma accounts for 20% of all splenectomies. The trauma results from excessive traction on the splenic attachments or from misplacement of retractors.

c. sSpontaneous rupture usually occurs because of massive splenomegaly due to an associated disease.

2. Splenosis is autotransplantation of splenicfragments throughout the abdominal cavity.

3. Aneurysms of the splenic artery4. Ectopic and accessory spleens

– An ectopic spleen is caused by a long splenic pedicle, which allows the spleen to wander about the abdomen.

– Accessory spleens are found in approximately 10% of autopsies. These spleens are usually located near the hilus or the tail of the pancreas and less frequently in the mesentery.

Complications after Splenectomy

A . Atelectasis of the left lower lung is the most common complication.

B. Injury to surrounding structures

a. The gastric wall may be injured in the course of controlling the short gastric vessels. In extreme cases, this injury may lead to necrosis of the gastric wall with delayed perforation.

b. The tail of the pancreas may be injured during attempts to secure hemostasis of the splenicpedicle.

C. Postoperative hemorrhage may result from inadequate hemostasis of the splenic pedicle or the short gastric vessels.

D. Subphrenic abscess may develop and is usually accompanied by a left pleural effusion.

E. Thrombocytosis postoperatively is common.

F. Postsplenectomy sepsis

1. The syndrome begins with nonspecific, mild, influenza like symptoms and progresses to high fever, shock, and death.– In general, the younger the patient and the more serious the

disease requiring the splenectomy, the greater is the risk for the development of overwhelming sepsis.

– In healthy adults who have the spleen removed for trauma, the incidence of overwhelming sepsis is low (<0.5%), but it is still higher than that in the normal population (0.01%).

– Approximately 80% of septic episodes occur within 2 years after splenectomy.

– Typically, the causitive organisms are encapsulated bacteria, including Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae.

2. Prevention and treatment

– Polyvalent pneumococcal vaccine should be given to all splenectomized patients, which will protect them from 80% of pathogenic pneumococci (the organisms that most commonly cause the sepsis).

– Vaccines for N. meningitidis and H. influenzaeshould be administered as well.

– Prophylactic penicillin may be given to high-risk pediatric patients.

Critical Points

1. The spleen is an important but not essential organ that has a role in filtering and sequestering circulating blood elements.

2. The spleen has an important immunologic role, filtering opsonized bacteria from the circulation and providing a site for antibody synthesis.

3. Hypersplenism should not be confused withsplenomegaly.– Hypersplenism refers to the exaggerated destruction of

sequestration of circulating red blood cells, white blood cells, or platelets.

– Splenomegaly refers to physical enlargement of the spleen only.

4. Primary hypersplenism is uncommon and is a diagnosis of exclusion, occurring mostly in women.

5. Most cases of hypersplenism are secondary to other pathologic conditions.– Disorders of splenic blood flow, including portal

hypertension or splenic vein thrombosis

– Hematopoietic disorders, including hereditary spherocytosis, hemolytic anemias, sickle cell disease, or congenital erythropoietic porphyria

6. Immunologic disorders, including idiopathic autoimmune hemolytic anemia, ITP, TTP, or Felty'ssyndrome.• ITP is one of the most common reasons for elective

splenectomy. In this condition, the spleen is generally normal in size.

7. Infiltrative diseases, including myeloid metaplasia, sarcoidosis, or Gaucher's disease

– Infection diseases, including bacterial, viral, parasitic, or fungal infections• S. aureus and streptococci are the most common etiologic

agents.

8. Traumatic rupture of the spleen can often be managed nonoperatively. Splenectomy is reserved for those patients who are unstable or who have additional, massive injuries.

9. The management of most cases of hypersplenism is medical. Splenectomy usually has only a secondary role, when symptoms are significant or medical therapy fails to control the disease.– The conditions where surgery is clearly indicated are

bleeding esophagogastric varices associated with splenicvein thrombosis, hereditary spherocytosis, splenic abscess, echinococcal cyst, primary splenic tumors, massive splenictrauma, or spontaneous rupture

10. Neoplastic diseases of the spleen are uncommon but may include primary tumors, metastatic tumors, or hematologic disorders such as lymphoma.

11. Surgery is frequently performed through a laparotomy incision but may also be performed laparoscopically.

12. Patients undergoing splenectomy are at risk for developing overwhelming postsplenectomy sepsis. This risk is greatest in young children. The risk can be decreased by prophylactically immunizing patients preoperatively or postoperatively, if necessary.