Week 4: Chapter 10

Spleen Anatomy

  • Spleen

    • Intraperitoneal, ovoid organ covered by peritoneum except bare area at hilum.

    • Contains splenic artery, splenic vein, and efferent lymphatic vessels passing through hilum.

    • Delicate and vulnerable, located in left hypochondrium.

    • Long axis parallels the 9-11th ribs.

  • Clinical Aspects

    • Normally does not extend inferior to the left costal margin.

    • Clinically challenging to palpate spleen through anterior lateral wall without splenomegaly.

    • Palpation may support splenomegaly diagnosis.

  • Neighboring Structures

    • Indentations/impressions from neighboring organs can simulate masses.

    • Familiarity with normal variants is essential to avoid misdiagnosis.

  • Hilus

    • Composed of splenic arteries and veins covered by lienorenal ligament (mesentery) which also houses pancreatic tail.

    • Lienorenal ligament connects spleen to left kidney.

    • Gastrosplenic ligament connects spleen to greater curvature of stomach.

    • Phrenicocolic ligament supports the inferior end of the spleen, but is not attached directly.

    • These ligaments stabilize the spleen, allowing it to be loosely positioned.

    • Laxity of peritoneal attachments allows hypermobility or wandering of spleen.

  • Variability

    • Splenic size and weight may vary based on:

    • Age.

    • Gender.

    • Other factors (not specified).

    • Normal spleen characteristics:

    • Smaller in women.

    • Decreases in volume and size with age.

    • Increases in size during certain conditions (not specified).

Spleen Structure

  • Fibrous Capsule

    • Surrounds spleen, thickened at splenic hilum.

  • Connective Tissue

    • Projects from splenic capsule, divides spleen into communicating compartments filled with splenic pulp (splenic tissue).

    • White Pulp

    • Produces lymphocytes clustered around splenic arterioles aiding lymphatic function.

    • Lymphatic Follicles

      • Responsible for the production of antibodies, which grow in number and size in response to antigens.

    • Red Pulp

    • Composed of blood-filled venous sinuses with macrophages, performing the phagocytic function of the spleen.

    • Venous sinuses capable of storing more than 300 mL of blood, restoring blood volume during systemic blood pressure reduction.

  • Vascular Supply

    • Highly vascular organ.

    • Receives arterial blood from the splenic artery, a branch of the celiac trunk.

    • Splenic artery courses along the superior pancreatic border, dividing into superior and inferior terminal branches before entering hilum.

    • Within hilum, splenic artery divides into six or more segmental branches, which further branch into smaller arterioles.

    • Splenic vein is joined by the inferior mesenteric vein, traveling posterior to the pancreatic tail and body.

    • Unites with superior mesenteric vein posterior to pancreatic neck to form portal vein.

Congenital Variants

  • Anomalies

    • Associated with heterotaxy syndrome include:

    • Asplenia/Aplasia

      • Congenital absence of spleen due to embryogenesis failure.

      • Indicated by absence of splenic tissue associated with right-sided heart and lung morphologies.

    • Splenic Hypoplasia

      • Reduced splenic mass and/or function from developmental defects or secondary to parenchymal involution.

    • Polysplenia

      • Rare disorder where left-right organ asymmetry fails during development.

      • Associated with several anomalies.

  • Accessory Spleen

    • Also termed supernumerary spleen.

    • Involves splenic tissue separating from the main spleen, typically located ectopically.

    • Most occurrences are small (~2.0 cm) and primarily near splenic hilum.

    • Sonographically, accessory spleens appear round, mildly echogenic, and homogeneous with posterior enhancement.

    • Generally of no clinical consequence.

Wandering or Ectopic Spleen

  • When the spleen migrates from its normal LUQ position to other locations, termed splenoptosis.

  • Examination required if prior splenectomy history is absent, performing thorough left-side examination from thorax to pelvis.

  • Higher incidence of splenic torsion and infarction due to the lack of normal peritoneal attachments.

  • More common in females.

  • Patients may be asymptomatic or experience varying degrees of pain.

  • Preferred treatment: splenopexy to reposition the spleen in LUQ, preventing torsion and preserving function.

Physiology of the Spleen

  • Functions overlap with those of other organs.

  • It is possible to live without a spleen.

  • Post-splenectomy patients may experience:

    • Leukocytosis.

    • Decreased circulating iron.

    • Decreased immune response.

    • Increased presence of defective blood cells.

  • Major Functions of the Spleen

    1. Reservoir and Filter

      • May act as a transfusion-type response during hemorrhage.

      • Majority of circulating blood travels through capillary walls into red pulp for filtration.

    2. Destruction of Red Blood Cells and Microorganisms

      • Through macrophages in red pulp, phagocytosing debris, microorganisms, and old blood cells (especially erythrocytes).

      • Culling Function

      • Identifies and removes defective cells such as spherocytes, sickle cells, and thalassemic cells from circulation as they traverse sinus walls.

      • Splenic Pitting

      • Abnormal erythrocytes with granules or parasites are not culled; these abnormalities are cleansed, and normal red blood cells are returned to circulation.

    3. Erythropoiesis

      • Responsible from approximately the fifth to sixth month of fetal life.

      • Bone marrow takes over primary function with age, but spleen retains capacity throughout adulthood.

    4. Defense Against Disease

      • Bloodborne antigens encounter lymphocytes in white pulp clustered around splenic arterioles initiating immune responses.

      • Provides sources for lymphocytes, macrophages, plasma cells.

      • Secondary defense able to phagocytose bacteria bypassed by lymph nodes.

Laboratory Values

  • Leukocytosis

    • Occurs when leukocyte count is higher than normal, indicating potential stressors like inflammation, infection, hemorrhage, carcinoma, or acute leukemia.

  • Leukopenia

    • Abnormally low level of WBCs, often not beneficial.

    • Causes include radiation, chemotherapy, lupus, vitamin B12 deficiency, and viral infections.

  • Hematocrit

    • Indicates percentage of blood volume occupied by RBCs.

    • Abnormal levels may result from altered erythropoiesis, anemias, hemorrhage, Hodgkin disease, or leukemia.

  • Thrombocytopenia

    • Abnormal decrease in platelets.

  • Bacteremia

    • Presence of bacteria in bloodstream.

  • Sepsis

    • Occurs when infection levels are high with abnormal immune response.

Sonographic Appearance and Technique

  • Appearance

    • Iso- or slightly hyperechoic to liver.

    • Homogeneous with low to mid-level echoes.

  • Examination Techniques

    • Imaging must manipulate transducer creatively; patient can be supine or in RPO/RLD, scanning intercostally.

    • Raising the left arm can enhance rib separation for imaging clarity.

    • Utilize varying respiration to optimize imaging (both inspiration and expiration).

  • Transducer specifications

    • Use a 3.5–5 MHz transducer with a small footprint located for optimal scanning through ribs.

    • Longitudinal imaging should encompass hilus and its blood vessels while demonstrating several parenchymal images.

    • Comparison with left hemidiaphragm and left kidney is essential.

  • Pitfalls

    • Common mistakes include mistaking fluid-filled stomach, adrenal mass, pancreatic mass, or left liver lobe for splenic mass or hematoma.

  • Measurement Monitoring

    • Long axis >12 cm typically indicates enlargement.

    • Spleen enlargement may alter echogenicity.

  • Doppler and Color Doppler

    • Useful for evaluating splenic and perisplenic vasculature.

    • Abnormalities in flow direction and dynamics characterize conditions such as portal hypertension, splenic vein thrombosis, and splenic artery aneurysms.

    • Absence of flow indicates avascular lesions like cysts or necrosis.

Imaging Techniques

  • Contrast-Enhanced Ultrasound (CEUS)

    • A cost-effective, safe method for identifying splenic trauma, injury, and solid lesions

    • Utilizes intravenous contrast agents (microbubbles) demonstrating vascular architecture and enhanced contrast compared to adjacent tissues.

  • Shear Wave Elastography

    • Measures tissue elasticity, used to assess spleen parenchyma stiffness.

    • Higher stiffness reported among patients with various conditions, potentially beneficial for predicting etiology.

Pathology

Splenomegaly

  • Enlargement of the spleen; most common abnormality observed on ultrasound.

  • May induce symptoms like:

    • LUQ discomfort or pain due to capsule stretching.

    • Lower extremity edema.

    • Increased pressure on adjacent organs (stomach, intestines).

  • Spleen generally should not extend below the lower pole of the left kidney.

  • Massive splenomegaly may lead to complications like hypersplenism.

Causes of Splenomegaly

  • Categorized into:

    • Portal Hypertension

    • Common cause due to congestion from portal hypertension, often associated with liver cirrhosis leading to blood flow reduction and portal congestion.

    • Increased pressure results in reversals in portal flow toward the liver and collateral vessels.

    • Collateral varices may present near the spleen, commonly splenorenal collateral.

    • Blood Disorders

    • Abnormalities such as polycythemia vera causing excess production of blood cells, increasing viscosity and leading to vascular congestion.

    • Congenital Spherocytosis

      • Abnormal spherical erythrocytes rather than flattened discs.

    • Sickle Cell Disease

      • Inherited disorder characterized by abnormal red blood cell shapes (sickle), leading to vascular occlusion and infarction.

      • Early stages show splenomegaly, later stages may lead to infarction and possible autosplenectomy.

      • Acute splenic sequestration crisis occurs with rapid anemia progression and compromised circulation, leading to sudden splenic enlargement.

    • Malignancies

    • Most commonly involve lymphoma; splenic enlargement occurs due to diffuse infiltration or bone marrow disease.

      • Symptoms include nodal enlargement, fever, fatigue, weight loss, etc.

    • Acquired Immunodeficiency Syndrome (AIDS)

      • Systemic infections affecting spleen size include Mononucleosis, Tuberculosis, Histoplasmosis.

    • Metabolic Diseases

    • Distension due to macrophages and vascular compromise; unique metabolic elements lead to enlargement.

    • Gaucher Disease characterized by abnormal fat/protein deposits, with clinical symptoms including bone pain.

    • Nieman-Pick Disease noted for rapid progression and fatality in female infants, presenting with splenomegaly, hepatomegaly, digestive issues.

Splenic Lesions

  • Various lesions found within the spleen include:

    • True cysts, secondary/pseudocysts, granulomas, abscesses, both benign and malignant neoplasms, and metastases.

Cysts

  • May be congenital or acquired.

  • Primary Cysts

    • Arise from epithelial or endothelial lining.

  • Secondary Cysts

    • Associated with inflammation, infections, or parasitic infestations.

    • Often complex, may present internal echoes or calcifications.

  • Posttraumatic/Pseudocysts

    • Account for ~80% of splenic cysts; form following hematomas that liquefy and develop fibrous capsules.

    • Delay splenic rupture can occur in ~50% of cases.

  • Parasitic Cysts

    • Commonly echinococcal (hydatid) in origin, presenting variable appearances sonographically.

  • Lymphangiomas

    • Rare, slow-growing complex cystic masses, often in children.

Abscesses

  • Normally multiple due to hematologic infections; can stem from endocarditis, dental infections, and more.

  • Symptoms may be absent or subtle but complex appearance is characteristic.

  • High mortality due to rupture risk; can present with LUQ pain, fever, also exhibiting high-level echoes and ring-down shadowing due to presence of gas.

Infarcts

  • Results from splenic artery occlusion, ultimately leading to tissue necrosis.

    • Symptoms vary from absent to acute LUQ pain worsened by deep inspiration.

    • Common risk factors: hematologic, cardioembolic disease.

  • Laboratory values may indicate hemolysis, leukocytosis, and elevated LDH levels.

  • Sonographic appearance: well-demarcated hypoechoic areas, increased echogenicity during fibrosis stages following infarction.

Trauma, Hematoma, and Rupture

  • The spleen is most frequently injured in blunt abdominal trauma.

  • Clinically, patients may show signs of hypovolemic shock and LUQ pain, with decreased hematocrit.

  • High mortality due to rapid hemorrhage from spleen, liver, or major vessels.

  • Complications can include sepsis due to bowel injury.

  • Subcapsular or intraparenchymal hematomas can result in rupture within a short timeframe.

    • Notably, 50% of rupture cases occur in less than a week.

  • Sonographic FAST examinations can detect fluid in peritoneum; however, hopefulness in discovering hemoperitoneum can falter in cases of solid organ injury.

  • CT scans are generally favored in trauma assessments; imaging is also challenged due to hematomas being isoechoic.

  • Spontaneous splenic rupture is rare but can lead to splenosis, involving autotransplantation of splenic tissue in the abdominal cavity.

Splenic Calcification

  • Generally incidental findings, appearing echogenic with variable acoustic shadowing.

  • Multiple Calcifications

    • Can resemble a constellation; often sequelae from granulomatous diseases (histoplasmosis, tuberculosis) or post-infarction.

  • Models of splenic artery calcification are common and should not be misidentified as lesions.

Malignant Neoplasms

Lymphoma

  • Most common malignancy impacting the spleen, primarily from the lymphatic system.

  • Both Hodgkin and non-Hodgkin lymphomas present clinically with nodal enlargement, fever, fatigue, weight loss, and signs of congestion.

  • Laboratory results often reveal elevated white blood counts and anemia.

Appearance Sonographically

  • May manifest as isolated hypoechoic masses or diffuse involvement with heterogeneous splenic parenchyma.

Leukemia

  • Primary malignancy of bone marrow and lymphatic system.

  • Chronic lymphocytic leukemia (CLL) is the most common in adults, with symptoms like anemia, elevated WBC, bruising, fatigue, and recurrent infections.

  • Splenomegaly may be the only notable finding.

Angiosarcoma

  • Aggressive primary malignant vascular neoplasm, typically presenting with LUQ mass, pain, malaise, fever, and weight loss.

  • Poor prognosis, high mortality rate within six months of diagnosis (70%).

  • Sonographic findings often include heterogeneous texture, complex masses, and increased Doppler flow observed within solid tumor components.

Metastasis

  • Metastatic lesions to the spleen are uncommon and usually arise from lung, breast, colorectal, and ovarian carcinomas.

  • The sonographic appearance can vary widely.

  • Most lesions present with a hypoechoic halo appearance.