Spleen and Thymus

Question 1

Splenic Functions

Answer 1

Removal of unwanted elements from the blood by splenic phagocytosis
– Red cells, platelets, bacteria, cell debris, and abnormal macromolecules produced in some inborn errors of metabolism

Major secondary organ of the immune system

• • Dendritic cells in the periarterial lymphatic sheath trap antigens and present them to T lymphocytes
• • T and B cells interact at the edges of white pulp follicles, leading to the generation of antibody-secreting plasma cells (found mainly within the sinuses of the red pulp)

Source of hematopoietic cells (extramedullary hematopoiesis)

Sequesters a portion of the formed blood elements

• • The human spleen lacks contractility limiting its function in this regard
• • Spleen harbors approximately 30% to 40% of the total platelet mass

Question 2

Congenital Abnormalities of Spleen

Answer 2

Congenital absence rare

Accessory spleens common = splenunliculi

Question 3

Hypersplenism/Splenomegaly

Answer 3

Thrombocytopenia +/- anemia +/- leukopenia
Hyperplasia of the marrow precursors of the deficient cell type
Correction of cytopenia(s) by splenectomy
Splenomegaly
May undergo traumatic rupture*

• Rupture more common with certain conditions such as infectious mononucleosis, malaria, typhoid fever, and lymphoid neoplasms and less likely with chronic congestive splenomegaly

Question 4

Nonspecific Acute Splenitis

Answer 4

Secondary to any blood-borne infection
Splenomegaly (up to 200 to 400 gm)
Soft and diffluent 
Acute congestion of the red pulp
Neutrophils, plasma cells, +/- eosinophils

Question 5

Congestive Splenomegaly

Answer 5

Systemic, or central, venous congestion

• cardiac decompensation involving the right side of the heart
• moderate enlargement of the spleen usually < 500 gm

Cirrhosis of the liver (schistosomiasis, etc.)
- striking massive congestive splenomegaly (1-5 kg.)

Obstruction of the extrahepatic portal vein or splenic vein
- spontaneous portal vein thrombosis with or without external compression or portal vein inflammation (pylephlebitis)

Spleen cut surface gray-red to deep red

• Red pulp is congested in early chronic congestion
• Becomes more fibrous and cellular (hypersplenism) late
• Gandy-Gamma nodules: foci of fibrosis containing iron and calcium salts secondary to hemorrhages

Question 6

Gandy-Gamma nodules

Answer 6

foci of fibrosis containing iron and calcium salts secondary to hemorrhages

Question 7

Splenic Infarcts

Answer 7

Caused by occlusion of the splenic arteries (cardiac emboli, sickle cell disease)
Can be septic with infectious endocarditis
Can lead to decreased splenic function
–> Increased risk of infections with encapsulated bacteria (pneumococcus, H. influenza, meningococcus)

Question 8

Splenic Neoplasms

Answer 8

Lymphangiomas and hemangiomas most common tumors

Primary lymphomas

• Usually diffuse large B cell or splenic marginal zone lymphoma
• Hepatosplenic alpha beta or gamma delta T-cell lymphomas
• — Primarily involves spleen and liver and often involves bone marrow
• —- Rare (under 100 cases) neoplasms of cytotoxic post-thymic immature T-cells
• —- Poor prognosis

Secondary involvement by lymphoid and myeloid neoplasms and metastatic carcinomas

Question 9

Splenic Neoplasms- mainly white pulp involvement

Answer 9

follicular lymphoma
CLL/SLL
Hodgkin lymphoma
Marginal zone lymphoma

Question 10

Splenc neoplasms- mainly red pulp involvment

Answer 10

hairy cell leukemia
CML
T-cell prolymphocytic leukemia

Question 11

Thymus

Answer 11

Epithelial organ secondarily infiltrated by lymphocytes and fat!

Embryology: medulla derived from the third (+/- fourth) pharyngeal pouch (endoderm); cortex from pharyngeal cleft (ectoderm)

Birth 10 to 35 gm; puberty, 20 to 50 gm.; elderly 5 to 15 gm

• Age-related involution: replacement by fibrofatty tissue
• Thymus can also involute with severe stress, including HIV infection

Have antigen independent T-cell maturation, negative selection of self-reactive clones and positive selection of MHC-recognizing clones

Question 12

Epithelial cells in the thymus

Answer 12

Cortex – Large epithelioid with pale cytoplasm

Medulla – Spindled elongated cells and thymic corpuscles

Question 13

Lymphoid cells in the thymus

Answer 13

= Thymocytes

Cortex – Medium sized blastic lymphocytes
CD1a+,TdT+,CD4+8+ = Immature

Medulla – Small mature appearing lymphocytes
CD1a-,TdT-,CD4+ or CD8+ = Mature

A few scattered B-lymphocytes (and granulocytes) may be present

Question 14

Myoid (muscle-like) cells

in the thymus

Answer 14

Related to myasthenia gravis (musculoskeletal disorder with antibodies that cause acetylcholine receptor loss)

Question 15

Other cells in the thymus

Answer 15

Macrophages and dendritic cells

Question 16

Developmental Disorders of Thymus- Ectopic thymus

Answer 16

• Can occur in the neck or on the pleural surface

Question 17

Developmental Disorders of Thymus- Ectopic parathyroids

Answer 17

Occasionally become enclosed within the thymic capsule

Question 18

Developmental Disorders of Thymus- DiGeorge syndrome

Answer 18

(+/- 22q11 del syndrome)

• Thymic hypoplasia or aplasia accompanied (Severe deficits in cell-mediated immunity and variable)
• Parathyroid developmental failures (Hypoparathyroidism)
• Often associated with other developmental defects as part of the 22q11 deletion syndrome

Question 19

Developmental Disorders of Thymus - Thymic cysts

Answer 19

Uncommon usually < 4 cm lesions usually discovered incidentally

Stratified to columnar epithelium and serous or mucinous contents

Neoplastic thymic masses often associated with cysts
In a symptomatic patient with a cystic thymic lesion ** must search for a neoplasm,** particularly a lymphoma or a thymoma

Question 20

Thymic Hyperplasia

Answer 20

= Thymic Follicular Hyperplasia

Appearance of lymphoid follicles containing predominantly ** B lymphocytes** within the thymus
Most frequently encountered in myasthenia gravis, being present in about 65% to 75% of cases

Similar changes sometimes encountered in other autoimmune disorders

• Graves disease
• Systemic lupus erythematosus
• Scleroderma
• Rheumatoid arthritis

Question 21

stuff that causes massive splenomegaly

Answer 21

Chronic myeloproliferative disorders
Chronic lymphocytic leukemia
Hairy cell leukemia
Lymphomas
Malaria
Gaucher disease
Primary splenic neoplasms

Question 22

Thymomas

Answer 22

• Tumors of thymic epithelial cells
• Myasthenia gravis in 30% to 45%

Background non-neoplastic T cells (thymocytes) usually present
Usually occurs in adults > 40 years
20% to 30% of tumors of the anterosuperior mediastinum
Sometimes occur in neck, thyroid, pulmonary hilus, posterior mediastinum
40% present with symptoms from impingement on mediastinal structures
Paraneoplastic syndromes
Cortical thymomas rich in thymocytes are more likely to be associated with autoimmune disorders

15-20% of patients with myasthenia gravis have thymomas
Other syndromes:
- Hypogammaglobulinemia, pure red cell aplasia, Graves disease, pernicious anemia, dermatomyositis-polymyositis, and Cushing syndrome)
With minimal invasion and complete excision > 90% 5-year survival
With extensive invasion (often metastatic) under 50% 5-year survival

Question 23

thymoma description

Answer 23

Lobulated, firm, gray-white masses up to 15 to 20 cm

Majority are encapsulated (20% to 25% penetrate capsule)

Question 24

Benign (encapsulated) thymoma

Answer 24

cytologically and biologically benign

Medullary-type epithelial cells or a mixture of medullary and cortical type cells

Question 25

Malignant thymoma

Answer 25

Type I invasive thymoma (20% to 25%): cytologically bland but biologically aggressive
Most commonly of the cortical-type

Type II thymic carcinoma (5%): cytologically malignant
Most are squamous cell carcinomas, either well or poorly differentiated.
2ND most common variant is lymphoepithelioma-like carcinoma

Question 26

Mixed thymoma

Answer 26

(benign or malignant) - admixture cortical-type thymic epithelial cells and a very rich in thymocytes