The spleen and thymus Flashcards
SPLEEN vitals
About 150 gm
12 cm in length
Congenital absence rare
Accessory spleens common
Splenic Functions
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
Splenic Functions
Major secondary organ of the immune system
- Dendritic cells in the periarteriallymphatic 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)
Splenic Functions
Source of hematopoietic cells
(extramedullary hematopoiesis)
Splenic Functions
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
Disorders Associated with Splenomegaly
I. Infections
Nonspecific splenitisof various blood-borne infections (particularly infective endocarditis) Infectious mononucleosis Tuberculosis Typhoid fever Brucellosis Cytomegalovirus Syphilis Malaria Histoplasmosis Toxoplasmosis Kala-azar Trypanosomiasis Schistosomiasis Leishmaniasis Echinococcosis
Disorders Associated with Splenomegaly
II. Congestive States Related to Portal
Hypertension
Cirrhosis of the liver
Portal or splenic vein thrombosis
Cardiac failure
Disorders Associated with Splenomegaly
III. LymphohematogenousDisorders
Hodgkin lymphoma Non-Hodgkin lymphomas and lymphocytic leukemias Multiple myeloma Myeloproliferativedisorders Hemolytic anemias
Disorders Associated with Splenomegaly
IV. Immunologic-Inflammatory
Conditions
Rheumatoid arthritis
Systemic lupus erythematosus
Disorders Associated with Splenomegaly
V. Storage Diseases
Gaucher disease
Niemann-Pick disease
Mucopolysaccharidoses
Disorders Associated with Splenomegaly
VI. Miscellaneous
Amyloidosis
Primary neoplasms and cysts
Secondary neoplasms
Some Causes of Splenomegaly
•Massive (>1000 gm)
- Chronic myeloproliferativedisorders
- Chronic lymphocytic leukemia
- Hairy cell leukemia
- Lymphomas
- Malaria
- Gaucher disease
- Primary splenic neoplasms
Hypersplenism/Splenomegaly
Overview
- Thrombocytopenia +/-anemia +/-leukopenia
- Hyperplasia of the marrow precursors of the deficient cell type
•Correction of cytopenia(s) by splenectomy
- Splenomegaly
- May undergo traumatic rupture*
splenomegaly rupture
- Rupture more common with certain conditions such as infectious mononucleosis, malaria, typhoid fever, and lymphoid neoplasms and less likely with chronic congestive splenomegaly
Nonspecific Acute Splenitis
- 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
Congestive Splenomegaly
•Systemic, or central, venous congestion
- cardiac decompensation involving the right side of the heart
- moderate enlargement of the spleen usually
Congestive Splenomegaly
Cirrhosis of the liver (schistosomiasis, etc.)
•striking massive congestive splenomegaly (1-5 kg.)
Congestive Splenomegaly
Obstruction of the extrahepatic portal vein or splenic vein
•spontaneous portal vein thrombosis with or without external compression or portal vein inflammation (pylephlebitis)
Congestive Splenomegaly
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
Splenic Infarcts
- 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)
Splenic Neoplasms
- Lymphangiomasand hemangiomas most common tumors
* Primary lymphomas
Splenic Neoplasms
•Lymphangiomasand hemangiomas most common tumors
- Involved by systemic or localized lymphoid and myeloid neoplasms
- Hepatosplenicgamma delta T-cell lymphoma
- Primarily involves spleen and liver and often involves bone marrow (anemia, thrombocytopenia)
- Neoplasm of cytotoxic post-thymicimmature T-cells
- Rare (
splenic neoplasms
•Primary lymphomas
•Usually diffuse large B cell or splenic marginal zone lymphoma
Thymus
overview
- 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 fibrofattytissue
- 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
Thymus
contains
- Thymicepithelialcells -cortical and medullary (Hassall corpuscles)
- Thymocytes-immature lymphocytes of T-cell lineage
- Myoid(muscle-like) cells -related to myasthenia gravis (musculoskeletal disorder with antibodies that cause acetylcholine receptor loss)
- Macrophages and dendritic cells
- A few B-lymphocytes and granulocytes
Thymus
cortex
CD1a+,TdT+,CD4+8+
Thymus
medulla or interlobular septum
CD1a-,TdT-,CD4+ or CD8+
thymus cytology cortex
medium sized blastic lymphoid cells, large pail epithelial cells
thymus cytology medulla
small lymphoid cells, spindled epithelial cells, hassals corpuscles
Developmental Disorders of Thymus
DiGeorgesyndrome(+/-22q11 del syndrome) -Thymichypoplasia or aplasia accompanied by parathyroid developmental failures
Thymiccysts
Ectopic parathyroids
Ectopic thymus
DiGeorgesyndrome(+/-22q11 del syndrome) -Thymichypoplasia or aplasia accompanied by parathyroid developmental failures
- severe deficits in cell-mediated immunity and variable hypoparathyroidism
- often associated with other developmental defects as part of the 22q11 deletion syndrome
Thymiccysts
•uncommon usually
Ectopic parathyroids
become enclosed within the thymiccapsule
Ectopic thymus
can occur in the neck or on the pleural surface
Thymic Hyperplasia
= ThymicFollicular 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, and rheumatoid arthritis)
Thymomas
Overview
- Tumors of ThymicEpithelial Cells
- with background non-neoplastic T cells (thymocytes)
- usually occurs in adults > 40 years
- Lobulated, firm, gray-white masses up to 15 to 20 cm
- Majority are encapsulated (20% to 25% penetrate capsule)
Thymomas
20% to 30%
20% to 30% of tumors of the anterosuperiormediastinum
•sometimes occur in neck, thyroid, pulmonary hilus, posterior mediastinum
Thymomas
40%
40% present with symptoms from impingement on mediastinal structures
Thymomas
•Paraneoplastic syndromes
•Cortical thymomasrich in thymocytesare more likely to be associated with autoimmune disorders
- Myasthenia gravis in 30% to 45%
- 15-20% of patients with myasthenia gravis have thymomas
- Others syndromes
- Hypogammaglobulinemia, pure red cell aplasia, Graves disease, pernicious anemia, dermatomyositis-polymyositis, and Cushing syndrome)
Thymomas
prognosis
- With minimal invasion and complete excision >90% 5-year survival
- With extensive invasion (often metastatic)
Thymomas
Benign (encapsulated) thymoma
(50%): cytologicallyand biologically benign
•Medullary-type epithelial cells or a mixture of medullary and cortical type cells
Thymomas
Malignant thymoma(invasive)
- Type I invasive thymoma
* Type II thymiccarcinoma
Thymomas
•Type I invasive thymoma
(20% to 25%):cytologically bland but biologically aggressive
•Most commonly of the cortical-type
Thymomas
•Type II thymic carcinoma
(5%):cytologically malignant
•Most are squamous cell carcinomas, either well or poorly differentiated.
- 2NDmost common variant is lymphoepithelioma-like carcinoma
- 50% of these have EBV
- Thymiccarcinomas express CD5 (T cell marker)
- Cytologicallybenign thymomasand other carcinomas are negative
Mixed thymoma(benign or malignant)
admixture cortical-type thymic epithelial cells and a very rich in thymocytes
Thymoma, medullary type
slide
The neoplastic epithelial cells are arranged in a swirling pattern and have bland, oval to elongated nuclei with inconspicuous nucleoli. Only a few small, reactive lymphoid cells are interspersed.
Malignant thymoma, type I.
slide
The neoplastic epithelial cells are polygonal and have round to oval, bland nuclei with inconspicuous nucleoli. Numerous small, reactive lymphoid cells are interspersed. The morphologic appearance of this tumor is identical to that of benign thymomasof the cortical type. In this case, however, the tumor was locally aggressive, invading adjacent lung and pericardium.
