L6: Path. Of The Lymphoid System (Abbott) Flashcards
Causes of INCREASED thymic size
Thymic lymphoma
Thymoma (and paraneoplastic syndromes)
Thymic brachial cysts
Thymic hematoma
Embryonic origin of thymus
Pharyngeal pouches 3/4
What type of organ is the thymus**
Lymphoepithelial:**
1) cortex for T-cell development and maturation
- lymphocytes, epithelial cells
2) Medulla for Ag presentation
- ep. Cells (Hassall’s corpuscles), dendritic cells, myoid cells
*can have lymphoma or thymoma
Fxs of thymus
- develop T-lymphocytes that arrive as precursors from bone marrow
- induce self-tolerance (thymic education)
Severe Combined Immunodeficiency (SCID)
- causes thymic hypoplasia
- Bassets and Corgis have defective function but mature cells**
- Jack Russells have the inability to generate lymphocytes
Causes of thymic ATROPHY
1) Involution (normal aging)
2) Lympholysis:
- viruses replicate in lymphoid tissues (parvo, distemper, panleuk)
- steroids cause T cell death
- nutritional: Acrodermatitis, zinc deficiency, starvation
- toxic: PCBs
Thymic hypoplasia and lymphoid atrophy –> clinically?**
IMMUNOLOGIC DYSFUNCTION:
- get sicker or more often than expected
- difficult to dx
CS of INCREASED thymic size
(Space-occupying)
- dyspnea, cough
- regurge
- edema, swollen head and neck
- chylothorax
Chars. Of thymoma***
- tumors derived from the EPITHELIAL COMPONENT of the thymus**
- neoplastic, NOT viral
- adult animals
- mets and invasion is NOT common (unlike lymphoma)***
- SPACE-OCCUPYING biggest problem
- encapsulated, anterior mediastinal mass
Paraneoplastic syndromes assoc. with thymomas
- Acquired autoimmune disorders: myasthenia gravis, polymyositis
- Exfoliative dermatitis
Diffusely pale, cystic, bulging “fish flesh” thymus, fairly homogenous in color
Thymoma (key clue: CYSTIC)
Thymoma is a tumor of the ___ component of the thymus***
Epithelial
-can have normal lymphs which can outnumber neoplastic cells
Lymphoma is a tumor of ____***
Lymphocytes/lymphoblasts
Clinical course of thymic lymphoma
- pleural effusion
- aggressive, invasive*
- neoplastic lymphs in the pleural cavity*
- middle aged to older dogs
Feline thymic lymphoma
- young, FeLV+ cats most common
- usually no involvement of other organs except bone marrow
Thymic Branchial cysts lined and filled by:
FIlled with mucoserous fluid, lined by ciliated, columnar epithelial cells
- develop from vestiges of fetal branchial arch system
- space-occupying mass
Causes of thymic hemorrhage/hematoma
Trauma Bleeding disorders (ie. Rodenticide)
Lymph node structure
- dynamic and changing depending on immune status
- cells and fluid moving constantly
Fxs of LN
- filtration of lymph from dependent areas
- capture infectious agents and foreign material
- localize immune response: process and present foreign Ag
- house lymphs, macs, and other Ag-presenting cells
Which LN are palpable only when enlarged?
Facial
Retropharyngeal
Iliac
Df for lymphadenomegaly
Hyperplasia
Inflammation (lymphadenitis)
Neoplasia
Lymph Node HYPERPLASIA**
- proliferation of lymphocytes due to Ag stimulation*
- node architecture is maintained**
- tan, homogenous, fish flesh**
- usually large immature lymphoblasts and small mature lymphocytes +/- increased plasma cells and/or macrophages
- Causes: Salmon poisoning, FIV
Gross appearance of lymphadenitis**
Swollen, gray-red, painful, may abscess
Chars. Of lymphadenitis**
- lymphocyte hyperplasia + inflammatory cells (neuts, macs) and fibrin**
- node is actually involved in the process, not just draining an affected site
- can spread to adjacent nodes
