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
Causes of decreased thymic size
Hypoplasia
Atrophy
Spleen fxs
- host immune response
- filtration via phagocytosis
- hematopoiesis
- reserve blood storage
Problems of the spleen
- splenomegaly
- splenic masses
- splenic rupture
- splenic torsion
- hypersplenism (rare)
- vague, non-specific signs
Reasons to remove spleen
-rupture
-torsion
-neoplasia
Symptomatic splenomegaly
-autoantibodies to RBCs or platelets
Causes of splenomegaly
- neoplasia
- vascular: hematoma, congestion, infarct
- nodular hyperplasia
- diffuse hyperplasia
- splenitis
Primary splenic tumors
- HSA
- Lymphoma
- Leiomyosarcoma
- Hemangioma
- MCT (cats)
Which splenic neoplasias make single masses?
Leiomyosarcoma
Hemangioma
HSA can be single or multiple nodular
Which splenic neoplasia makes diffuse masses in the SP?
Myeloid leukemia
MCT
Lymphoma (diffuse or nodular)
Hematoma can mimic HSA
- single nodule
- exudes blood
- clotted blood +/- organization
What can cause splenic congestion?
- Pentobarbital
- R sided heart failure
- portal hypertension
- splenic torsion
Gross appearance of nodular hyperplasia of the spleen
-smooth, red or tan, nodular, bulging
What is nodular hyperplasia?
Hyperplastic lymphoid elements plus congestion
-mimics HSA
Diffuse hyperplasia (SP)
- spleen is “activated” to remove abnormal or opsonized cells or microbes from circulation
- diffuse non-friable enlargement grossly
- EMH is a regenerative response
Splenitis
- diffuse enlargement 2ary to any blood-borne infection
- nodular or multinodular
- abscess or granulomas +/- lymphoid hyperplasia
Relative prevalence of splenic disease in dogs
Nodular hyperplasia/hematoma > HSA > LSA > other neoplasias
Relative prevalence of splenic disease in cats
MCT or LSA > leukemia > hyperplastic nodules/HSA > hematomas
Outcomes of splenic rupture**
- Acute: Fatal internal hemorrhage**
- Chronic: healing which may produce notches, fissures, divisions, accessory spleens
Siderotic plaques***
- DOGS only
- very common senile change on the capsule of the SP
- mineralization caused by hemorrhage into capsule of the spleen that gets phagocytized
- incidental finding
Accessory/ectopic spleens
- CATS more common
- omentum most common location
- hard to distinguish from HSA mets
White/tan nodules on the spleen most likely:
Nodular hyperplasia
Forms of canine lymphoma
1) Multicentric** (80%)
2) Alimentary
3) Mediastinal - rare
4) Cutaneous - mycosis fungoides
5) Leukemic (majority of animals with solid tumors do NOT have detectable neoplastic cells in the peripheral blood**)
Difference b/w staging and grading tumors
Staging: where the tumor is
Grading: histologic nature of the tumor (ie. T vs. B cell lymphoma)
Dx of lymphoma
- Gross: LN soft, fish flesh, homogenous
- Cytology: homogenous population, high mitotic index
- Biopsy: effacement of normal architecture*** (invasion of capsule and perinodal tissue, filling of subcapsular sinus w/ tumor cells)
Hypercalcemia of malignancy
- Hypercalcemia due to pseudohyperparathyroidism from lymphoma
- tumor produces PTH-like substance
- CS: PU/PD due to Ca inhibition of ADH, ST mineralization
Most common neoplasm of cats
Feline Lymphoma
Chars. Of feline lymphoma
- 10-20% FeLV+
- middle aged cats
- Forms:
1) alimentary (most common)
2) mediastinal (young kittens, FeLV+)
3) multicentric
4) solitary (usually kidneys or CNS)
5) cutaneous (rare)
Ddx for lymphoma in the nasal cavity
- cryptococcus
- adenocarcinoma
Ddx for multicentric lymphoma
FIP
Systemic fungal infection
2 plasma cell tumors
- Multiple myeloma
- Solitary plasmacytoma
Multiple myeloma
- in bones w/ active hematopoiesis
- causes lytic bone lesions, monoclonal gammopathy
- poor prognosis
Solitary plasmacytoma
- location: digits, ears, lip
- NOT assoc. with serum Ig elevation
- excision usually curative
