Lymphoid Path

Question 1

Thymus structure

Answer 1

develops from pharyngeal pouches 3+4
Lymphoepithelial origin (2 types of cells): lymphocytes and epithelial cells

Question 2

Thymus function

Answer 2

Cortex: T-cell development and maturation (precursors from BM)
Medulla: antigen presentation
Induction of self tolerance (thymic ed)

Question 3

Decreased thymic size

Answer 3

hypoplasia, atrophy

Question 4

increased thymic size

Answer 4

lymphoma, thymoma, branchial cysts, hematoma

Question 5

Thymic Hypoplasia

Answer 5

Severe combined immunodeficiency (SCID):

1. defective function but mature cells (bassets, corgis)
2. inability to generate lymphocytes (jack russell)

Question 6

Thymic atrophy

Answer 6

involution: normal aging
Lympholysis: viral, steroid induced, nutritional, toxic

Question 7

Why is thymic hypoplasia and lymphiod atrophy important?

Answer 7

IMMUNOLOGICAL DYSFUNCTION

vague signs, difficult to diagnose

Question 8

Increase in thymic size consequence

Answer 8

affect on adjacent structures, becomes space occupying lesion
CS: Dyspnea, cough, regurgitation, edema, swollen head/neck, chylothorax

Question 9

Thymoma

Answer 9

Derived from epithelial component of thymus
May contain NORMAL lymphocytes, can outnumber neoplastic cells
Adult animals: 8-10yr
Metastasis and invasion is NOT common. Space-occupying

Question 10

Paraneoplastic syndrome

Answer 10

Commonly associated with thymomas

Acquired autoimmune disorders: myasthenia gravis, polymyositis, megaesophagus, exfoliative dermatitis

Question 11

Thymic lymphoma

Answer 11

tumor of lymphocytes/lymphoblasts
Usually T-cell
Aggressive, invasive

Question 12

Feline thymic lymphoma

Answer 12

especially important in young, FeLV+
2-3yr old
Usually no other organ involvement except BM

Question 13

Thymic branchial cysts

Answer 13

developmental disorder, slow growing

cysts contain mucoserous fluid, lined by ciliated, columnar epithelial cells

Question 14

Thymic hemorrhage/hematoma

Answer 14

D/t trauma or bleeding disorders (rodenticides)

Question 15

Lymph node structure

Answer 15

Dynamic! cells and fluid constantly moving
Node structure changes depending on immune status
Cortex: follicles are B-cell, paracortex is T-cell

Question 16

LN function

Answer 16

defensive barriers
Filtration of lymph from dependent areas
localization of immune response

Question 17

Ddx for lymphadenomegaly

Answer 17

Hyperplasia (reactive)
Inflammation (lymphadenitis)
Neoplasia (lymphoma, metastatic)

Question 18

LN hyperplasia

Answer 18

proliferation d/t antigenic stimulation
Lesions: Arcitecture of node maintained, fish flesh tan and homogenous
Large immature lymphoblasts and small mature lymphocytes +/- increased plasma cells and/or macrophages

Question 19

Causes LN hyperplasia

Answer 19

Salmon poisoning (neorickettsia helmenthoeca)
FIV

Question 20

Lymphadenitis

Answer 20

Lesions: swollen, grey-red, more likely engorged and painful
Micro: hyperplasia + inflammatory cells and fibrin (neuts and macros)
Affected node involved in process, not just draining affected site

Question 21

Spleen function

Answer 21

Host immune response
Fultration of unwanted elements from blood via phagocytosis
Hematopoiesis, life long source of lymphocytes and macros
Reserve blood storage

Question 22

Reasons to remove spleen?

Answer 22

Rupture, torsion, neoplasia, symptomatic splenomegaly, +/- immune-med disease

Question 23

Spleen neoplasia

Answer 23

Hemangiosarcoma
Lymphoma
leiomyosarcoma
hemangioma
mast cell tumor (cats)
Mets

Question 24

Vascular dz spleen

Answer 24

Hematoma (can mimic hemangiosarc), congestion, infarct (acute vs, chronic)

Question 25

Other splenic changes

Answer 25

nodular hyperplasia, diffuse hyperplasia, splenitis

Question 26

Splenic congestion

Answer 26

pentobarbital, heart failure, portal hypertension, splenic torsion Diffuse increased size Engorged, exudes blood on cut surface

Question 27

Nodular hyperplasia spleen

Answer 27

nodular, red or tan hyperplastic lymphoid elements plus congestion mimics hemangiosarc

Question 28

Spleen diffuse hyperplasia

Answer 28

activation of spleen to remove abnormal or opsonized cells (RBCs), or microbes from circulation extramedullary hematopoeisis = regenerative response

Question 29

Splenic rupture

Answer 29

Acute: fatal internal hemorrhage Chronic: healing which may produce notches, fissures, divisions, accessory spleens

Question 30

Siderotic plaques

Answer 30

in DOGS very common senile change on the capsule Incidental finding!

Question 31

Accessory/ectopic spleens

Answer 31

Cats | can be indistinguishable from seeding of peritoneum by metastatic hemangiosarc

Question 32

Canine Lymphoma

Answer 32

Multicentric 80% majority of animals with solid tumors don't have detectable neoplastic cells in circulation Causes effacement of normal architecture

Question 33

Feline lymphoma

Answer 33

very common, most common neoplasm of cats associated often with FeLV Alimentary most common