Lecture 15: Blood and Lymph

Question 1

Describe the species variation seen in the thymic gland

Answer 1

All species have a thoracic lobe

ruminants and pigs have a large cervical lobe

cats and horses have a small cervical lobe

dogs don’t have a cervical lobe

Question 2

Describe the structure of the thymus

Answer 2

There is a cortex and medulla

Lymphoid tissue contains educated T lymphocytes from the bone marrow and they can circulate to secondary lymphoid organs

Epithelial tissue is present to support the T cells - hassells corpuscles

Question 3

What are the 2 consequences of thymic dysfunction?

Answer 3

immunodeficiency
autoimmunity

Question 4

How is an abnormal thymus classified grossly?

Answer 4

too small
too big

Question 5

Why might a thymus be too small?

Answer 5

aplasia due (severe combine immunodeficiency disorder)

hypoplasia (normal involution or lymphoid atrophy)

Question 6

What is SCID and what species does it affect?

Answer 6

It is severe combine immunodeficiency disorder. It is a genetic reduction in cell mediated and humoral immunity

It can occur in humans, mice, dogs, and horses

Question 7

What causes equine SCID and what are the consequences?

Answer 7

An autosomal recessive disorder related to Arabian horses

It results in recurrent infection and death
- virus: adenovirus
- fungi - pneumocystis carinii

Question 8

What are the gross lesions associated with equine SCID?

Answer 8

bronchopneumonia
very small thymus, lymph nodes, and spleen

Question 9

What is lymphoid atrophy and why does it occur?

Answer 9

Small thymus. You must differentiate from normal involution

It could be caused by infection/toxins/chemotherapy/radiation/malnutrition/stress
- virus: feline or canine parvo/equine herpes 1/BVDV/canine distemper

It results in an acquired immunodeficiency

Question 10

Compare 2 neoplastic processes that can occur in the thymus

Answer 10

thymoma (from thymic epithelium)
- dogs mainly (also cats/horse/pig/goat)
- older animals
- benign
- uncommon
- can be associated with immune-mediated disease like myasthenia gravis

lymphoma (from T cells)
- cats (FeLV) and cattle (bovine thymic lymphoma)
- young
- aggressive

Question 11

At necropsy you find an enlarged thymus, what are 2 differentials?

Answer 11

thymoma or lymphoma

Cannot differentiate grossly

Question 12

Describe the structure of lymph nodes

Answer 12

They are soft, pale, tan, and oval

The outer cortex is full of B cells and the inner cortex is full of T cells

The medulla contains medullary cords (macrophage/monocyte system) in the medullary sinuses

Lymph and blood circulates

Question 13

How are lymph node abnormalities classified?

Answer 13

too big
too small
generalized
localized

Question 14

How is reactive lymphoid hyperplasia differentiated from lymphoma?

Answer 14

The architecture of hyperplasia is still intact whereas lymphoma destroys the tissue architecture

Question 15

What are 2 categories of small lymph nodes?

Answer 15

aplastic

hypoplastic

Question 16

What can cause lymph node aplasia?

Answer 16

SCID related lymph node hypoplasia

Question 17

What might cause hypoplastic lymph nodes

Answer 17

aging
reduced antigen stimulation
viruses (BVDV/CDV)
cachexia
malnutrition

Question 18

4 main causes of lymphadenopathy and what are their primary features?

Answer 18

reactive lymphoid hyperplasia which can be due to infection stimulation either localized or generalized

acute or chronic lymphadenitis which is infection and inflammation causing caseous lymph nodes with reduced architecture

primary neoplasia like lymphoma which is usually systemic

metastatic neoplasia which is usually localized due to draining lymph from carcinomas

Question 19

On necropsy you have a horse with lymphadenopathy. The lymph nodes contain caseous material and have lost their architecture. What process has occurred and what is one differential you have?

Answer 19

acute lymphadenitis due to streptococcus equi equi infection (strangles)

Question 20

Describe the structure of the spleen

Answer 20

There is a thick muscular capsule

White pulp will stain blue/purple on H and E stain and it contains B cell follicles and T cell (PALS)
- cell mediated and humoral immunity

Red pulp will stain red on H and E stain and it contains the macrophage/monocyte system and red pulp vascular space
- phagocytosis of pathogens or senescent (pathologic) or altered (physiologic) RBC
- RBC storage
- extramedullary hematopoiesis

Question 21

Describe species variations in the spleen that are clinically relevant

Answer 21

The gastrosplenic ligament
dogs and pigs = large
ruminants = small

Storage vs defence capacity
- most will have defense capacity
- dog and horses (also cats) have larger storage capacity

Question 22

How are abnormal spleen classified?

Answer 22

too big
too small
bloody
not bloody
uniform
nodular

Question 23

What are 2 possible causes of a spleen that is too small and why might they occur?

Answer 23

contraction (blood) due to excitement or shock

lymphocyte causes:
- SCID related lymphoid hypoplasia
- cachexia
- aging

Question 24

What is the gross appearance of a spleen that is too small?

Answer 24

small with a wrinkled capsule

Question 25

What are the 4 categories of splenomegaly? What do they look like grossly

Answer 25

uniform with blood: dark red/blue/black and will ooze when cut uniform without blood: meaty/firm/no oozing nodules with blood nodules without blood: firm

Question 26

What are 3 main causes of a big bloody spleen?

Answer 26

congestion due to torsion or barbituates acute hemolytic anemia acute hyperemia due to acute septicemia

Question 27

What are 4 main causes of a big meaty spleen

Answer 27

chronic infection chronic hemolytic anemia due to macrophage hyperplasia and extramedullary hematopoiesis lymphoid hyperplasia diffuse neoplasia

Question 28

What type of neoplastic conditions causes diffuse neoplastic splenic infiltrates?

Answer 28

round cell tumors - lymphoma - mast cell - histiocytic - round cell

Question 29

What are 4 causes of a big spleen with bloody nodules?

Answer 29

hematomas due to trauma, or secondary to a splenic mass incomplete contraction or some areas which is uncommon but primarily occurs in dogs acute splenic infarcts which is a hallmark sign of classical swine fever hemangiosarcoma

Question 30

A pig necropsy reveals an enlarged spleen with bloody nodules, which reportable disease should you be thinking about?

Answer 30

classical swine fever

Question 31

What are 4 main causes of a big spleen with nodules (no blood)

Answer 31

nodular hyperplasia primary neoplasia secondary neoplasia inflammation (abcess/granuloma)

Question 32

List the types of benign tumors of the spleen

Answer 32

there are none

Question 33

What is a common incidental finding in the spleen of old dogs

Answer 33

siderofibrotic plaques aka gamna gandi bodies