Lecture 15: Blood and Lymph Flashcards
Describe the species variation seen in the thymic gland
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
Describe the structure of the thymus
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
What are the 2 consequences of thymic dysfunction?
immunodeficiency
autoimmunity
How is an abnormal thymus classified grossly?
too small
too big
Why might a thymus be too small?
aplasia due (severe combine immunodeficiency disorder)
hypoplasia (normal involution or lymphoid atrophy)
What is SCID and what species does it affect?
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
What causes equine SCID and what are the consequences?
An autosomal recessive disorder related to Arabian horses
It results in recurrent infection and death
- virus: adenovirus
- fungi - pneumocystis carinii
What are the gross lesions associated with equine SCID?
bronchopneumonia
very small thymus, lymph nodes, and spleen
What is lymphoid atrophy and why does it occur?
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
Compare 2 neoplastic processes that can occur in the thymus
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
At necropsy you find an enlarged thymus, what are 2 differentials?
thymoma or lymphoma
Cannot differentiate grossly
Describe the structure of lymph nodes
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
How are lymph node abnormalities classified?
too big
too small
generalized
localized
How is reactive lymphoid hyperplasia differentiated from lymphoma?
The architecture of hyperplasia is still intact whereas lymphoma destroys the tissue architecture
What are 2 categories of small lymph nodes?
aplastic
hypoplastic
What can cause lymph node aplasia?
SCID related lymph node hypoplasia
What might cause hypoplastic lymph nodes
aging
reduced antigen stimulation
viruses (BVDV/CDV)
cachexia
malnutrition
4 main causes of lymphadenopathy and what are their primary features?
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
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?
acute lymphadenitis due to streptococcus equi equi infection (strangles)
Describe the structure of the spleen
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
Describe species variations in the spleen that are clinically relevant
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
How are abnormal spleen classified?
too big
too small
bloody
not bloody
uniform
nodular
What are 2 possible causes of a spleen that is too small and why might they occur?
contraction (blood) due to excitement or shock
lymphocyte causes:
- SCID related lymphoid hypoplasia
- cachexia
- aging
What is the gross appearance of a spleen that is too small?
small with a wrinkled capsule
What are the 4 categories of splenomegaly? What do they look like grossly
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
What are 3 main causes of a big bloody spleen?
congestion due to torsion or barbituates
acute hemolytic anemia
acute hyperemia due to acute septicemia
What are 4 main causes of a big meaty spleen
chronic infection
chronic hemolytic anemia due to macrophage hyperplasia and extramedullary hematopoiesis
lymphoid hyperplasia
diffuse neoplasia
What type of neoplastic conditions causes diffuse neoplastic splenic infiltrates?
round cell tumors
- lymphoma
- mast cell
- histiocytic
- round cell
What are 4 causes of a big spleen with bloody nodules?
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
A pig necropsy reveals an enlarged spleen with bloody nodules, which reportable disease should you be thinking about?
classical swine fever
What are 4 main causes of a big spleen with nodules (no blood)
nodular hyperplasia
primary neoplasia
secondary neoplasia
inflammation (abcess/granuloma)
List the types of benign tumors of the spleen
there are none
What is a common incidental finding in the spleen of old dogs
siderofibrotic plaques aka gamna gandi bodies
