thymus and spleen

Question 1

These are spleens from different species. What species are they from?

Answer 1

top left: dog/cat

top right: Cattle

bottom two: avian

Question 3

What do you find in white pulp?

What cell types are commonly here?

Answer 3

• peri-arterial lymphatic sheaths
  
  • t-cell areas around central arteries
• lymphiod nodules
  
  • b-cell areas adjacent to PALS
    
    • may contain germinal centers
• marginal zone
  
  • external to lympohoid nodules and PALS
    
    • interfdace with red pulp
• T/B cells, plasma cells, macrophages, and dendritic cells are present

Question 4

Label the picture.

Answer 4

Question 5

At what point are you exiting the white pulp and going into red pulp?

Describe the red pulp?

What cells do you find here?

Answer 5

• as blood percolates through those central arteries, it’s going to exit into the penicillar arteries
• sinuses
  
  • discontinuous endothelium
• splenic cords
  
  • reticular fibers and macrophages, T/B cells, plasma cells, macrophages
    
    • extramedullary hematopoiesis

Question 7

What can occur with chronic hemorrhage in spleen?

Answer 7

• can have siderotic plaque formation
• macrophages will come in, try to clean up the hemorrhage
• tend to localize product subcapsularly
  
  • can see grossly

Question 8

What’re some functions of the spleen?

Answer 8

• Filtration
  
  • erythrocyte removal
• immunologic
  
  • all our blood borne antigens and our WBC (to some extent) will filter through the spleen
• storage
  
  • blood
  • iron
• hematopoiesis
  
  • extramedullary erythropoiesis
    
    • in adults, can indicate blood loss or another disease process happening in the body
  • B/T lymphocyte proliferation

Question 9

What’s occuring here?

Answer 9

• Increased cellularity,
• Increase of white matter.
• Lymphoma.
• If we were to look at this up close, we’d see a monomorphic cell population.
• Subgrossly, we’re seeing an expansion of the white pulp zones

Question 10

Looks pretty messed up, eh? Describe what you think is happening here.

• Is there anything normal here?

Answer 10

• Note that both white and red matter are hypocellular, kind of washed out and eosinophillic.
• This is a necrosis, a micro view of a splenic infarct.
• If we devitalize the entire area, both our white pulp and our red pulp components will be affected
• The right side of the image is normal splenic tissue

Question 11

You see this in necropsy. What possible differentials can you think that can create this lesion?

Answer 11

• Nodular hyperplasia - ageing lesion
• Proliferation of both the white matter and the red matter, microscopically
• Abscesses, granulomas
• Hematoma - hemoabdomen
  
  • trauma
  • associated with nodular hyperplasia (IDK why)
• Neoplasia - lymphoma, hemangiosarcoma, histiocytic sarcoma
  
  • Of both native and incoming metastatic components

Question 12

When a spleen responds to injury it can increase or decrease cellularity. What normal and abnormal situations can make the spleen increase its cellularity?

Answer 12

Normal:

• hyperplasia of resident cells
  
  • macrophages and lymphoid (nodular hyperplasia)
• inflammation
  
  • splenitis
• hemorrhage
  
  • hemosiderosis –> plaques

Abnormal:

• neoplasia
  
  • can be of resident cell population or metastatic process

Question 13

What’s going on in this image?

Answer 13

• Grossly, nodular hyperplasia is a differential. Exact diagnosis would have to come from histo.
• Gross on this would be a Focal splenic nodular
• Differential: nodular hyperplasia
• Any trauma to the spleen can result in the formation of a hematoma
• Or if that splenic capsule ruptures, we can actually have hemoabdomen and bleed into the cavity

Question 14

You suspect this animal has septicemia. What lesions are these?

• What organisms can cause the formation of these?

Answer 14

• Multifocal splenic abscesses
• organisms:
  
  • trueperella pyogenes
  • corynebacterium psuedotuberculosis
  • Streptococcus spp can also do this

Question 15

What abnormality is picutured?

What disease process is associated with this?

What’s circled?

Answer 15

• Hemosiderosis
• Extramedullary hematopoiesis
• metarubicyte
  
  • normal stage of erythrocyte development
  • last stage before the nucleated erythrocyte kicks out the nucleus of cell

Question 16

You see an old chicken with this spleen. What’s occuring here?

What causes this?

Acute or chronic?

Answer 16

• granulomatous splenitis
• Mycobacterium avium ssp avium
• Chronic
  
  • indicator of chronicity:
    
    • rim of fibrous connective tissue around granulomas

Question 17

What changes do you see to this spleen?

What neoplasm can look like this?

Answer 17

• changes:
  
  • Nodular splenomegaly
  • splenic
• hemangiosarcoma

Question 19

You see a sheet of neoplastic lymphocytes in spleen. What process makes this lesion?

Answer 19

Lymphosarcoma

Question 20

What changes are being noted in the microscopic image?

What disease comes to mind after seeing the microscopic image?

Answer 20

• neoplastic endothelium
  
  • flat, elongate cells are forming vascular channels
    
    • key feature of hemangiosarcoma
• Hemangiosarcoma

Question 21

I say: monotonous sheets of cells with mitotic figures

you say:

Answer 21

duh, lymphoma

Question 22

What can be attributed to when spleen decreases cellularity in response to injury?

Answer 22

either all the cells in a region die, or we can have selective atrophy of the lymphoid component

• Necrosis
  
  • lymphoid
  • infarction
• Lymphoid atrophy

Question 24

You necropsy a pig and find these lesions. What’s happening to the spleen?

What can cause this in pigs?

Answer 24

• splenic infarcts
  
  • diffuse splenomegaly
• classical swine fever
  
  • damages endothelium too
  • hope to never see this in US

Question 25

VM1: OH MY GOD!! A neoplasm is forming on spleen of an older cow!

VM2: *instill knowledge*

Answer 25

VM2: LOL, come on buddy. That’s siderotic plaque on the spleen.

• result of chronic hemorrhage
• common incidental finding in older animals
• not a pathologic finding

Question 26

What’s happened to the spleen?

What can cause this?

What’s being pointed at?

Answer 26

• fracture of spleen
• trauma
• splenic explants

Question 29

What’s being arrowed in this image?

Answer 29

Question 30

VM1: Is that a parasite?

VM2: *insert knowledge here*

Answer 30

VM2: SMH, Hassall’s corpuscle

• cornified

Question 31

What can cause diffuse splenomegaly?

Answer 31

* Congestion: CHF, torsion, septicemia, viremia, barbiturates * Active congestion - During septicema, we'd have an acute vasodilation process in that spleen and an influx of neutrophils as well * Passive congestion. Chronic heart failure, or torsion. Decreased drainage from the spleen * Barbiturates - In Dogs especially, barbiturates have a relaxing effect on the spleen. * Extramedullary hematopoiesis: AIHA, anaplasmosis * Fixed-phagocyte (macrophage) hyperplasia: AIHA, anaplasmosis * Leukemia/lymphoma

Question 34

What are some changes you can see in the histo slide of a thymus?

Answer 34

* We still have Hassall's corpusules here, but not seeing a lot of lymphocytes. * The medulla almost has the same cellularity as the cortex. * In this case, the thymus didn't form, so it's hypoplastic

Question 37

Two different neoplasms from two different thymuses are under the microscope. Which disease is causing the lesion in each picture? which metastasizes?

Answer 37

left: * thyoma * neoplastic epithelial cell * seeing too much pink than we would with lymphoma * not metastatic right: * thymic lymphoma * sheets of neoplastic lymphocytes * will commonly metastasize

Question 39

Primary splenic neoplasms can arise from cell populations that normally exist in the spleen. List the neoplasms associated with each cell type. * lymphocytes * macrophages * endothelial cells * smooth muscles

Answer 39

* lymphoma/lymphosarcoma * no such thing as benign lymphoma so the terms are interchangeable * histiocytic sarcoma * hemangiosarcoma * leiomyoma or leiomyosarcoma

Question 43

What can cause a decrease in size of spleen?

Answer 43

* splenic contraction/atrophy * hemorrhage/hypovolemia (shock) * lymphoid atrophy (ageing) * splenic infarcts * hemosiderotic plaques * tosion * amyloidosis * hemosiderosis * splenic explants (accessory spleens)

Question 44

What's more likely an anemic infarct or a hemorrhagic infarct in the spleen?

Answer 44

Hemorrhagic * very spongy organ * have collateral circulation so probably have trouble have anemic infarct * ruptured endothelial cells will allow hemorrhage into the area * will see raised red lesion there

Question 48

Compare cortex and medulla of the thymus.

Answer 48

Cortex: * produces immunocompetent naive T-cells * send to medulla * epithelial reticular cells: isolates naive T-cells from antigen exposure * Tingible-body macrophages: * breaks down deleted T-cells Medulla: * contains mature immunocompetent naive T-cells * Hassall's corpuscles: cornified epithelial cells

Question 49

What's the key feature of the thymus' function?

Answer 49

continuous capillaries form blood-thymus barrier

Question 52

What can cause hypoplasia in thymus? WHat can cause atrophy of thymus?

Answer 52

hypoplasia: thymus never forms * Combined Immunodeficiency (CID) in Arabian foals * genetic mutation * SCID in mice: Severe Combined Immunodeficiency atrophy: * stress * corticosteroid treatment * Iatrogenic treatment with steroids can also lead to premature atrophy of thymus

Question 53

What can cause inflammation in thymus? What can cause neoplasia in thymus?

Answer 53

inflammation: * thymitis * not common change due to being a transient organ neoplasia: * thyoma * epithelial cells (found in cortex) * lymphosarcoma * lymphocytes could undergo transformation

Question 54

What happens to a foal with SCID?

Answer 54

* Main crux of this is that there's a defect in the rearrangement of those VDJ segments. * Those are necessary to actually form the B and T cell receptors. * If they don't form these receptors, those cells are stimulated to undergo apoptosis within the thymic cortex * If they undergo apoptosis, they never mature * If they don’t mature, we don't have an immune system * Will have neither B or T cells * That's why it's called Severe COMBINED Immunodeficiency

Question 56

What change to thymus occurs after sexual maturity? What disease process gets confused with the above answer?

Answer 56

* involution of thymus * thymic atrophy

Question 57

What can cause thymitis in pigs?

Answer 57

* circovirus infection in pigs * get a pyogranulamatous response in the thymus * rare

Question 59

What disease is commonly associated with Thyoma?

Answer 59

* Thymomas are somewhat frequently correlated with Myasthenia gravis * Remember that Myasthenia gravis is a neuromuscular disorder, where you have autoantibodies formed against the Acetylcholine receptor * For some reason, in humans, there's a massive increase in the severity of disease and the number of those antibodies if they also have a thymoma * If you have a dog with MG, take thoracic rads to check for a thymoma