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thymus and spleen Flashcards

1
Q

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

A

top left: dog/cat

top right: Cattle

bottom two: avian

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3
Q

What do you find in white pulp?

What cell types are commonly here?

A
  • 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
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4
Q

Label the picture.

A
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5
Q

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

Describe the red pulp?

What cells do you find here?

A
  • 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
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7
Q

What can occur with chronic hemorrhage in spleen?

A
  • can have siderotic plaque formation
  • macrophages will come in, try to clean up the hemorrhage
  • tend to localize product subcapsularly
    • can see grossly
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8
Q

What’re some functions of the spleen?

A
  • 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
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9
Q

What’s occuring here?

A
  • 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
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10
Q

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

  • Is there anything normal here?
A
  • 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
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11
Q

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

A
  • 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
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12
Q

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

A

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
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13
Q

What’s going on in this image?

A
  • 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
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14
Q

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

  • What organisms can cause the formation of these?
A
  • Multifocal splenic abscesses
  • organisms:
    • trueperella pyogenes
    • corynebacterium psuedotuberculosis
    • Streptococcus spp can also do this
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15
Q

What abnormality is picutured?

What disease process is associated with this?

What’s circled?

A
  • Hemosiderosis
  • Extramedullary hematopoiesis
  • metarubicyte
    • normal stage of erythrocyte development
    • last stage before the nucleated erythrocyte kicks out the nucleus of cell
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16
Q

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

What causes this?

Acute or chronic?

A
  • granulomatous splenitis
  • Mycobacterium avium ssp avium
  • Chronic
    • indicator of chronicity:
      • rim of fibrous connective tissue around granulomas
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17
Q

What changes do you see to this spleen?

What neoplasm can look like this?

A
  • changes:
    • Nodular splenomegaly
    • splenic
  • hemangiosarcoma
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19
Q

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

A

Lymphosarcoma

20
Q

What changes are being noted in the microscopic image?

What disease comes to mind after seeing the microscopic image?

A
  • neoplastic endothelium
    • flat, elongate cells are forming vascular channels
      • key feature of hemangiosarcoma
  • Hemangiosarcoma
21
Q

I say: monotonous sheets of cells with mitotic figures

you say:

A

duh, lymphoma

22
Q

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

A

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

  • Necrosis
    • lymphoid
    • infarction
  • Lymphoid atrophy
24
Q

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

What can cause this in pigs?

A
  • splenic infarcts
    • diffuse splenomegaly
  • classical swine fever
    • damages endothelium too
    • hope to never see this in US
25
Q

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

VM2: *instill knowledge*

A

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
26
Q

What’s happened to the spleen?

What can cause this?

What’s being pointed at?

A
  • fracture of spleen
  • trauma
  • splenic explants
29
Q

What’s being arrowed in this image?

A
30
Q

VM1: Is that a parasite?

VM2: *insert knowledge here*

A

VM2: SMH, Hassall’s corpuscle

  • cornified
31
Q

What can cause diffuse splenomegaly?

A
  • 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
34
Q

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

A
  • 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
37
Q

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

which metastasizes?

A

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
39
Q

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
A
  • lymphoma/lymphosarcoma
    • no such thing as benign lymphoma so the terms are interchangeable
  • histiocytic sarcoma
  • hemangiosarcoma
  • leiomyoma or leiomyosarcoma
43
Q

What can cause a decrease in size of spleen?

A
  • splenic contraction/atrophy
    • hemorrhage/hypovolemia (shock)
    • lymphoid atrophy (ageing)
  • splenic infarcts
  • hemosiderotic plaques
  • tosion
  • amyloidosis
  • hemosiderosis
  • splenic explants (accessory spleens)
44
Q

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

A

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
48
Q

Compare cortex and medulla of the thymus.

A

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
49
Q

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

A

continuous capillaries form blood-thymus barrier

52
Q

What can cause hypoplasia in thymus?

WHat can cause atrophy of thymus?

A

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
53
Q

What can cause inflammation in thymus?

What can cause neoplasia in thymus?

A

inflammation:

  • thymitis
    • not common change due to being a transient organ

neoplasia:

  • thyoma
    • epithelial cells (found in cortex)
  • lymphosarcoma
    • lymphocytes could undergo transformation
54
Q

What happens to a foal with SCID?

A
  • 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
56
Q

What change to thymus occurs after sexual maturity?

What disease process gets confused with the above answer?

A
  • involution of thymus
  • thymic atrophy
57
Q

What can cause thymitis in pigs?

A
  • circovirus infection in pigs
    • get a pyogranulamatous response in the thymus
    • rare
59
Q

What disease is commonly associated with Thyoma?

A
  • 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

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