Pathology of lymphoid organs, spleen, and thymus Flashcards
Lymphadenopathy
Enlargement of the lymph nodes
Reactive hyperplasia
- presence of germinal centres (proliferation of B cells)
- increased macrophages in the subscapular sinuses
- expanded paracortex (space between follicles) (= proliferation of T cells)
- Plasma cells in the sinuses
- Increased amounts of incoming lymph
Hypertrophy vs. hyperplasia of lymph nodes
Lymphoid tissues are highly proliferative, thus they do not undergo hypertrophy but only hyperplasia
Why in reactive lymph nodes do the germinal centers appear polarized with light pole directed to source of antigen?
Lymphocytes in a blast stage in the germinal centers. T Lymphocytes are directed towards subscapular side which is the direction antigens come from.
What do germinal centers look like in response to injury?
“Starry sky appearance” The white areas, the “stars” are macrophages eating
Why does lymph node hypoplasia or atrophy occur?
Starving animal, Severe Combined Immundeficiency (SCID), viral infections
Major serious characteristic of Parvovirus
Necrosis of crypts of intestine, necrosis at the level of the bone marrow, same happens in lymph nodes and the spleen
What are some causes of necrosis of lymphoid tissues?
Equine Herpesvirus, Parvo, BVDV
Necrosis of lymph nodes
Would happen in all LNs- systemic infection. Consists of lysis of cells of the lymphoid follicles. Grossly not visible, they would just be smaller than usual. BVDV and parvo would target cells of highly proliferative tissue compartments such as lymphoid tissue.
Anthracosis in the lungs, how it affects the tracheobronchial lymph nodes
Dependent LN would be pigmented as well by the carbon. True with any pigmented disease.
Lymphadenitis
Infectious agent present within the lymph node. Targeting the lymph node. (different than reactive hyperplasia stand alone) however, you would definitely have reactive hyperplasia at the same time.
Reaction of LN to infections
- Reactive lymph node
- Inflammation as a result of direct infection
- Lymphadentisis as a result of drainage from infected site
Serous lymphadenitis
Early stage of infection. Can develop into suppurative or granulomatous.
Corynebacterium pseudotuberculosis (not TB) affect on LNs.
Big lymph node with necrosis. Concentric arrangement of necrotic material. Multiple episodes of necrosis, causing the layered appearance. Common in small ruminants and sheep. Ovine CLA (Ovine Caseous Lymphadenitis). Chronic suppurative lymphadenitis
How do the lymph nodes get infected in Ovine Caseous Lymphadenitis?
Skin wounds- tail docking, castration, shearing.
What is Porcine Jowl abscess caused by?
Streptococcus porcinus
What is Equine strangles caused by? How does it affect LNs?
Streptococcus equi. Resp. infection but also swollen lymph notes. Serous or sero-purulent exudate
Postwwaning Multisystemic Wasting Syndrome (PMWS)
Wasting disease of pigs- they usually die within 6-12 weeks of age. Caused by Porcine Circovirus 2. Granulomatous lymphadentitis and lymphoid depletion. Giant cells- typical of granulomatous inflammation.
Lymphadenitis Secondary infections of the lymph nodes- what is the main one that causes this?
Granulomatous in the lungs. I.e. Bovine Tuberculosis will cause chronic granulomatous lymphadentitis.
- another example) Wooden Tongue, Bovine (Actinobacillus ligneresii). Pyogranulomatous lymphadentitis and glossitis.
- Rhodococcus equi- Pyogranulomatous enteritis and lymphdentitis.
- bovine, Johne’s disease. Granulomatous enteritis and lymphadentitis.
Main tumour of the lymph nodes
Lymphomas (90% of tumours of the lymph nodes)
Lymphoma histologically characterized by?
BLUE! Lots of lymphocytes! And Starry Sky appearance on medium- high power.
Classification of Lymphomas
- Helps us determine low grade or high grade. Basically how long the patient has to live.
- Anatomic location- Can arise anywhere in the body- any tissue and organ of the body. (Spleen forms, etc. sometimes confined, sometimes can spread, lymphoma of the skin- can look like dermatitis, lymphoma of the kidneys)
- Immuno-phenotype: benign or malignant? T cell, B cell, or NK cell lymphoma? ALL lymphomas are malignant. But B cell are more responsive to chemotherapy. While T cell lymphomas are less responsive.
- Cellular morphology- large cell lymphocytes or small cell lymphocytes. The larger they are, the more malignant they are.
Lymphoma vs. Infection?
Bilateral lymphadenopathy- lymphoma
Unilateral lymphadenopathy- infection
Alimentary
Gastric and intestine involved at the same time. (most common form of lymphoma in cats- with mesenteric lymph node involvement)
Bovine Lymphoma (2 forms, a few characteristics)
Enzootic bovine lymphoma (adult), sporadic bovine lymphoma (not viral induced, big mass in mediastinum (middle cavity of thorax- heart lungs, trachea, etc.), 6 mos- 2 yo animals, cutaneous form)
Equine alimentary lymphoma
Frequent in large intestine (more frequently than small intestine) mesenteric lymph nodes affected.
Immunophenotype
Most important thing when dealing with lymphomas!!! (not anatomic, etc.) B or T cells? Will tell you whether treatable and how to manage it. Not determined from histology or cytology. Immunohistochemistry and PCR is how you determine immunophenotype!!
Metastatic neoplasia
Lymph nodes are the most common site of metastasis for any tumour. FNA or cytology or histology- always check lymph nodes. Will tell you what is the prognosis of the tumours? Metastatic carcinoma- you would find the cells in the LN- coming from the primary tumour.
Splenic amyloidosis
Sick bird, you will have splenic amyloidosis in a bird. Major feature of inflammation in a bird
Siderofibrosis (siderotic plaques)
Incidental finding. Common. Dog (older especially, due to repeated contraction of the spleen- microhaemorrhages on the capsule- reparative processes). Iron (haemosiderin) and Calcium deposits and fibrous tissue. Important so you don’t remove the spleen when you see this during surgery!
When you necrosis of the LNs, what is else is almost always affected?
The spleen
Haemosiderosis
Haemosiderin- end result of the break down of RBCs. Haemolytic anaemias or increased turnover of RBCs. Increased production of haemosiderin. Phagocytosis produced. Brown change on histological sections. Severe cases of haemolytic anaemias can have enlarged spleen.
Splenic atrophy
Same as LN atrophy- not common- if it happens, it happens in aging and immunodeficiency conditions such as SCID.
Splenic contraction
Occurs in normal physiological processes. Occurs when you need more blood in the organism. I.e. haemalytic anaemia- intravascular or extravascular. like a big haemorrhage. Contracts the spleen to push more blood into circulation. (extramedullary haematopoeisis- during disease process and the spleen kicks in to help make or takeover making RBCs for the bone marrow)
Splenomegaly
Main cause- barbituate euthanasia. Postmortem of euthanized animal. You will find a big spleen. (passive congestion aka active or passive hyperaemia) ex in dogs) GDV- torsion of stomach and spleen (since attached)- therefore occlusion of the veins (more than arteries) so no drainage of blood from the spleen- more accumulation of blood into the red pulp…
Indentation or C shape- compresses half way with the organ. Likely to be spleen with GDV.
Splenic infarcts
Not common in the spleen- can be mistaken for uneven contraction of the spleen (pockets of blood, normal). Infarcts can occur due to vasculitis, virus, bacterium. Thrombosis, therefore infarction. Classical example- cholera- vasculitis therefore splenic infarction. No way to grossly tell the different between an infarct or haematoma- the only way to tell is peritonitis at the level of the infarct. Infarct, then reaction of the capsul to the problem, so a bit of fibrin, loss of glistening, or smoothness of the capsule.
Splenic Haematomas
Accumulation of blood usually as a result of traumatic injury i.e. car accident. They can also develop with time. Difference between haematoma and a tumour is difficult. Most likely consequence- major risk is rupture. If you have rupture in abdominal- major haemorrhage- shock (hypovolaemic). Multiplie haematomas at the same time. With time, organization of the haematoma (fibrous tissue septa within the nodule- therefore less likely to rupture because of less blood inside).
Splenic rupture
due to traumatic injuries. Spleen sits beneathe the abdominal cavity. Gross appearance varies. But normally indentations, bits and pieces of spleen. Common consequences of splenic ruptures even if mild injuries. Splenosis- seeding of splenic tissue on the surface of omentum.
Splenosis
Seeding of splenic tissue on the surface of the omentum following splenic rupture. Little accessory spleens- baby spleens.
Splenitis
Acute (congestive splenitis)
How does the spleen respond to bacterial insult?
Same as LNs. Antigens in blood (vs. lymph or tissues). Role of the spleen to react to them in some way. Depends if it is bacteraemia and septicaemia (other card explains)
Bacteraemia vs. Septicaemia
- Bacteraemia- circulating bacteria not doing much just traveling (abscess in oral cavity then this could occur, for example, can make abscesses elsewhere)
- Septicaemia- proliferating bacteria. Salmonella for example. They like to proliferate in blood. Proliferation and release of toxins.
Anthrax
Causes acute congestive splenitis. Spleen is always affected because it is in the blood. Blood like blackberry jam (acute hyperaemia). Rapid tests for anthrax before you do the post mortem because dangerous.
Other than Anthrax, what is another cause of acute congestive splenitis?
African swine fever
Caseous Lymphadenitis- what does this impact?
Mostly affects LNs but can spread to the spleen
Streptococcus sp.- pyogenic bacteria- affects spleen how?
Any pyogenic bacteria can cause abscesses in the spleen. anywhere else in the body
Hyperplastic diseases of the spleen
Usually incidental findings. Hyperplasia of lymphocytes. Hard to tell the difference between this and lymphoma. Anything that is in the spleen can undergo hyperplasia. Extramedullary haematopoiesis- RBCs- meaty and enlarged because of increased cellularity.
White pulp hyperplasia looks like?
Many little white nodules. Red pulp does not look the same.
Bacteraemia- what does this cause in the spleen?
- White pulp hyperplasia (reactive- trying to produce more lymphocytes to fight the infection)
- Formation of abscesses or granulomas. Embolis of bacteria and inflamm. cells. can stop in the spleen and abscess or granuloma can develop
Septicaemia- what happens in the spleen?
Acute congestive splenitis. Inflammation is going to be widespread throughout the organ. Plenty of inflamm. cells, usually neutrophils. Big, dark, and oozing blood.
How is the spleen helpful in infectious diseases?
Spleen can tell you what is going on in infectious diseases
2 tumours that are frequent in the spleen
- Haemangiosarcoma
2. Lymphoma
Haemangiosarcoma
Most common tumour in dogs in the spleen. Presentation can look like a tumour with multiple coalescing big nodules full of blood- can look like haematomas. Multiple blood filled nodules bulging from capsular surface. 2/3 tumours in the spleen will be malignant. 2/3 of the malignant will be haemangiosarcomas. Need histology to confirm because you cannot make a gross diagnosis. This tumour is HIGHLY METASTATIC. Likely to already have metastasis somewhere- commonly the liver, right auricle of the heart, sometimes rise at the same time. Rupture is the typical presentation- they can be asymptomatic until rupture. Haemoperitoneum, metastasizing in peritoneum and omentum.
Haemangioma
Benign tumour of vessels.
Lymphoma
Primary lymphoma of the spleen. Spleen has plenty of lymphoid tissue- good spot to occur. Enlarged spleen with lots of lymphocytes in the white and red pulp. Or sometimes development of nodules of white tissue. Diffuse or nodular. DDx- nodular hyperplasia or lymphoma- look very similar. Histologically not easy to tell the difference either.
Histiocytic sarcoma
Bernese mountain dogs. Macrophage or DC cell origin. Malignant histiocytes. Big macrophages with giant cells. INvolves spleen and LN and can spread to other organs
Sarcomas
Arise from the capsule, smooth muscle, trabeculae of the spleen,… because you have mesenchymal cells in the spleen, this can occur.
If you have a big mass and you don’t know what it is- what are the three most common options? How do you sort it?
Haematoma, Haemangioma, Haemangiosarcoma.
Histology- many samples.
Not possible to tell grossly.
Thymus- 3 main conditions
Thymus disappears early in life- but you retain remanants in mediastinal areas- source of problem in some neoplastic diseases. ** spleen in mediastinum**
- Thymic atrophy/hypoplasia – NOT INVOLUTION
- Inflammation (thymitis)
- Neoplasia
Thymic atrophy/ hypoplasia
EHV-4- lymphocytolysis, canine and feline parvo- lymphocytolysis, SCID
Thymic neoplasia
Thymoma, big masses in the mediastinum- close to the trachea. Cranial to the heart. Usually very large. Firm, white, haemorragic or necrotic sometimes.
Benign or malignant.
Can look nodular. If it is nodular- most likely thymoma instead of lymphoma.
Common in cats but not as much in other species.
