Lymph Node Pathology Flashcards
What are the primary lymphoid organs?
the bone marrow and the thymus
What are the secondary lymphoid organs?
lymph nodes, spleen and MALT
Describe the morphology of a lymph node?
the lymph node is a small well circumscribed oval surrounded by a fibrous capsule. The hilum of the lymph node has the artery and vein and the efferent lymphatic. The afferent lymphatics enter through the capsule. Inside the lymph node there is an outer cortex and inner medulla.
What is located in the outer cortex of the lymph node?
B cells in follicles and germinal centres
What is located in the paracortex of the lymph node?
T cells
What is located in the medulla of the lymph node?
blood vessels, sinuses and the medullary cords
What are the medullary cords?
lymphatic tissue in the medulla where B cells go for their final differentiation
What cells are located in the sinuses of the lymph nodes?
macrophages and eosinophils
What are high endothelial venules?
the post capillary venules in lymphatic tissue that have plump endothelial cells to allow lymphocytes to enter the lymph node by crossing the high endothelial venules
How can you tell the difference between a follicle and a germinal centre?
in the germinal centre cells are larger and have more cytoplasm and there is a pale area in the centre surrounded by a mantle zone (the naive B cells surrounding the germinal centre)
What happens to B cells once they have matured into plasma cells in the medullary cords?
they can either stay in the medullary cords and release antibodies from there or they can circulate in the blood to go to the tissues
What happens to T cells once they have matured into effector T cells?
they need to go to the site of the infection so will circulate in the blood or lymph
Where are high endothelial venules located?
in the paracortex
What immunological marker is used to stain for B cells in the lymph node?
CD20
What immunological marker is used to stain for T cells in the lymph node?
CD3
What is the role of macrophages in the germinal centre?
to phagocytose the apoptotic B cells
What does the presence of germinal centres in a lymph node indicate?
that there is a humoral immune response occuring - this happens often - even when there is not an overt infection
What are some causes of reactive lymphadenopathy?
localised infection in the area of drainage, systemic infection, non infective systemic disease e.g. rheumatoid arthritis, drugs, other
What are some causes of neoplastic lymphadenopathy?
leukaemic infiltration, lymphoma, metastases
What is the histopathological pattern of a lymph node due to a microbial infection causing acute lymphadenitis?
neutrophil infiltration, oedema, follicular hyperplasia - nodes will be painful due to rapid expansion
Why is chronic lymphadenopathy not painful?
because there is not rapid expansion of the lymph node
What causes follicular hyperplasia?
auto immune disease and microbial infection
What causes paracortical hyperplasia?
viral infection and drugs
What is sinus histiocytosis?
an increase in macrophages in the sinuses
What causes sinus histiocytosis?
non specific - nodes draining cancers, infections
What causes granulomatous inflammation?
TB, sarcoidosis, crohns, toxoplasmosis
What primary tumours cause neoplastic lymphadenopathy?
Hodgkin’s lymphoma and non hodgkin’s lymphoma
Why aren’t lymph node biopsies put in formalin?
because they may be caused by infection so may need to be cultured
What would lymphoma look like on an FNA of the lymph node?
a more uniform population of cells than the normal mixed spread
What marker is on T cells throughout their development?
CD2
What marker is on B cells throughout their development?
CD19
What is the most common cell type in lymphoma?
lymphoid cells at a mature (post bone marrow) stage
Where does lymphoma usually occur?
as discrete masses in tissues outside of bone marrow - but can involve bone marrow but their usually minimal or no blood involvement
What are some risk factors for lymphoma?
immunosupression or immunodeficiency, autoimmune diseases, EBV, H. pylori, chemotherapy, radiation, chemical
What chromosomal translocation is in most follicular lymphomas?
t(14,18) - this results in the IgH locus on chromosome 14 being put with the Bcl-2 locus from chromosme 18 which results in over expression of Bcl-2 (an anti-apoptotic protein)
What chromosomal translocation is in Burkitt’s lymphoma?
chromosome 8 containing MYC is translocated onto an immunoglobulin gene region which results in upregulation of MYC (an oncogene) which results in greater cell proliferation
What is the role of EBV in lymphoma?
EBV infects B lymphocytes where it remains latent - but to remain latent requires T cells - if there is loss of T cell immunity this results in expression of viral proteins which activates signalling pathway and causes polyclonal B cell proliferation which may result in lymphoma
What are the clinical features of lymphoma?
lymphadenopathy, symptoms of extranodal involvement e.g. breast mass or gastric symptoms, hepatosplenomegaly, fever, night sweats, weight loss
What is involved in the diagnosis of lymphoma?
tissue biopsy with morphology, immunohistochemistry, flow cytometry and genetic studies
What is the neoplastic cell in Hodgkin’s lymphoma called?
a Reed-Sternberg cell - a big cell with a bilobed nucleus and big eosinophilic nucleoli
What are the two main groups of non-hodgkin’s lymphoma?
B cell (85%) and T cell
What is the commonest type of non-hodgkin’s lymphoma?
diffuse large cell B lymphoma
What does diffuse large cell B lymphoma look like histologically?
on low power can see a diffuse population and on high power can see the cells are large with large nucleoli
What does follicular lymphoma look like histologically?
cells form follicles
What is the immunophenotype of follicular lymphoma?
surface immunoglobulin +ve, express B cell antigens CD19 and CD20, CD10+, CD5-, CD43-, BCL-2 +
How can you differentiate between a normal follicle and a follicular lymphoma?
by staining for BCL-2
What is the difference between chronic lymphocytic leukaemia and small lymphocytic lymphoma?
both have the same cell involved - a cell which looks like a normal lymphocyte - but the site of involvement is what differentiates the diagnosis (leukaemia in bone marrow and blood and lymphoma in the lymph node)
What is the immunophenotype of CLL/SLL?
surface immunoglobulin weak, express B cell antigens CD19 and CD20, CD10-, CD5+, CD23+
What is the difference in presentation between Hodgkin’s and non hodgkin’s lymphoma?
Hodgkin’s is typically in a single axial group of lymph nodes where as NHL is typically multiple nodes including peripheral nodes, hodgkin’s has an orderly spread whereas NHL doesnt, hodgkin’s rarely involves the mesenteric nodes or waldeyer’s ring whereas NHL often does, hodgkin’s rarely presents extra nodally whereas NHL often does
What histological feature is present in acute myeloid leukaemia?
auer rods
What does chronic myeloid leukaemia look like on a blood film?
lots of mature neutrophils
What translocation is common in chronic myeloid leukaemia?
t(9,22) resulting in fusion of BCR-ABL - an unregulated tyrosine kinase
What is the treatment for chronic myeloid leukaemia?
imantinib - inhibits BCR-ABL kinase
