Lymphoid Path Flashcards
Thymus structure
develops from pharyngeal pouches 3+4 Lymphoepithelial origin (2 types of cells): lymphocytes and epithelial cells
Thymus function
Cortex: T-cell development and maturation (precursors from BM)
Medulla: antigen presentation
Induction of self tolerance (thymic ed)
Decreased thymic size
hypoplasia, atrophy
increased thymic size
lymphoma, thymoma, branchial cysts, hematoma
Thymic Hypoplasia
Severe combined immunodeficiency (SCID):
- defective function but mature cells (bassets, corgis)
- inability to generate lymphocytes (jack russell)
Thymic atrophy
involution: normal aging
Lympholysis: viral, steroid induced, nutritional, toxic
Why is thymic hypoplasia and lymphiod atrophy important?
IMMUNOLOGICAL DYSFUNCTION
vague signs, difficult to diagnose
Increase in thymic size consequence
affect on adjacent structures, becomes space occupying lesion
CS: Dyspnea, cough, regurgitation, edema, swollen head/neck, chylothorax
Thymoma
Derived from epithelial component of thymus
May contain NORMAL lymphocytes, can outnumber neoplastic cells
Adult animals: 8-10yr
Metastasis and invasion is NOT common. Space-occupying
Paraneoplastic syndrome
Commonly associated with thymomas
Acquired autoimmune disorders: myasthenia gravis, polymyositis, megaesophagus, exfoliative dermatitis
Thymic lymphoma
tumor of lymphocytes/lymphoblasts
Usually T-cell
Aggressive, invasive
Feline thymic lymphoma
especially important in young, FeLV+
2-3yr old
Usually no other organ involvement except BM
Thymic branchial cysts
developmental disorder, slow growing
cysts contain mucoserous fluid, lined by ciliated, columnar epithelial cells
Thymic hemorrhage/hematoma
D/t trauma or bleeding disorders (rodenticides)
Lymph node structure
Dynamic! cells and fluid constantly moving
Node structure changes depending on immune status
Cortex: follicles are B-cell, paracortex is T-cell
LN function
defensive barriers
Filtration of lymph from dependent areas
localization of immune response
Ddx for lymphadenomegaly
Hyperplasia (reactive)
Inflammation (lymphadenitis)
Neoplasia (lymphoma, metastatic)
LN hyperplasia
proliferation d/t antigenic stimulation
Lesions: Arcitecture of node maintained, fish flesh tan and homogenous
Large immature lymphoblasts and small mature lymphocytes +/- increased plasma cells and/or macrophages
Causes LN hyperplasia
Salmon poisoning (neorickettsia helmenthoeca) FIV
Lymphadenitis
Lesions: swollen, grey-red, more likely engorged and painful
Micro: hyperplasia + inflammatory cells and fibrin (neuts and macros)
Affected node involved in process, not just draining affected site
Spleen function
Host immune response
Fultration of unwanted elements from blood via phagocytosis
Hematopoiesis, life long source of lymphocytes and macros
Reserve blood storage
Reasons to remove spleen?
Rupture, torsion, neoplasia, symptomatic splenomegaly, +/- immune-med disease
Spleen neoplasia
Hemangiosarcoma Lymphoma leiomyosarcoma hemangioma mast cell tumor (cats) Mets
Vascular dz spleen
Hematoma (can mimic hemangiosarc), congestion, infarct (acute vs, chronic)
Other splenic changes
nodular hyperplasia, diffuse hyperplasia, splenitis
Splenic congestion
pentobarbital, heart failure, portal hypertension, splenic torsion
Diffuse increased size
Engorged, exudes blood on cut surface
Nodular hyperplasia spleen
nodular, red or tan
hyperplastic lymphoid elements plus congestion
mimics hemangiosarc
Spleen diffuse hyperplasia
activation of spleen to remove abnormal or opsonized cells (RBCs), or microbes from circulation
extramedullary hematopoeisis = regenerative response
Splenic rupture
Acute: fatal internal hemorrhage
Chronic: healing which may produce notches, fissures, divisions, accessory spleens
Siderotic plaques
in DOGS
very common senile change on the capsule
Incidental finding!
Accessory/ectopic spleens
Cats
can be indistinguishable from seeding of peritoneum by metastatic hemangiosarc
Canine Lymphoma
Multicentric 80%
majority of animals with solid tumors don’t have detectable neoplastic cells in circulation
Causes effacement of normal architecture
Feline lymphoma
very common, most common neoplasm of cats
associated often with FeLV
Alimentary most common
