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SYSTEMIC PATHOLOGY - 1 > 16b - Lymphoid System > Flashcards

16b - Lymphoid System Flashcards

1
Q

Lymph nodes

A
  • Oval to bean shaped organs which are distributed along lymphatic vessels
  • Co-ordinate and direct the body’s immune response via immune cells
  • *constantly respond to antigenic stimuli even in absence of clinical disease
  • *reversed arrangement in swine
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2
Q

Outer cortex of a lymph node

A
  • Follicular structures (primary follicles)
    o When antigenically stimulated=develop into SECONDARY follicles
  • *mostly B-lymphocytes, but also macrophages and dendritic cells
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3
Q

Inner cortex (paracortical region) of a lymph node

A
  • Primarily T lymphocytes
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4
Q

Medulla of a lymph node

A
  • MEDULLARY CORDS
    o Macrophages
    o B cells
    o Plasma cells
  • MEDULLARY SINUSES
    o Surrounded by macrophages which phagocytosis foreign material
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5
Q

What is the lymph circulation?

A
  • Enters via lymphatic vessels
  • Subscapular sinuses
  • Trabecular sinus
  • Medullary sinuses
  • Efferent lymphatics
  • Thoracic duct
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6
Q

What are the 2 changes of lymph nodes that can be appreciated grossly?

A
  1. Increase in size
  2. Decrease in size
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7
Q

What are the differentials for small lymph nodes?

A
  • Lymphoid atrophy
  • Lymph node degeneration
  • Lymph node hypoplasia
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8
Q

What are some reasons for lymph node atrophy/degeneration? (5)

A
  1. Senile atrophy
  2. Cachectic atrophy
  3. Toxins
  4. Chemotherapy/irradiation
  5. Many viral infections cause degenerative changes
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9
Q

Senile atrophy of lymph nodes

A
  • Aged dogs, cats and primates
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10
Q

Cachectic atrophy of lymph nodes

A
  • COMMON
    o Especially in old sheep and goats with dental attrition
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11
Q

Many viral infections cause degenerative changes of lymph nodes (lymphocytolysis): examples

A
  • Feline panleukopenia virus
  • Canine parvovirus
  • Canine distemper virus
  • Bovine viral diarrhea virus
  • Feline immunodeficiency virus
  • *with chronicity often result in lymph node atrophy
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12
Q

What does lymph node atrophy/degeneration look like histologically?

A
  • Overall reduced cellularity/lymphoid depletion +/- lymphocytolysis
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13
Q

What are the differentials for enlarged lymph nodes?

A
  • Lymphadenitis
  • Lymphoid hyperplasia
  • Hyperplasia of monocyte/macrophage system
  • Primary neoplasia
  • Metastatic neoplasia
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14
Q

Lymphadenopathy OR lymphadenomegaly

A
  • Lymph node enlargement of UNKNOWN or UNSPECIFIED cause
  • Localized or generalized
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15
Q

Local enlargement of lymph node

A
  • Reflects a pathological process LIMITED to drainage area
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16
Q

Generalized enlargement of lymph node is seen with

A
  • Sepsis
  • Certain infectious disease (TB, brucellosis)
  • Lymphoma
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17
Q

Lymphadenitis

A
  • Inflammatory response to an infectious agent with the lymph node
  • Acute or chronic
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18
Q

What is the difference between lymphadenitis and reactive lymphoid hyperplasia?

A
  • Reactive lymphoid hyperplasia=node is immunologically reactive but FREE OF LOCAL INFECTION
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19
Q

What is acute lymphadenitis usually the result of?

A
  • Regional lymph node draining a site of inflammation and subsequently becoming infected
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20
Q

What are some examples of acute lymphadenitis?

A
  • Infection of tracheobronchial lymph nodes in pneumonia
  • Infection of mesenteric lymph nodes with enteritis
  • With sepsis, many nodes involved
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21
Q

What does acute lymphadenitis look like GROSSLY?

A
  • Enlarged/swollen
  • Soft
  • Moist
  • Hyperemic
  • Often bulge on cut surface
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22
Q

What is welling of lymph nodes in acute lymphadenitis due to?

A
  • Edema
  • Exudate
    o Usually serous, but may be hemorrhagic or suppurative
  • Proliferation of lymphoid/monocyte-macrophage system
23
Q

What are the characteristic features of chronic lymphadenitis?

A
  • Increased size
  • Firm texture due to fibrosis
  • With prolonged inflammation it may be
    o Irregularly shaped
    o Dry
    o Hardened
24
Q

What are 2 types of chronic lymphadenitis?

A
  1. Chronic suppurative lymphadenitis (ex. lymph node abscess)
  2. Granulomatous lymphadenitis
25
Q

Chronic suppurative lymphadenitis (ie. Lymph node abscess)

A
  • Swollen lymph node with a necrotic/pus-filled center in response to PYOGENIC (pus production) BACTERIA
26
Q

What are 4 examples of chronic suppurative lymphadenitis?

A
  1. Equine strangles
  2. Porcine jowl abscess
  3. Streptococcal adenitis in dogs
  4. Caseous lymphadenitis
27
Q

Equine strangles

A
  • Streptococcus equi subsp. Equi
  • Inflammation of upper respiratory tract
    o Abscesses in mandibular, retropharyngeal and parotid lymph nodes
28
Q

Porcine jowl abscess

A
  • Streptococcus porcinus colonizes oral cavity and tonsils
    o Spreads to regional lymph nodes (usually mandibular lymph node)
29
Q

Streptococcal adenitis in dogs

A
  • Streptococcus sp. (Lancefield group G)
  • Occurs in minor endemics in kennels
30
Q

What is streptococcal adenitis in dogs characterized by?

A
  • Pharyngitis
  • Fever
  • Conjunctival discharge
  • Enlargement of submaxillary nodes with abscessation
31
Q

Caseous lymphadenitis

A
  • Common disease of sheep and goats
  • Caused by Corynebacterium pseudotuberculosis
  • *in both species: may be slow spread with time to produce abscesses in internal organs (lung, liver, spleen, etc.)
32
Q

Caseous lymphadenitis in sheep

A
  • C. pseudoTB penetrates body via cuts (shear wounds) OR rarely through inhalation
    o Drains into regional lymph nodes
  • Young: tends to be confined to superficial lymph nodes
    o cervical and sub-iliac most frequently affected
33
Q

Caseous lymphadenitis in goats

A
  • affects lymph nodes of head and neck
  • may be acquired through buccal mucosa in addition to skin wounds
34
Q

What else is corynebacterium pseudotuberculosis responsible for?

A
  • Ulcerative lymphangitis in horses and cattle
  • Pectoral abscesses in horses
35
Q

What does caseous lymphadenitis look like grossly?

A
  • Chronic suppurative inflammation and caseous necrosis of lymph nodes
  • *concentric laminations withing areas are characteristic
    o Result of progressive necrosis and reformation of a connective tissue capsule
36
Q

Granulomatous lymphadenitis

A
  • Nodular or diffuse
  • Characterized by large, firm solid nodes that may exhibit areas of caseous necrosis and/or discrete granulomas with mineralization
37
Q

Nodular granulomatous lymphadenitis can be caused by

A
  • Mycobacterium bovis (bovine TB)
  • Mycobacterium avium subsp. Paratuberculosis (Johne’s disease)
  • Actinobacillus lignieresi (wooden tongue)
  • Migrating parasitc larvae
38
Q

Mycobacterium bovis (nodular granulomatous lymphadenitis)

A
  • Single to multiple discrete white to yellow nodules with central caseous necrosis
  • Initially regional lymph nodes, but can disseminate affect more
39
Q

What does Mycobacterium bovis (nodular granulomatous lymphadenitis) look like grossly?

A
  • Enlarge lymph nodes with single to multiple (coalescing) pale caseous nodular lesions
  • Often gritty (mineralized) centers
  • Confluence of multiple lesions may produce locally extensive or diffuse patterns
40
Q

Mycobacterium avium supsp. paratuberculosis (nodular granulomatous lymphadenitis)

A
  • Nodular aggregates of:
    o epitheloid macrophages
    o multinucleated giant cells
    o fewer lymphocytes and plasma cells
  • surrounding central regions of necrosis +/- mineralization
  • acid-fast bacilli are located in lesions
41
Q

what is generally seen with diffuse granulomatous lymphadenitis?

A
  • Enlarged, dry firm nodes
42
Q

What can cause diffuse granulomatous lymphadenitis?

A
  • Porcine Circovirus type-2 (PCV-2)
  • Histoplasma capsulatum
  • Blastomyces dermatitidis and Cryptococcus neoformans
43
Q

Porcine circovirus type-2 (diffuse granulomatous lymphadenitis)

A
  • Postweaning multisystemic wasting syndrome (PSWS)
  • Granulomatous inflammation with large botryoid intracytoplasmic viral inclusions with macrophages
44
Q

Histoplasma capsulatum (diffuse granulomatous lymphadenitis)

A
  • Facultative INTRACELLULAR pathogen of macrophages
  • Characterized by DIFFUSE involvement of MONONUCLEAR PHAGOCYTE system
    o Marked proliferation of macrophages in spleen, lymph nodes, liver, lungs and intestine=enlarged lymph nodes, spleen and liver
45
Q

Blastomuyces dermatitidis and Cryptococcus neoformans (diffuse granulomatous lymphadenitis)

A
  • Affects regional lymph node draining the affecting areas (skin, lungs, etc.)
46
Q

Lymph node hyperplasia

A
  • Changes lead to lymph node enlargement
  • May involve lymphoid tissues and/or cells of monocyte-macrophage system (sinus histiocytosis)
  • *common reactive lesion
    o Local or generalized
    o Occurs in response to presentation of foreign mater/antigen OR in response to circulating interleukin levels
  • Seen during EARLY LYMPHADENITIS
47
Q

What is a classic example of reactive lymph node hyperplasia?

A
  • Local lymph nodes draining site o local infection OR a site of vaccination
48
Q

What does lymph node hyperplasia look like grossly?

A
  • Moderate enlargement of affected lymph nodes
  • May bulge on cut section
49
Q

What does lymph node hyperplasia look like histologically?

A
  • Proliferation of lymphoid follicles with prominent germinal centers
  • Increased T-cells in paracortex
  • Increased plasma cells in medullary cords
50
Q

Lymph node metastasis (secondary neoplasia)

A
  • Common with carcinomas, malignant melanomas, and mast cell tumors
  • GROSSLY: may see lymph node enlargement
  • HISTOLOGICALLY: few cells with peripheral/medullary sinuses OR may be effacement of normal architecture by neoplastic cells
  • *lymph node involvement is one basis for clinical staging of tumour malignancy
51
Q

Stage 0 for tumor malignancy

A
  • No palpable regional lymph nodes OR nodes appear normal
52
Q

Stage 1 for tumor malignancy

A
  • Regional node palpably enlarged, but still freely movable
53
Q

Stage 2 for tumor malignancy

A
  • Regional node palpably enlarged and fixed

SYSTEMIC PATHOLOGY - 1 (24 decks)

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