Lymph Nodes
Major lymph nodes in animals…
 Animals have a complex lymphatic system.
 The major lymph nodes in animals can vary slightly depending
on the species, but here are some of the commonly recognized
ones:
1. Submandibular lymph nodes: These lymph nodes are located beneath the lower jaw, near the
angle of the mandible.
 Drain lymph from the head, face, and oral cavity.
2. Prescapular lymph nodes:
 Found in the region just behind the shoulder blades,
 Receive lymph from the front legs, chest wall, and shoulder
area.
3. Axillary lymph nodes: Situated in the armpit region,
 Receive lymph from the forelimbs and chest wall.
Major lymph nodes in animals…
4. Inguinal lymph nodes: Located in the groin area,
 Receive lymph from the hind limbs, genitalia, and lower abdomen.
5. Popliteal lymph nodes: These lymph nodes are situated in the region behind the knee joint,
 Receiving lymph from the hind limbs and lower leg.
6. Mesenteric lymph nodes: Found in the abdominal cavity
 Receive lymph from the intestines and associated abdominal
organs.
7. Medial iliac lymph nodes: Situated near the pelvic region,
 Receive lymph from the pelvic organs and hind limbs
Major lymph nodes in animals…
Indications for lymph node examination
 Lymph node examination in animals is often indicated in the
following situations:
A. Enlarged lymph nodes:
 The presence of enlarged lymph nodes, also known as
lymphadenopathy
 Enlarged lymph nodes may be detected during a physical
examination or noted by the pet owner.
 Lymphadenopathy can occur due to various reasons, including
o infections,
o inflammation,
o immune-mediated diseases, or
o cancerous processes.
Indications for lymph node examination…
B. Suspected infections:
 Lymph nodes play a crucial role in the immune response, and their
enlargement can be a sign of an ongoing infection.
 When an animal presents with clinical signs such as fever, lethargy,
loss of appetite, or localized signs of infection, examining the
corresponding lymph nodes can aid in diagnosing the specific
infectious agent involved.
C. Evaluation of cancer:
 Often performed when there is a suspicion of cancer or metastasis.
 Cancer cells can spread to the lymph nodes through the lymphatic
system, leading to the enlargement and alteration of the affected
lymph nodes.
 Examining the lymph nodes can help determine the presence of
cancerous cells and assess the extent of the disease.
Indications for lymph node examination…
D. Monitoring treatment response:
 Lymph node examination can be used to monitor the response to
treatment.
 By evaluating changes in theo size,
o consistency, or
effectiveness of therapeutic interventions.
o cellular composition
F. Investigating immune-mediated diseases:
 Some immune-mediated diseases can affect the lymph nodes,
leading to their enlargement or alteration.
 can help in diagnosing and managing these conditions, which may
include conditions such as
o Lymphadenitis,
Or
associated with immune-mediated disorders
o Lymphadenopathy
Collection and processing lymph node examination
The collection and processing of lymph node examination in
animals typically involve the following steps:
A. Physical examination:
 Before proceeding with lymph node examination, a thorough
physical examination of the animal is performed.
 This helps identify any enlarged or abnormal lymph nodes that
may require further evaluation.
B. Sedation or anesthesia:
 Depending on the animal's temperament and the invasiveness of
the procedure, sedation or anesthesia may be requiredo to ensure the safety and comfort of the animal during the
examination.
Collection and processing lymph node examination…
C. Lymph node palpation:
 carefully palpate (feel) the lymph nodes throughout the
animal's body.
 This allows them to assess the size, shape, consistency, and
mobility of the lymph nodes.
 Abnormal findings, such as enlarged or firm lymph nodes,
may indicate underlying disease or conditions.
D. Lymph node sampling:
 If abnormalities are detected during palpation, proceed with
lymph node sampling.
 This can be done througho Fine-needle aspiration (FNA),
o Core needle biopsy, or
o Surgical excision.
Collection and processing lymph node examination…
 The choice of sampling method depends on the suspected
underlying condition and the need for further evaluation.
o Fine-needle aspiration (FNA):
≠ It involves inserting a thin needle into the lymph node and
applying gentle suction to obtain a sample of cells.
≠ This procedure is minimally invasive and can be performed with
or without sedation.
o Core needle biopsy:
≠ It involves using a larger needle to obtain a small tissue sample
from the lymph node.
≠ This method provides a larger tissue sample for more extensive
evaluation.
o Surgical excision:
≠ In some cases, when a more thorough evaluation is required, the
entire lymph node or a portion of it may be surgically excised for
examination.
Collection and processing lymph node examination…
E. Sample processing:
 Once the lymph node sample is obtained,
 it is processed for further evaluation.
 This typically involves
o fixation,
o embedding in paraffin, and
o sectioning to obtain thin slices for microscopic examination.
F. Microscopic examination:
 Examined under a microscope by a trained veterinary pathologist.
They evaluate
o the cellular composition,
o architecture, and
o any abnormalities present.
Interpretation lymph node examination
A normal lymph node
• A normal lymph node in animals typically exhibits certain
characteristics:
Size:
 Can vary depending on the species and individual animal.
 Generally, they are small, ranging from a few millimeters to a few
centimeters in diameter.
 the size can change in response to various factors such as
inflammation or infection.
Shape:
 Oval or bean-shaped, although variations can occur.
Interpretation lymph node examination…
Consistency:
 has a soft and pliable consistency.
 It should not feel excessively firm, hard, or fluctuant.
Mobility:
 Usually mobile and can be gently moved within its surrounding
tissues.
 It should not be firmly attached or fixed to nearby structures.
Palpation:
 When palpating , it should not be excessively tender or painful.
 Apply Gentle pressure
Interpretation lymph node examination…
 Normal lymph node Cells present in normal lymph nodes include
 Small, medium, and large lymphocytes.
 Small lymphocytes in normal lymph node.
 Round cells smaller than neutrophils,
 Have a relatively large round nucleus, often with an indented or
cleft shape, dense chromatin,
 A thin rim of blue cytoplasm,
 They comprise roughly 75% to 95% of the cells.
 Medium lymphocytes normal lymph node
 Similar in size to neutrophils,
 Have more stippled chromatin than the small lymphocytes,
 have slightly more cytoplasm that is also a moderate blue,
 Comprise about 5% to 15% of the cells in a normal lymph node.
Interpretation lymph node examination…
 Large lymphocytes
 larger than neutrophils and
 have a nucleus with stippled or granular chromatin.
 make up about 5% to 10% of the cells in a normal lymph node
(Fig. A).
 Normal lymph nodes may also have few plasma cells,
macrophages, neutrophils, and eosinophils. There are also
usually fragments of lymphocyte cytoplasm, called
lymphoglandular bodies, in lymph node smears.
 These are small, round to irregular basophilic, sometimes
granular structures.
Interpretation lymph node examination…
Fig. A. Normal equine lymph node (Wright’s-Giemsa stain_
Lymph nodes disorders
A. Reactive lymph node
• A lymph node that has undergone changes in response to an
immune response or other stimuli.
• This can occur due to a wide range of factors, including
 infection, inflammation, trauma, or even certain medications.
 When lymph nodes are undergoing an immune response to an
antigen, the cell types are usually similar to those seen in the
normal lymph node, but there are often increased numbers of
plasma cells as well as increased proportions of medium and
large-sized lymphocytes.
 The percentage of small lymphocytes is relatively reduced, but
still greater than 50% of the cells.
Lymph nodes disorders…
Reactive lymph nodes can exhibit several characteristics:
• Enlargement:
 Often become enlarged, which is known as lymphadenopathy.
 The degree of enlargement can vary depending on the
o underlying cause, and
o the individual animal.
 Enlarged lymph nodes may be palpable during a physical
examination or may be detected through imaging techniques.
• Tenderness or pain:
 Reactive lymph nodes can be tender or painful to touch.
 Animals may show signs of discomfort or exhibit pain when the
affected lymph nodes are palpated.
 This tenderness is often a result of the inflammatory response
occurring within the lymph node.
Lymph nodes disorders…
• Presence of inflammatory cells:
 Microscopic examination of reactive lymph nodes may reveal an
increased number of inflammatory cells, such as
o lymphocytes,
o neutrophils, or
o macrophages.
• Change in consistency:
 Reactive lymph nodes may exhibit changes in consistency
compared to normal lymph nodes.
 They can become firm, rubbery, or even fluctuant, depending on
the underlying cause.
 The texture of reactive lymph nodes can provide valuable clues
to veterinarians when evaluating an animal's health.
Lymph nodes disorders…
Fig. 18. Reactive equine lymph node. Increased numbers of plasma cells and
medium-sized lymphocytes are present (Wright’s-Giemsa stain)
Lymph nodes disorders…
B. Lymphadenitis
• The inflammation of lymph nodes, which can occur due to
various reasons.
• Pathogens can enter the lymphatic system and cause
inflammation within the affected lymph nodes.
• Common examples include
 bacterial infections like abscesses,
 viral infections like feline leukemia virus (FeLV) or
 feline immunodeficiency virus (FIV), or
 fungal infections like blastomycosis.
Lymph nodes disorders…
 Increased numbers of inflammatory cells are seen in a lymph node
that is itself inflamed or is draining an area of inflammation.
 The type of inflammation is determined by the predominant
inflammatory cell type.
 A lymph node with a predominance of neutrophils is said to have
neutrophilic, suppurative, or purulent inflammation.
 If bacteria are seen, the inflammation is also termed ‘‘septic.’’ This
is common in cases of strangles, caused by Streptococcus equi,
that infect the lymph node, causing abscessation (Fig. C).
 Eosinophilic lymphadenitis, with or without mast cells, may occur
in hypersensitivity responses and parasitic and some fungal
infections (Fig. D).
Lymph nodes disorders…
Fig. C. Equine lymph node with normal cell population replaced by
degenerative neutrophils and Streptococcus equi bacteria, often in
chains (Wright’s-Giemsa stain)
Lymph nodes disorders…
Fig. D. Equine lymph node with eosinophilic lymphadenitis and mast
cells. This would be a typical reaction to hypersensitivity (Wright’sGiemsa stain).
Lymph nodes disorders
C. Lymphoma (lymphosarcoma)
• a type of cancer that affects the lymphatic system.
• It can occur in various species, including dogs, cats, and even
exotic animals.
• Lymphoma is easily recognized cytological when there is a
homogenous population of large lymphoblasts (Fig. D).
Lymph nodes disorders
Fig. D. Equine lymph node, lymphoblastic lymphoma. The
majority of cells are large (Wright’s-Giemsa stain)