Big Lymph Nodes

Swollen Lymph Nodes in Pets: What They Mean and What Comes Next

You’re scratching behind your dog’s ears or rubbing under your cat’s jaw when you feel it: a firm, round lump that wasn’t there before. Or maybe your vet found it during a routine exam and mentioned that your pet’s lymph nodes are enlarged. Either way, it’s the kind of discovery that sends your mind racing. Enlarged lymph nodes (a condition called lymphadenopathy) can point to something as treatable as a local infection or as serious as cancer, and the only way to know is to investigate.

At Advanced Veterinary Medical Center, our diagnostic capabilities allow us to evaluate swollen lymph nodes thoroughly and determine what’s causing them. Whether the answer turns out to be a bacterial infection, an immune system reaction, or something that needs more advanced care, we’ll walk you through the findings and your options step by step. Request an appointment if you’ve noticed a lump or swelling on your pet, or if your vet has flagged a lymph node concern and you’d like a second opinion. We’re here to help.

What Do Lymph Nodes Actually Do?

Lymph nodes are small structures, roughly the size of a jelly bean when normal, distributed throughout your pet’s body. They filter lymph fluid, trap bacteria and other foreign invaders, and produce the white blood cells responsible for mounting an immune response. Think of them as surveillance stations: constantly monitoring the fluid draining from surrounding tissues, and ready to activate when something harmful shows up.

Where lymph nodes are located is something every pet owner should have a basic sense of. The major lymph node locations you can feel during a home check include:

• Mandibular nodes: under the jaw
• Prescapular nodes: in front of the shoulders
• Axillary nodes: in the armpits
• Inguinal nodes: in the groin
• Popliteal nodes: behind the knees

In cats, lymph nodes follow a similar pattern but tend to be smaller and harder to feel without practice. Lymph node checks are a routine part of every physical exam at Advanced Veterinary Medical Center, which is one reason staying current with wellness visits matters; our team establishes what’s normal for your individual pet, making meaningful changes easier to catch over time.

What Causes Lymph Nodes to Swell?

Lymphadenopathy is a clinical sign, not a diagnosis. It tells you the immune system is responding to something, but it doesn’t tell you what. The underlying cause determines everything: how serious the situation is, and how it gets treated.

The three main categories:

1. Infection or inflammation: the most common cause
2. Cancer: including lymphoma and metastatic spread from other tumors
3. Immune-mediated or other conditions: less common but worth ruling out

Infections and Inflammation: The Most Common Culprit

Bacterial, viral, fungal, and parasitic infections can all trigger lymph node swelling. Whether you see one enlarged node or many depends on how localized or widespread the problem is.

Localized infections cause regional swelling near the source:

• A dental abscess often enlarges the mandibular (jaw) nodes
• A paw wound may swell the popliteal node behind that knee
• An ear infection can affect nodes around the head and neck

Systemic infections affect multiple node groups at once. Common examples include:

• Lyme disease, spread by tick bites, causes swollen nodes alongside joint pain and fever
• Leptospirosis, a bacterial infection spread through contaminated water, can affect multiple organ systems
• Fungal disease is worth considering in California, where environmental fungi like coccidioides can affect pets who spend time outdoors

Dental disease is one of the most underrecognized triggers for reactive lymph nodes. Keeping up with regular dental care reduces the bacterial load that can affect the surrounding lymphatic system, which is another reason oral health matters beyond just the mouth.

Cancer: When Swollen Nodes Signal Something More Serious

Lymphoma is the most common cancer affecting lymph nodes in dogs and cats. Canine lymphoma typically appears as painless, firm, symmetrical swelling across multiple lymph node groups, and many dogs continue eating, playing, and acting normally in the early stages, which is part of why it’s sometimes caught late.

Common forms of lymphoma include:

• Multicentric: affects multiple node groups throughout the body; the most common form in dogs
• Alimentary: targets the GI tract
• Mediastinal: involves nodes in the chest
• Cutaneous or extranodal: affects skin or individual organs

Feline lymphoma behaves differently; in cats, the gastrointestinal form is more common than the multicentric type, and you often won’t feel enlarged lymph nodes as dramatically like dogs.

Lymphoma isn’t the only concern. Many types of cancer in pets can spread regionally through the lymphatic system, so evaluating nearby lymph nodes near any known mass is standard practice.

Other Causes Worth Ruling Out

Less common causes of lymph node swelling include:

• Immune-mediated conditions, where the immune system responds abnormally to its own tissues
• Drug or vaccine reactions, which typically resolve once the trigger is removed
• Lymphedema, a condition involving impaired lymphatic drainage that can mimic node enlargement

Because there are so many reasons for lymph nodes to enlarge, it’s critical to use diagnostics to work through these possibilities systematically so nothing gets overlooked.

How Do Vets Diagnose the Cause of Swollen Lymph Nodes?

Step 1: Physical Examination

The first step is always a thorough hands-on exam. Our team assesses each node group for:

• Size and shape
• Texture (soft, firm, or irregular)
• Symmetry (one side or both)
• Mobility (does it move freely, or is it fixed to surrounding tissue?)
• Tenderness

The pattern matters. Painless, firm, symmetrically enlarged nodes across multiple regions points in a very different direction than a single warm, tender node near a recent wound. We also look at the broader picture: fever, weight loss, decreased energy, skin changes, oral disease, or other organ involvement.

Step 2: Fine-Needle Aspiration (FNA)

Fine-needle aspiration is typically the next step, and it’s simpler than it sounds. A small needle is inserted into the node to collect a cellular sample, which is then evaluated under a microscope. It’s quick, minimally invasive, and usually done without sedation. For many cases, FNA provides a clear, fast answer.

Step 3: Biopsy (When Needed)

Sometimes cytology alone isn’t enough. A core needle or surgical biopsy may be recommended when:

• FNA results are unclear or inconclusive
• Small-cell lymphoma is suspected (a subtype that cytology can underdiagnose)
• Tissue architecture is needed for full classification

The decision between cytology and biopsy depends on what the initial sample shows and what additional information would change the treatment plan.

Step 4: Staging and Additional Testing

If lymphoma is suspected, staging determines how widely the disease has spread. This typically includes:

• Complete bloodwork and urinalysis
• Chest radiographs
• Abdominal ultrasound
• Bone marrow evaluation (in some cases)
• Flow cytometry or immunophenotyping to classify B-cell vs. T-cell subtypes

Advanced Veterinary Medical Center’s in-house diagnostics include laboratory services, digital radiography, and ultrasound, so staging can begin here without multiple referral trips.

Treatment Options: What Happens Next?

Treatment depends entirely on what’s causing the swelling. Here’s a general overview:

For lymphoma specifically, it’s important to understand the difference between remission (the disease becomes undetectable) and cure (the disease is gone permanently). Most dogs with lymphoma respond well to treatment initially and achieve meaningful additional time with good quality of life. Our surgery services support cases that require mass removal or biopsy in-house, and for families not pursuing aggressive treatment, palliative care focused on comfort is a fully supported option.

How to Monitor Your Pet’s Lymph Nodes at Home

You don’t need medical training to keep tabs on your pet’s lymph nodes between visits. A simple monthly check takes about two minutes and can catch changes early.

1. Find a calm moment: after a walk or during a quiet cuddle session works well
2. Use your fingertips to gently feel along the jaw, in front of the shoulders, in the armpits, at the groin, and behind the knees
3. Note anything that feels firm, round, or larger than usual, especially if it wasn’t there last month
4. Check both sides: symmetry (or lack of it) is useful information
5. Contact us if something has changed: don’t wait for the next scheduled visit if a node seems noticeably different

Staying current with wellness care gives our team consistent physical exam data over time, which makes trend-spotting much more reliable than a single snapshot.

Frequently Asked Questions

Can a swollen lymph node go away on its own?

Sometimes. A node responding to a minor, self-limiting infection may return to normal as that infection clears. However, lymph nodes that stay enlarged beyond two to three weeks, continue growing, or appear alongside other symptoms like lethargy or weight loss should be evaluated rather than watched indefinitely.

Is my pet in pain if their lymph nodes are swollen?

Not necessarily. Reactive nodes from infection are often tender, and pets may pull away when you touch them. Lymphoma nodes, on the other hand, are typically painless, which is one reason they can go unnoticed for a while. The absence of pain is not reassurance that the cause is minor.

How quickly does this need to be addressed?

If your pet is acutely unwell: feverish, not eating, or having trouble breathing alongside the swelling, come in promptly or use our urgent care during open hours. For persistent swelling without acute illness, getting in within a week is a reasonable timeline.

Is lymphoma curable?

For most dogs and cats, the realistic goal is remission rather than cure. Many patients achieve meaningful additional time with excellent quality of life during treatment. We’ll give you an honest picture of what the process typically looks like for your specific pet.

Getting to an Answer Together

Finding a swollen lymph node is worth taking seriously, but it doesn’t have to send you spiraling. Many causes are entirely treatable, and even serious diagnoses like lymphoma come with real options when they’re caught and addressed thoughtfully. At Advanced Veterinary Medical Center, we combine advanced diagnostics with genuine care for both you and your pet, and we don’t stop at “good” when there’s a chance for something better.

If something is concerning you, contact us or request an appointment and let’s figure it out together.