A firm lump of 5 to 15 mm under the jaw, in front of the shoulder, or behind the knee is a lymph node until proven otherwise, and most of them are reactive rather than cancerous. Size alone does not sort it: a 12 mm node that shrinks over 14 days is a different animal from a 12 mm node that doubles in 10. Measure with calipers, write the number, and let the trend decide.
Four node locations and their normal sizes
You can feel 4 pairs on a cat without imaging, and each one drains a specific area, which is why the location of the lump is the first clue.
| Node | Where to feel | Normal length | Drains | Common local cause |
|---|---|---|---|---|
| Submandibular | Under the jaw, 1-2 cm back from the chin | 5-10 mm | Teeth, gums, lips, nose | Dental disease, mouth ulcer |
| Prescapular | In front of the shoulder, under the 1st rib edge | 5-10 mm | Front leg, chest wall, neck | Bite abscess, claw infection |
| Axillary | Behind the 3rd rib, deep under the front leg | 3-8 mm | Front leg, mammary tissue | Injection site, mastitis |
| Popliteal | Behind the knee, in the 1 cm fat pad | 5-10 mm | Hind leg, paw, tail base | Paw wound, cat bite |
A node over 15 mm in any of those 4 spots is enlarged by definition. A node that is 8 mm but rock hard, fixed to the skin, or painful is also abnormal, so size is 1 of 4 criteria, not the whole test.
14 days: the numbers that separate the 3 outcomes
| Day | Length (mm) | Consistency | Other nodes | Action |
|---|---|---|---|---|
| 0 | 8-20 | Soft to firm, movable | 1 enlarged | Measure, photo, dental check |
| 3 | 7-18 | Firm, still movable | 1-2 enlarged | Re-measure, note appetite |
| 7 | 6-16 | Firm or softening | 1-3 enlarged | Book if 15 mm or growing |
| 14 | 5-12 | Soft, shrinking | 1, back to normal | Close the log if smaller |
Three trajectories matter. Shrinking by 30% or more over 14 days usually means a reactive node and needs nothing further. Unchanged at 10 to 15 mm for 14 days with no other sign is a gray zone that earns 1 fine needle aspirate. Growing by 50% or more, or any node over 25 mm at any point, skips the calendar and goes straight to testing.
Three causes behind a single enlarged node
1. Reactive hyperplasia. The node is doing its job against infection nearby: dental disease in 1 to 3 teeth, an ear infection, a bite abscess, or a healing wound on the paw. This is the commonest cause in cats under 8 years old, the node is usually tender and movable, and it shrinks within 14 to 28 days once the source is treated.
2. Lymphoma and other neoplasia. A node that is firm, rubbery, painless, and grows over 10 to 21 days is the classic pattern, and it can appear in a cat that is still eating. Cats with lymphoma often have 1 node 3 times the size of the others before any general sign shows, which is why 1 aspirate at week 2 is worth more than 3 more weeks of watching.
3. Infection the cat cannot clear. Fungal disease, mycobacteria, FeLV, FIV, and bartonella can all produce a single stubborn node, sometimes with a 0.5 to 1 cm draining tract that will not heal. Indoor cats are not exempt, and a cat adopted as an adult has an unknown history for the first 2 to 3 years.
Check 1: fine needle aspirate
A 22 to 25 gauge needle, 3 to 5 passes, 2 to 4 slides, and no sedation in most cats. It answers 1 question: what cells are in the node. A reactive node shows a mixed population with plasma cells and no dominant type; lymphoma shows a monomorphic sheet of large cells; infection shows neutrophils and organisms. Cost is commonly 60 to 150 USD with cytology, results in 1 to 3 days, and a non-diagnostic sample happens in about 1 of 5 cases, which then needs a core biopsy under sedation.
Check 2: FeLV and FIV test plus a blood panel
The second test is a 3-in-1 rapid test for FeLV antigen and FIV antibody, plus a CBC and chemistry panel from the same blood draw. It answers the question the aspirate cannot: is there a systemic cause and is the cat safe to treat. Expect 40 to 120 USD, results in 15 minutes for the rapid test and 1 to 2 days for the panel. A cat with a 15 mm node, a normal aspirate, and a negative retrovirus test at day 14 usually needs nothing more than a recheck in 30 days.
Four records for the 14 days
Record 1: length in millimeters at day 0, 3, 7, and 14, measured at the widest point with the same calipers. Record 2: consistency on a 3-point scale (soft, firm, hard) plus whether it moves under the skin. Record 3: the other 7 palpable nodes, since 1 enlarged node and 3 enlarged nodes are different diseases. Record 4: appetite in grams eaten per day, weight every 7 days, and any new sneezing, eye discharge, or limping. Four records turn a vague story into a 10-minute exam.
When the lump is not a node
A swelling on a paw that is between the toes, or a lump that is fixed to the skin and has a pore, is more likely an abscess, cyst, or tumor than a node, and the pattern is described in a swollen paw. Nodes that enlarge in 3 or more places at once point toward systemic disease rather than a local one, and the general map is in swollen lymph nodes. If the cat chewed a plant or a household product in the 72 hours before the swelling, run the exposure list in the toxicology tool before the visit.
The vet line: 5 findings that end the 14 days early
Book now for a node over 25 mm, growth of 50% or more inside 7 days, a node fixed to skin or deep tissue, 3 or more enlarged nodes, or any node with fever above 39.5 C or weight loss of 5% in 30 days. Bring the log, the photos, and the millimeter numbers. The visit itself takes 15 to 20 minutes, and the 2 tests together usually cost 100 to 270 USD, which is the price of not watching a lymphoma for another month.
Five steps for day 1
- Measure the lump at its widest point in millimeters and photograph it beside a ruler.
- Feel all 8 node sites and note which ones you can find.
- Open the mouth and look at the teeth and gums on the same side.
- Start a daily note of grams eaten and any new sneeze or limp.
- Put day 14 in the calendar with the numbers you must compare.
Terms mentioned in this article
Frequently asked
Does a swollen lymph node mean cancer?
Most single enlarged nodes in cats are reactive, meaning they are responding to infection nearby such as dental disease or a bite wound, and they shrink within 14 to 28 days once the source is treated. Lymphoma is the main cancer concern and it usually shows a firm, painless node that grows over 10 to 21 days. A fine needle aspirate at week 2 separates the two in 1 to 3 days.
How big is too big for a cat lymph node?
Over 15 mm in the submandibular, prescapular, or popliteal spot is enlarged, and over 25 mm at any point skips observation and goes to testing. Size is only 1 of 4 criteria: a node that is rock hard, fixed to the skin, painful, or joined by 2 or more other enlarged nodes is abnormal at 8 to 10 mm as well, so measure and feel, not just measure.
What do the 2 tests actually cost and show?
A fine needle aspirate with cytology commonly runs 60 to 150 USD and reports in 1 to 3 days, showing which cells fill the node. The FeLV and FIV rapid test plus a CBC and chemistry panel runs about 40 to 120 USD, with the rapid result in 15 minutes, and shows whether a retrovirus or systemic disease is driving the swelling. Together they cost 100 to 270 USD.