A nodule is a small, abnormal clump of tissue that can form in almost any part of your body. In medical terms, “nodule” typically refers to a rounded growth measuring up to about 3 centimeters (roughly the size of a grape). Anything larger is usually called a mass. Nodules show up most commonly in the lungs, thyroid, skin, adrenal glands, and vocal cords, and the vast majority turn out to be harmless.
How Size Defines a Nodule
Size is the single most important feature that separates a nodule from other types of growths. In the lungs, for example, any rounded spot on an imaging scan that measures 3 cm or less counts as a nodule. Anything smaller than 3 mm is called a micronodule, and anything larger than 3 cm is classified as a mass, which gets a more urgent workup. On the skin, the term usually applies to firm lumps that extend deeper than the surface layer, distinguishing them from smaller, shallower bumps.
These size cutoffs matter because they directly influence what happens next. Smaller nodules are far less likely to be dangerous, and many need nothing more than a follow-up scan months later to confirm they haven’t changed. Larger ones may require a biopsy or additional imaging sooner.
Lung Nodules
Lung nodules are among the most commonly discovered type, often found by accident on a chest CT scan done for an unrelated reason. At least 95% of all pulmonary nodules turn out to be benign. Most are granulomas (small areas of inflammation from a past infection) or tiny lymph nodes within the lung tissue.
The chance that a lung nodule is cancerous rises with its size. For nodules smaller than 6 mm, the probability of malignancy is less than 1%. For those between 6 and 8 mm, the risk is roughly 1% to 2%. Nodules that appear partly hazy on a scan (called ground-glass nodules), persist beyond three months, and measure larger than 10 mm carry a higher risk, between 10% and 50%.
Doctors also look at shape and texture. A smooth, round nodule with dense calcification in the center almost always signals old scar tissue from a healed infection. A nodule with spiky, irregular edges or one that distorts the blood vessels around it raises more concern for malignancy. Amorphous, patchy calcium deposits within a nodule are also more suspicious than the uniform pattern seen in benign granulomas.
How Lung Nodules Are Monitored
For solid nodules under 8 mm, the standard approach is watchful waiting with repeat low-dose CT scans. Depending on the nodule’s size and your individual risk factors (smoking history, family history, occupational exposures), the first follow-up scan may come anywhere from 3 to 12 months after discovery. Some guidelines recommend up to three scans over roughly two years to track any changes.
Growth rate is the key metric. Doctors measure how quickly a nodule’s volume doubles. A doubling time longer than 600 days suggests a benign process. A doubling time under 400 days is more suspicious and typically triggers further investigation, such as a PET scan or biopsy. Nodules larger than 8 mm at discovery often skip the waiting period entirely and go straight to advanced imaging or tissue sampling.
Thyroid Nodules
Thyroid nodules are extremely common. Ultrasound can detect them in up to 68% of the general population, meaning most people walking around have at least one without knowing it. The overwhelming majority are benign and never cause symptoms.
Because they’re so prevalent, not every thyroid nodule needs a biopsy. As a general rule, nodules smaller than 1 cm are left alone regardless of how they look on ultrasound. For nodules 1 cm or larger, the decision depends on their appearance. Features that raise suspicion include a solid, dark (hypoechoic) texture, irregular borders, tiny calcium specks (microcalcifications), and a shape that’s taller than it is wide. Nodules that look spongy or are mostly fluid-filled carry very low cancer risk, and biopsy is usually only considered once they reach 2 cm or larger.
When a biopsy is needed, it’s done with a thin needle guided by ultrasound. The procedure takes only a few minutes and is performed in an office setting. Most people describe it as mild pressure with brief, sharp discomfort.
Skin and Subcutaneous Nodules
Nodules that form in or under the skin are the type you’re most likely to find on your own. They feel like firm lumps beneath the surface, and they can range from pea-sized to a few centimeters across.
The most common culprits are lipomas, which are soft, painless collections of fat cells just under the skin. They move slightly when pressed and are almost always harmless. Epidermoid cysts are another frequent cause. These are firm, round lumps that form when skin cells get trapped below the surface and slowly accumulate. They can become tender if they get inflamed or infected but are otherwise benign.
Less commonly, subcutaneous nodules can signal a systemic condition. People with rheumatoid arthritis sometimes develop firm nodules near joints, particularly the elbows and fingers. These nodules are painless and tend to come and go with disease activity. Any new lump under the skin that’s growing, feels hard and fixed in place, or is painless but rapidly enlarging warrants evaluation.
Adrenal Nodules
Adrenal nodules, often called adrenal incidentalomas, are usually discovered on abdominal CT or MRI scans performed for other reasons. About 80% turn out to be non-functional benign growths, meaning they don’t produce excess hormones and don’t cause any symptoms.
The remaining 12% to 23% can be hormonally active, quietly overproducing stress hormones, adrenaline-related compounds, or the hormone that regulates blood pressure and potassium. Because this overproduction can affect your heart, blood pressure, and metabolism without obvious symptoms, every adrenal nodule gets a basic hormonal screening. This typically involves an overnight test to check cortisol levels, a urine or blood test for adrenaline-related hormones, and, if you have high blood pressure or low potassium, a test for aldosterone. If the results are normal and the nodule is small, periodic imaging is usually all that’s needed.
Vocal Cord Nodules
Vocal cord nodules form on the edges of the vocal cords from repeated friction, usually caused by overuse or misuse of the voice. They’re sometimes called singer’s nodes or screamer’s nodes. Teachers, coaches, singers, and anyone who regularly strains their voice is at higher risk.
The hallmark symptom is a hoarse, raspy, or breathy voice that doesn’t seem to recover with rest. You may also notice your voice tiring more quickly or breaking at certain pitches. The severity depends on the nodule’s size and how much it prevents the vocal cords from closing and vibrating together properly.
Treatment is almost always conservative. Voice therapy with a speech-language pathologist is the first-line approach, focusing on techniques to reduce strain and let the nodules heal. Surgery is reserved for nodules that don’t respond to therapy.
How Nodules Are Biopsied
When a nodule needs closer examination, doctors take a tissue sample using one of two main methods. Fine-needle aspiration uses a very thin needle to suction out a small cluster of cells. It works well for fluid-filled or cystic nodules, superficial lumps, and thyroid nodules. It’s quick, minimally painful, and rarely causes complications.
Core-needle biopsy uses a slightly larger needle to extract a small cylinder of tissue, preserving the structure of the cells. This provides more information than a fine-needle sample and is preferred for solid masses where the internal architecture matters for diagnosis. Studies comparing the two methods show core-needle biopsy generally achieves higher accuracy, with sensitivity rates of 85% to 100% compared to 35% to 95% for fine-needle aspiration. The tradeoff is a slightly more involved procedure, though it’s still performed with local numbing and takes only minutes.
Your doctor’s choice between the two depends on the nodule’s location, size, and what they suspect it might be. In many cases, if a fine-needle sample comes back inconclusive, a core-needle biopsy follows.