General medical words
What Do Bilateral and Unilateral Mean?
Bilateral and unilateral · say it: by-LAT-er-ul / yoo-nih-LAT-er-ulAlso written: bilateral, unilateral, bibasal, both sides, one side
Short answer
Bilateral means on both sides of the body and unilateral means on one side only, and reports usually also name the side.
What it means
Many body parts come in pairs or have a left and right side, such as the lungs, kidneys, breasts, eyes, knees and hips. Bilateral means a finding affects both sides. Unilateral means it affects only one. When a finding is unilateral, the report normally says which side, left or right.
A report might say "bilateral pleural effusions" (fluid around both lungs) or "unilateral leg swelling" (one leg). Related words include "bibasal" (at the bottom of both lungs) and "contralateral" (on the opposite side). Writers use these words so the next doctor knows at once whether to look at one side or both, and the word often appears in the name of the scan or operation itself.
These words describe location only. They do not by themselves say whether something is more or less serious. Some conditions are expected to appear on both sides, and others are usually one-sided, so doctors read the word together with the finding it describes.
Where you may see it
- Scan reports, such as "bilateral renal cysts" on an ultrasound
- Hospital notes and examination findings, such as "bilateral ankle swelling"
- Procedure names, such as "bilateral mammogram" or "bilateral knee replacement"
- Chest X-ray reports, such as "bibasal atelectasis"
📄 How it looks on a report
Bilateral renal cysts, the largest on the left measuring 2 cm.
🙅 What it does not mean
- Bilateral does not mean twice as serious. It describes where, not how bad, and many bilateral findings are common and harmless.
- Unilateral does not mean less important. Some one-sided findings, such as swelling in just one leg, need more attention than the same finding on both sides.
- A "bilateral mammogram" is just a mammogram of both breasts, not a sign that something was found.
🗒️ Questions to ask your doctor
🧾 Reports where you will see “Bilateral and unilateral”
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💊 Medicines whose labels mention “Bilateral and unilateral”
Plain-English explanations of each medicine, from its official FDA label.
- Amitriptyline
An antidepressant of the tricyclic type
- Amlodipine
a calcium channel blocker, a type of medicine that relaxes blood vessels
- Artemether and Lumefantrine
an antimalarial medicine, which is a fixed combination of two blood-stage antimalarial ingredients (artemether, an artemisinin derivative, and lumefantrine)
- Atorvastatin
a statin, a cholesterol-lowering medicine of the HMG-CoA reductase inhibitor type
- Bisoprolol Fumarate
a beta-blocker, which the label describes as a synthetic, beta 1-selective (cardioselective) adrenoceptor blocking agent
- Bupropion Hydrochloride
an aminoketone antidepressant, a type of medicine used to treat depression
- Ciprofloxacin
a fluoroquinolone antibacterial medicine
- Citalopram
a selective serotonin reuptake inhibitor (SSRI), a type of antidepressant medicine
- Clopidogrel
A platelet inhibitor of the P2Y12 type (a thienopyridine). It is a blood thinner that keeps platelets from sticking together.
- Divalproex Sodium
An anti-epileptic (anti-seizure) drug of the valproate type. The label also uses it to treat manic episodes of bipolar disorder and to prevent migraine headaches.
🔗 Read more from trusted sources
- “Bilateral and unilateral” on MedlinePlus ↗
US National Library of Medicine
- NCI Dictionary definition ↗
US National Cancer Institute: “bilateral”
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More words: general medical words
General information about a medical word, not advice about your own results. Ask the clinician who ordered the test what it means for you.