asymmetry
Meaning of asymmetry: Unevenness between two parts that should match, a finding whose weight depends entirely on where in the body it appears.
Definition of asymmetry
Asymmetry is a lack of correspondence between parts that would normally match, most often the left and right sides of the body. No one is perfectly even, so small differences are ordinary and mean nothing. What draws attention is asymmetry that is new, that is increasing, or that appears in a structure where the two sides are normally closely matched.
Where does it matter most?
| Setting | What asymmetry can indicate |
|---|---|
| Face | Sudden drooping on one side, from a nerve palsy or a stroke |
| Chest x-ray | A shadow on one side only, from pneumonia, fluid or a collapsed lobe |
| Mammogram | A density present on one side and not the other, which is investigated further |
| Skin lesion | An uneven outline, the first letter of the mole checklist |
| Limbs | Swelling of one leg, suggesting a clot or blocked lymph drainage |
| Pupils | Unequal size, which can reflect nerve or eye disease |
Why does the pattern of joint disease matter?
Few findings separate the arthritis types as efficiently as which joints are involved on each side. Rheumatoid arthritis is characteristically symmetrical: the same small joints of both hands, in a mirror image. The arthritis that accompanies psoriasis is characteristically asymmetrical, picking off a knee, a single toe or a few scattered fingers. Gout classically begins in one joint alone. None of these rules is absolute, but a clinician noting whether the pattern matches side to side is narrowing the list before any test is ordered.
When is it simply normal?
Almost always, in small amounts. Faces are subtly uneven, and photographs mirrored down the midline look unfamiliar for exactly that reason. Breasts commonly differ in size. Legs differ slightly in length. Hands differ in strength and size with handedness. Feet often take different shoe sizes. Testicles hang unevenly. The clinical question is not whether the two sides match perfectly but whether something has changed from a person's own previous state, and how quickly. That is why comparison with an earlier photograph, an old scan or the account of a long-standing difference frequently settles the matter more efficiently than any new test.
How is it described in a report?
Radiology and pathology reports use the word in a narrow sense. On a mammogram an asymmetry is a specific category of finding: tissue visible in one view or on one side without the shape or edges of a true mass. Terms such as focal asymmetry and developing asymmetry describe how confined it is and whether it is new compared with previous images, and that distinction drives what happens next.
Used in a sentence
Facial asymmetry was noted with drooping of the left corner of the mouth.
Good to know
Mild asymmetry is present in almost everyone, so it is a change from a person's own baseline, rather than a departure from perfect evenness, that carries clinical weight.
Word origin
Where “asymmetry” comes from
From the Greek a-, meaning without, and symmetria, meaning due proportion, itself built from syn, together, and metron, measure.