A normal variant on X-ray is an unusual appearance of normal anatomy. The significance of this is that this may mimic abnormality and result in unnecessary testing and treatment. Normal variants are numerous throughout the body. There is even a large book with hundreds of pages dedicated to this subject in radiology which many radiology doctors use in their practice.
Normal variants can involve blood vessels, bones, the urinary tract or just about any part of the anatomy. These normal variants can mimic abnormality, especially on X-rays. Since X-rays are composed of shadows based on how much they block X-rays, the appearance can be particularly confusing on X-ray since the detail is not as good as CT or MRI.
A normal variant such as a blood vessel crossing a bone can mimic a broken bone. In the chest, a tumor can be mimicked by calcifications in the cartilage portion of the rib, especially up high by the first rib. A fold of skin overlying the chest, can look like a collapsed lung. An elongated liver that comes down to the pelvis can look like a mass on X-ray. There are numerous other examples that radiologists are trained to recognize.
The radiologist may mention the term normal variant in the report or simply ignore it as a normal variant. There are certain times when the radiologist may not be completely sure. In these cases, a CT or MRI may be needed. This will usually make it clear. For example, an MRI of the wrist can be obtained to see if a lucent line crossing a bone is a blood vessel or break in the bone. A fold of skin overlying the chest can be evaluated with a chest CT if there is concern for a collapsed lung.
The doctor who ordered the test may also use his findings on the physical exam to determine if a normal variant may represent abnormality. For example, if there is a faint line crossing a wrist bone, your doctor can see if it hurts over that bone. A broken bone will hurt whereas a blood vessel crossing a bone will not. A collapsed lung will usually result in some symptoms of breathlessness or chest pain. If the radiologist suggests a possible collapsed lung because of a skin fold, and you came in for a cough and fever, then this does not fit and will likely be attributed to a skin fold.
Therefore, normal variants are not of any concern and will usually be recognized by the radiologist and mentioned as either normal or ignored completely since we usually don’t describe normal anatomy. Normal variants on X-ray may pose some confusion at times, and more testing may be needed to clear it up. Your doctor will also use their findings to see if a potential abnormality is truly an abnormality.