An anatomical variation, anatomical variant, or anatomical variability is a presentation of body structure with morphological features different from those that are typically described in the majority of individuals. Anatomical variations are categorized into three types including morphometric (size or shape), consistency (present or absent), and spatial (proximal/distal or right/left).[1]
Variations are seen as normal in the sense that they are found consistently among different individuals, are mostly without symptoms, and are termed anatomical variations rather than abnormalities.[2]
Anatomical variations are mainly caused by genetics and may vary considerably between different populations. The rate of variation considerably differs between single organs, particularly in muscles.[2] Knowledge of anatomical variations is important in order to distinguish them from pathological conditions.
A very early paper published in 1898, presented anatomic variations to have a wide range and significance,[3] and before the use of X-ray technology, anatomic variations were mostly only found on cadaver studies. The use of imaging techniques have defined many such variations.[4]
Some variations are found in different species such as polydactyly, having more than the usual number of digits.