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). 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. Anatomical variations are mainly caused by

genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar worki ...

and may vary considerably between different

population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using ...

s. The rate of variation considerably differs between single organs, particularly in

muscle Skeletal muscles (commonly referred to as muscles) are Organ (biology), organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other ...

s. 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, and before the use of

X-ray X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...

technology, anatomic variations were mostly only found on cadaver studies. The use of imaging techniques have defined many such variations. Some variations are found in different species such as polydactyly, having more than the usual number of digits.

Variants of structures

Muscles

Kopsch gave a detailed listing of muscle variations. These included the absence of muscles; muscles that were doubled; muscles that were divided into two or more parts; an increase or decrease in the origin or insertion of the muscle; and the joining to adjacent organs. The palmaris longus muscle in the forearm is sometimes absent, as is the plantaris muscle in the leg. The sternalis muscle is a variant that lies in front of the pectoralis major and may show up on a mammogram.

Bones

Usually there are five

lumbar vertebra The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse ...

e but sometimes there are six, and sometimes there are four.

Joints

A discoid meniscus is a rare thickened lateral meniscus in the knee joint that can sometimes be swollen and painful.

Organs

The lungs are subject to anatomical variations.

Clinical significance

Accessory small bones called ''ossicles'' may be mistaken for avulsion fractures.

References

{{Reflist

External links

Atlas of human anatomical variations
Anatomy