OVERVIEW AND BASIC CONCEPTS PART-7
ANATOMICAL VARIATIONS
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Structural variation occurs to differing degrees of severity ranging from normal to incompatible with life. Anatomical variation usually has no effect on normal function.
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Anatomical variations are often discovered during imaging or surgical procedures, at autopsy, or during anatomical study in individuals who had no awareness of or adverse effects from the variation.
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A congenital anomaly or birth defect is a variation often evident at birth or soon afterward due to aberrant form or function. Birth defects also can range from mild to severe. Although many birth defects can be treated, others are fatal.
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It is important to know how such variations and anomalies may influence physical examinations, diagnosis, and treatment.Anatomy textbooks describe (initially, at least) the structure of the body as it is most often observed in people, that is, the most common pattern.
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However, occasionally a particular structure demonstrates so much variation within the normal range that the most common pattern is found less than half the time! Beginning students are frequently frustrated because the bodies they are examining or dissecting do not conform to the atlas or text they are using (Bergman et al., 1988).
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Often, students ignore the variations or inadvertently damage them by attempting to produce conformity. However, you should expect anatomical variations when you dissect or inspect prosected specimens.
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In a random group of people, individuals obviously differ superficially from each other in physical appearance. The bones of the skeleton vary not only in size but more subtly in their basic shape and in lesser details of surface structure.
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A wide variation is found in the size, shape, and form of the attachments of muscles. Similarly, considerable variation exists in the patterns of branching of neurovascular structures (veins, arteries, and nerves). Veins demonstrate the greatest degree of variation and nerve the least. Individual variation must be considered in physical examination, diagnosis, and treatment.
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Most descriptions in this text assume a normal range of variation. However, the frequency of variation often differs among human groups, and variations collected in one population may not apply to members of another population.
10.Some variations, such as those occurring in the origin and course of the cystic artery to the gallbladder, are clinically significant. Being aware of these variations is essential in medical practice, particularly surgery.
11.Clinically significant variations are described in clinical correlation (blue) boxes identified with an Anatomical Variation icon (at left).Humans exhibit considerable genetic variation beyond sexual and racial differences, such as polydactyly (extra digits).
12.Approximately 3% of newborns show one or more significant birth defects. Other defects (e.g., atresia or blockage of the intestine) are not detected until symptoms occur.
13.Discovering anatomical variations in cadavers is actually one of the many benefits of firsthand dissection, because it enables students to develop an awareness of the occurrence of variations and a sense of their frequency.