Normal variants of the musculoskeletal system are commonly encountered entities. Kohler was the first to seriously address this topic in his book, Borderlands of the Normal and Early Pathologic Findings in Skeletal Radiology, which was published in 1968 and was limited to the skeletal system (Kohler A, Zimmer EA. Borderlands of the normal and early pathologic findings in skeletal radiology. Thieme, New York, 1993). Theodore E. Keats, who passed away in 2012, expanded the concept of normal variation to all of the subspecialties of imaging with the publication in 1973 of his masterpiece, Atlas of Normal Roentgen Variants That May Simulate Disease (Keats TE. Atlas of normal roentgen variants that may simulate disease, 3rd ed. Year Book Medical, Chicago, 1984). As Dr. Keats so eloquently wrote in the Preface to the first edition, “The problem of normal variation is a lifelong one for the radiologist, and the mark of his experience is often his ability to recognize a wide range of these entities. Variation is inseparably related to the study of normal anatomy. In addition, the error of overdiagnosis of a normal variation as evidence of pathology may be more serious than omission and may lead to needless and harmful therapy.” Dr. Mark Anderson and Dr. Keats have kept this book “alive” for the future as Keats Atlas of Normal Roentgen Variants That May Simulate Disease, which is now in its ninth edition and published in 2013.