Anatomical variations in Anatomage: Considerations for surface anatomy

Surface anatomy is a principal subdomain in human anatomy education1 that directly relates to everyday clinical practice. From traditional dissections and cross-sectional images, surface anatomy learning has evolved considerably with the advent of virtual dissection tables (e.g., Anatomage). Students can now “see through” the skin of the digital human model and visualize deeper anatomical structures, thereby relating them to surface landmarks.2 While there is no doubt that the virtual dissection tables benefit anatomy education in general,3-5 their potential in supporting accurate surface anatomy learning is underreported. Considering its increasing importance in the recent decades, the need to identify inconsistencies and to evaluate the reliability of teaching resources in the context of age, sex, and ethnicity is essential.6 To accomplish this, we attempted to review the four digital bodies in Anatomage (the Caucasian and Asian; male and female), assessing the location of the viscera against the surface landmarks that are generally depicted in anatomy textbooks (Gray's Anatomy 42e; Last's Anatomy, 12e; Moore's Anatomy, 9e). Surface projection of structures that are clinically examined from the anterior aspect of the body (such as the base of the appendix or apex of the heart) was plotted using standard dermal or skeletal landmarks. For those structures that are related to vertebral levels, the structure and the corresponding vertebra(e) were digitally isolated; the position of the organ was confirmed by drawing a horizontal line on the superior and inferior surfaces of the vertebra. Orientation of the body was standardized with the Anatomage presets of front-facing, back-facing, or side-facing views; measurements were done with the device's inbuilt ruler. We observed no one-for-all reference for surface anatomy in the Anatomage; after careful evaluation it was identified that the Caucasian female model showed lesser variations in the cervical, the Asian male in the thoracic, and the Asian female in the lumbar region. While the Caucasian male esophagus had an artifact extension starting at C4 thereby misguiding its surface marking, most other structures in the cervical region were similar in location to referenced texts. In the thoracic region, the tracheal bifurcation was seen at T4-5 in all models, the cardiac apex was variable (Figure 1), the thoracic duct did not follow the course as described in the textbooks in both males and was entirely absent in both female models. In the abdomen, the length of the spleen varied considerably (70–175 mm), the largest found in the Asian male, thereby affecting the organ's typical surface projection. The pylorus itself was not at L1 in three of the four bodies (Figure 2), thereby questioning its traditional nomenclature of transpyloric plane. All other major discrepancies found between the bodies, as compared to standard textbook surface anatomy details are listed in Table 1. 1T2 3T2-T3 2T3 2T4 1,3T4-5 1,2,3ICS 5 3Rib 5 or 6 2L4 1,3L4-5 1,2McBurney 3Rarely 1,2L1 3L1-2 1,2L1 3L1-L2 1,2L1 3L1-L2 Typically, no two individuals are perfectly identical in their internal anatomical features; normal anatomical variations will be encountered with any human interaction, be it in dissections, reading radiographic images, or examining or operating on a patient. So, variations in the digital human datasets reconstructed from post-mortem sectional images of donated human bodies are not surprising especially when it was not possible to standardize the positioning or control the physiological factors such as the depth of respiration.7 These distorted normal anatomical relationships and technical artifacts could be of concern to an undergraduate student who is used to standard textbook details and illustrations that are highly normalized to a typical, healthy male Caucasian. However, on a positive note, these differences might remind the learners about potential anatomical variations among patients that cannot be ignored while performing routine physical examination or minor medical procedures.8 Several medical institutions are constantly moving away from the use of real human specimens due to logistic reasons.9 This global issue of non-dissection-based anatomy learning can be effectively addressed by using radiological image datasets and ultrasound imaging that are affordable and available alternatives for examining real bodies. They are especially helpful to visualize more human anatomical information and to appreciate underlying variations at a larger scale10-12 in the curriculum. Anatomage is equipped with numerous radiology datasets that provide users a glimpse of different morphology, variations, and pathologies of the human body. However, regarding the volumetric datasets, only a few are loaded into each table, and the prevailing anatomical variations in fewer bodies would exaggerate their incidences. Therefore, though ubiquitous, Anatomage can only be considered a supplement to medical teaching13 and yet not the sole reference to learn surface anatomy owing to its limited volumetric datasets. We suggest that the manufacturers reflect on how the volumetric data for these digital human models was prepared and digitized, thereby providing a disclosure statement on the underlying variations and artifacts. To balance the real-life anatomical variations scenario with the expected learning outcomes of students, these variant details could be included in the menu, or a pop-up note that shows up when the structure of interest is navigated. While it is not necessary to digitally correct all the variations, the future versions of the table could consider adding a note on the “typical anatomy details” where possible, like the commonly used vertebral levels, or normal size of organs that are clinically relevant. For example, splenomegaly would promote a clinical discussion at the bedside, but a self-study learner using the Anatomage might not be able to appreciate the large spleen in the Asian male without being aware of the normal dimensions. Instead, they would benefit better if such variations were documented on the model, and the normal size provided as an outline or a pop-up reference note. Manufacturers could also consider digitally adding all missing organs (like the appendix or the thoracic duct in the Caucasian male) as they did for the cisterna chyli or lymph nodes in the Asian male, to promote consistency in the resources. In summary, the users should be aware of the considerable anatomical variations and pathologies between the digital bodies used in Anatomage. While each of the four bodies can be used to study a different anatomical region in more accurate detail, a comprehensive use of all the different bodies will benefit students the most. They should be reminded that learning from different bodies is also an opportunity to inform the potential variations between individuals that they would regularly encounter in their clinical practice. Vivek Perumal: Conceptualization; methodology; writing – review and editing; supervision. Kevin Jerrold Chan: Investigation; data curation; writing – original draft. Sreenivasulu Reddy Mogali: Methodology; writing – review and editing; supervision.