Clinical Anatomy 00:00–00 (2015)

Letter to the Editor Surface Anatomy of the Trunk Based on CT Data To the Editor, When I first read the series of papers by S. Ali Mirjalili and colleagues in the October 2012 issue (vol. 25, no. 7) of Clinical Anatomy, I said to myself “What a clever idea to reassess our teaching of surface anatomy using data from CT scans of living persons.” Since these papers reported a few findings that differed from accepted knowledge, I attempted to replicate such data by analyzing CT scans of the trunk in 33 men and 33 women having undergone this procedure to rule out injury or illness, and found to have none. In their introductory paper, Mirjalili and Stringer (p. 816) noted “Individual variation is such that surface anatomy is not and never should be an exact science.” Indeed, the data I gathered on my 66 subjects impressed me most by demonstrating a high level of individual variation. I even began to wonder whether or not we should be asking students to memorize surface anatomy correlations that are so often violated. But that is a topic for another discussion. What I want to address in this letter is the thought that crossed my mind that some of the variation I observed was due to differences between subjects in the level of their inspiratory effort while the CT was being taken. At Stony Brook, as is commonly done elsewhere, patients undergoing a CT of the trunk are asked to take a breath and hold it. Clearly, some individuals will take a deep breath, and others one not so deep. In order to test the effect of this factor on positions of structures relative to the rib cage and vertebral column, I identified 10 additional patients who had undergone five or more trunk CTs within a year. These patients were often quite ill (hence the frequent scans) and would in no way be suitable for use in a normal study of surface anatomy. But that was not the purpose of my effort. It was simply to see what variation occurred between different scans of the same person. Looking at sagittal reformats of the scans, I used a lower position of the dome of the diaphragm relative to the xiphisternal joint, and a greater inferior angle between the first rib and the T1/T2 disc, to identify instances in which these sick patients took deep breaths or shallow

breaths. As should have been expected, I observed that the sternum moves superiorly relative to the vertebral column during a deep inspiration, causing the vertebral levels corresponding to the jugular notch, sternal angle, and xiphisternal joint to rise, in some instances by more than an entire vertebra. In four of these 10 patients, I also looked at soft tissue projections onto the rib cage and vertebral column. Again as I should have expected, soft tissue structures projected to lower anterior ribs and intercostal spaces when the patient’s breath was deeper. Conversely, although the position of softtissue structures relative to the vertebral column differed somewhat from scan to scan of any individual patient, I was surprised to find that for many structures the differences were not consistently related to depth of inspiration. My conclusion is that trunk CTs taken on subjects instructed to take a breath and hold it will give different surface anatomical relationships than actually occur in that same person during quiet respiration. Also, it is worth noting that the manner in which a pillow is placed behind the subject’s head and shoulders can significantly alter the plane of the vertebral column relative to the plane of the scanner (a fact I attempted to correct for when doing my analyses). Finally, since patients are routinely asked to keep their arms elevated during a trunk CT, the high angle (40 degrees) between the long axis of the clavicle and a transverse plane means that the midclavicular line will lie 1–2 cms more medially than when the arms are at the side. I strongly encourage other interested anatomists to see if they can verify or refute my observations. Until more information is available, one should be judicious about changing trunk surface anatomy teaching based on CT scans.

Jack Stern* Department of Anatomical Sciences School of Medicine, Stony Brook University

*Correspondence to: Jack Stern, Department of Anatomical Sciences, School of Medicine, Stony Brook University, Stony Brook, New York 11794-8081. E-mail: [email protected] Received 2 December 2014; Accepted 3 January 2015 Published online in Wiley Online Library (wileyonlinelibrary. com). DOI: 10.1002/ca.22511

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2015 Wiley Periodicals, Inc.

Surface anatomy of the trunk based on CT data.

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