Approaching Cross-Sectional Images

When first encountering a cross-sectional image, whether a cadaveric specimen or a CT scan, orienting yourself to the image will consist of the following steps:

1.	First identify the general body region from which the image is derived, i.e. head, neck, thorax, abdomen, pelvis, perineum, or an extremity. The body region is usually readily evident based on the shape and size of the cross-section coupled to readily identifiable structures such as the brain in the head region or the lungs in the thorax region.
2.	Remember the proper orientation of the image as is conventional in CT radiology, i.e. anterior surface of the body is up, posterior surface is down, right side of the body is to your left, and left side of the body is to your right.
3.	Narrow the general body region down into smaller sub-regions or levels. This is accomplished by noting 1) the presence or absence of organs and 2) the shape and size of organs. For example, consider the two thoracic images below, one from the upper region of the thorax (image 1) and one from the lower region of the thorax (image 2).
	The lungs (L) in the more superior region of the thorax (image 1) comprise a smaller cross-sectional area than they do in the lower thorax (image 2). Note also the presence of the heart (H) and absence of the trachea (T) in the lower thorax (image 2); in contrast the upper thorax (image 1) lacks the heart but possesses the trachea. As your knowledge of gross anatomy grows, so will your ability to further subdivide body regions viewed in cross-section. For example, the trachea terminates by bifurcating into two primary bronchi at roughly the level of the 4th thoracic vertebra. Thus based on knowledge relating to the major respiratory passages, image 1 is at or above T4 while image 2 is below T4.
4.	Note the relative position and shape of individual organs present in the section. For example, the esophagus lies in the midline posterior to the trachea, the lungs occur laterally in pleural cavities, etc. Pathologies observed in CT scans are deviations from the expected cross-sectional position, size, and shape of organs or the presence of new, unexpected structures such as tumors.

You may view the cross-sectional images of the website either sequentially or non-sequentially. If you choose to go through the images of a region sequentially, we recommend the following order of viewing: