Anatomy of the abdominal viscera (Proceedings)

This presentation will review the abdominal viscera: what they are, where they suppose reside, where they may reside and how to evaluate them with imaging-radiology, CT, ultrasound.

Anatomy

Anatomy (from the Greek ἀvατομíα anatomia, from ἀvατέμvειν ana: separate, apart from, and temnein, to cut up, cut open) is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includeshuman anatomy, animal anatomy (zootomy) and plant anatomy (phytotomy). In some of its facets anatomy is closely related to embryology, comparative anatomy/ and comparative embryology,[1] through common roots in evolution.

Anatomy is subdivided into gross anatomy (or macroscopic anatomy) and microscopic anatomy.[1] Gross anatomy (also called topographical anatomy, regional anatomy, or anthropotomy) is the study of anatomical structures that can be seen by unaided vision with the naked eye.[1] Microscopic anatomy is the study of minute anatomical structures assisted with microscopes, which includes histology (the study of the organization of tissues),[1] and cytology (the study of cells).

The history of anatomy has been characterized, over time, by a continually developing understanding of the functions of organs and structures in the body. Methods have also improved dramatically, advancing from examination of animals animals through dissection of cadavers (dead human bodies) to technologically complex techniques developed in the 20th century including X-ray, ultrasound, and MRI imaging.

Anatomy should not be confused with anatomical pathology (also called morbid anatomy or histopathology), which is the study of the gross and microscopic appearances of diseased organs. (From Wikipedia, the free encyclopedia)

In anatomy, a viscus (pronounced /'v•sk•s/) is an internal organ, and viscera is the plural form.[1][2] The viscera, when removed from a butchered animal, are known collectively as offal. Internal organs are also known as "innards", or less formally, "guts" (which may also refer to the gastrointestinal tract).

The adjective visceral, also splanchnic,[3] is used for anything pertaining to the internal organs. Historically, viscera of animals were examined by Roman pagan priests like the haruspices or the augurs in order to divine the future by their shape, dimensions or other factors. This practice remains an important ritual in some remote, tribal societies.

What are they:

     • Diaphragm

     • Greater omentum

     • Liver

     • Gallbladder

     • Bile ducts

     • Spleen

     • Kidneys

     • Ureters

     • Urinary bladder

     • Urethra

     • Prostate

     • Ovaries

     • Uterus

     • Cervix

     • Adrenal Glands

     • Stomach

     • Small intestine

     • Large intestine

     • Mesenteric lymph nodes

     • Sacral, hypogastric and medial iliac lymph nodes

     • Vessels-arteries, veins, lymphatics

Things I have learned:

Radiology:

     • This technology uses ionizing radiation and thus it can potentially harm the patient.

     • The conventional radiographic study allows for the overall appreciation of opacity, size, shape, position and contour of many, but not all, of the abdominal viscera.

     • It is a cost-effective method to obtain an "overall" appreciation of many organs.

     • What can be visualized in a survey radiographic study is very dependent on image quality, the patient's composition and the variations in opacity amongst the tissues being imaged.

     • There needs to be approximately 35% difference between two adjacent soft tissue structures in the absorption/transmission of x-rays with conventional radiology to be able to appreciate these structures as distinct entities.

     • Four opacities can be visualized radiographically-gases, fat, soft tissues and bone.

     • All of the soft tissues are approximately the same opacity; as such, adjacent soft tissues cannot be distinguished distinctly in the conventional radiographic study.

     • Contrast media-gas, barium and iodinated water soluble media are used to change the opacity of tissues; thus allowing them to be visualized using this imaging method.

     • The imaging detail obtainable in the conventional radiographic study is hampered by superimposition of structures.

     • With digital technology, the image can be manipulated electrically-sometimes for better and sometimes for worst.

CT Imaging

     • The CT technology uses a large amount of ionizing radiation and thus it is believed to induce cancer in some patients.

     • The CT study allows for better appreciation of abdominal detail than conventional radiology.

     • The enhanced detail occurs because of better resolution between soft tissue structures-there only needs to be approximately a 5% difference in the absorption/transmission of x-rays with CT imaging to be able to appreciate between two adjacent soft tissue structures.

     • The enhanced detail occurs because of better resolution between tissues of different opacities.

     • The enhanced detail occurs because of less superimposition of the structures being imaged.

     • The cost of doing the study is a limiting factor.

     • The image can be manipulated electrically-usually for the better but periodically for the worst.

     • Contrast media-gas, barium and iodinated water soluble media are used to change opacity of tissues; thus allowing them to be better visualized using this imaging method.

Ultrasound:

     • This technology does not use ionizing radiation.

     • The ultrasound study is a cost-effective imaging method to assess the composition of "soft tissues".

     • The ultrasound study is hampered by gas, bone, metal and barium.

     • Not all soft tissue structures are easily defined-the right adrenal gland, ureters and pancreas can be very difficult to visualize.

     • The imaging quality is very user dependent.

     • The imaging quality is often equipment dependent.

     • The imaging quality may be patient dependent.

     • In additional to defining size, shape, position and contour, the ultrasound study allows you to assess the "echotexture" of the soft tissue structures being imaged.

     • There are four echotextures-anechoic, isoechoic, hypoechoic and hyperechoic.

     • A cellular lesion in a cellular organ of the same echotexture i.e. isoechoic, often is not visualized unless it changes the size, shape and/or vascular structures of that organ.

     • A fluid containing lesion in a cellular organ system can usually be visualized.

     • Size, shape and echotexture do matter when trying to define a lesion.

     • Contrast media are available but not practical to use in most situations.

MRI and nuclear medicine:

     • I do not use these imaging methods every day so I will limit my presentation to what my experience has been with a limited number of studies.

     • Both imaging methods allow for appreciation of tissue composition and function.

     • Both imaging methods require equipment that is not readily available to veterinarians in most situations.

     • Both imaging methods can be relatively expensive to use.

     • MRI does not use ionizing radiation

     • Nuclear medicine studies do us ionizing radiation.

     • Contrast media are commonly used to enhance imaging information during the MRI study.

     • I periodically use MRI to assess soft tissue composition i.e. to look for a nodule in the adrenal gland.

     • I periodically use nuclear medicine to look for specific diseases or organ function: portosystemic shunt, renal function.