Gross Pathology Description and Interpretation
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Gross Pathology Description and Interpretation Drs. Jeff Caswell & Brandon Plattner [email protected] [email protected] Department of Pathobiology University of Guelph 1 Gross Pathology Description and Interpretation Drs. Jeff Caswell & Brandon Plattner [email protected] [email protected] Department of Pathobiology, University of Guelph ©2012 Jeff Caswell and Brandon Plattner hese notes are intended to supplement the fresh specimens shown in gross pathology laboratories Tfor VETM 3450, but do not replace the need to attend these wet labs. Developing competence in the skill of pathologic description and interpretation needs practice, which can only be achieved by pal- pation and observation of real specimens. Students are responsible for material in Part 1 of these notes. Parts 2 and 3 are not required reading, but should be helpful in learning, reinforcing and integrating the material. Acknowledgements: This work is based partly on material from previous gross pathology laboratory instructors, and we wish to acknowledge the contributions of these individuals: Drs. Brian Wilcock, An- drew Brooks, John S. Lumsden and Geoff Wood. 2 Contents art I. Introduction to Patholog- Location of lesions 21 Case A: Observations 51 ic Description and Interpreta- Distribution: diffuse lesions 24 Case A: Interpretation 52 tion 4 Distribution: generalized random Case B: Observations 53 P1. Observe the specimen 5 multifocal 26 Case B: Interpretation 54 2. Identify abnormalities 5 Distribution: focal 27 Case C: Observations 55 3. Describe the abnormalities 7 Distribution: localized 28 Case C: Interpretation 56 i. Location 8 Distributions corresponding to Case D: Observations 57 ii. Distribution 9 specific anatomic structures 29 Case D: Interpretation 58 iii. Size & extent 10 Size & extent 32 iv. Shape, demarcation & con- Shape 34 art V. Pathologic Interpreta- tour 10 tion: Case Examples 59 v. Colour 11 Demarcation 35 Case 1: Questions 60 vi. Texture & strength 11 Surface contour: depression 36 PCase 1: Answers 61 4. Make an Surface contour: elevation 37 Interpretive Summary: Case 2: Questions 62 Colour: red 38 Morphologic Diagnosis 12 Case 2: Answers 63 Colour: tan and white 40 5. Full Case Interpretation: art VI. Appendices 64 Etiology, Pathogenesis, Colour: yellow & green 42 Clinical Correlates 13 Colour: black 43 Appendix 1: The vocabulary of pathology 65 art II. Recognition of artefacts Texture 44 PAppendix 2: Some anatomic pre- 16 Strength 48 fixes 66 Part III. Use and Interpretation art IV. Are Necropsy Examina- of Descriptive Terms 20 tions Useful to Practitioners? 50 P P 3 Part I. Introduction to Pathologic Description and Interpretation he discipline of pathology is the study Tof the changes occuring in tissues Investigating gross lesions during disease, including both the struc- tural or morphologic changes (lesions) and 1. Observe the tissues molecular abnormalities. Pathology also addresses the causes and mechanisms by 2. Identify the abnormalities which these abnormalities develop, and 3. Describe the abnormalities: their functional consequences. Veterinar- ians need to understand the tissue changes Objective, factual, concise, organized that occur in disease for at least two rea- sons: on a conceptual level to understand 4. Make an interpretive summary: how a cause of disease results in clinical Likely pathologic process, morphologic diagnosis signs, and on a practical level by observing and interpreting lesions to determine the 5. Full case interpretation: cause of a disease and to explain clinical observations. Etiology, pathogenesis, clinical correlates Experienced veterinarians often glance at a and its cause. Determining that a lesion lesion and immediately recognize the likely 1. Observe the specimen even exists is not always easy, and requires cause and expected clinical signs. How- that we are able to appreciate that the tis- Observation is at the heart of pathology, ever, at an earlier stage of learning—or for sue in question differs from normal. It is a as it is for many other disciplines, observa- cases with atypical or unusual lesions—it is mistake to rush to the description; instead, tion is a skill that can be developed with useful to develop these skills in sequence. take time to observe the tissue and con- practice and aided by knowledge. It should be obvious that these methods sider how it differs from normal. are not unique to pathology, since exactly the same investigative approach is used 2. Identify abnormalities There are two pitfalls in this regard. in other medical disciplines. The general A lesion is any observable change in a tis- Firstly, a knowledge of anatomy is re- approach to evaluating tissue specimens is sue, if it is considered to be abnormal. The quired; we must be able to identify not similar to other aspects of clinical investi- ability to detect and describe lesions is a only the tissue we are looking at, but also gation, and is summarized as follows. critical first step in investigating how the the orientation within the animal (which lesion happened, its functional significance, is the cranial aspect of the tissue?), as well 5 energy reserves of the animal and ambi- ent temperatures. Hypostatic congestion Consider three questions involves the gravitational pooling of blood when identifying abnormalities in tissues: after death, depending on the position of the body. This often results in reddening 1. Is it a normal anatomic structure? of one lung, while the other remains of normal colour. Blood pools in the viscera 2. Is it a post mortem artefact? as blood vessels dilate after death, making the intestines, lungs and sometimes other 3. Is it different from the normal tissue? tissues appear red-purple and congested. This pooling of blood may be segmental in the intestines, while other areas may be blanched due to the pressure of adjacent viscera. as anatomic structures within the tissue rapid in intestine. These changes occur Imbibition of blood or bile pigments re- such as cortex, medulla, blood vessels, etc. particularly quickly in warm weather, and sults in discoloration of tissues. Hemoglo- Secondly, we must be able to recognize ar- in animals such as sheep and swine where bin imbibition is commonly seen in car- tefacts that commonly develop after death, the insulating effect of fleece or fat pre- casses subjected to freezing and thawing, so we are not distracted by them and vents dissipation of body heat after death. and in autolysed fetuses, with breakdown thereby overlook the important lesions. Autolyzed tissues have diffuse or localized of red blood cells and diffusion of hemo- areas of softening and pallor, which can globin causing red staining of tissues and Postmortem changes develop after the be distinguished from antemortem necro- of fluids in body cavities. The green-black death of the animal, and other changes sis by the lack of grossly or histologically discoloration of bile imbibition is particu- may occur at the time of death. It is im- visible zone of reaction or inflammation larly evident in areas of liver and loops of portant that you are familiar with these in surrounding tissues. Rigor mortis is bowel which are in contact with the gall changes, and able to differentiate them the post-mortem contraction of striated, bladder after death. Gas production by from significant antemortem tissue lesions. smooth and cardiac muscle. Rigor results saprophytic bacteria can result in the rapid The most pervasive of these changes is in stiffening of the carcass during the development of emphysema in the liver, autolysis, or “self-digestion” of tissues. 1-6 hours after death, and then dissipates and tympany of the gastrointestinal tract. Autolysis develops at different rates in over the following 24-48 hours although This may even lead to postmortem rup- different tissues, being slow in muscle, and there is much variation depending on the ture or displacement of the viscera, and 6 prolapse of the rectum. Putrefaction can induce green-black discoloration of tissue Descriptions should be well-organized, so that the reader develops a clear (pseudomelanosis) due to the breakdown mental picture of the lesion without needing to re-read previous sections. of blood and formation of iron sulfides. The best organizational structure will vary depending on the specimen, Post mortem trauma (abrasions, fractures) but the following is a guideline: can be differentiated from that sustained • If multiple types of lesions are present, describe one at a time during life by the absence of hemorrhage • Descriptions generally start with an overview of the location and distri- or an inflammatory reaction. Similarly, post mortem scavenging lacks evidence of adja- bution of the lesion, then move on to the fine details of the lesion’s size, cent tissue hemorrhage, and often involves shape, colour, texture, etc. damage to the eyes, rectum and external • We usually describe the most important abnormalities first, and describe genitalia. artefactual changes last, if at all. Arguably, this may introduce subjectivity to an otherwise objective factual description, but such reports are more 3. Describe the abnormalities easily understood by the reader. Description is the basis for scientific com- munication, by which we are able to share texture and strength. It is appropriate to pathologic description as an experienced information about lesions or diseases. emphasize that description must be ob- pathologist. In contrast, your interpreta- Description is the basis of the pathology jective and factual, not judgemental or tion of what is happening in the tissue is report, which forms the legal record and interpretive. In short, we are simply acting a subjective process that requires insight, archive of the findings. Description allows as recorders of what is present without knowledge and experience. It is in develop- the veterinarian to discuss cases with col- prematurely deciding on the pathologic ing this interpretation that your knowledge leagues, and is an essential element when process, cause, or significance. There will of veterinary pathology and of veterinary submitting tissues to diagnostic laboratory. be many instances where this idea of a medicine is put to use.