Dermatopathology. Christine J. Ko

      To Ulla, Anna, Jessica, and Sara who let me pursue

      my career while they took care of everything else.

      – Ronald J. Barr

      To Peter, Dylan, and Owen.

      – Christine J. Ko

      Preface

      The purpose of this book is to focus on a selection of commonly tested entities, showing low‐power to high‐power views. Major differences among diagnoses that are sometimes confused are emphasized on “Key Differences” pages to help train the eye to rapidly notice distinctive features. As a picture is worth a thousand words, text is kept to a minimum. This book should be used as a companion to dermatopathology textbooks and as a pictorial reference/study tool, given that this approach is utilized by the experienced dermatopathologist when constructing examination questions. Major distractors are based on gestalt rather than etiology or conventional classifications; lookalikes that are the most deceptive often have no obvious relationship to the correct diagnosis. This book will also be helpful to the dermatopathology novice as it introduces a simple and effective way to approach a slide and, to that end, common diagnoses have been specifically included (i.e., actinic keratosis, basal cell carcinoma).

      Acknowledgments

      Dr James H. Graham, MD, master of dermatopathology and dermatology, who taught me most of what I know. (Ronald J. Barr)

      Dr Ronald Barr, Dr Scott Binder, my dermatopathology colleagues at Yale (Dr Jennifer McNiff, Dr Earl Glusac, Dr Shawn Cowper, Dr Anjela Galan, Dr Marcus Bosenberg, Dr Peggy Myung, Dr Gauri Panse, Dr William Damsky, and Dr Antonio Subtil Deoliveira [still part of my Yale dermatopathology family]), Dr Jean Bolognia – their insights over the years have been invaluable. We also acknowledge the residents at Yale, those in Thailand, and Hadas Skupsky, who rotated with Dr Barr, all of whom gave constructive feedback on how to improve the atlas. Thanks is also due to the team at Wiley‐Blackwell for all their efforts to improve the book. (Christine J. Ko)

About the Companion Website

This book is accompanied by a companion website:

      www.wiley.com/go/ko/dermatopathology4e

      The website includes:

       Interactive multiple choice questions

       PowerPoints of all figures from the book for downloading

Introduction

Recognizing a disease process on a histopathologic slide becomes instantaneous, with increasing familiarity. Breaking this process down into the “how” is difficult, especially given that the steps may not be the same for each individual. Nonetheless, on a basic level, it is important to separate a solitary growth (“tumor” or “lesion”) from a rash (“inflammatory” process; Figures 1–3), focus on the most obvious pathologic finding, and run through a differential diagnosis. With experience, that “obvious” pathologic finding (i.e., where to start) becomes second nature. The diseases in this atlas are grouped, arbitrarily, by such findings (see the Index by Pattern). Notably, basic algorithms are ultimately overly simplistic, and there is overlap of the two major divisions in Figure 1 (tumor versus rash). For example, clear cell acanthoma can architecturally mimic psoriasis, mycosis fungoides can appear to be a dermatitis, and epithelioid sarcoma can be confused with a palisading granulomatous process.

Key concepts in cognitive psychology come into play during visual recognition, and having some understanding of how the brain processes visual information can be helpful in training the eye to see (Table 1). In figure–ground separation, the brain focuses on a perceived figure and tends to ignore the background. Thus, an important initial step in diagnosing disease when viewing microscopic slides is to train the brain to accurately identify the most important features (“figure”). In order to make sense of visual stimuli, the brain also automatically groups information. With all else being equal, similar objects will be grouped together, closer objects will be grouped together, and objects perceived as having a similar color/texture or common enclosure (“common region”) will be grouped together. Clues such as body site (Figure 4) and absence of obvious pathology (Figure 5 and Table 2) can also be useful.

Table 1 Visual recognition in dermatopathology as related to cognitive psychology.

Dermatopathology		Cognitive psychology concept
Overview (2×/4× ocular)	“Tumor” versus “rash”ArchitectureBody siteCell type	GestaltFigure–ground separationGrouping
Higher magnification (10×/20×/40× ocular)	Confirm cell type/morphologyFiner details of architecture	Grouping using finer detailsSimilarityProximityCommon region

Figure 1 Gestalt impression of a slide

       A major initial breakpoint in evaluating a specimen on a slide is the determination of the type of process: tumor/growth versus rash/inflammatory

      Note In some cases, it is not readily apparent if the process is a tumor or an inflammatory process (examples include mycosis fungoides, a form of cutaneous T‐cell lymphoma, as well as deep fungal infections, which can induce florid epidermal hyperplasia mimicking a squamous cell carcinoma).

Figure 2(A) Location of the tumor

       Important characteristics to consider for a tumor/growth include location (A), architecture (B), cell type (C), and benignancy versus malignancy (D). The eye can be trained to focus in on the blue areas (figure–ground separation; grouping)