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KEY POINTS

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  1. The epidermis consists of continually regenerating stratified epithelium, and 90% of cells are comprised of ectodermally derived keratinocytes.

  2. Dermal fibers are predominantly made of type I and III collagen in a 4:1 ratio. They are responsible for the mechanical resistance of skin.

  3. Staphylococcus aureus is the most common isolate of all skin infections. Impetigo, cellulitis, erysipelas, folliculitis, furuncles, and simple abscesses are examples of uncomplicated infections, whereas deep-tissue infections, extensive cellulitis, necrotizing fasciitis, and myonecrosis are examples of complicated infections.

  4. Hemangiomas arise from benign proliferation of endothelial cells surrounding blood-filled cavities. They most commonly present after birth, rapidly grow during the first year of life, and gradually involute in most cases.

  5. Basal cell carcinoma represents the most common tumor diagnosed in the United States, and the nodular variant is the most common subtype.

  6. Squamous cell carcinoma is the second most common skin cancer, and primary treatment modalities are surgical excision and Moh’s microsurgery. Cautery and ablation, cryotherapy, drug therapy, and radiation therapy are alternative treatments.

  7. Tumor thickness, ulceration, and mitotic rate are the most important prognostic indicators of survival in melanoma. If a sentinel node contains metastatic cancer, prognosis is determined by the number of positive nodes, the primary tumor thickness, mitotic rate and ulceration, and the age of the patient.

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INTRODUCTION

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The skin is a complex organ encompassing the body’s surface and continuous with the mucous membranes. Accounting for approximately 15% of total body weight, it is the largest organ in the human body. Enabled by an array of tissue and cell types, intact skin protects the body from external insults. However, the skin is also the source of a myriad of pathologies that include inflammatory disorders, mechanical and thermal injuries, infectious diseases, and benign and malignant tumors. The intricacies of this organ and associated pathologies are reasons the skin and subcutaneous tissue remain of great interest and require the attention of various surgical disciplines that include plastic ­surgery, dermatology, general surgery, and surgical oncology.

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ANATOMY AND HISTOLOGY

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Background

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Components of epithelial, connective, vascular, muscular, and nervous tissue are organized into three histologic layers (epidermis, dermis, and hypodermis), which vary in consistency between various body parts (Fig. 16-1). The thickness of each layer, distribution of dermal appendages, density and type of nerve endings, and melanocyte distribution are just some of the variables that differ by location and purpose. The epidermis and its appendages are of ectodermal origin, whereas the dermis and hypodermis are of mesodermal origin.1

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Figure 16-1.

Schematic representation of the skin and its appendages. Note that the root of the hair follicle may extend beneath the dermis into the subcutis.

Graphic Jump Location
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Epidermis

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The epidermis consists of stratified epithelium that undergoes continuous regeneration. Ninety to ninety-five ...

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