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Infectious Diseases of the Gastrointestinal Tract

Surgical pathologists who evaluate specimens from the gastrointestinal (GI) tract for possible infections must first attempt to differentiate histologic changes suggesting infection from other inflammatory processes. After this determination, dedicated attempts must be made to diagnose the specific infectious organisms. The surgical pathologist’s ability to detect infectious processes in tissue sections has grown exponentially with the advent of new histochemical and immunohistochemical stains, in situ hybridization,…

Non-Neoplastic and Neoplastic Disorders of the Appendix

Congenital and Acquired Anatomic Anomalies of the Appendix Abnormal Location, Size, and Absence of the Appendix The appendix can have a host of anatomic abnormalities, including atypical location, duplication, and congenital absence. The position of appendix is determined by the rotation of the gut and position of the cecum during embryonic development. Retrocecal appendix is the most common abnormal location of the appendix. An abnormally long…

Gastrointestinal Mesenchymal Tumors

Gastrointestinal Stromal Tumor Gastrointestinal stromal tumors (GISTs) are the most common soft tissue tumors of the gastrointestinal (GI) tract, with a worldwide annual incidence of about 15 cases per million. Although there was historic controversy over the distinction between GIST, smooth muscle tumors, and nerve sheath tumors, by the late 1990s, it was established that GISTs exhibit differentiation of interstitial cells of Cajal and represent a…

Neoplasms of the Small Intestine

The small intestine represents 75% of the length and 90% of the surface area of the gastrointestinal (GI) tract, yet neoplasms of the small intestine are rare, accounting for only 1% to 2% of all GI neoplasms and fewer than 1% of all cancers in the United States. Four major types of primary neoplasms arise in the small intestine. They are, in order of descending frequency,…

Non-Neoplastic and Inflammatory Disorders of the Small Bowel

Patterns of Small Bowel Disorders The most common indication for histologic assessment of small bowel mucosa is to evaluate for a malabsorption disorder. Although the spectrum of small intestinal diseases that can result in symptoms of malabsorption can seem daunting at first, most diseases produce histologic findings that fall into a limited number of injury patterns. A pattern-based approach is useful because, in practice, it is…

Epithelial Polyps and Neoplasms of the Stomach

Gastric carcinoma is the second most common gas-trointestinal (GI) cancer worldwide, only behind colorectal carcinoma, with more than 1 million cases diagnosed annually. With the increasing use of endoscopy, the diagnosis of early gastric cancer is more frequent, and previously rare or unrecognized preneoplastic lesions have been described and better characterized. Diagnosis of gastric neoplasms and preneoplastic conditions has clinical management implications that impact surveillance or…

Non-Neoplastic Disorders of the Stomach

The recognition of the central role of Helicobacter pylori in the development of what was once the most common form of chronic gastritis has elicited a significant interest in non-neoplastic gastric pathology. This has been paralleled by easier access to upper endoscopic examinations, which has allowed the characterization of various patterns of gastritis with defined etiologic associations. The prevalence of H. pylori gastritis has significantly decreased…

Tumors of the Esophagus

Squamous Papillomas Clinical Features These are uncommon, incidental findings at endoscopy that usually occur in women in the fifth decade of life. The vast majority are solitary; some may present as a papillomatosis. They are thought to be a reactive proliferation secondary to gastroesophageal reflux disease (GERD). In the Western population, most lesions arise in the distal esophagus, whereas mid-esophagus is the most common site of…

Non-Neoplastic Disorders of the Esophagus

The esophagus is designed to simply serve as a conduit to carry food into the stomach. It does not have any digestive, endocrine, or metabolic role. As a result, most non-neoplastic disorders affecting the esophagus are a result of mechanical, chemical, or immune-mediated injury to the relatively resilient nonkeratinizing squamous mucosa. These disorders can be broadly categorized into inflammatory, infectious, congenital and acquired structural abnormalities; motility,…

Other Malignant Soft Tissue Tumors, Including Those of Uncertain Type

The neoplasms described in this comprehensive chapter are a heterogeneous group of tumors, having for the most part uncertain histogenesis and no known normal tissue counterpart. Each is characterized by its own distinctive clinical and pathologic features. These tumors can be further subdivided into those that are translocation associated —Ewing sarcoma, extraskeletal myxoid chondrosarcoma, synovial sarcoma, alveolar soft part sarcoma, desmoplastic small round cell tumor, CIC…

Soft Tissue Tumors of Intermediate Malignancy of Uncertain Type

In previous editions of this textbook, several entities of uncertain type were placed into either benign or malignant categories. Although these entities still remain an enigma with regard to line of cellular differentiation, larger clinicopathologic studies of each of these entities have revealed a better understanding of their clinical behavior. Whereas some of these entities were initially placed into the “benign” category (e.g., ossifying fibromyxoid tumor,…

Miscellaneous Benign Soft Tissue Tumors and Pseudotumors

This chapter discusses a heterogeneous group of benign tumors or pseudotumors, many of which are characterized by abundant myxoid stroma (intramuscular myxoma, juxta-articular myxoma, cutaneous myxoma, ganglion). Evidence indicates that the cells in these lesions are fibroblastic or have some features of myofibroblasts. Tumoral Calcinosis Tumoral calcinosis is a distinct clinical and histologic entity characterized by tumorlike periarticular deposits of calcium hydroxyapatite that are found mainly…

Cartilaginous and Osseous Soft Tissue Tumors

Benign extraosseous cartilaginous lesions are uncommon and usually present as tumorlike masses. In the past, the term soft part chondroma or extraskeletal chondroma was used arbitrarily for small, well-defined, solitary nodules of hyaline cartilage that are unattached to bone and occur primarily in the distal extremities (especially the fingers and hand). These lesions, however, must be distinguished from the cartilaginous rests of branchial origin (usually found…

Soft Tissue Tumors Showing Melanocytic Differentiation

The overwhelming majority of human tumors showing melanocytic differentiation occur in the skin and represent benign melanocytic nevi, their variants, and malignant melanomas. However, a small percentage of tumors showing melanocytic differentiation occur in unusual locations, such as the meninges (melanocytoma), in association with nerves, and in visceral and somatic soft tissue locations. This chapter addresses several unusual soft tissue and visceral tumors showing melanocytic differentiation,…

Peripheral Neuroblastic Tumors

Peripheral neuroblastic tumors arising from the sympathoadrenal lineage of neural crest during development include neuroblastoma, ganglioneuroblastoma, and ganglioneuroma. Although some ganglioneuromas were once believed to arise independently of neuroblastoma, the International Neuroblastoma Pathology Committee now states that “all ganglioneuromas were once neuroblastomas at an early time in their development.” Etiologic and Genetic Factors Much has been discovered regarding the genetic and transcriptional regulation of neural crest…

Malignant Peripheral Nerve Sheath Tumors

Malignant Peripheral Nerve Sheath Tumor Malignant tumors arising from or displaying differentiation along the lines of the various elements of the nerve sheath (e.g., Schwann cell, perineurial cell, fibroblast) are collectively referred to as malignant peripheral nerve sheath tumors (MPNSTs). Because MPNSTs recapitulate the appearance of various cells of the nerve sheath, they range in appearance from tumors that resemble a neurofibroma to those resembling an…

Benign Tumors of Peripheral Nerves

Benign peripheral nerve sheath tumors differ from other soft tissue tumors in several important respects. Most soft tissue tumors arise from mesodermally derived tissue and display a range of features consonant with that lineage. Nerve sheath tumors arise from tissues considered to be of neuroectodermal or neural crest origin and display a range of features that mirrors the various elements of the nerve (e.g., Schwann cell,…

Benign Tumors and Tumorlike Lesions of Synovial Tissue

The synovial membrane forms the lining of joints, tendons, and bursae. In addition, its cells synthesize hyaluronate, a major component of synovial fluid, and facilitate the exchange of substances between blood and synovial fluid. The synovial membrane varies considerably in appearance, depending on local mechanical factors and the nature of the underlying tissue. The synovial surface of joints subjected to high pressure is flat and acellular,…

Perivascular Tumors

Perivascular tumors recapitulate the appearance of the modified myoid cells that support or invest blood vessels (i.e., glomus cell and pericyte). Sometimes referred to as perivascular myoid tumors, these include glomus tumor and its variants, myopericytoma, myofibroma/myofibromatosis, and sinonasal glomangiopericytoma (hemangiopericytoma-like tumor). So-called hemangiopericytoma, although a distinctive lesion histologically, does not display true pericytic differentiation but shares many histologic, immunophenotypic and cytogenetic features with solitary fibrous…

Tumors and Malformations of Lymphatic Vessels

The lymphatics are an extensive unidirectional system of blunt-ending vessels that regulate normal tissue pressure by retrieving excess fluid from the interstitium, transporting it to regional lymph nodes, and returning it to the venous system by way of the thoracic duct. The lymphatic system makes its appearance during the sixth week of human embryonic development as an outgrowth from the venous system. On a molecular level,…