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Mesenchymal Tumors of the Central Nervous System

Introduction Mesenchymal tumors are believed to originate from precursor mesodermal cells that develop into bone, cartilaginous or connective tissues such as blood vessels, adipocytes, smooth muscle cells, and fibroblasts. Thus, tumors considered in this category cover the entire spectrum of soft tissue and bone tumors. The mesenchymal tumors affecting the central nervous system (CNS) are presumed to arise from the mesodermal cells surrounding the brain parenchyma,…

Meningiomas

Introduction and Proposed Etiologies Meningiomas are among the most common of central nervous system (CNS) neoplasms and are by far the most common of the extra-axial tumors. Our understanding of meningioma classification, grading, and molecular genetics has evolved greatly over time and continues to be refined. Both environmental and genetic factors have been implicated in meningioma formation, although most examples are idiopathic. Meningioma genetics is covered…

Embryonal Neoplasms of the Central Nervous System

Definition and Synonyms Embryonal tumors of the central nervous system (CNS) manifest as highly cellular, poorly differentiated, and mitotically active neoplasms that are reminiscent of the developing embryonic nervous system. Such tumors constitute the most common group of malignant pediatric brain tumors. Often referred to as “small blue cell tumors,” they are biologically aggressive and have a tendency to disseminate along cerebrospinal fluid (CSF) pathways. This…

Pineal Parenchymal Tumors

Introduction, Definitions, and Synonyms The pineal gland is a unique midline organ located posterior to the third ventricle in the quadrigeminal cistern. It is surrounded by the splenium of the corpus callosum above, the thalami laterally, and the quadrigeminal plate and vermis below, together delineating the pineal region. Histologically, human pineal gland parenchyma is mainly composed of pineocytes with a few supportive astrocytes and is subdivided…

Neuronal and Glioneuronal Neoplasms

Brief Historical Overview The neuronal and mixed glioneuronal category of central nervous system (CNS) tumors has been expanding over the past 60 years. In the first edition of the Armed Forces Institute of Pathology (AFIP) fascicle (1952) and the first edition of the WHO classification of central nervous system tumors (1979), the only tumors included within this category were the ganglioglioma, gangliocytoma, and their anaplastic counterparts…

Other Glial Neoplasms

Introduction Not all brain tumors fit neatly into well-defined diagnostic categories within accepted classification systems. Such is the case with the three rare neoplasms discussed in this chapter: angiocentric glioma, astroblastoma, and chordoid glioma. Each of these has a unique and readily recognized histologic pattern, variably defining molecular and immunohistochemical features, and occurs within a specific clinicopathologic setting. These features also set them apart from the…

Ependymomas and Choroid Plexus Tumors

Ependyma and choroid plexus play critical structural and biologic functions within the central nervous system (CNS); the neoplasms that recapitulate these cell types are the most common intraventricular and intramedullary spinal cord tumors. This chapter covers the various categories of ependymal and choroid plexus neoplasms and presents a practical approach to differentiating these tumors from possible diagnostic mimics in both adult and pediatric patients. Special attention…

Nondiffuse Astrocytoma Variants

The designation of “astrocytoma” includes a small subset of tumors with astrocytic differentiation that are better circumscribed than the diffuse astrocytomas. These tumors arise in the pediatric population most frequently, but are also occasionally noted in adults and include the pilocytic astrocytoma, pleomorphic xanthoastrocytoma (PXA), and subependymal giant cell astrocytoma (SEGA). Each of these has distinct localizations, histologic appearances, molecular genetic profiles, and a natural history…

Astrocytic and Oligodendroglial Tumors

Introduction and Brief Historical Overview The infiltrative, or “diffuse,” gliomas include astrocytomas and oligodendrogliomas. Taken together, these are the most frequent primary neoplasms of the central nervous system (CNS) parenchyma. Bailey and Cushing first classified these neoplasms by their cellular differentiation patterns in 1926, and this approach was improved upon over the ensuing decades by using histopathologic features to classify, grade, and prognosticate. The diffuse gliomas…

Integrating Molecular Diagnostics With Surgical Neuropathology

Human disease is increasingly appreciated to have an underlying genetic basis. This is particularly true of neurologic disease, where genetic variants have been shown to increase risk or directly cause schizophrenia, autism spectrum disorder, and neurodegenerative diseases including Alzheimer disease, Parkinson disease, amyotrophic lateral sclerosis, and spinocerebellar ataxias. Genetic alterations that may be either inherited through the germline across multiple generations or arise de novo in…

Neuroradiology: The Surrogate of Gross Neuropathology

Introduction In 1895, German physicist Wilhelm Konrad Röntgen (1845–1923) published his groundbreaking research on a newly appreciated and mysterious form of electromagnetic radiation, which he designated the “x-ray.” To his amazement, these x-rays could penetrate the body's soft tissues and reveal the bones concealed from the naked human eye. Recognized with the first Nobel Prize in physics in 1901, Röntgen launched an era of medical discovery…

Intraoperative Consultation and Optimal Processing

Intraoperative consultation is unquestionably one of the most important and often most challenging tasks for the surgical pathologist. Of all the organ systems, neurosurgical specimens appear to be particularly problematic. Each surgical specimen and clinical setting offers its own unique challenge. Nevertheless, some time-tested principles can be applied in virtually all situations to provide the most reliable diagnostic interpretation. In this chapter the various aspects of…

Normal Brain Histopathology

Introduction The practice of surgical neuropathology can be challenging for the generalist and specialist alike. Much of the difficulty results from the intrinsic complexity of the human central nervous system (CNS), an organ that is unrivaled in regional variation and specialized organization. Nevertheless, a basic understanding of the types of cells and their regional organization in the normal brain is necessary for the practice of surgical…

Neuropathology Patterns and Introduction

CNS Tumor Classification Schemes and Additional “Neuropathology Patterns” The first comprehensive classification of nervous system tumors, formulated by Percival Bailey and Harvey Cushing in 1926, was founded on presumed parallels between embryologic and neoplastic cells. In large part, this histogenetic “cell of origin” model still forms the basis for today's nomenclature, although much of the terminology has changed considerably. Renewed interest in the role of developmental…

Applications of Molecular Testing to Differential Diagnosis

Soft tissue sarcomas are a complex family of rare malignant neoplasms that show mesenchymal differentiation. Benign soft tissue tumors are more common than their malignant counterparts. Both benign and malignant mesenchymal tumors can cause diagnostic confusion. The previous chapters of this book have discussed the characteristics of these tumors as groups based on their morphologic similarities and stressed the features that allow their proper classification primarily…

Lower Genital Soft Tissue Tumors

Since the initial description of pseudosarcomatous fibroepithelial stromal polyps of the distal female genital tract in the early 1960s, various relatively site-specific mesenchymal lesions of the lower genital tract have been recognized. These lesions are often diagnostically challenging because of their morphologic overlap, which in part stems from their likely shared origin from the specialized subepithelial stroma of the distal female genital tract. Ancillary studies such…

Mesenchymal Tumors of the Gastrointestinal Tract

Epithelial neoplasms predominate in the gastrointestinal (GI) tract, as they do in all parenchymal organs and organ systems. However, a wide array of mesenchymal neoplasms also arises in the GI tract, some of which are exclusive or nearly exclusive to such sites. Other mesenchymal tumors that also arise in somatic soft tissue have distinctive features in the GI tract. Most mesenchymal neoplasms are uncommon or rare,…

Cutaneous Mesenchymal Tumors

Cutaneous mesenchymal tumors are considered separately in this chapter because many of the tumors are either unique to or predominate in the skin or show specific features when presenting in the skin. The morphologic spectrum of cutaneous soft tissue tumors is wide and varied, and it includes spindle cell, epithelioid, myxoid, and pleomorphic patterns, in addition to clear cell features. The largest morphologic category is that…

Cartilaginous and Osseous Soft Tissue Lesions

Soft tissue tumors and other mass-forming lesions exhibiting osteocartilaginous differentiation are commonly encountered in diagnostic soft tissue pathology. They comprise diverse entities with distinct clinicopathologic features and clinical behaviors. However, it is important to remember that, occasionally, nonmesenchymal tumors may also display osseous and cartilaginous differentiation. Hence, to avoid diagnostic errors, a systematic approach to such tumors is advisable. The following simple four-step algorithm can be…

Vascular Tumors

The vascular system is composed of arteries and veins and their derivatives, capillaries, and lymphatic channels. Although large arteries and veins are readily distinguished histologically, their smaller counterparts can be difficult to differentiate morphologically. In general, veins have a thinner smooth muscle layer and a larger luminal diameter than arteries, and a well-defined internal elastic lamina is not seen on routine sections or with elastic stains.…