Chordoma

Abstract

As the name implies, the notochord is a cord of cells originating from the (ectodermally derived) primitive node. The notochord arises during early embryogenesis and is responsible for inducing neuralization of adjacent ectoderm (to form the primitive neural tube) and chondrification of adjacent mesoderm (to form the spinal column). Once these tasks are accomplished, the notochord is supposed to regress without leaving a trace. It has long been recognized, however, that remnants of the notochord may persist, especially at its rostral (skull base) and caudal (coccyx) ends (1). Small masses of notochordal remnants (called ecchordoses physaliphora) (Fig. 30-1) may then give rise to tumors of low malignant potential, appropriately named chordomas. Not surprisingly, these tumors are virtually confined to the midline of the body and occur most frequently in the sacrococcygeal region (approximately 50% of cases) and skull base (approximately 30% of cases) (2). It is in this latter location where the chordoma usually comes to the attention of the surgical neuropathologist, as it is one of the most commonly encountered skull base tumors (3,4). While intracranial chordomas generally present in adults (most series report an average age of around 40 years), they may also be seen in children, where they tend to pursue a more aggressive course (5,6). We must, therefore, always consider chordomas when examining midline skull base (clival) tumors, particularly in young and middle-aged adults. Typical chordomas are composed of lobules of cohesive polygonal cells arranged in nests and cords embedded in a mucopolysaccharide matrix (Fig. 30-2). Cells with numerous intracytoplasmic vacuoles (physaliferous cells) may be conspicuous, both on histologic and cytologic preparations (Fig. 30-3). Mitotic activity is variable, and has not been correlated with clinical behavior (although a recent small study of intracranial chordomas showed a significantly higher labeling index with the cell-cycle marker MIB-1 in chordomas which subsequently recurred within the study period) (7). Coagulative tumor necrosis is unusual, and may portend a more aggressive course. Similarly, rare tumors may show sarcomatous transformation, and have been referred to as “dedifferentiated” chordomas, analogous to the terminology used for similarly afflicted lipomatous and cartilaginous tumors (8,9).