The Deep Cortex of the Lymph Node: Morphological Variations and Functional Aspects

Abstract

The lymph node has long been known to comprise a medulla radiating from its hilus and a cortex located along most of its periphery. This “peripheral cortex” contains folliculonodules, each consisting of a follicle and a nodule (or germinal center), separated by an extrafollicular zone (Sainte-Marie and Sin 1970). The node is also known to comprise a third main component which, for about the past two decades, has frequently been referred to as the “paracortex” and commonly illustrated as a rather uniform layer underlying the entire peripheral cortex (Gutman and Weissman 1972; Goldschneider and Mcgregor 1973; Cottier et al. 1973; Kearney 1974; Greaves et al. 1974; Weissman et al. 1978). However, such a topographical concept of the third component is inconsistent with earlier observations which instead reported the component to comprise elements with diverse appearances. A review of the literature led us to distinguish these elements into two types: nodule-like and ill-defined elements (Table 1). Obviously, the varied terminology used to designate these elements reflected great variations in the histology of the third nodal component and/or an inadequate knowledge of its histology. Therefore, we undertook a detailed study aiming to clarify the histology of this component, which, for reasons presented below, we will refer to as the “deep cortex” by contrast to the peripheral cortex containing the folliculonodules and the extrafollicular zone. The findings summarized here demonstrate that the deep cortex is actually formed of basic structures, which we have now come to term “deep cortex units” or more simply “units,” after having used the term “pseudofollicle” for a while (Table 1).