Figure 2.

Course of GB development and devolution in 1-μm Giemsa-stained, Epon sections. a and b: Primitive GBs develop as focal nodules (between brackets) as the result of cell proliferation in the wall of a mother vessel (m) and extend both into the lumen and out into the extravascular connective tissue. Note intimate association with lipid-containing cells (lip). c–e: Maturing GBs encroach on mother vessels, reducing their single large lumens into two or more much smaller lumens (arrows) or obliterating them altogether (e). Note centrally placed, osmophilic, lipid-containing cell (lip) in e. f: Devolving GB has begun to reorganize into normal-appearing microvessels. One newly formed microvessel has acquired a lumen containing red blood cells (white arrow) whereas lumens are just beginning to form in two others (black arrows). g and h: End-stage GB is transformed into relatively normal microvessels (black arrows in g). Residual lipid-containing cells in h (black arrows), much smaller than at earlier stages of GB evolution (compare with a, b, and e), are immediately adjacent to each of three newly formed microvessels. Scale bars, 25 μm.