Microcirculatory pathways in normal human spleen, demonstrated by scanning electron microscopy of corrosion casts

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Abstract
Confusion regarding microcirculatory pathways in normal human spleen has arisen due to extrapolation from pathological material and from other mammalian spleens, not to mention difficulties in tracing intricate three-dimensional routes from the study of thin sections or cut surfaces of tissue. We examined microcirculatory pathways in normal human spleens freshly obtained from organ transplant donors. A modified corrosion casting procedure was used to obtain an open view of vessels and their connections. Our results demonstrate: (1) „arteriolar-capillary bundles”︁ within lymphatic nodules and extensive branching of arterioles; in the marginal zone (MZ); (2) the marginal sinus around lymphatic nodules; (3) the peri-marginal cavernous sinus (PMCS) outside the MZ or immediately adjacent to the nodule itself; the PMCS receives flow via ellipsoid sheaths and MZ, or directly from arterial capillaries, and drains into venous sinuses; (4) fast pathways for flow into venous sinuses via ellipsoid sheaths; (5) arterial capillary terminations in the reticular meshwork of the red pulp or MZ („open”︁ circulation); direct connections to venous sinuses also occur („closed”︁ circulation), although rarely; and (6) numerous open-ended venous sinuses in the MZ, allowing a large proportion of the splenic inflow to bypass the red cell filtration sites in the reticular meshwork and at venous sinus walls.