Arteriovenous shunts in the human spleen

Abstract

The mission of this study was to determine whether or not arteriovenous connections, indicative of a "closed" type of circulation, existed in the human spleen. Spleens from four patients requiring therapeutic splenectomy were the basis for this report. Scanning electron microscopy of plastic corrosion casts, prepared from these four spleens, revealed direct vascular conduits between splenic pulp arteries or arterial capillaries and the venous sinuses in the red pulp. Also demonstrated were a few arteriovenous shunts between pulp arteries or arterial capillaries and pulp or trabecular veins. Inclusion of sized microspheres in low-viscosity perfusion plastic illustrated that some diameters of the connecting shunts were 7-10 mum, with other shunts even smaller. Not only do arteriovenous connections exist in human spleens, but their frequency, as revealed by methods accentuating three-dimensional aspects of the splenic microcirculation, justify future reconsiderations of the functional significance of this closed type of circulation. Examination of samples of the same intact spleens, prepared by freeze-fracture and conventional critical-point drying, also revealed an "open" type circulation structure, namely, pore-patterned sinus walls that could facilitate blood cell movement from pulp cords into venous sinuses. Scanning electron microscopy thus has provided direct evidence that human spleens have both "open" and "closed" circulatory pathways in their microvasculature.

The spleen of the one humped camel (Camelus dromedarius) has a unique histological structure

“…The diameter of the PAMS has been determined in several animals (Seki & Abe, 1985). The splenic circulation may be open (Thomas, 1967 ;Fukuta et al 1976 ;Irino et al 1977 ;Blue & Weiss, 1981a), closed (Simon, 1970Murkami et al 1973) or a combination of both (Barnhart et al 1976 ;Chen, 1978). There are sinusal type spleens, e.g.…”

The human spleen as revealed by scanning electron microscopy

“…Only recently has the three-dimensional world of the spleen begun to emerge through striking displays by SEM provided in nine publications (16)(17)(18)(23)(24)(25)(26)(27)(28). Most of these have dealt with nonhuman spleens (1 6,25-28).…”

“…Several variations in handling of the spleens were tried during this study (16)(17)(18). The preferred method in effect since July 1974, but excluding spleens from patients being staged for Hodgkin's therapy, involved perfusion of a sequence of solutions under physiologic pressure into freshly excised spleens via the splenic artery.…”

“…Four variations of technique proved suitable. Specimens stored in sucrose cacodylate buffer at 4°C were dehydrated in either 1) ascending concentrations of acetone (16,17) with critical point drying in a Parr bomb containing Freon 116, or ' 2) in graded concentrations of ethanol with amyl acetate substitution (1 7) including critical point drying in COz, or 3) in ascending concentrations of ethanol (17,18) plus critical point drying in Freon 13. The fourth procedure utilized the cryofracture technique described by Humphreys and associates (19).…”

“…Storage for several months in 4°C sucrose cacodylate can be tolerated, although hazardous. plastic casts were made of the microvasculature of 4 perfusion-fixed spleens according to published procedure (16,18). Inclusion of sized plastic microspheres (2-4 pm and 7-10 pm from 3 M Corp., St. Paul, MN) in the Batson plastic solution aided size judgments.…”