Blood Microcirculation in the Lymph Node

In microangiographicstudies of dog and rat lymph nodes, we demonstrated the morphology of the blood microcirculation within the various elements of the node. The distribution and organization of the arterioles, capillaries, and venules revealed a definite and recurring pattern which will help to explain certain physiologic and pathologic events. A detailed study of the blood microcirculation of lymph node was warranted because the lymph node is the site of important humoral and cellular exchanges between the circulating blood, the circulating lymph, and the cells of the lymphoid tissue (7, 9). Microangiography supplemented by stereomicroangiography is, in our experience, an excellent method to study the complex lymphatic organ. This has not been previously undertaken. One of the earliest descriptions of the blood supply of the lymph node is that of Frey in 1861 (6). After reviewing the papers by His (8) and Frey, Calvert (1) studied this problem extensively and in offered a diagrammatic schema of the blood flow in the lymph node. Schulze (10) in 1927 described a peculiar venule with a high endothelial lining, found exclusively in the lymph node, and named it the postcapillary venule. Calvert and later Dabelow (2), based their findings on india ink injections with subsequent histologic examination and evaluation of thick, cleared specimens. Method In order to opacify the microvasculature of the lymph node, we utilized two approaches: (a) replacement of the circulating blood by radiopaque materials and (b) intravenous injection of contrast medium which remained in circulation until the organs were removed. For the replacement technic the animals were anesthetized with Diabutal.2 Catheters were placed in the aorta and the inferior vena cava. The radiopaque material was injected into the aorta at pressures slightly above the normal physiologic blood pressure. In dogs the average infusion pressure 180 mm Hg. total of contrast medium exceeded 5 times the average animal blood volume. The catheters in the inferior vena cava were connected to a reservoir permitting free flow. Usually only 50–65 per cent of the volume injected was regained from the venous outflow. The contrast materials were 10 per cent Micropaque3 or Thoria-Sol4 suspended in physiologic saline solution or in human or dog plasma. Ten milligrams of Lipo-Hepin5 were added to every liter of infusion. Usually the animal's respiration and heart action ceased after 300 to 500 ml was injected. The method of opacification by contrast medium remained in circulation was as follows: without anesthesia, 6 to 8 ml of Thorotrast6 was injected into the tail vein of male rats weighing approximately 150 g. The animals were sacrificed twenty-five to thirty-five minutes later. Microangiography The removed lymph nodes were fixed in formalin and embedded in paraffin. Sections 80 to 100 microns thick were taken for microradiography and sections 4 microns thick for histology. Contact micro-radiographs of the thick sections were obtained on Kodak High Resolution photographic plates. Bony Landmarks The majority of the films were taken in an oblique projection with a vertical x-ray beam, this position being necessary for local retention of the Pantopaque. In examination of such a film it is helpful to identify certain landmarks such as the atlas, foramen magnum, clivus, hypoglossal and jugular foramina, the mastoid air cells, and the bony labryinth (Fig. 1, A). The establishment of the position of these structures serves as a guide to the levels of the brain and cranial nerves amid the distortions of unusual projections. Cisterns As the contrast medium leaves the upper cervical canal and flows through the foramen magnum, the column becomes constricted locally; then, as it re-expands, a triangular area is seen posteriorly, representing the lower part of the cisterna magna (Fig. 2, A). No further examination of that cistern is possible, however, with the patient in the prone position. Anteriorly, the opaque material flows down and outlines the smooth margins of the pontomedullary cisterns, bounded by the clivus ventrally and the pons and medulla dorsally. Gass stated that the rostral end of the contrast agent as it accumulates over the clivus assumes the appearance of a natural limiting “cap” This effect would presumably be produced by the material coming up against the limiting membrane which Liliequist described in this situation (Fig. 5). The soft-tissue shadows of the cervical cord, medulla, and pons may be seen through the contrast medium.