Embryological significance of lymphangioma.

Since 1938 when Goetsch studied injected surgical specimens, the growth of cystic hygromas has always been considered as a continuous budding from the walls of the tumour cavity. This phenomenon was compared to the foetal centrifugal development of peripheral lymphatics from the walls of the primary lymphatic sacs, in keeping with Florence Sabin's theory of lymphatic embryology (1912). Although the microscopical observations made by Goetsch were remarkable, their interpretation ought to be revised, as Sabin's theory has since proved wrong. Her observations on embryos were made by injecting primary lymphatic sacs with a dye. The central lymphatic system was filled, showing several large cavities. At a later stage more peripheral networks were filled, and these were interpreted as ramifications from the walls of the primary lymphatic sacs (Fig. 1). This theory must be discarded, as it was based upon retrograde injection, a method that is not adequate for studying the development of a vascular system. Lymphatic vessels do not generate by centrifugal growth from veins and lymph cavities. At a very early stage (9 to 12 mm.) of foetal development, mesenchymal slits appear in the reticulum of a rich venous plexus (Fig. 2A). By coalescence of these spaces, large lymphatic cavities are formed (Fig. 2B) which open secondarily into the venous system (Fig. 2C). Later, they decrease in size and straighten out, following the direction of the veins (Fig. 2D). This theory of the lymphatic system development was put forward by Huntington (1911) and confirmed for humans by Kampmeier (1931), who studied serial sections and reconstructions ofhuman embryos (Fig. 2). Should the primary lymphatic spaces fail to join the central system, cystic formation is induced. The lack of communication between a lymphatic sac and the venous system produces a cystic hygroma. This is the reason why cystic hygromas are found in