Studies on the Lymph Node-Venous Communications 111. The Presence of Saccular Sinuses and their Possible Function*

Abstract

From analysis of serial sections of the canine medial retropharyngeal lymph node, sinuses with a
saccular configuration have been delineated. Maximum dimensions of the saccular sinus analyzed
varied from 13-25 μ through the depth of the serial sections, a distance of approximately 0.5 mm.
The saccular sinus opened at either end into a normal, irregularly-shaped sinus. Continuity was observed
between a distinctly separate tubular vessel and the saccular sinus. The vessel appears to
arise obliquely from the saccular sinus and is first seen as an evagination, approximately 100 μ in
length, of the endothelial border of the saccular sinus. At the region of continuity, the vessel was
approximately 10 μ in diameter and increased to approximately 25 μ in diameter where fully separated
from the saccular sinus. Approximately 20 μ from the region of vessel-saccular sinus continuity,
endothelial strands projected across the vessel lumen. Reconstructions of approximately
36 μ of this area disclosed that these strands were tricuspid and arch-shaped in structure and could
function as a valve. These structw:es are discussed in relationship to the direct lymph node-venous
transfer of tracer substances.
When the lymphatic duct becomes obstructed as a result of either induced or pathological
obstacles, functional extranodal lymphaticovenous communications appear to
act as a bypass mechanism (1-8). Experimental evidence has demonstrated the presence
of lymph node-venous communications, has shown that short-tenn, rapid passage of
tracer substances and cells may be pressure related, and has suggested that certain anatomical
structures may serve as a mixing chamber with two possible exits (9, 10). Histological
evidence is presented herein to document the presence of a system of anatomical
structures which may serve as the morphological pathway for intranodal pressurerelated
transfer from lymph node sinuses directly to the venous system.