The simplest form of phlebitis is that just referred to in which a thrombus causes a chronic inflammation of the wall of the vein. We may also have an inflammation of the wall from inflammations in the neighbourhood which may or may not induce thrombosis secondarily.
These conditions were formerly of frequent occurrence and much discussed in medical literature. Thrombo-phlebitis mostly results from the entrance of septic matter into a vein, whose mouth lies open in a wound, but it may occur from the extension of a septic inflammation along the sheath •of the vein and thence inwards.
Septic matter introduced into the calibre of a vein induces coagulation of the blood which, from the circumstances of the case, is usually already stagnant. The thrombus thus formed is not a simple one, but •contains septic microbes, namely, pyogenic micrococci. There is thus a strong irritant inside the vein, and this induces an acute inflammation of its wall. There is an exudation of leucocytes and of blood-plasma, which accumulate in the interstices of the wall and infiltrate the external and middle coats. The exudation rapidly becomes purulent, and the coats are still futher opened out. Viewed from within there may be little collections of pus visible beneath the internal coat like pustules. The pus passes into the calibre of the vein, and as the thrombus softens the vein will often come to be filled with pus. The softening of the thrombus is partly the result of the presence of the pus, but is partly also from septic decomposition. The contents of the vein, by the softening of the thrombus, are allowed to pass into the circulation, although fresh thrombosis may from time to time shut them off. The phenomena of Pyaemia result from the carriage of septic matter by the blood and the consequent infection of distant parts. From the veins, the most direct connection is with the lungs, where septic embolism is set up. But there is frequently an extension beyond the lungs by the systemic arteries to heart, kidneys, etc.
Hunter, Works, edited by Palmer, 1837, iii., 581; Hodgson, Dis. of art. and veins, 1815; Rokitansky, Handb. der path, anat., ii., 1844; Virchow, Ges. Abhandl., 1857; Ebeling, Ueber Phlebitis, 1880; Panton, Uterine phlebitis, Glasg., 1840; Lee, Origin of inflam. of veins, 1850.