Mechanisms of presentation of carotico-cavernous fistulae.

The clinical features of carotico-cavernous fistulae are too well known for detailed description to be necessary. The proptosis, chemosis, venous engorgement in and around the orbit, oculomotor palsy, pulsation of the globe, and the subjective and objective bruit over the orbit and forehead are familiar to all. It is perhaps not always appreciated that the bruit may, on occasions, precede the appearance of the other features by weeks or even months. There are, however, several modes of clinical presentation, and a number of different aetiological processes responsible. The lesion may present as the conventional unilateral carotico-cavernous fistula; the bilateral fistula; the contralateral fistula, in which the pulsating exophthalmos is on the side opposite to the actual fistula; or the alternating fistula. This has been written in these words advisedly, because there is a tendency to accept such expressions too readily and too literally without giving enough thought to their meaning. For instance, does bilateral pulsating exophthalmos mean that the patient has two symmetrical carotico-cavernous fistulae? Or does the alternation of ocular symptoms mean that one fistula has healed but by coincidence the same patient has developed another on the opposite side? It is because this must very rarely be the case that this paper has been written, to consider the mechanismn by which clinical presentations of different types comes about, and also to describe two unfamiliar aetiological processes.