The exact nature of the communication between the two vascular channels may be estimated from the fact that proptosis--usually the first symptom to make its appearance--seldom becomes apparent till one or two months have elapsed after the accident. It would appear, therefore, probable, that the artery is not ruptured but merely weakened at the time of the injury, the weakened arterial wall gradually giving way before the force of the blood-stream till a definite communication is formed between the two channels.
The male sex, by reason of its greater liability to severe injuries, is generally the one involved, especially between the ages of 20 and 30.
=Symptomatology.= 1. _Proptosis_--usually the first symptom to develop--seldom makes its appearance till after the lapse of one to two months. The eyeball is protruded in the downward and outward direction, the main pulsating tumour presenting at the upper and inner quadrant of the orbit. Proptosis is generally steadily progressive, and, in the most marked cases, the globe may be almost pushed out of its socket. In any case the ‘whites’ of the eye are unduly prominent.
2. _Aneurysmal symptoms._ The tumour pulsates synchronously with the heart’s beat, whilst compression of the common carotid of the same side results in cessation of pulsation and great diminution in the size of the aneurysmal swelling. On releasing the compression force the tumour regains its original size in two or three beats of the heart, and, for a short time, pulsates more forcibly than before. A definite thrill is imparted to the examining finger, and, on auscultation, a loud murmur is heard, not only over the tumour itself, but also widely conducted over the bones of the vault, especially along the line of the superior longitudinal sinus. The free collateral circulation between the angular and ophthalmic arteries permits of the involvement of vessels in the inner orbital and upper nasal regions. This is well shown in the case depicted in Fig. 61.
[Illustration: FIG. 61. A CASE OF TRAUMATIC ORBITAL ANEURYSM.]
3. _Pressure symptoms._ The impairment of venous flow in those radicles which drain into the cavernous sinus is evidenced by the marked engorgement of palpebral, conjunctival, episcleral, and retinal veins. Obstruction to lymph flow is shown by a hazy cornea, chemosis, and œdema of the parts surrounding the orbit. The danger thus incurred by the cornea is rendered more serious by the inability on the part of the patient to close the eyelids over the protruded globe. Keratitis and sloughing of the globe are to be feared. From muscular involvement, squints and diplopia are frequently observed. The pupil may be fully dilated through paralysis of the third nerve.