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atheroma being factors of consequence, Strauss6 emphasises them as of etiological
import, but the absence of these conditions elsewhere in the vascular tree rather
discredits this hypothesis.
The gross morbid anatomical findings in these cases are interesting, for it is by
their study that it is possible to explain the variety of symptoms that present
themselves.
The majority of these aneurysms are small and for that reason were termed
miliary aneurysms by Charcot and Bouchard.14 They are situated for the most part
on the larger cerebral vessels at points of bifurcation or junction with other vessels.
In the one case their presence is easily detected, but in the other it is only by careful
dissection of the vessels and gentle teasing of the brain substance that they are revealed.
It is considered that in cases of spontaneous subarachnoid haemorrhage,
where no cause can be found, the fault lies in the too perfunctory search for
their presence. The more common sites for their occurrence are the junction of the
posterior communicating artery with the posterior cerebral artery, the junction
of the middle cerebral with the anterior cerebral artery, and the anterior cerebral
artery at its union with the anterior communicating artery.
The aneurysms themselves are usually about the size of a split pea, but may
attain the size of a cherry. Occasionally, however, they are found to be larger, and
it is in these cases that careful examination reveals that the tumour consists mainly
of blood clot. The aneurysm has slowly leaked, the escaping blood clotting round
the aneurysm so as to give a false appearance of its actual size. In some cases the
history of previous attacks of subarachnoid haemorrhage before the final and terminal
rupture will direct attention to the actual condition.
Of the aneurysms that rupture, about half do so into the subarachnoid space.
Of the others, the force of the escaping blood tears up the brain tissue so that a hæmatoma
is formed. The frontal lobe is not an unusual site and occasionally the ventricular
system is found full of blood from haemorrhage which has burst into one or other lateral
ventricle.
Before proceeding further a word must be said concerning the usual etiological
factors that are discussed in investigation of disease.
The age of the patient at which the aneurysm leaks or ruptures has such wide
limits as to encompass the whole range of life. It is, perhaps, most common between
the years of 25-40, but it is also met between the ages of 10-70.
As to sex, race, trauma, or other predetermining causes, nothing of value can
be said.
In the main it is true to say that these aneurysms give rise to no symptoms
before rupture. Collier and Adie15 state that they may simulate the presence of a
cerebral tumour, but for the most part these are aneurysms that have slowly leaked,
and have increased in size in the manner stated above. Moreover, haemorrhage,
which has occurred into the frontal lobe, has on occasions been mistaken for a tumour
in that region, but here again it is after rupture.
Symptomatology.
Few cases, therefore, reach the surveillance of the clinician before the wall of
the aneurysm has given way; and, as the escape of blood may vary from a gentle
ooze to a sudden forceful rupture, the symptomatology correspondingly varies.
If due to a slow leak, the small opening may be shut off periodically, giving rise
to headaches which are often mistaken for migraine. When the escape is more free,
the blood becomes mixed with the cerebro-spinal fluid in the arachnoid space and
gives rise to irritation. It may flow towards the opening in the spinal theca, the film
becoming deposited round the roots of the spinal and cranial nerves.
The symptoms and signs that arise are produced by the irritant action of the
blood on the structures with which it comes in contact, together with a raised intracranial
tension.
Headache is a constant feature, the pain being frequently occipital in position
and neuralgic in type, extending down into the region of the neck, and accompanied
in most cases by nausea and vomiting.