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After the recovery from the initial shock, it is the presence of this subarachnoid
blood which gives rise to the cortical irritation which is so often difficult to treat,
and furthermore this blood, as has been pointed out above, affects the absorption of
C.S.F. by the arachnoid villi and so gives rise to the post-traumatic mental disturbances
which in many cases have been labelled neurasthenic headaches. These cases
are frequently summarily dismissed as functional or compensation headaches as no
fracture can be demonstrated by the X-ray, when the use of the lumbar puncture
needle at the time of the injury would have shown clearly the presence of subarachnoid
bleeding and have elucidated the cause of the pain.
Of the spontaneous causes, blood may reach the subarachnoid space by divers
routes.
In the usual type of cerebral hæmorrhage where there is rupture of the lenticulostriate
artery, the force of the escaping blood may be so great as to tear the brain
tissue or burst through the pia mater, or the haemorrhage may burst into the cerebral
ventricles pass via tbe iter to the fourth ventricle where it enters the subarachnoid
space through the foramina of Luska and Majendie. And finally we have bleeding
from vessels actually situated in the subarachnoid space itself, and it is to these that
I wish more especially to direct attention.
Etiology and
pathology.
The variety of pathological circumstances which give rise to this condition
may be divided from the etiological standpoint into general and local, although this
can be taken by no means as a barrier with unyielding boundaries.
In the group of general or remote as opposed to local factors, are included the
hæmorrhagic diseases and will be peremptorily dismissed, so that the attention is
narrowed down to diseases and defects affecting the subarachnoid vessels themselves.
Since 1859, when in the Guy's hospital reports Sir William Gull4 published his
paper on intracranial aneurysms, it has been recognised that the subarachnoid vessels
are peculiarly liable to aneurysmal formation, and from that time controversies have
waged as to the etiology of the condition.
Eppinger5 1887 considered that these aneurysms were due to an inherent or
congenital defect in the vessel wall, a condition which has since been termed by
Strauss, Globus and Ginsburg6 as a " vascular dyscrasia."
Much supporting evidence has been forthcoming to substantiate this theory,
for other vascular defects have been found in cases in which cerebral aneurysms were
present. Parkes Weber7 presented a specimen to the Museum of the Royal College
of Surgeons in which there was congenital aortic stenosis and ruptured congenital
aneurysm. Green8 had a case of stenosis of the aortic isthmus and a bicuspid aortic
orifice in addition to cerebral aneurysms, and both Greenfield9 and Hall10 have encountered
spontaneous intracranial hæmorrhage in different members of the same
family.
This evidence, in addition to the fact that these aneurysms may occur in young
children, supports the view as to their congenital origin, as also does the presence of
other congenital abnormalities in the arterial tree, such as coarctation of the aorta,
absent aortic valves and telangiectases.
From the microscopic aspect, Fearnsides11 states that they are not inflammatory
and that there is "a congenital weakness in the arterial walls at junctional points."
Turnbull12 gives as his opinion, that these aneurysms are the result of an inherent
weakness in the vessels—" on section, the elastic and muscular tissue of the media is
found to be absent."
Forbes13 has called attention to the muscular defects in the media of cerebral
vessels at the point of their bifurcation, which constitute, as he said, the locus minoris
resistentiæ and are considered by him to be of congenital origin.
As to other causes of intracranial aneurysm, periarteritis nodosa is rare, inflammatory,
and not confined to the cerebral vessels. Syphilis stands out pre-eminently
as a possibility, but it is found that the majority of these cases have a negative
Wassermann reaction and must, therefore, be excluded.
Mycotic aneurysms exist only as a commensal of septic conditions as infective
endocarditis and their etiology is therefore apparent. As to arteriosclerosis and