Cerebral Aneurysms

PATHOGENESIS

The exact cause of aneurysm formation may be multifactorial. Artery

A Aneurysms were once thought to be 'congenital' due to h -JA - the finding of developmental defects in the tunica media.

These defects occur at the apex of vessel bifurcation as do aneurysms, but they are also found in many extracranial vessels as well as intracranial vessels; saccular aneurysms in contrast are seldom found outwith the skull. Tunica media defects are often evident in children, yet aneurysms are rare in this age group. It now appears that defects of the internal elastic lamina are more important in aneurysm formation and these are probably related to arteriosclerotic damage.

Aneurysms often form at sites of haemodynamic stress where for example, a congenitally hypoplastic vessel leads to excessive flow in an adjacent artery.

Hypertension may play a role; more than half the patients with ruptured aneurysm have pre-existing evidence of raised blood pressure. (Aneurysm formation is common in patients with hypertension from coarctation of the aorta.)

Of those patients with intracranial aneurysms, 90% presenting to neurosurgeons have SAH and 7% have symptoms or signs from compression of adjacent structures. The remainder are found incidentally. 1. Rupture (90%).

The features of SAH have already been described in detail (page 271); they include sudden onset of headache, vomiting, neck stiffness, loss of consciousness, focal signs and epilepsy.

Since the severity of the haemorrhage relates to the patient's clinical state and this in turn relates to outcome, much emphasis has been placed on categorising patients into 5 level grading systems, e.g. Hunt and Hess, Nishioka. Recently a new scale has been formed and approved by the World Federation of Neurosurgeons, incorporating the Glasgow Coma Scale (page 29):

Glasgow

WFNs

Coma

Grade

Score

Motor deficit

Glasgow Coma Score

I

15

absent

eye opening 1-4

e.g. no eye opening (1)

II

14-13

absent

verbal response 1-5

no verbal response (1)

III

14-13

present

motor response 1-6

spastic flexion to pain (3)

IV

12-7

present or absent

!M5

= 5

V

6-3

present or absent

This grading scale correlates well with final outcome and provides a prognostic index for the clinician. In 276 addition, it enables matching of patient groups before comparing the effects of different management techniques.

Internal elastic----

lamina

Uneven wall of fibrous tissue

Aneurysm ""

Aneurysm ""

Wall thinnest at fundus

CLINICAL PRESENTATION

This grading scale correlates well with final outcome and provides a prognostic index for the clinician. In 276 addition, it enables matching of patient groups before comparing the effects of different management techniques.

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