Cerebral Angiography, Digital Substraction Angiography ( DSA)

Invention of Cerebral Angiography is an important historical landmark in evolution of Neuroradiology and Neurosurgery. 

In 1927, Dr Egas Moniz developed a technique of injecting a contrast material into the arteries . The dye or contrast used was Thorotrast. 

When a contrast or dye which is soluble in blood is injected into the common carotid artery the blood vessels become visible and look opaque on background of X-ray image of skull.  This technique of imaging the blood vessels of the brain is known as cerebral angiography. Rapid sequences of the X-ray images are obtained after injecting contrast into common carotid artery. Similar images could also be obtained when contrast is injected into the femoral artery.  Cerebral angiography allows visualization of blood vessels in and around the brain.

Before 1927, may be called  X-ray era, i.e., in the begining of 20th century, neurosurgery was possible by localization of the lesion by neurological examination and using the X-ray techniques. Application of X-rays in investigations like ventriculogram, encephalography, myelogram were used to localize lesions. 
Roentgen invented application of x-rays imaging in 1896.
Walter Dandy described pneumoencephalography and pneumoventriculography in 1918.
In 1921, myelography was introduced when jean Sicard a French clinician and his pupil Jacques Forestier injected analgesics into the spine of a patient suffering from low back pain and subsequently found that the oil they used as a carrier for the analgesic, lipiodol, was radio-opaque.
The invention of myelography encouraged the Portuguese neurologist Egas Moniz to develop ' Arterial Encephalography'.

After 1927, the dignostic ability of the physician changed dramatically. Using the technique of cerebral angiography, Norman Dott, in 1931,  demostrated cerebral aneurysm on cerebral angiography and later, Walter Dandy was able to operate a case of intracranial aneurysm, in 1933.

Cerebral angiography depicts the vessels along with X-ray of the skull. 

Later, with the use of computer, the background of skull image could be substracted. So, the artery or vein is visualized better. So, the technique of substracting the bony details  is called Digital Substraction  Angiography  ( DSA ). But, if somebody wants to see relation of the aneurysm against the bony landmark of the skull, it is still possible in DSA because the bone image was substracted digitally and computer again can depict the same.  Thus, DSA is gold standard investigation for detection and surgical planning for intracranial aneurysms.

                                                     Image of DSA , here the internal carotid artery is seen , the image is lateral view of the skull but the bony details have been digitally substracted so that one can focus on the ICA and its branches. ICA is seen as in neck, carotid siphon as a loop and intracranial branches. The first intracranial branch of ICA   which runs anteriorly is ophthalmic artery. Second intracranial branch which runs poseriorly is Posterior communicating artery. Anterior Choroidal artery is another intrcranial branch of ICA which is seen to traverse posteriorly on lateral view of DSA.

First investigation for investigating a suspected case of spontaneous subarachnoid hemorrhage is CT scan of the brain. Non-contrast CT scan reveals the site of the bleed, like blood in the anterior inter-hemispheiric space is suggestive of SAH due to rupture of anterior communicating artery. Then, the second investiation is to know the detail of the aneurysm, which is done by DSA.

Since, DSA is an invasive procedure, so the another option is to go for CT angioprphy. MR angiography ( MRA) is a noninvasive procedure and it does not require any injection. But MRA is less sensitive than CT angiography and DSA.

Digital Substraction Angiography ( DSA) involves passing a catheter in the femoral artery over the anterior aspect of the thigh in the femoral triangle and then advancing the catheter upward. Then, injection of a contrast material ( Dye) through a catheter. Once catheter is at the arch of aorta it needs to be negotiated to the carotid artery and vertebral artery. So, anatomy of arch of aorta is important.

                                         The contrast is injected into the Femoral artery on right side and then catheter is advanced upward into the arota under the fluroscopic guidance. At the arch of aorta the catheter is negotiated into the artery depending upon the need of DSA. On the right side there is first branch of arch of aorta, brachiocephalic trunk. Right common carotid artery is a branch of brachiocephalic trunk.
Left common carotid artery is a direct branch of arch of aorta. Left subclavian artery is also a direct branch of arch of aorta and vertebral artery is a second branh of subclavian artery.

Spontaneous subarachnoid hemorrhage due to ruture of intracranial aneurysm commonly occurs in the age group of 40-60 years with a peak incidence in the fifties.
Aneurysm bleed is the commonest cause of spontaneous SAH ( about 85%). 
Other common causes of spontaneous SAH are:  artriovenous malformations ( AVM), hemorrhage from tumor, pituitary apoplexy, vasculopathy ( like collagen vascular disease, amyloid angiopathy , arterial dissection) , haematological ( anticoagulant therapy, leukaemia, hepatic or renal disease induced coagulopathy ) and drugs like cocaine, amphetamine and ephedrine.

Subarachnoid hemorrhage (SAH) is a neurological emergency  characterized by hemorrhage into the subarachnoid space, and may present as sudden, severe headache ( as bolt from blue ) which patient may state that he or she may have never experienced before. Sentinel hemorrhage occurs in about 40% of patients with SAH. This is also known as " warning leak". Nuchal rigidity or meningismus is noted in 50% of patients due to meningeal irritation following SAH. Hemiparesis, focal neurological deficits including cranial nerve deficits are other common features. Fundus examination may reveal papilloedema and subhyaloid hemorrhage.

On the basis of GCS and Focal deficit, the severity of the clinical presentation of the patients may be graded into 5 grades , according to the World Federation of Neurological Surgeons  (WFNS).
In WFNS Grade 1 the patients are of GCS 15/15 and have no focal deficit. And, if patient's GCS is 13 or 14 then it is Grade 2. And patient has a focal deficit with a GCS of 13 or 14, his grade becomes Grade 3.   poor GCS of 7-12 makes a patient of grade 4 and if patients GCS is 6 or less then his garde becomes 5, irrespective of the presence or absence of focal deficit.

NCCT ( NECT) , i.e., Noncontrast or nonenhanced CT scan of the barin is the first investigation of choice. It shows hyperdensity in the subarachnoid space and may indicate the site of bleed. or example, anterior communicationg artery aneurysm bleed shows blood or hyperdensity in the anterior interhemispheric cisterm. the ruture of the Middle cerebral artery may present with hematoma in the temporal lobe or in the sylvian fissure of that side.

Fischer's grading of SAH on the basis of CT findings:
In Grade 1: there is no detectable blood on CT scan
Grade 2 : Diffuse thin  SAH  less than 1 mm thickness, & if thickness of clot is more than 1mm then it is labeled as Grade 3.
Grade 4: Intraventricular or intracerebral clot with diffuse or no subarachnoid hemorrhage

If  CT scan is normal and still there is strong suspicion of SAH, then the next  investigation is Lumbar Puncture, which reveals xanthochromia. 

Common locations of intracranial aneurysms include Anterior communicating artery ( 30%), the junction of the ICA and Pcom ( 25% ), MCA bifurcation ( 20% ), ICA bifurcation ( 7.5%). Around 7% arise from the basilar bifurcation and 3% arise from the PICA, a branch of vertebral artery.

Digital Substraction Angiography ( DSA) or CT Angiography ( CTA) is the investigation of choice. MR angiography ( MRA) does not use any contrast and it is a good non invasive screening investigation.

Source: Wikipedia