**7.1 Angiography**

Angiography is the gold standard for diagnosis and assessing disease progression. The hallmark findings of cerebral angiography are occlusion of intracranial internal carotid arteries (**Figure 2**) and abnormal smog-like arteriolar network [moyamoya vessels] at the base of the brain (**Figure 3**). The Circle of Willis and its main branches, leptomeningeal vessels and transdural anastomosis between ophthalmic artery, external carotid artery and vertebral artery are frequently seen. Involvement of posterior circulation is less commonly observed.

Suzuki et al. staged the disease progression into the following stages based on the angiographic findings [3, 22, 27].


Apart from these changes, aneurysm formation can also be seen in angiography. A revised version of Suzuki staging system was given by Mugikura et al. (**Table 1**), where staging is done based on angiographic severity of stenosis of the middle cerebral artery and anterior cerebral artery [30].

Both the staging systems highlight that with the progression of the disease, the contribution of blood supply from ICA decreases and an intricate collateral network is formed which derives its blood flow from vessels outside the cerebral circulation.

### **Figure 2.**

*Neuroimaging of a 40 years old lady who presented with ICH. Non-contrast CT axial sections of brain (a, b, c) show intraventricular hemorrhage involving bilateral lateral ventricles (L > R), third and fourth ventricle. Angiographic images (d, e) show occlusion of the supraclinoid segment of the left internal carotid artery and attenuation on the right side with lenticulostriate collaterals showing a "puff of smoke" appearance (f).*

### **Figure 3.**

*Neuroimaging of a young boy of 6 years of age who presented with recurrent ischemic strokes. MRI brain axial sections show altered signal intensity areas hypointense on T1 (a) and hyperintense on T2 (b, c)) in bilateral frontoparietal cortex involving the MCA territory. Angiographic images show multiple tortuous collaterals involving both anterior (d) and posterior circulation (d, e, f) giving the typical* **"puff of smoke"** *appearance on cerebral DSA (f).*

