Puff of smoke sign | Radiology Signs

Answer:

The puff of smoke sign is the hazy, reticular blush of innumerable dilated basal collateral vessels seen at the skull base on catheter angiography once the supraclinoid internal carotid artery and the proximal middle and anterior cerebral arteries have become progressively stenotic or occluded. The collaterals are hypertrophied lenticulostriate, thalamoperforating and leptomeningeal perforators recruited to bypass the steno-occlusive segment, and their fine calibre and overlapping course prevent resolution of individual vessels, so they opacify as a smoky cloud rather than as discrete arteries. Angiographic severity is graded by the six Suzuki stages, in which the collateral network first appears, peaks and then disappears as the external carotid supply takes over. The distinction that matters clinically is between moyamoya disease, an idiopathic bilateral arteriopathy strongly linked to the RNF213 p.R4810K variant in East Asian populations, and moyamoya syndrome, the same angiographic pattern secondary to sickle cell disease, neurofibromatosis type 1, cranial irradiation, Down syndrome, tuberculous meningitis or intracranial atherosclerosis. Children present with transient ischaemic attacks and infarction, adults more often with intraventricular or basal ganglia haemorrhage from rupture of the fragile collaterals. MRI and MR angiography show absent flow voids in the terminal internal carotid arteries with multiple punctate basal ganglia flow voids, and perfusion imaging with acetazolamide challenge quantifies the reserve that surgical revascularisation, direct superficial temporal artery to middle cerebral artery bypass or an indirect synangiosis, is intended to restore.

Why is it called so?

The dense tangle of tiny basal collaterals has fuzzy, indistinct margins that resemble a drifting puff of cigarette smoke, which is what the Japanese word moyamoya describes.

Pathophysiology

The arteriopathy is not inflammatory or atherosclerotic. Concentric fibrocellular intimal thickening with smooth muscle cell proliferation and a tortuous, duplicated internal elastic lamina narrows the terminal internal carotid artery and the proximal circle of Willis while the media thins. As the lumen closes over years, pre-existing perforating arteries enlarge to carry basal ganglia and hemispheric flow. These vessels operate at supraphysiological pressures, develop microaneurysms and fibrin deposition in their walls, and eventually rupture, which explains the adult haemorrhagic presentation. Late in the disease the moyamoya network itself involutes as transdural collaterals from the external carotid circulation take over supply.

Alternative names: Moyamoya vessels; basal moyamoya collaterals

Other associated named signs: Ivy sign of leptomeningeal collateral enhancement on FLAIR and post-contrast T1, and the brush sign of prominent deep medullary veins on susceptibility-weighted imaging

References

1. Demartini Z Jr, Teixeira BC, Koppe GL, Gatto LAM, Roman A, Munhoz RP. Moyamoya disease and syndrome: a review. Radiol Bras. 2022;55(1):31-37. PMID: 35210662.