LAUSR

The first report of Moyamoya disease was published in Japan in 1957 as “hypogenesis of bilateral internal carotid arteries.” In 1963, it was suggested that this pattern of cerebrovascular involvement may constitute a new diagnostic entity, and the disease was named after the unique pattern of net like vessels at the base of brain. These vessels on angiography appear like “something hazy like a puff of cigarette smoke drifting in the air” or Moyamoya in Japanese. Much progress has been made in the understanding of this disease in the last 60 years. Moyamoya disease is now known to be characterized by fibro-cellular proliferation of the tunica intima and thinning of the tunica media of the terminal internal carotid artery and/or the proximal parts of middle and anterior cerebral arteries. The progressive stenosis results in ischemia of the brain with release of neoangiogenic factors. This produces a proliferation of collaterals initially from the lenticulostriate and thalamo perforating arteries, followed by pial collaterals and transdural collaterals. The progressive stenosis and occlusion with collateral formation results in a so-called internal carotid-external carotid conversion of the anterior cerebral circulation. Both the resultant ischemia and the abnormal collateral network contribute towards the symptoms of Moyamoya disease such as ischemic and hemorrhagic strokes, transient ischemic attacks, headache, fatigue, and so on. This pattern of vascular involvement secondary to conditions such as cranial irradiation, infection, and certain genetic disorders like neurofibromatosis is called as Moyamoya syndrome, while Moyamoya disease is restricted to idiopathic conditions. Treatment has also evolved over time and includes antiplatelet agents in addition to direct and indirect revascularization surgeries. Despite all this progress, the diagnosis of Moyamoya disease continues to rely on angiographic demonstration of (i) stenosis or occlusion at the end of the internal carotid artery, the proximal anterior cerebral and/or middle cerebral artery; (ii) an abnormal vascular network in the vicinity of the stenotic occlusion visualized in the arterial phase; and (iii) the above findings must be seen bilaterally. Recent guidelines continue to retain digital substraction cerebral angiography as the gold standard while sanctioning the use of magnetic resonance angiography for diagnosis. Clinicians involved in the care of patients with Moyamoya disease, also need to understand the extent of ischemic and hemorrhagic lesions in the brain, the complex hemodynamics of cerebral circulation in this condition and stage the progression of the disease to tailor interventions accordingly. A summary of the existing imaging techniques available for the evaluation of Moyamoya disease is provided in Table 1. It appears that transcranial color-coded duplex ultrasound (TCCS) provides a simple, inexpensive, real-time, repeatable, bedside measure of many important parameters utilized for both diagnosis and follow up of Moyamoya disease. In the 1980's and 1990's, transcranial ultrasound in the form of transcranial Doppler was used to study the hemodynamic patterns in Moyamoya disease. Researchers identified three patterns of flow when extracranial and intracranial arteries were compared—high–high, high–low, and low–low. A good correlation between stage of involvement based on magnetic resonance angiography, and flow velocities and pulsatility indices of anterior, middle, and posterior cerebral arteries on transcranial Doppler have been observed. Further advances in transducer technology incorporating duplex imaging in transcranial ultrasound permitted direct visualization of the basal vessels. Since then many studies have reported on typical findings of Moyamoya disease on TCCS such as increased flow velocities due to stenosis and numerous arterial vessels suggestive of collateral vessels at the base of the brain. Zheng et al. used TCCS to study the posterior cerebral artery along with carotid duplex studies of extracranial internal carotid artery in 55 patients with Moyamoya disease and reported a good association between these ultrasound parameters and previous ischemic or hemorrhagic stroke. In this context, the study by Wang et al.—“Transcranial color Doppler sonography as an alternative tool for evaluation of terminal internal carotid artery steno-occlusion in Moyamoya disease” makes an important contribution. In 90 patients (171 hemispheres), with Moyamoya disease diagnosed using digital subtraction angiography, they performed TCCS studies using standard techniques to evaluate terminal internal carotid arteries (TICA). They compared their finding to the gold standard digital substraction angiography. Received: 4 November 2021 Accepted: 5 November 2021