**3. Diagnostic criteria**

Various guidelines have been published over time and again. In 1996 and 1997 Japan published diagnostic criteria for the pathology and treatment of MMD [11]. In 2012, Japan published the latest guidelines based on 1997 guidelines [11].

Though cerebral angiography remains the gold standard for the diagnosis (**Table 1**), novel guidelines added a staging based on scores of magnetic resonance (MR) angiography (MRA) [12].

Stenosis or occlusion at the end of ICA and/or the initial segment of the ACA and/or MCA.

At least two obvious shadows of the blood flow are displayed on the same scan level at the basal ganglia region, suggesting the existence of an abnormal vascular network.

The above manifestations are bilateral, but bilateral lesions may be staged differently.

The total score was the sum total of MRA results and each side (right and left were scored individually) as shown in the **Tables 2** and **3**.

As per the new guidelines, other diseases viz. atherosclerosis, autoimmune diseases, meningitis, brain tumours, Down syndrome, Recklinghausen's disease, head injury and cerebrovascular damage after head irradiation, should be excluded [12].

Pathological findings suggestive of MMD are fibrocellular thickening of arterial intima, waviness of internal elastic lamina, thinning of the media, variable stenosis and occlusion of the implicated vessels, presence of anastomotic and perforating branches around the circle of Willis and pial reticular conglomerate of small blood vessels [12].

Definitive MMD: Either angiographic or MRA appearance of vessels bilaterally with the exclusion of alternative diagnosis [13].


## **Table 1.**

*Stages and cerebral angiographic findings.*


### **Table 2.**

*Classification and scoring based on the MRA findings.*


### **Table 3.**

*Total score calculated individually for the right and left side.*

Probable MMD: Either angiographic or MRA appearance of vessels unilaterally with the exclusion of alternative diagnosis [13]. Unilateral MMD may progress to bilateral MMD in 10 to 39% of the cases.

If the autopsy is performed with no previous angiography, pathological findings similar to those mentioned above may serve in the diagnosis of MMD [13].

Quasi MMD or Rui MMD:Evidence of stenosis or occlusion of distal ICA or proximal MCA or ACA with abnormal vascular network either unilateral or bilateral, in association with an underlying disease [13]. Concurrent occurrence of congenital disease is common in children, and acquired disorderis common in adults.

Unstable MMD: Defined as "rapid progression or repeated stroke". It is a clinically challenging condition. It is more prevalent in patients younger than threeyears and those with an associated underlying disease. It is a possible risk factor associated with perioperative ischemic complication [14].

## **Figure 1.**

*Flow chart showing the clinical manifestation of Moyamoya disease based on underlying pathogenic mechanism.*

Moyamoya disease/syndrome symptoms can be broadly categorised into two, by the underlying mechanism (**Figure 1**). The first category of symptoms is oligemia like transient ischemic attack (TIA), stroke, and oligemia like transient ischemic attack (TIA), stroke, and seizures. Amongst the ischemic symptoms, completed strokes are more common in children, a possible explanation being their inability to identify and complain about TIAs [11]. The second category of symptoms are due to the compensatory mechanisms' harmful consequences to ischemia like a haemorrhage from fragile collateral vessels and headaches from dilated transdural collaterals [10].
