Table I.

The pathological grading standard.

Grade	Microscopic description
-	No lesion.
	0.
+	1. Focal edema of gray and white matter, cells dissolved;
	2. Focal atrophy of gray and white matter, hyperchromatic nuclei and cytoplasm;
	3. Focal slight cellular proliferation (mainly gliacyte);
	4. Slight perivascular edema;
	5. Slight vascular engorgement and hemorrhage;
	6. Slight inflammatory cell infiltration;
	7. Slight gray matter atrophy;
	8. Slight ependymal cells proliferation.
	It was graded as ‘+’ when conformed to one of all above, score of which was 1.
++	1. Multifocal edema of gray and white matter, cells dissolved;
	2. Focal atrophy of gray and white matter, hyperchromatic nuclei and cytoplasm;
	3. Focal cellular proliferation (mainly gliacyte);
	4. Medium vascular edema and hemorrhage;
	5. Medium inflammatory cells infiltration;
	6. Medium perivascular edema.
	It was graded as ‘++’ when conformed to one of all above, score of which was 2.
+++	1. diffuse edema of gray and white matter, cells dissolved;
	2. Multifocal atrophy of gray and white matter, hyperchromatic nuclei and cytoplasm;
	3. Focal mass cellular proliferation (mainly gliacyte);
	4. Severe vascular edema and hemorrhage;
	5. Severe inflammatory cell infiltration.
	It was graded as ‘+++’ when conformed to one of all above, score of which was 3.