الفهرس 
AnatomyOnly 14 pages are availabe for public view
 |  | from | 168 |  |  |
| | | from | 168 | | |
Abstract
G
lioma is the most common intracranial primary tumor of the central nervous system and accounts for about 70% of primary adult malignant brain tumors. The optimum therapeutic treatment and prognosis evaluation largely depends on the tumor pathological grades.
The World Health Organization (WHO) categorizes gliomas in to four grades (grade I, II, III, IV), with grade I being benign and grade IV being most malignant. The accurate grading of brain tumors is too important as management of high grade gliomas differs from that of high grade gliomas.
Magnetic resonance imaging (MRI) is the initial investigation of choice in patients with suspected glioma and plays a major role in the initial differential. The usually used MRI sequences in case of suspected glioma (conventional and T1WI post contrast) don’t show the internal structure of the glioma.
The susceptibility weighted imaging (SWI) sequence is a useful recent addition to MRI sequences used in case of suspected brain space occupying lesion (SOL). It has been designed to utilize the susceptibility difference between the deoxygenated blood in veins and the surrounding brain parenchyma to provide a high degree of contrast.
Signal intensity on SWI is based on both the T2* effect and the susceptibility differences between the tissues imaged. SWI is extremely sensitive for the detection of venous blood (deoxygenated hemoglobin), hemorrhage (throughout stages of hemoglobin degradation), and calcification.
SWI provides invaluable insight into glioma internal architecture. The basic base for evaluation of intracranial neoplasms on SWI are those low signal intensity structures termed ”intratumoural susceptibility signals (ITSS)” that cannot be detected by conventional MR imaging. ITSS refers to linear or dot-like areas of low signal within the tumor on non-CE SWI. ITSS may correspond to intralesional micro-hemorrhage, calcification, or tumoral neo-vascularity.
As we know, the continued growth of the tumor needs neo-vascularization. Pathological neo-angiogenesis has been demonstrated to be associated with tumoral differentiation and aggressiveness.
Grading of tumors with ITSS in SWI correlates with histologic grading of glioma and enriches preoperative prognosis.
ITSS describes the intratumoral susceptibility signal characteristics which may be due to micro-hemorrhage, neo-angiogenesis or calcification.
The ITSS grading scheme is as follows:
Grade 0: no ITSS.
Grade 1: 1–5 dot-like or fine linear ITSSs.
Grade 2: 6–10 dot-like or fine linear ITSSs.
Grade 3: 11 or more dot-like or fine linear ITSSs.
SWI is sensitive to hemorrhage and calcification and both show low signal on SWI. They can be differentiated on the SWI phase image to assist in characterization of the physical contribution of ITSS.
SWI phase imaging helps in identification of intratumoral calcification that aids in narrowing the differential diagnosis. Heme iron and calcium generate opposing phase shift values that are exploited on the SWI phase image. Diamagnetic substances such as calcium demonstrate positive or clockwise shift on phase imaging and shows bright signal; however, paramagnetic substances such as deoxyhemoglobin, hemosiderin, and ferritin demonstrate negative or anticlockwise shift on phase imaging and shows dark signal.
In our study, there were a strong positive correlation between both conventional imaging and pathological grading and between pathological and SWI grading.
Using SWI sequence in grading of glioma will be very beneficial with patient who have contraindication to contrast.
In conclusion, SWI using 3T MR system may provide quite useful information for preoperative glioma grading. There seems to be a strong correlation between pathological grading and that assessed with SWI.
The main disadvantage for SWI is the extra time added to the usual time of MRI protocol used in cases of intra cranial SOL resulting in motion artifact. The T3 machines solved this problem as SWI takes less time in T3 machines.
The limitations of our study included, relatively small sample size, the number of pathologically proven grade I and III glioma patients were very limited and we could not use new WHO 2016 classification of brain tumors in our research because of financial issues.