A definite diagnosis and characterization of intra-cranial masses based on structural MRI alone may be difficult and MRS with other non-invasive techniques can represent an advance in the specificity of cerebral lesion diagnosis [16]. MRS limits the use of invasive diagnostic approaches such as brain biopsy [17].
This study revealed that conventional MRI with contrast-enhanced images could have low specificity in differentiation between primary or metastatic multiple cerebral neoplasms, and there was diagnostic overlap between some multiple neoplastic and non-neoplastic lesions with 89.33% sensitivity, 44% specificity, and 78% accuracy. This was in agreements with Omuro et al. who stated that differentiation between tumors and non-neoplastic lesions using conventional MRI may be challenging, while MRI is a sensitive technique for detection of brain lesions, the specificity and capability of it for distinguishing between benign and malignant lesions are limited, and with Karen et al. who said that although conventional MRI provides images with excellent structural detail, it cannot always be used alone to accurately identify specific tumor type and grade or to differentiate neoplastic from non-neoplastic lesions [18, 19]. Sensitivity, specificity, PPV, and NPV for determining a high-grade glioma with conventional MR imaging were 72.5%, 65.0%, 86.1%, and 44.1%, respectively [20].
MRS can add clinically relevant information about metabolites in common brain abnormalities. It is clinically ready for diagnostic, prognostic, and treatment assessment of brain tumors; various demyelinating disorders, and infectious brain lesions [21]. Cho/Cr, Cho/NAA, NAA/Cho, and NAA/Cr ratios are the most concerned ratios. This may be of help in the diagnosis and differentiation between many lesions that may be confusing on the conventional MRI imaging [22].
According to our MRS results, the studied 100 lesions were classified into non-neoplastic and neoplastic lesions, and there was statistical significance for their differentiation by MRS as regards the Cho/Cr, Cho/NAA, NAA/Cr, Cho/NAA + Cr, and NAA/Cho ratios (M ± SD) with P < 0.001 (significant). This was coincidence with many other studies that revealed large differences in metabolite levels in acute stroke, chronic multiple sclerosis, and brain tumors [23,24,25] and Brandáo et al. study which concluded that increase in Cho levels and Cho/Cr and Cho/NAA ratios is highly suggestive of neoplasm [26]. There is extensive literature demonstrating the metabolite ratios of Cho/Cr, NAA/Cr, as well as the presence of lipids and lactate to be useful in grading tumors and predicting tumor malignancy [20]. While Moller-hartman et al. stated that the abnormality specific to tumors was the elevated CHO [27]. Also, our results showed that most of the neoplastic and non-neoplastic lesions showed elevated lipid and lactate peak respectively which increased with tumor aggressiveness. This agreed with Nooman et al. [28] results that revealed lactate and lipid levels in low and high grade tumors but with no significant difference between primary and metastatic tumors and Van-der G who stated that the presence of the lactate peaks was usually consistent with aggressive tumors [29].
Other metabolites such as AA, A, and S/P peaks were seen only in 3/4 abscess. This agree with the results that summarized spectral characteristics of intracranial abscesses as presence of cytosolic amino acids (detected at 0.9 ppm): presence of lactate (detected at 1.3 ppm), acetate (detected at 1.92 ppm), succinate (detected at 2.4 ppm), and occasionally lipids (detected at 0.8–1.2 ppm) [30, 31].
In our studies, all spectroscopic parameters showed non-significant results for differentiation between primary and metastatic neoplastic lesions when measured within the lesions; however, there was a statistical significance of Cho/NAA and Ch/Cr ratios (P value < 0.001*) for such differentiation when measured in the perilesional regions. This was in agreements with many other studies who found that investigation of peri-enhancing tumor regions may be useful for discriminating metastases from primary brain tumors, whereas gliomas are often invasive lesions with elevated Cho in surrounding tissue, metastatic lesions tend to be more encapsulated and do not show high Cho signals or other abnormalities outside the region of enhancement [32,33,34].
The results of this work revealed that there were mixed diffusion changes in most of the studied lesions and the measured ADC value ranges showed overlap in neoplastic and non-neoplastic lesions with no statistical significance for their differentiation. Also, the calculated ADC values showed no significant difference either measured within or outside the margins of primary and metastatic neoplasms, P value = 0.165 and 0.142 respectively “insignificant.”
This was matched with results of Fawzy et al, who said that regarding DWI, we found a heterogeneous signal and different values for ADC according to the lesions’ consistency and there was no significant correlation between the histological components and the ADC values [35]. Also, Al-Okaili et al. and other studies found that DWI feature for primary neoplasms is variable and although the ADC value of high-grade gliomas has been shown to be lower than that of low grade gliomas, there is substantial overlap; thus, ADC maps alone are insufficient for predicting type and grade of glial neoplasms and it could not differentiate between these tumors [36,37,38,39].
Our works showed that the combined MRS and DWI with calculated ADC values added to cMRI results succeeded in diagnosing 96% of the studied lesions. This was in agreement with Abdel-Monem et al. study which concluded that the combination of MRS with cMRI and calculated ADC values added more information in the differentiation of brain tumors and were more useful when done together than each alone which markedly elevate the diagnostic accuracy rate [40].
There were a few limitations of this study. First, the low number of some studied lesions, especially that of non-neoplastic etiology such as tuberculoma, abscesses, and vascular lesions. Second, when we applied DWI, there was difficulty in positioning the region of interest in cystic/necrotic lesions as well as in the pre-lesional regions of some lesions that are not associated with edema. Lastly, the diagnosis of multicentric cerebral focal lesions with primary and secondary brain neoplasm differentiation is still a challenging problem based on conventional MRI alone, and according to the results of this study, it was found that a combination of proton MRS and DWI with ADC calculation can provide additive information helping in lesion characterization which improves the diagnosis and management plane.