|Year : 2016 | Volume
| Issue : 2 | Page : 303-311
The role of diffusion-weighted MRI in the evaluation and differentiation of space-occupying brain lesions
Amira I Baghdady, Mohamed A Maaly, Adel M El-wakeel, Waleed A Mousa
Department of Radiodiagnosis, Faculty of Medicine, Menoufia University, Menoufia, Egypt
|Date of Submission||03-Jan-2015|
|Date of Acceptance||17-Apr-2015|
|Date of Web Publication||18-Oct-2016|
Mohamed A Maaly
Department of Radiodiagnosis, Faculty of Medicine, Menoufia University, Menoufia, 32511
Source of Support: None, Conflict of Interest: None
The aim of this study was to assess the role of diffusion-weighted MRI in the evaluation and differentiation of space-occupying brain lesions in patients whose conventional MRI (cMRI) examination revealed abnormal imaging features suggestive of space-occupying brain lesions.
Diffusion-weighted imaging provides information about the physiological properties of the tumor that have been linked to cellularity, structural integrity, and necrotic transformation of brain or tumor tissue. MR diffusion imaging has become a powerful, multifaceted tool both for very basic clinical needs and for advanced, specialized diagnosis and treatment planning.
This study included 75 patients who presented with acute focal neurological deficit or with manifestations of space-occupying brain lesions. All of these patients were subjected to cMRI examination of the brain and to diffusion-weighted MRI. Postprocessing of apparent diffusion coefficient (ADC) maps was generated for all patients. Standard mean ADC values were calculated automatically and expressed in 10−S mm2/s. The cutoff value of 1 × 10−3 mm2/s was used to differentiate restricted areas from nonrestricted areas.
Patients and methods:
Among the 75 studied patients, the final diagnosis was intracranial neoplastic lesions (group A) in 46 patients (61.3%), non-neoplastic tumor-like lesions (group B) in 17 patients (22.6%), intracranial suppuration (group C) in seven patients (9.3%), and intracerebral hemorrhage (group D) in five patients (6.6%). Analysis of calculated ADC values using the t-test, the U-test, analysis of variance, and the c2-test revealed statistical difference of ADC values between high-grade/low-grade gliomas, abscesses, and intracranial necrotic neoplasms including glioblastoma multiforme, lymphoma/high-grade astrocytoma, medulloblastoma/ependymoma and pilocytic astrocytoma, and epidermoid/arachnoid cysts.
On the basis of simplicity of the method and the results obtained, diffuse-weighted imaging should be used routinely as a valuable noninvasive tool besides cMRI, whenever available, to reach a definitive final diagnosis.
Keywords: apparent diffusion coefficient, MRI, space-occupying brain lesions
|How to cite this article:|
Baghdady AI, Maaly MA, El-wakeel AM, Mousa WA. The role of diffusion-weighted MRI in the evaluation and differentiation of space-occupying brain lesions. Menoufia Med J 2016;29:303-11
|How to cite this URL:|
Baghdady AI, Maaly MA, El-wakeel AM, Mousa WA. The role of diffusion-weighted MRI in the evaluation and differentiation of space-occupying brain lesions. Menoufia Med J [serial online] 2016 [cited 2020 Feb 24];29:303-11. Available from: http://www.mmj.eg.net/text.asp?2016/29/2/303/192445
| Introduction|| |
Nervous system neoplasms and neoplastic-like lesions are histologically diverse groups that occur at any site in the brain or its linings and which can be derived from primitive embryologic precursor cells, non-neoplastic normal cellular constituents, embryologically misplaced tissues, or neoplastic transformation of normal cellular constituents .
Currently there is widespread use of MRI to determine the tumor extent for surgical and radiotherapy planning, as well as for post-therapy monitoring of tumor recurrence or progression. MRI provides an initial diagnosis of an intracranial mass lesion with a success rate of 30–90% depending on tumor types ,. However, biopsy is still generally considered the gold standard for determining the cancer type and degree of malignancy .
Differentiating brain infections from brain tumors (abscesses from necrotic or cystic brain tumors and encephalitis from diffuse gliomas) is a fundamental clinical issue as the strategies for their management and their prognosis differ completely. Unfortunately, this differentiation remains a diagnostic challenge for both neurologists and radiologists. It is shown that conventional MRI (cMRI) has only 61.4% sensitivity in differentiating brain cystic neoplasms from abscesses as their main differential diagnosis ,.
The medical management strategies for abscess and neoplasms are different, and correct diagnosis of cystic brain lesions must be obtained before treatment can begin. Knowledge of the exact nature of the lesion helps neurosurgeons to determine the best management. For example, cerebral abscess can be stereotactically aspirated, followed by intravenous antibiotic therapy, hence avoiding craniotomy , and ultimately reducing the morbidity and mortality accruing from delayed diagnosis .
Diffusion-weighted imaging (DWI) provides a way to assess the diffusion properties of the water molecules in tissues of the brain that may be substantially altered by diseases. According to Fick's law, true diffusion is the net movement of molecules due to a concentration gradient. With MRI, molecular motion due to concentration gradients cannot be differentiated from molecular motion due to pressure gradients, thermal gradients, or ionic interactions. Therefore, when measuring molecular motion with DWI, only the apparent diffusion coefficient (ADC) can be calculated . It has been used to study the normal brain and various diseases such as ischemia, tumors, epilepsy, and white matter disorders ,,.
Calculated ADC values from the core of the lesion added more information to MRI in the differentiation and grading of brain tumors . Regarding brain tumors, DWI can help in differentiating brain lymphoma from high-grade glioma (astrocytoma) and butterfly glioblastoma multiforme . DWI is used successfully in differentiation between pediatric posterior fossa tumors: primarily medulloblastoma, fourth ventricular ependymoma, and juvenile pilocytic astrocytoma . It can negate the need for biopsy if DWI is performed along with MR spectroscopy.
Calculated ADC values can be used to identify brain abscess and can help differentiate it from a cystic brain tumor (e.g. cystic gliomas, brain metastases) or nontumor ring-enhancing brain lesion (e.g. tumefactive multiple sclerosis) . DWI is an excellent tool used in differentiating epidermoid from arachnoid cysts; such differentiation is sometimes impossible by cMRI .
Although patient symptoms and clinical examinations may suggest the diagnosis of cerebrovascular stroke, only brain imaging studies can confirm the diagnosis and differentiate hemorrhage from ischemia with high accuracy. DWI proved to be valuable in the characterization of intracerebral hemorrhage, at the same time exhibiting advantages in delineating ischemic pathophysiology .
| Patients and Methods|| |
This study was conducted on 75 patients (40 males and 35 females); their ages ranged from 2 to 72 years, with a mean of 35.5 years. All patients with symptoms of space-occupying brain lesions were referred to private diagnostic radiology and medical imaging centers in Egypt. Informed consent was obtained from all patients after full explanation of the benefits and risks of the procedure. All patients were subjected to full history taking and thorough clinical and neurological examination.
MRI examination of the brain
cMRI examination of the brain was performed on all patients using a 1.5-T superconducting MR scanner. Screening patients for any contraindications to the MRI examination, such as presence of cardiac pacemakers, was done. The contrast material used in the study was gadolinium-DTPA (Magnevist) at a dose of 0.2 ml/kg body weight and no reactions were detected to contrast material injection in our study. The standard head coil was used as the receiver coil. The cMRI examination included the following: a precontrast series that included axial, sagittal, and coronal T1 WI [550/15 ms (TR/TE)] spin echo, axial and coronal T2WI (3000/120 ms) turbo spin-echo, and fast fluid attenuation inversion recovery (FLAIR) [8000/140/2800 ms (TR/TE/TI)] was obtained using sections of 3 mm thickness. Postcontrast series included axial, coronal, and sagittal T1 WI spin echo sequences. We evaluated the cMRI with regard to lesion signal characteristics and the presence of hemorrhage, necrosis, peritumoral edema, mass effect, and contrast enhancement.
Diffusion imaging with apparent diffusion coefficient calculation of brain lesions
DWI was performed for all patients in the axial plane using single shot echo-planar spin-echo sequence EPI [3.400/100 ms (TR/TE)], matrix 192 × 192, slice thickness 5 mm, gap 1.5 mm with a duration of 120 s, and b = 0, b = 500, and b = 1000 applied in the X, Y, and Z directions. Postprocessing of ADC maps was done using the standard software supplied on the machine console to obtain the ADC value and map; the lowest ADC values were measured using an region of interest in the center of the lesion, while preferably avoiding cystic and necrotic areas. Standard mean ADC values were calculated automatically and expressed in 10−3 mm 2/s. A cutoff value of 1 × 10−3 mm 2/s was used to differentiate restricted areas from nonrestricted areas.
Final diagnosis was reached either by surgical findings and histopathological examination (in 53 patients), by post-treatment radiological and clinical follow-up (in 17 patients), or by a consensus of clinical and imaging modalities (in five patients).
The statistical analysis of the data obtained in the present study was carried out using SPSS version 20 software programs (SPSS Inc., Chicago, Illinois, USA). Quantitative data were statistically described in terms of mean and SD, whereas qualitative data were expressed as frequency and percentages. The diagnostic performance of the calculated ADC values in glioma grading was evaluated using receiver operating characteristic curve analysis. Comparison between groups was made using the Student t-test for independent samples for quantitative data when normally distributed and the Mann–Whitney U-test for independent samples when not normally distributed. P values less than 0.05 were considered statistically significant. The c 2-test was computed for 2 × 2 tables when the row and column variables were independent, without indicating the strength or direction of the relationship.
| Results|| |
This study included 75 patients and they were classified into four groups based on their final diagnosis; the tumor group included 46 patients (61.3%) (26 male and 20 female patients), subdivided into 29 with supratentorial and 17 with infratentorial neoplasms; the group with non-neoplastic tumor-like lesions included 17 patients (22.6%) (seven male and 10 female patients); the group with intracranial suppuration included seven patients (9.3%) (four male and three female patients); and the group with intracerebral hemorrhage included five patients (6.6%) (three male and two female patients).
Among the supratentorial neoplastic lesions, glioblastoma multiforme was found in six patients (20.6%), meningioma in six patients (20.6%), and intracranial metastases in five patients (17.2%). GIII glioma was detected in two patients (6.8%), GII glioma in three patients (10.3%), and oligodendroglioma in two patients (6.8%). Primary central nervous system (CNS) lymphoma was diagnosed in three patients (10.3%), supratentorial primitive neuroectodermal tumor in one patient (3.4%), and suprasellar/pineal region germinoma in one patient (3.4%). Among the infratentorial neoplastic lesions, medulloblastoma was found in five patients (29.4%), GII pontine glioma in five patients (29.4%), and pilocytic astrocytoma in four patients (23.5%). Ependymoma was found in two patients (11.7%) and hemangioblastoma in one patient (5.8%).
The group with non-neoplastic tumor-like lesions included six cases of epidermoid cysts (60%), four cases of arachnoid cysts (40%), four cases of demyelinating diseases (multiple sclerosis/acute disseminated encephalomyelitis), and three cases of encephalitis. The group with intracranial suppuration included five cases of pyogenic brain abscesses and two cases of subdural empyema. The group with intracerebral hemorrhage included five cases of intracerebral hematoma of different chronological ages (hyperacute, late subacute, and chronic stages).
Diffusion image evaluation
Among the neoplastic lesions, 27 of 46 (58.6%) were found to be restricted, and 19 of 46 (41.3%) were nonrestricted. Among all the non-neoplastic lesions, the restricted lesions were 24 of 29 (82.7%) and the nonrestricted lesions were five of 29 (17.2%) ([Figure 1]). No statistical significance was found between the diffusion pattern and the nature of the lesion (χ2 = 0.16, P = 0.68).
|Figure 1: The percentage of diffusion pattern among neoplastic and non-neoplastic lesions.|
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Calculated ADC values were not useful in the differentiation of tumors as benign or malignant, but they were significantly effective in the grading of malignant tumors. In the current study, we reported statistical significance between glioma grade and diffusion (t-test = 2.11, P = 0.015). ADC values were useful to distinguish high-grade malignant tumors (anaplastic astrocytoma and GBM from low grade astrocytomas) ([Table 1]). At a cutoff value of 0.985 × 10−3 mm 2/s, gliomas with lower ADC values were suggested to be of high-grade type (receiver operating characteristic curve analysis, sensitivity = 87.5%, specificity = 12.5%). There was no difference between ADCs to distinguish metastases from high-grade astrocytomas (t-test = 0.859, P = 0.296) ([Figure 2] and [Figure 3]).
|Figure 2: Receiver operating characteristic (ROC) curve for apparent diffusion coefficient (ADC) values of high-grade and low-grade glioma.|
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|Figure 3: A 61-year-old male patient who presented with epileptic fits and left hemiparesis; a right temporal cortical and subcortical infiltrative lesion, surrounded by GI vasogenic edema with associated mass effect can be seen. (a, b) Fluid attenuation inversion recovery (FLAIR) and T1 GAD: the lesion showed heterogeneous hyperintense signal on FLAIR with moderate heterogeneous contrast enhancement. (c) Axial diffusion-weighted imaging (DWI) showed hyperintensity in the solid (enhancing) portion of the mass (arrow) and hypointensity in the cystic/necrotic portion (arrowhead). (d) Apparent diffusion coefficient (ADC) image showing heterogeneous hypointensity in the solid portion (arrow) compared with the cystic/necrotic portion, which is hyperintense (ADC value measured 0.75 × 10-3 mm2/s), denoting restricted diffusion. Collectively, the findings are in favor of high-grade glioma; histopathological examination confirmed the diagnosis WHO GIV gliomas (glioblastoma multiform).|
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|Table 1: The overall diffusion coefficient values for high-grade and low-grade glioma|
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In the current study, there was statistical significance of diffusion coefficient values in differentiation between CNS lymphoma and high-grade astrocytoma including GBM (t-test = 1.94, P = 0.049) ([Table 2]). Six cases of meningioma had a wide range of ADC values (0.5–1.2 × 10–3 mm 2/s) depending on its histological type. Regarding pediatric posterior fossa tumors, we found strong statistical significance of diffusion coefficient values in differentiation between medulloblastoma, ependymoma, and pilocytic astrocytoma [analysis of variance (ANOVA) test = 3.22, P = 0.025] ([Table 3], [Figure 4] and [Figure 5]).
|Table 2: Overall apparent diffusion coefficient values for primary central nervous system lymphoma and high-grade astrocytoma|
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|Table 3: Overall apparent diffusion coefficient values for medulloblastoma, ependymoma and pilocytic astrocytoma|
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|Figure 4: A 61-year-old female patient who presented with altered mental status; the corpus callosum can be seen. (a, b): Axial fluid attenuation inversion recovery (FLAIR) and T1 GAD images: the lesion showed hyperintensity of posterior corpus callosum and splenium with avid enhancement after contrast administration. (c, d) Axial diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) images showing hyperintensity on DWI, with corresponding hypointensity on ADC images (ADC value measured 0.5 × 10-3 mm2/s) denoting restricted pattern of diffusion. Collectively the imaging findings are suggestive of central nervous system (CNS) lymphoma; histopathological examination confirmed the diagnosis.|
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|Figure 5: A 2-year-old boy who presented with signs of increased intra cranial pressure and cerebellar manifestations; an infratentorial left cerebellar space-occupying lesion can be seen compressing the fourth ventricle with consequent active moderate obstructive hydrocephalus and mild contralateral midline shift. (a, b) Axial T2W and T1 GAD images: the lesion displayed heterogeneous hyperintensity with intense heterogeneous enhancement after contrast administration. (c, d) Axial diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) map image: the bulk of the lesion showed evident diffusion restriction, being hyperintense on DWI and strikingly hypointense on ADC images (ADC value measured 0.5 × 10-3 mm2/s). Collectively the findings are consistent with a high-grade neoplastic lesion, likely medulloblastoma; histopathological examination confirmed the diagnosis WHO GIV medulloblastoma.|
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All cases (5/5) of pyogenic brain abscesses were hyperintense on diffusion-weighted images and had low ADC values when compared with those in normal-appearing brain. The ADC values ranged from 0.5 to 0.6, with a mean of 0.560 ± 0.005 × 10–3 mm 2/s (SD). In our study, necrotic tumors included six cases of GBM and five cases of metastases. Overall, the ADC values of necrotic tumors ranged from 0.44 to 2.0, with a mean of 0.925 ± 0.497 × 10–3 mm 2/s (SD). One patient showed high signal intensity on DWI and low ADC values, mimicking that of abscess; it was multiple metastatic brain lesions from cancer colon. The reason for restricted diffusion was possibly due to necrosis of the central portion of the tumor containing mucinous fluid, which was found at surgery. Analysis of the values of ADC using the unpaired t- test indicate a significant difference between cerebral abscesses and necrotic brain tumors (t-test = 1.98, P = 0.044*) ([Table 4]). In the same context of brain infections, we found a significant difference between encephalitis and diffuse low-grade infiltrating glioma of the temporal and frontal lobes (U-test = 3.98, P = 0.002*) ([Figure 6]).
|Table 4: Overall apparent diffusion coefficient values for necrotic intracerebral tumors and abscesses|
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|Figure 6: A 46-year-old female patient with a history of rheumatic heart disease who presented with fever and right hemiparesis; a left centrum semi-oval cystic space-occupying lesion, surrounded by GI vasogenic edema can be seen. (a, b) Axial T2W and T1 GAD: the lesion showed T2 hyperintense core and hypointense rim, with avid peripheral rim enhancement after contrast administration. (c, d) Axial diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) images showed hyperintensity on DWI, with corresponding evident hypointensity within the lesion core on the ADC image (ADC value measured 0.6 × 10-3 mm2/s, reflecting restricted diffusibility). Collectively, the findings are in favor of left focal pyogenic cerebral abscess; postoperative data and post-treatment follow-up confirmed the diagnosis.|
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All cases (6/6) of epidermoid cysts were hyperintense on DWI with low ADC values, reflecting restriction of diffusion, in contrast to cases of arachnoid cysts (4/4), which showed hypointense signal on DWI with high ADC values. The ADC values of epidermoid cysts ranged from 0.5 to 0.6 (0.58 ± 0.040) × 10–3 mm 2/s (mean ± SD). The ADC values of arachnoid cysts ranged from 3 to 4 (3.5 ± 0.408) × 10–3 mm 2/s (mean ± SD). Analysis of the values of ADC indicate a significant difference between epidermoid and arachnoid cysts (t-test = 3.22, P = 0.001*).
Four cases of intracerebral hematoma (including hyperacute, late subacute, and hemorrhagic transformation of arterial infarction) showed restriction of diffusion with low ADCs [ADC = 0.533 ± 0.115 × 10−3 mm 2/s (mean ± SD)], and one case of chronic hematoma demonstrated increased diffusivity (ADC = 2 × 10−3 mm 2/s) ([Figure 7]).
|Figure 7: A 59-year old male patient with a history of chronic hypertension who complained of headache and right hemiparesis. MRI examination 12 days after the onset of symptoms showed a left temporal space-occupying lesion. (a, b) Axial T2WI and T1WI: the lesion showed T2 hyperintense core surrounded by hypointense rim [large arrowheads on (a)], T1 hyperintense signal (late subacute hemorrhage). (c, d) Axial diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) map: the lesion displayed hyperintense signal with relative corresponding hypointensity on ADC image reflecting low ADC and restriction of diffusion (ADC = 0.6 × 10-3 mm2/s), still with preservation of the peripheral hypointense rim (hemosiderin, ferritin). Small arrowheads point to small foci of hemorrhage of variable chronological ages. Collectively, the imaging findings are matching with left intracerebral hematoma in late subacute stage with no underlying lesions identified. Follow-up assessment confirmed the diagnosis.|
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| Discussion|| |
cMRI is the cornerstone in the initial evaluation of brain tumors . However, in some instances, cMRI is not effective for the differentiation of tumor type or for detection of tumor grade . DWI can increase both the sensitivity and specificity of MR imaging in the evaluation of brain tumors by providing information about tumor cellularity, which may in turn improve the prediction of tumor grade .
Calculated ADC values were significant and useful in the grading of gliomas . In our study, ADC values calculated from tumoral area were higher in low-grade astrocytoma than in higher-grade ones; the lower ADCs suggested high-grade astrocytomas including GBM, whereas higher ADCs suggested low-grade ones, including diffuse GII pontine glioma in children. This agreed with the results of Dragana Ristic et al. , who showed a significant difference in mean ADCs between grade II glial tumors and grade III and IV glial tumors. These findings can be because high-grade tumors are characterized by increased cellularity, microvascular proliferation, and/or necrosis, and they concluded that diffusivity of glial tumors is inversely related to the cellularity and that ADC is inversely proportional to cellular density ,.
This agreed with our results; regarding high-grade gliomas, all patients showed restriction of diffusion, except one patient with right frontal cystic astrocytoma who showed increased diffusion pattern and hyperintense ADC signal. High-grade glioma demonstrated lower ADC values ranging from 0.6 to 1.5, with a mean value of 0.84 ± 0.274 × 10−3 mm 2/s (SD). Regarding low-grade glioma, all patients showed no restriction of diffusion, except one patient with diffuse pontine GII glioma. Comparatively higher ADC values were noticed, ranging from 0.8 to 1.2, with a mean value of 1.142 ± 0.138 × 10−3 mm 2/s (SD). In the current study, such in-vivo prediction of glioma grade by DWI goes in concordance with histopathological examinations, with matching correlation between ADC values and results of pathology among the studied cases. Higher tissue cellular density and higher mitotic index were identified in GIII and GIV gliomas (corresponding with low individual and mean ADC values) compared with GII gliomas that showed relatively expanded extracellular space due to less compact tissue cellular density (corresponding with high individual and mean ADC values). Thus, in the present study, we concluded that there was statistical significance between glioma grade and diffusion pattern (X 2 9.17, P = 0.0102).
ADCs could not be used on individual cases to differentiate tumor types of the same grade . This was emphasized in our study; a false-positive result was encountered in one case; whereas cMRI and DWI revealed a diagnosis of high-grade glioma (astrocytoma), histopathological examination revealed high-grade (anaplastic) oligodendroglioma.
Meningiomas had a wide range of ADCs. Meningiomas with low ADC values tended to be malignant or highly atypical, whereas meningiomas with the highest ADC values had increased water content due to either a specific histologic subtype of meningioma or the presence of associated pathologic abnormality . In our study, marked diffusion restriction with minimum recorded ADC values was noted in two cases of pathologically proved anaplastic meningioma (WHO GII-III): one case of intraventricular meningioma showing periventricular intraparenchymal invasion (ADC = 0.5 × 10–3/mm 2) and one case of fronto-parietal convexity meningioma showing ADC = 0.5–0.6 × 10–3/mm 2. In these two cases, histopathological examination revealed hypercellular tumor matrix with markedly decreased extracellular space. The mean ADC of malignant meningiomas was found to be lower than that of benign meningioma (0.505 ± 0.007 vs. 0.895 ± 0.146). This goes in accordance with the results of Bano et al.  through a study carried out on 26 patients with histologically verified meningiomas, in which they found that the mean ADC of malignant meningiomas (0.64 ± 0.05) was significantly lower as compared with benign meningiomas (1.04 ± 0.12).
It is difficult to differentiate necrotic glioblastomas, cystic metastases, and abscesses with cMRI. All can appear as expansile rim-enhancing masses with prominent perifocal edema . In our study, restriction of diffusion was identified in all cases (5/5) of brain abscesses. The ADC analysis yielded a result of 0.56 ± 0.005 × 10–3 mm 2/s (mean ± SD). In contrast, necrotic brain tumors including six patients with glioblastoma multiforme and five patients with intracranial metastases showed variable degrees of regional restricted diffusion pattern, but with relatively higher ADC values compared with the abscess group. The ADC analysis for glioblastoma multiforme yielded a result of 0.855 ± 0.324 × 10–3 mm 2/s (mean ± SD) and that for cystic intracranial metastases yielded a result of 1.004 ± 0.641 × 10–3 mm 2/s (mean ± SD).
Collectively in the current study, the mean ADC values at the central cavities of cerebral abscesses [0.56 ± 0.005 × 10–3 mm 2/s (mean ± SD)] were found to be lower than those in necrotic intracerebral tumors [0.925 ± 0.497 × 10–3 mm 2/s (mean ± SD)]. These findings agreed with those obtained in the previously mentioned published studies, such as that by Toh et al. , who reported that abscesses demonstrated high signal intensity with corresponding ADC signal loss due to comparatively low ADC values. Reddy et al.  in their study found that 93 of 97 patients with brain abscess were hyperintense on DWI with significantly low ADC values (0.87 ± 0.05 × 10–3 mm 2/s), compared with 48 nonabscess lesions (2.89 ± 0.05 × 10–3 mm 2/s). Also, Leuthardt et al.  revealed that all abscess lesions were markedly hyperintense, with diminished ADC values.
In our study, three cases of encephalitis (all of them diagnosed to be herpetic) showed restriction of diffusion; the mean ADC value of 0.593 ± 0.012 × 10–3 mm 2/s (mean ± SD) differentiating them from infiltrative/low-grade gliomas in which the mean ADC value was 1.193 ± 0.006 × 10–3 mm 2/s (mean ± SD) reflecting no diffusion restriction. The restricted diffusion is explained by cytotoxic edema in tissues undergoing necrosis. These results agreed with those of El-Sirafy et al. , who stated that low-grade and infiltrative gliomas showed no evidence of restricted diffusion on DWI, and with the results of Hamon et al. , who reported that DWI can contribute to the differential diagnosis between herpetic encephalitis and low-grade infiltrating glioma, whose ADC is generally identical to or higher than that of healthy parenchyma (i.e. no diffusion restriction).
Three cases of primary CNS lymphoma were diagnosed in the current study; all of them showed restriction of diffusion. Calculated ADC values were generally low for primary CNS lymphoma; the mean ADC value was 0.53 ± 0.055 × 10−3 mm 2/s, whereas the mean ADC for high-grade astrocytoma was 0.84 ± 0.275 × 10−3 mm 2/s. In the current study, we observed statistical difference between primary CNS lymphoma and high-grade astrocytoma using DWI and calculated ADC values (P = 0.049). This matched with the results of Kitis et al.  and Kuker et al. , who reported that ADC values of the primary CNS lymphomas were lower than those of other intracerebral tumors, close to an acute infarct.
Regarding pediatric posterior fossa tumors, restriction of diffusion was identified in five cases of medulloblastoma, whereas no restriction of diffusion was identified in two cases of fourth ventricular ependymomas. The ADC values were significantly higher in ependymomas (1.425 ± 0.813) than in medulloblastoma (0.564 ± 0.038) (P = 0.041). The enhancing solid tumor in four cases of juvenile pilocytic astrocytoma showed no diffusion restriction. The ADC values were significantly higher in juvenile pilocytic astrocytoma (1.19 ± 0.008) than in medulloblastoma (P = 0.002). Thus, we illustrated remarkable statistical difference among pediatric cerebellar tumors using calculated ADCs (ANOVA test, P = 0.025). It was observed that the range of ADC values within JPAs and ependymomas did not overlap with that of medulloblastomas. These results were reinforced by Karaarslan and Arslan  and Rumboldt et al. , who reported statistically significant differences between pilocytic astrocytoma, ependymoma, and medulloblastoma, with 100% specific cutoff ADC values for differentiating juvenile pilocytic astrocytoma and medulloblastoma. They observed that ADC values were significantly higher in pilocytic astrocytomas (1.65 ± 0.27) than in ependymomas (1.10 ± 0.11) and medulloblastomas (0.66 ± 0.15) (ANOVA test, P = 0.0001).
Tsuruda et al. , Maeda et al. , and Dechambre et al.  reported in succession that DWI could differentiate epidermoid from arachnoid cysts, in that the ADCs of epidermoid cysts were equal to or higher than that of brain parenchyma, whereas ADCs of arachnoid cysts were similar to those of cerebrospinal fluid. This agreed with our study; restriction of diffusion was identified in six cases of epidermoid cysts (mean ADC = 0.58 ± 0.040), whereas increased diffusibility was identified in four cases of arachnoid cysts (mean ADC = 3.50 ± 0.408).
Finally, our study showed five cases of intracerebral hemorrhage: three cases of late subacute hematoma showing restricted diffusion pattern [ADC = 0.533 ± 0.115 × 10−3 mm 2/s (mean ± SD)]; one case of hyperacute hematoma with restricted diffusion pattern (ADC = 0.5 × 10−3 mm 2/s); and one case of chronic hematoma showing increased diffusivity (ADC = 2 × 10−3 mm 2/s). These findings matched those of Khedr et al.  and Attia et al.  who concluded that MRI DWI was accurate in the detection, characterization, and staging of hyperacute and subacute hemorrhage as well as hemorrhagic components of arterial and venous infarctions.
| Conclusion|| |
DWI is a useful and effective imaging technique for the differentiation of a wide variety of space-occupying brain lesions. DWI is an excellent tool in differentiating brain abscesses from necrotic neoplasms, and epidermoid from arachnoid cysts. DWI helps in differentiating medulloblastomas from fourth ventricular ependymomas, and encephalitis (particularly herpetic) from diffuse gliomas. DWI can help in differentiating brain lymphoma from high-grade glioma. DWI can help in determination of glioma grade as well as in characterization and staging of intracranial hemorrhage. DWI entailed less imaging time; also, DWI is available in many imaging centers.
Conflicts of interest
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2], [Table 3], [Table 4]