Diffusion-weighted imaging in the evaluation of intracranial lesions

Multiparametric Framework Magnetic Resonance Imaging Assessment of Subtypes of Intracranial Germ Cell Tumors Using Susceptibility Weighted Imaging, Diffusion-Weighted Imaging, and Dynamic Susceptibility-Contrast Perfusion-Weighted Imaging Combined With Conventional Magnetic Resonance Imaging

BACKGROUND

Intracranial germ cell tumors (iGCTs) are classified into two pathological subtypes (germinomas [GEs] and nongerminomatous germ cell tumors [NGGCTs]), with distinct treatment strategy and prognosis. Accurate preoperative determination of iGCT subtypes is essential to guide clinical decision-making and prognosis assessment.

PURPOSE

To investigate the diagnostic value of diffusion-weighted imaging (DWI), susceptibility weighted imaging (SWI), and dynamic susceptibility-contrast perfusion-weighted imaging (DSC-PWI) combined with conventional magnetic resonance imaging (cMRI) in finding subtypes of iGCTs.

STUDY TYPE

Retrospective.

POPULATION

A total of 40 patients (45% male and 55% female) with iGCTs.

FIELD STRENGTH/SEQUENCE

A 3 T; <T1WI, T2WI, T1WI + C, DWI, SWI, DSC-PWI>.

ASSESSMENT

The parameters of DWI and DSC-PWI were calculated based on extracted parameters of multiparametric MRIs. The characteristics of SWI and cMRI were also compared in GEs and NGGCTs.

STATISTICAL TESTS

The diagnostic efficacy of the minimum apparent diffusion coefficient (ADCmin), time-to-peak (TTP), relative mean transit time (rMTT), relative cerebral blood flow (rCBF), relative cerebral blood volume (rCBV) maps, and cMRI features in iGCT classification was evaluated by receiver operating characteristic curve (ROC) analyses. We calculated the sensitivity, specificity, AUC, and Youden index of the hybrid MR evaluation methods. A prospective cohort (five GEs and five NGGCTs) was designed as a simulation set to test the model. The significance threshold was set at P < 0.01.

RESULTS

The ADCmin (1039.100 ± 453.830 vs. 1400.050 ± 394.650), rCBF values (20.650 ± 6.260 vs. 51.170 ± 6.570), and TTP values (24.450 ± 3.160 vs. 28.950 ± 5.120) were significantly lower in GEs than in NGGCTs. The combination of ADCmin, DSC-PWI, and cMRI showed the heights AUC (AUC = 0.962). The iGCT multiparametric framework showed the AUC was 0.958 in the simulation set.

DATA CONCLUSION

The iCGT multiparametric framework might be an effective diagnostic approach of iGCT subtype. The application of cMRI (T1WI, T2WI, and Gd-T1WI) with advanced imaging modalities (DWI, SWI, and PWI) had the best performance for classifying iGCT subtypes.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 2.

The role of "penumbra sign" and diffusion-weighted imaging in adnexal masses: do they provide a clue in differentiating tubo-ovarian abscess from ovarian malignancy?

Purpose

To evaluate the role of “penumbra sign”, diffusion-weighted imaging (DWI), and the apparent diffusion coefficient (ADC) value in differentiating tubo-ovarian abscess (TOA) from ovarian malignancy.

Material and methods

Thirty-six patients with 50 adnexal masses (tubo-ovarian abscess, n = 24; ovarian malignancy, n = 26), who underwent magnetic resonance imaging (MRI) with DWI, were retrospectively evaluated. “Penumbra sign” (hyperintense rim on T1W images), diffusion restriction, and mean apparent diffusion coefficient (ADC) values from cystic (c-ADC) and solid (s-ADC) components were evaluated for all the masses.

Results

“Penumbra sign” on T1W images was significantly more common in the TOA group (n = 21, 87.5%) than in the ovarian malignancy group (n = 2, 7.7%) (p < 0.001). Similarly, diffusion restriction in the cystic component was more frequent in the TOA group (n = 24, 100% vs. n = 2, 10.5%; p < 0.001). In contrast, diffusion restriction in the solid component was more common in the ovarian malignancy group (n = 5, 20.8% vs. n = 26, 100%; p < 0.001). The mean c-ADC value was significantly lower in TOAs (p < 0.001). A c-ADC value of 1.31 × 10^-3 mm²/s may be an optimal cut-off in distinguishing TOAs from ovarian malignancies. Conversely, the mean s-ADC value was significantly lower in the ovarian malignancy group (p < 0.001). An s-ADC value of 0.869 × 10^-3 mm²/s may be an optimal cut-off in differentiating ovarian malignancies from TOAs (p < 0.001). ROC curve analysis showed that c-ADC values had a higher diagnostic accuracy than s-ADC values.

Conclusions

“Penumbra sign” on T1W images, diffusion characteristics, and ADC values provide important clues in addition to conventional MR imaging features in differentiating TOA from ovarian malignancy.

Diffusion-weighted magnetic resonance imaging for detection of postoperative intracranial pyogenic abscesses in neurosurgery

BACKGROUND

Diffusion-weighted magnetic resonance imaging (MRI-DWI) is the modality of choice for detecting intracranial abscesses; however, it is unclear whether prior brain surgery has an influence on its diagnostic value. Thus, we assessed the robustness of MRI-DWI and determination of an ADC cutoff value for detecting intracranial abscesses in patients who underwent brain surgery.

METHODS

We retrospectively evaluated 19 patients prior to surgery for postoperative supratentorial parenchymal abscesses by means of MRI-DWI. Forty randomly selected patients with routine postoperative MRI-DWI were used for comparative analyses. Clinical and serum biomarkers (C-reactive protein, interleukin-6, white blood cell count) as well as from results of early postoperative imaging findings (computed tomography and/or MRI scan) were recorded. Additionally, ADC values, T1±gadolinium, and T2/fluid-attenuated inversion recovery sequences were investigated.

RESULTS

After initial surgery, early postoperative control imaging showed evidence of hemorrhage and/or hemostatic agents within the resection cavity in 10/19 patients of the abscess group and in 16/40 patients of the control group. No postoperative ischemia was detected. Neither hemostatic agents nor blood affected the mean ADC values in both the reference group (blood 2.96 ± 0.22 × 10^-3 mm²/s vs. no blood 2.95 ± 0.26 × 10^-3 mm²/s, p = 0.076) and in the abscess group (blood 0.87 ± 0.07 × 10^-3 mm²/s vs. no blood 0.76 ± 0.06 × 10^-3 mm²/s, p = 0.128). The mean ADC value within the resection cavity was significantly lower in the abscess group (1.5 T 0.88 ± 0.41 vs. 2.88 ± 0.20 × 10^-3 mm²/s, p < .01; 3.0 T 0.75 ± 0.24 vs. 3.02 ± 0.26 × 10^-3 mm²/s, p < 0.01). The optimal ADC cut-off for the differentiation of an abscess from normal postoperative findings was found at 1.87 × 10^-3 mm²/s (area-under-the-curve 1.0, sensitivity = 100%, specificity = 100%). Moreover, no differences between the abscess patients and the control group were seen with respect to the analyzed serum biomarkers.

CONCLUSION

MRI-DWI provides a robust tool to discriminate postoperative abscess formation from normal postoperative changes.

Diffusion-weighted imaging in relation to morphology on dynamic contrast enhancement MRI: the diagnostic value of characterizing non-puerperal mastitis

Objectives

To demonstrate the value of diffusion-weighted imaging (DWI) in the characterisation of mastitis lesions.

Methods

Sixty-one non-puerperal patients with pathologically confirmed single benign mastitis lesions underwent preoperative examinations with conventional MRI and axial DWI. Patients were categorised into three groups: (1) periductal mastitis (PDM), (2) granulomatous lobular mastitis (GLM), and (3) infectious abscess (IAB). Apparent diffusion coefficient (ADC) values of each lesion were recorded. A one-way ANOVA with logistic analysis was performed to compare ADC values and other parameters. Discriminative abilities of DWI modalities were compared using the area under the receiver operating characteristic curve (AUC). P < 0.05 was considered statistically significant.

Results

ADC values differed significantly among the three groups (P = 0.003) as well as between PDM and IAB and between PDM and GLM. The distribution of non-mass enhancement on dynamic contrast-enhanced (DCE) MRI differed significantly among the three groups (P = 0.03) but not between any two groups specifically. There were no differences in lesion location, patient age, T₂WI or DWI signal intensity, enhancement type, non-mass internal enhancement, or mass enhancement characteristics among the three groups.

Conclusions

ADC values and the distribution of non-mass enhancement are valuable in classifying mastitis subtypes.

Key points

• Mastitis subtypes exhibit different characteristics on DWI and DCE MRI.

• ADC values are helpful in isolating PDM from other mastitis lesions.

• Distribution of non-mass enhancement also has value in comparing mastitis subtypes.

Cerebral tuberculomas in a patient with hairy cell leukaemia treated with cladribine

A 67-year-old man was treated with cladribine for hairy cell leukaemia. A few weeks later, he presented with persistent headaches, intermittent hypoesthesia of the right upper limb and language impairment. Brain CT scan showed 3 contrast-enhancing lesions. MRI revealed infracentimetric nodular lesions with restricted diffusion. One of the lesions was surgically removed and tested positive for acid-fast bacilli. Moreover, Mycobacterium tuberculosis was confirmed by PCR. Antituberculous drugs were prescribed for 12 months, with complete resolution of neurological deficits. This case highlights the risk of mycobacterial infections associated with both hairy cell leukaemia and cladribine use, and the importance of screening and treatment of latent forms of tuberculosis in patients undergoing treatment with immunosuppressive drugs.

Distinguishing between germinomas and pineal cell tumors on MR imaging

BACKGROUND AND PURPOSE

Tumors of pineal cell origin have different prognosis and treatment than those of germ cell origin. The recent literature suggests that these tumors often look alike. Our study aimed to differentiate between pineal cell tumor and germinoma based on ADC values, the homogeneity of the mass, and MR imaging characteristics.

MATERIALS AND METHODS

We enrolled 20 patients who had pretreatment MR imaging scans with histologic verification of tumors of pineal cell origin and germinomas. The tumors were measured for the ADC values and for homogeneity by the coefficient of variation of ADC values, and T1WI and T2WI signal intensity values.

RESULTS

The 20 subjects (8 females and 12 males) ranged in age from 1.5-64.9 years, with a mean age of 23.9 years (SD 17.7 years). The mean age of those with germinomas was 13.7 years (SD 3.8 years), less than the mean of 29.4 years for those with pineal cell tumors (SD 19.9 years; P = .016). These 2 groups showed no significant difference in coefficients of variation on T1WI, T2WI, and ADC images. However, germinomas showed statistically significant higher ADC values (mean 1590.69 ± 532.96 × 10(-6) mm(2)/s) than pineal cell tumors (mean 883.58 ± 317.48 × 10(-6) mm(2)/s; P = .02). An accuracy of 89.5%, sensitivity of 83.3%, specificity of 92.3%, PPV of 83.3%, and NPV of 92.3% were yielded for an ADC threshold of 1250.00 × 10(-6) mm(2)/s.

CONCLUSIONS

Germinomas showed higher ADC values than the pineal cell tumors (P = .02), and the patients were younger. Otherwise, there were no definitive imaging characteristics that distinguished pineal cell tumors from germinomas.

[Multimodal magnetic resonance imaging of brain tumors]

Magnetic resonance imaging arose as a reference for diagnosis, pre-therapeutic and follow-up of brain tumors. Among parameters obtained from standard MRI (of low specificity), only volumetric growth allows prognostic information. The multiple "advanced" sequences have leaded to increase both sensitivity and specificity of brain MRI. Yet, perfusion-weighted imaging and spectroscopy provide metabolic information, and diffusion tensor imaging and cortical activation provide functional information. Characterization, grading, therapeutic management and follow-up have improved, with prognostic information.

Diffusion-weighted imaging characteristics of primary central nervous system germinoma with histopathologic correlation: a retrospective study

RATIONALE AND OBJECTIVES

The aim of this study was to quantify, using diffusion-weighted magnetic resonance imaging, the microscopic rate of water diffusion in pure germinoma and to determine whether or not the apparent diffusion coefficient (ADC) values correlated with the different histologic components.

MATERIALS AND METHODS

A retrospective analysis of echoplanar diffusion-weighted magnetic resonance images was conducted on 10 patients with 11 germinoma lesions. All images were obtained using 1.5-T magnets with a b value of 1000 s/mm(2). Regions of interest were drawn separately within the solid and the cystic or necrotic components of each germinoma, as well as within the normal gray and white matter of the respective cases, to calculate ADCs. The diffusion characteristics of the germinomas were assessed using mean and normalized ADC values. Histologic samples from all cases were blindly reviewed and then correlated with the ADC values.

RESULTS

Data are expressed as mean +/- standard error. Evaluation of the solid components revealed that 36% of germinomas (4 of 11) had predominantly restricted diffusion (ADC(solid), 694.71x10(-6)+/-74.54x10(-6) s/mm(2); ADC ratio, 0.84+/-0.07) compared to normal brain. The majority (55% [6 of 11]) had normal diffusion (ADC(solid), 947.64x10(-6)+/-54.38x10(-6) s/mm(2); ADC ratio, 1.14+/-0.10). Only 9% (1 of 11) had increased diffusion (ADC(solid), 1172.30x10(-6)+/-48.52x10(-6) s/mm(2); ADC ratio, 1.67+/-0.16). The cystic and necrotic components had a mean ADC ratio of 2.55+/-0.25. There was no significant correlation between the histologic components and the ADC values of germinomas.

CONCLUSIONS

The vast majority of germinomas demonstrated predominantly restricted (36%) or normal (55%) diffusion. The histologic components were not correlated with the ADC values.

Neuroimaging in neuro-oncology

Neuroimaging of brain tumors has evolved from a strictly morphology-based discipline to one that encompasses function, physiology, and anatomy. This review outlines the current imaging standard for patients with brain tumor and summarizes the latest advances in physiology-based imaging methods that complement traditional brain tumor imaging protocols. Emphasis is on the strength and limitations of the current imaging standards and on an overview of several advanced imaging methods including diffusion-weighted magnetic resonance imaging (MRI), perfusion MRI, and proton magnetic resonance spectroscopic (MRS) imaging. Basic physical principles behind each imaging method are briefly presented, along with a more in-depth discussion of clinical application and potential pitfalls of each technique.

The role of diffusion-weighted magnetic resonance imaging in intracranial cystic lesions

We aimed to define the diffusion-weighted magnetic resonance (MR) imaging features of intracranial cystic lesions and to investigate possible special features for the differential diagnosis. One hundred and twenty patients with intracranial cystic lesions were included in the study. There were 29 arachnoid cysts, eight epidermoid cysts, 34 primary tumors, 18 abscesses, 29 metastases and two hydatid cysts. Echo-planar diffusion-weighted MR imaging was obtained in addition to conventional cranial MR scans. The morphologic features of the cystic portion and the wall of the cyst and signal intensities on diffusion-weighted images were evaluated. All abscesses and epidermoid cysts were hyperintense on diffusion-weighted images. Arachnoid cysts, hydatid cysts, primary tumors, and metastases were hypointense except five cystic tumors. These five primary or metastatic necrotic tumors showed high signal intensity on diffusion-weighted images due to hemorrhage or superinfection. The walls of the cystic tumors were usually hyperintense on diffusion-weighted images in contrast to the wall of the abscesses, which were iso-hypointense. This was a statistically significant finding for the differentiation between tumors and abscesses (p<0.05). Diffusion-weighted MR imaging is a useful technique for the evaluation of the intracranial cystic lesions and provides additional beneficial information to conventional MR imaging. However, the presence of hemorrhage and superinfection of the tumors may cause a signal increase that results in misinterpretetations. In these cases, the appearance of tumor wall may be useful for differentiating abscesses from tumors.

Tumors in pediatric patients at diffusion-weighted MR imaging: apparent diffusion coefficient and tumor cellularity

PURPOSE

To prospectively assess whether there is a relationship between the apparent diffusion coefficient (ADC) and the histopathologic cell count and whether the ADC can enable differentiation of benign and malignant extracranial mass lesions in children.

MATERIALS AND METHODS

Institutional ethics approval and parent or guardian consent were obtained. Eleven malignant and eight benign lesions in 19 children (11 girls, eight boys; median age, 3.9 years; age range, 11 days to 15.5 years) who underwent magnetic resonance (MR) imaging of extracranial mass lesions-including a diffusion-weighted sequence (with b values 0, 500, and 1000 sec/mm(2))-and histopathologic analysis to prove findings were studied. The median ADC within each mass lesion was compared with the median cell count for 10 high-power microscopic fields in the specimen. The inverse regression between cell count and ADC was calculated. The difference in ADC between benign and malignant lesions was assessed by using the Mann-Whitney U test.

RESULTS

There was an inverse relationship between ADC and cell count, expressed as ADC (in x10(-3) mm(2)/sec) = 0.56 + (66.2/cell count), with a relatively good fit to the observed data (analysis of variance R(2) = 0.541, F = 20.0, P < .001). The ADCs of benign lesions ranged from (0.84-2.83) x 10(-3) mm(2)/sec (median, 1.35 x 10(-3) mm(2)/sec; standard deviation, 0.68). The ADCs of malignant lesions ranged from (0.73-1.53) x 10(-3) mm(2)/sec (median, 1.00 x 10(-3) mm(2)/sec; standard deviation, 0.29). There was no significant difference in ADC between benign and malignant lesions (Mann-Whitney U = 22, P = .069). All highly cellular (>150 cells per high-power field) lesions had an ADC lower than 1.5 x 10(-3) mm(2)/sec.

CONCLUSION

Although there is a significant relationship between cellularity and ADC, cell count probably is not the sole determinant of the ADC. Use of the ADC cannot enable accurate differentiation of malignant and benign lesions.

The contribution of diffusion-weighted MR imaging in multiple sclerosis during acute attack

PURPOSE

The aims of the study are firstly, to determine the difference in diffusion-weighted imaging (DWI) in normal appearing white matter (NAWM) between patients with acute multiple sclerosis (MS) and controls; secondly, to determine whether there is a correlation between EDSS scores and DWI in acute plaques and also NAWM.

MATERIALS AND METHOD

Out of 50 patients with acute MS attack, 35 patients had active plaques with diffuse or ring enhancement on postcontrast images. Eighteen healthy volunteers constituted the control group. While 26 of 35 had relapsing-remitting, 9 had secondary progressive MS. Apparent diffusion coefficients (ADC) of the active plaques, NAWM at the level of centrum semiovale and occipital horn of lateral ventricle in the patients and NAWM in control group were measured. ADC values of active plaques were compared with WM of the patients and the control group. The relationship of ADC value of active plaques and WM in MS with expanded disability status scale (EDSS) was investigated by using Mann-Whitney U-test.

RESULTS

Of 63 plaques totally, 26 and 37 of the active plaques had diffuse and ring enhancement, respectively. There was no statistically significant difference between ADC value of active plaques and EDSS (p>0.05). However, there was a statistically significant difference between ADC value of WM occipital horn and EDSS (p<0.05). ADC value of active plaques were higher than WM in both groups (p<0.001). The difference between ADC value of WM at the centrum semiovale (p<0.05) and occipital horns (p<0.001) in patients and controls was statistically significant. There was no statistically significant difference between EDSS scores, ADC value at centrum semiovale and WM around occipital horn and active plaques in subgroups (p>0.05).

CONCLUSION

Apparently normal tissue in MS patients may show early abnormalities when investigated carefully enough, and there is an even though moderate correlation between EDSS and ADC values and early alterations of ADC value are starting in the occipital white matter along the ventricles. This has to be verified in larger series.

Feasibility of a RARE-based sequence for quantitative diffusion-weighted MRI of the spine

The feasibility of a diffusion-weighted single-shot fast-spin-echo sequence for the diagnostic work-up of bone marrow diseases was assessed. Twenty healthy controls and 16 patients with various bone marrow pathologies of the spine (bone marrow edema, tumor and inflammation) were examined with a diffusion-weighted single-shot sequence based on a modified rapid acquisition with relaxation enhancement (mRARE) technique; four diffusion weightings (b-values: 50, 250, 500 and 750 s/mm(2)) in three orthogonal orientations were applied. Apparent diffusion coefficients (ADCs) were determined in the bone marrow and in the intervertebral discs of healthy volunteers and in diseased bone marrow. Ten of the 20 volunteers were repeatedly scanned within 30 min to examine short-time reproducibility. Spatial reproducibility was assessed by measuring ADCs in two different slices including the same lesion in 12 patients. The ADCs of the lesions exhibited significantly higher values, (1.27 +/- 0.32)x10(-3) mm(2)/s, compared with healthy bone marrow, (0.21 +/- 0.10)x10(-3) mm(2)/s. Short-time and spatial reproducibility had a mean coefficient of variation of 2.1% and 6.4%, respectively. The diffusion-weighted mRARE sequence provides a reliable tool for determining quantitative ADCs in vertebral bone marrow with adequate image quality.

Brain MRI: tumor evaluation

The designation "brain tumors" is commonly applied to a wide variety of intracranial mass lesions that are distinct in their location, biology, treatment, and prognosis. Since many of these lesions do not arise from brain parenchyma, the more appropriate term would be "intracranial tumors." The term "tumor" is used to include both neoplastic and non-neoplastic mass lesions, and should be considered in its broadest sense to simply indicate a space-occupying mass. This review describes an imaging-based approach for evaluating intracranial tumors. Conventional MRI is discussed in the setting of a regional classification system. This system provides a framework for analysis, and imaging clues can then be applied to narrow the differential possibilities. Emphasis is placed on advanced MRI techniques and their utility for deciphering common diagnostic problems.

Pituitary macroadenomas: preoperative evaluation of consistency with diffusion-weighted MR imaging--initial experience

PURPOSE

To prospectively evaluate use of diffusion-weighted (DW) magnetic resonance (MR) images and apparent diffusion coefficient (ADC) maps for determination of the consistency of macroadenomas.

MATERIALS AND METHODS

The study protocol was approved by the institutional ethics committee, and informed consent was obtained from all patients. Twenty-two patients with pituitary macroadenoma (10 men, 12 women; mean age, 54 years +/- 17.09 [standard deviation]; range, 21-75 years) were examined. All patients underwent MR examination, which included T1-weighted spin-echo and T2-weighted turbo spin-echo DW imaging with ADC mapping and contrast material-enhanced T1-weighted spin-echo imaging. Regions of interest (ROIs) were drawn in the macroadenomas and in normal white matter on DW images, ADC maps, and conventional MR images. Consistency of macroadenomas was evaluated at surgery and was classified as soft, intermediate, or hard. Histologic examination was performed on surgical specimens of macroadenomas. Mean ADC values, signal intensity (SI) ratios of tumor to white matter within ROIs on conventional and DW MR images, and degree of enhancement were compared with tumor consistency and with percentage of collagen content at histologic examination by using analysis of variance for linear trend.

RESULTS

The mean value of ADC in the soft group was (0.663 +/- 0.109) x 10(-3) mm(2)/sec; in the intermediate group, (0.842 +/- 0.081) x 10(-3) mm(2)/sec; and in the hard group, (1.363 +/- 0.259) x 10(-3) mm(2)/sec. Statistical analysis revealed a significant correlation between tumor consistency and ADC values, DW image SI ratios, T2-weighted image SI ratios, and percentage of collagen content (P < .001, analysis of variance). No other statistically significant correlations were found.

CONCLUSION

Findings in this study suggest that DW MR images with ADC maps can provide information about the consistency of macroadenomas.

Brain abscess and cystic brain tumor: discrimination with dynamic susceptibility contrast perfusion-weighted MRI

Differentiating between brain abscesses and cystic brain tumors such as high-grade gliomas and metastases is often difficult with conventional MRI. The goal of this study was to evaluate the diagnostic utility of perfusion MRI to differentiate between these pathologies. MRI was performed in 19 patients with rim-enhancing brain lesions (4 pyogenic abscesses, 8 high-grade gliomas, 7 metastases). In addition to standard MR sequences, trace diffusion-weighted MRI with apparent diffusion coefficient (ADC) maps and perfusion-weighted MRI by using a first-pass gadopentetate dimeglumine T2*-weighted gradient echo single-shot echo-planar sequence were performed. Relative cerebral blood volume (rCBV) ratios were obtained via the values of the capsular portions of the lesions and the normal white matter. All the abscesses had markedly hyperintense signals in trace diffusion images, whereas they had significant hypointense signals in ADC images. In perfusion-weighted images, the capsular portions of the abscesses demonstrated low colored areas compared with the normal white matter and the rCBV ratio calculated was 0.76 +/- 0.12 (mean +/- SD). All but two of the cystic tumors showed low signal intensity on trace diffusion-weighted images and high signal intensity on ADC maps. Hyperintense signal was found in two brain tumors mimicking brain abscesses on trace diffusion images. The rCBV values in high-grade gliomas and metastases were 5.51 +/- 2.08 and 4.58 +/- 2.19, respectively. The difference between abscesses and cystic tumors was statistically significant (P = 0.003). Perfusion MRI may allow the differentiation of pyogenic brain abscess from cystic brain tumors, making it a strong additional imaging modality in the early diagnosis of these two entities.

Glioblastoma multiforme with atypical diffusion-weighted MR findings

The aim of this study is to review the diffusion-weighted MRI findings of glioblastomas, to investigate those with atypical characteristics and to emphasise the reasons responsible for the atypical features on diffusion-weighted MR images. 48 cases of histologically proven glioblastomas were included in this study. In addition to conventional sequences of routine tumour protocol, diffusion-weighted MRI with spin-echo echo-planar sequence was performed. The cystic-necrotic components of the lesions, according to the conventional sequences, were determined on the diffusion-weighted MR images and were classified as typical or atypical. The presence of high signal intensity was accepted as an atypical feature while low signal intensity was accepted as typical. The apparent diffusion coefficient (ADC) values of the cystic components were calculated. The statistical significance of the typical and atypical glioblastomas was evaluated with the students t-test. In six of the cases apparent high signal intensity in diffusion weighted MR images was interpreted. In three cases the high signal intensity occupied all of the cystic component and in the other three most of the cystic component. The ADC values of the lesions varied between 0.86 x 10(-3) mm(2) s(-1) and 1.39 x 10(-3) mm(2) s(-1) (mean value 1.06+/-0.17 x 10(-3) mm(2) s(-1)). In 42 of the lesions the cystic-necrotic component demonstrated low signal intensity and the ADC values varied between 1.56 x 10(-3) mm(2) s(-1) and 3.32 x 10(-3) mm(2) s(-1) (mean value 2.36+/-0.46 x 10(-3) mm(2) s(-1)). The difference between ADC values of atypical and typical lesions was statistically significant (p<0.001). The vast majority of glioblastomas do not exhibit restricted diffusion in diffusion-weighted MRI, but some of them display homogeneous or heterogeneous high signal intensity and decrease of ADC values. Diffusion-weighted MRI alone is not helpful in the differentiation of malignant tumours from abscesses with low ADC values and similar conventional MRI findings.

Update on brain tumor imaging

Brain tumor imaging has evolved from a strictly morphology-based discipline to one that encompasses function, physiology, and anatomy, enabled by advances in imaging and computer technology. This review outlines the current imaging standard for patients with brain tumors and summarizes the latest advances in physiology-based imaging methods that complement traditional brain tumor imaging protocol. Emphasis is placed on the strengths and limitations of the current imaging standards and on an overview of several advanced imaging methods, including diffusion-weighted magnetic resonance imaging, perfusion magnetic resonance imaging, and proton magnetic resonance spectroscopic imaging. Basic physical principles behind each imaging method are briefly presented, along with a more in-depth discussion of the clinical applications and potential pitfalls of each technique.

Apparent diffusion coefficient measurements in the hippocampus and amygdala of patients with temporal lobe seizures and in healthy volunteers

PURPOSE

The goals of this work were to measure the apparent diffusion coefficients (ADCs) for both hippocampus and amygdala of persons diagnosed with temporal lobe epilepsy (TLE) and unilateral hippocampus pathology on magnetic resonance imaging and to evaluate the sensitivity of diffusion-weighted (DW) images in determination of the lateralization of the epileptogenic focus.

METHODS

Thirteen cases with a TLE diagnosis and 21 healthy subjects were evaluated. Fluid-attenuated inversion recovery and T2W images of TLE cases revealed hippocampal volume loss and signal intensity changes. DW images were obtained by spin-echo echo-planar sequences vertical to the hippocampal axis. Qualitative and quantitative ADCs for left and right hippocampus and the amygdala of the controls and the patients were determined. Hippocampal ADCs were obtained independently at the head, body, and tail levels of the hippocampus. Statistical evaluation was conducted with Kruskal-Wallis and Mann-Whitney U tests. Predictive cutoff levels of hippocampal ADCs for identifying pathologic areas were established through receiver operating characteristic (ROC) curve analysis.

RESULT

On conventional images, 5 of 13 cases had right hippocampal pathology, and 8 of 13 cases had left hippocampal pathology. There were no bilateral hippocampal changes in signal intensity and no cases with bilateral atrophy. The amygdala was normal in all patients except one case of hyperintense signals. No statistical differences were found between the hippocampal and amygdaloid ADCs of the control subjects (P > 0.05). However, there was a significant difference between the ADCs for the side with hippocampal pathology and the ADCs for the contralateral side, and the control group (P < 0.001). No statistical difference was detected for the amygdala (P > 0.05). Hippocampal and amygdaloid ADCs of the contralateral lesion and the values of the control group were not statistically significantly different (P > 0.05). ROC curve analysis indicated 136 as the best cutoff level for hippocampal pathology.

CONCLUSION

DW trace images are insensitive in lateralization of hippocampal pathology; however, lateralization can be achieved through ADC measurements of the hippocampus. An increase in ADC on the affected side should be considered as indicating pathology. On the other hand, amygdaloid ADC values remain inaccurate.

Diffusion-weighted MRI in the evaluation of renal lesions: preliminary results

The purpose of this study was to evaluate the capability and the reliability of diffusion-weighted MRI in the evaluation of normal kidney and different renal lesions. 39 patients (10 normal volunteers and 29 patients with known renal lesions) underwent MRI of the kidneys by using a 1.5 T superconducting magnet. Axial fat suppressed turbo spin echo (TSE) T(2) and coronal fast field echo (FFE) T(1) or TSE T(1) weighted images were acquired for each patient. Diffusion-weighted (DW) images were obtained in the axial plane during breath-hold (17 s) with a spin-echo echo planar imaging (SE EPI) single shot sequence (repetition time (TR)=2883 ms, echo time (TE)=61 ms, flip angle=90 degrees ), with b value of 500 s mm(-2). 16 slices were produced with slice thickness of 7 mm and interslice gap of 1 mm. An apparent diffusion coefficient (ADC) map was obtained at each slice position. The ADC was measured in an approximately 1 cm region of interest (ROI) within the normal renal parenchyma, the detected renal lesions and the collecting system if dilated. ADC values in normal renal parenchyma ranged from 1.72 x 10(-3) mm(2) s(-1) to 2.65 x 10(-3) mm(2) s(-1), while ADC values in simple cysts (n=13) were higher (2.87 x 10(-3) mm(2) s(-1) to 4.00 x 10(-3) mm(2) s(-1)). In hydronephrotic kidneys (n=6) the ADC values of renal pelvis ranged from 3.39 x 10(-3) mm(2) s(-1) to 4.00 x 10(-3) mm(2) s(-1). In cases of pyonephrosis (n=3) ADC values of the renal pelvis were found to be lower than those of renal pelvis of hydronephrotic kidneys (0.77 x 10(-3) mm(2) s(-1) to 1.07 x 10(-3) mm(2) s(-1)). Solid benign and malignant renal tumours (n=7) showed ADC values ranging between 1.28 x 10(-3) mm(2) s(-1) and 1.83 x 10(-3) mm(2) s(-1). In conclusion diffusion-weighted MR imaging of the kidney seems to be a reliable way to differentiate normal renal parenchyma and different renal diseases. Clinical experience with this method is still preliminary and further studies are required.

Diffusion-weighted MR imaging in the preoperative assessment of brain abscesses

BACKGROUND

Diffusion-weighted MR imaging (DWI) has recently shown promise in differentiating ring-enhancing lesions such as brain abscess and malignant neoplasm. The ability of DWI to strongly suggest brain abscess enables a neurosurgeon to alter stereotactic planning to optimize diagnosis. We report our experience with DWI in 5 patients with lesions on MR imaging and review the literature to assess the usefulness of this technique in the preoperative evaluation of cerebral abscess.

METHODS

The MR images of 5 patients presenting with ring-enhancing lesions that ultimately proved to be brain abscesses were retrospectively reviewed. In addition to standard MR sequences, trace DWI and apparent diffusion coefficient (ADC) calculations were performed on all patients. Additionally, 15 recently published articles or references in press concerning DWI in cerebral abscesses were reviewed.

RESULTS

All lesions were markedly hyperintense on DWI and had diminished ADC. Thirty-eight of 39 previously reported abscesses were hyperintense on DWI with reduced ADC. Of 165 nonpyogenic lesions with DWI findings, 87 were hypointense or isointense, 78 lesions had variable hyperintensities, and few manifested the degree of hyperintensity observed with abscesses. Most of these included chordomas and epidermoids, which are not likely to be confused with abscesses.

CONCLUSIONS

Restricted water diffusion, as indicated by hyperintensity on DWI and low ADC, in ring-enhancing lesions assists in differentiating brain abscess from necrotic tumor. This information facilitates stereotactic surgical planning: abscesses should be preferentially centrally aspirated, whereas necrotic brain tumors should have diagnostic tissue biopsied from cavity walls. Although not definitive for brain abscess, restricted water diffusion is an important MR imaging sign and is useful in neurosurgical treatment strategies for ring-enhancing lesions.