Nuzhat Husain

Comparative Evaluation of Fungal, Tubercular, and Pyogenic Brain Abscesses with Conventional and Diffusion MR Imaging and Proton MR Spectroscopy

BACKGROUND AND PURPOSE: It is difficult to differentiate the cause of brain abscesses with the use of CT and MR imaging. We did a comparative evaluation of pyogenic, tubercular, and fungal brain abscesses by using conventional, diffusion-weighted imaging (DWI), and proton MR spectroscopy (PMRS) with an aim to define the unique features that may differentiate among the pyogenic, tubercular, and fungal brain abscesses. MATERIALS AND METHODS: We performed a retrospective analysis on 110 patients with surgically proved brain abscesses. Imaging studies included T2, T1, postcontrast T1, DWI, and PMRS. Apparent diffusion coefficient (ADC) of the wall and cavity of the abscesses were quantified. The morphologic, physiologic, and metabolite features of pyogenic (n = 91), tubercular (n = 11), and fungal (n = 8) abscesses were compared. RESULTS: The pyogenic abscesses had smooth (55/91) and lobulated (36/91) walls, whereas the tubercular abscesses had smooth (4/11), lobulated (6/11), or crenated walls (1/11) with no intracavitary projections. The fungal abscesses showed irregular walls (lobulated 4/8, crenated 4/8) with intracavitary projections (8/8). The wall as well as the cavity showed low ADC in the pyogenic and tubercular abscesses. In the fungal abscesses, the wall and projections showed low ADC (8/8); however, the cavity itself showed high ADC (8/8). PMRS showed cytosolic amino acids (89/91), acetate (25/91), and succinate (18/91) in the pyogenic abscesses, whereas lipid/lactate (11/11) was seen in the tubercular abscesses. The fungal abscesses showed lipid (4/8), lactate (7/8), amino acids (4/8), and multiple peaks between 3.6 and 3.8 ppm assigned to trehalose (5/8). CONCLUSION: Based on the morphologic, ADC, and metabolite information, it may be possible to differentiate among the pyogenic, tubercular, and fungal brain abscesses.

Role of Diffusion-weighted Imaging and In Vivo Proton Magnetic Resonance Spectroscopy in the Differential Diagnosis of Ring-enhancing Intracranial Cystic Mass Lesions

Objectives: Proton magnetic resonance spectroscopy (PMRS) and diffusion-weighted imaging (DWI) were compared to determine which technique is more effective in the differential diagnosis of cystic intraparenchymal ring-enhancing lesions with variable perifocal edema. Methods: Fifty-two patients (abscesses [n = 29], tumor cysts [n = 20], and benign cysts [n = 3]) formed the basis for comparative evaluation in this study. The criteria for abscess diagnosis were apparent diffusion coefficient (ADC) values less than 0.9 ± 1.3 × 10−3 mm2/s and presence of lactate cytosolic amino acids (AAs) with/without succinate, acetate, alanine, and glycine on PMRS. Criteria for nonabscess cyst identification were ADC values of 1.7–3.8 × 10−3 mm2/s and presence of lactate and choline on PMRS. On the basis of these criteria, patients were categorized into abscess (n = 29) and nonabscess (n = 23) groups. Sensitivity and specificity of PMRS and DWI with respect to the final diagnosis were calculated based on the efficacy of these techniques. Results: Apparent diffusion coefficient values in 21 patients with abscesses were observed within the range of defined criteria, whereas in 8 patients, ADC values were beyond the range of defined criteria. Lactate and AAs with or without other metabolites were observed in 25 of 29 cases of abscesses on PMRS. In the nonabscess group, ADC values of cystic lesions in all patients were consistent with respect to the defined criteria. Only lactate was seen in 14 of 23 patients, whereas both lactate and choline were visible in 6 patients. In 3 patients with neurocysticercosis, AAs (n = 2), lactate (n = 3), acetate (n = 1), succinate (n = 3), choline (n = 2), and alanine (n = 3) were seen. The sensitivity of DWI and PMRS for differentiation of brain abscess from nonbrain abscess was 0.72 and 0.96, respectively, whereas the specificity was 1 for both techniques. Conclusion: Demonstration of restricted diffusion on DWI with reduced ADC is highly suggestive of brain abscess; however, in the absence of restriction, PMRS is mandatory to distinguish brain abscesses from cystic tumors.

Biological correlates of diffusivity in brain abscess

Restricted diffusion in brain abscess is assumed to be due to a combination of inflammatory cells, necrotic debris, viscosity, and macromolecules present in the pus. We performed diffusion‐weighted imaging (DWI) on 41 patients with proven brain abscesses (36 pyogenic and five tuberculous), and correlated the apparent diffusion coefficient (ADC) from the abscess cavity with viable cell density, viscosity, and extracellular‐protein content quantified from the pus. On the basis of the correlation between cell density and ADC in animal tumor models and human tumors in the literature, we assumed that the restricted ADC represents the cellular portion in the abscess cavity. We calculated restricted and unrestricted lesion volumes, and modeled cell density over the restricted area with viable cell density per mm3 obtained from the pus. The mean restricted ADC in the cavity (0.65 ± 0.01 × 10–3 mm2/s) correlated inversely with restricted cell density in both the pyogenic (r = −0.90, P = <0.05) and tuberculous (0.60 ± 0.04 × 10–3 mm2/s, r = −0.94, P = <0.05) abscesses. We conclude that viable cell density is the main biological parameter responsible for restricted diffusion in brain abscess, and it is not influenced by the etiological agents responsible for its causation. Magn Reson Med, 2005.

Prospective evaluation of in vivo proton MR spectroscopy in differentiation of similar appearing intracranial cystic lesions

Proton MR spectroscopy (PMRS) has been found to be useful in differentiating various cystic intracranial lesions. The purpose of the present study was to prospectively evaluate the spectral pattern of various cystic lesions of brain with similar imaging appearances and to determine the accuracy of this technique in the differential diagnosis of these lesions. Fifty-one patients with intracranial cystic lesions (21 abscesses, 20 gliomas, 3 hydatid cysts, 3 arachnoid cysts, 1 case each of glioependymal cyst, xanthogranuloma, infarction and acoustic neuroma) were evaluated with conventional MR imaging and in vivo PMRS. Ex vivo PMRS of the cystic contents aspirated at surgery in 31 cases was also done to confirm the in-vivo results. Preoperative diagnosis of the lesions was based on the results of in vivo PMRS. In vivo PMRS accurately predicted the pathology in 92% of the cases. We conclude that in-vivo PMRS complements imaging in better characterization of cystic intracranial mass lesions.

Discriminant analysis to classify glioma grading using dynamic contrast-enhanced MRI and immunohistochemical markers.

IntroductionThe purpose of the present study was to look for the possible predictors which might discriminate between high- and low-grade gliomas by pooling dynamic contrast-enhanced (DCE)-perfusion derived indices and immunohistochemical markers.MethodsDCE-MRI was performed in 76 patients with different grades of gliomas. Perfusion indices, i.e., relative cerebral blood volume (rCBV), relative cerebral blood flow (rCBF), permeability (ktrans and kep), and leakage (ve) were quantified. MMP-9-, PRL-3-, HIF-1α-, and VEGF-expressing cells were quantified from the excised tumor tissues. Discriminant function analysis using these markers was used to identify discriminatory variables using a stepwise procedure. To look for correlations between immunohistochemical parameters and DCE metrics, Pearsons correlation coefficient was also used.ResultsA discriminant function for differentiating between high- and low-grade tumors was constructed using DCE-MRI-derived rCBV, kep, and ve. The form of the functions estimated are “D1 = 0.642 × rCBV + 0.591 × kep − 1.501 × ve − 1.550” and “D2 = 1.608 × rCBV + 3.033 × kep + 5.508 × ve − 8.784” for low- and high-grade tumors, respectively. This function classified overall 92.1% of the cases correctly (89.1% high-grade tumors and 100% low-grade tumors). In addition, VEGF expression correlated with rCBV and rCBF, whereas MMP-9 expression correlated with kep. A significant positive correlation of HIF-1α with rCBV and VEGF expression was also found.ConclusionDCE-MRI may be used to differentiate between high-grade and low-grade brain tumors non-invasively, which may be helpful in appropriate treatment planning and management of these patients. The correlation of its indices with immunohistochemical markers suggests that this imaging technique is useful in tissue characterization of gliomas.

Quantification of physiological and hemodynamic indices using T1 dynamic contrast-enhanced MRI in intracranial mass lesions

To estimate precontrast tissue parameter (T10) using fast spin echo (FSE) and to quantify physiological and hemodynamic parameters with leakage correction using T1‐weighted dynamic contrast‐enhanced (DCE) perfusion imaging.

Spectroscopic increase in choline signal is a nonspecific marker for differentiation of infective/inflammatory from neoplastic lesions of the brain

We report in vivo proton magnetic resonance (MR) spectroscopic findings in three benign infective/inflammatory lesions (one case each of tuberculoma, fungal granuloma, and xanthogranuloma), which showed high choline along with the presence of lipid/lactate, a feature characteristically described in neoplastic lesions. Histopathology of the lesions showed inflammatory cellular infiltrates with areas of necrosis/caseation. The spectroscopic‐visible increased choline resonance in these lesions is probably the result of cellularity. We conclude that increased choline, along with the presence of lipid/lactate is a nonspecific finding and may not be of much value in the differentiation of neoplastic from nonneoplastic infective/inflammatory intracranial mass lesions. J. Magn. Reson. Imaging 2001;14:8–15.

Differences in virulence attributes between cytolethal distending toxin positive and negative Campylobacter jejuni strains.

Campylobacter jejuni is a common gastrointestinal bacterial pathogen. Although cytolethal distending toxin (CDT) is proposed to be an important virulence determinant of this pathogen, how CDT(+) and CDT(-) strains differ in their biological properties remains largely unknown. The virulence properties of CDT(+) and CDT(-) strains were studied on HeLa cells and in the suckling mouse model. Presence of the cdtB gene in Campylobacter species was determined by PCR. Five each of CDT(+) and CDT(-) C. jejuni strains were subjected to adherence, invasion and cytotoxicity assay on the HeLa cell line. Bacterial culture supernatants with and without CDT activity were inoculated intragastrically into 2-day-old suckling mice. The mice were sacrificed within 48 h. Histopathological examination of stomach, jejunum, ileum and colon was performed by haematoxylin/eosin staining. cdtB was detected in 88 % and 14 % of C. jejuni and Campylobacter coli strains, respectively. CDT(+) C. jejuni strains adhered to and invaded HeLa cells in significantly higher numbers than CDT(-) strains [CDT(+) vs CDT(-), adherence 2.7 x 10(4)+/-3.5 x 10(4) vs 2.7 x 10(2)+/-1.9 x 10(2); invasion 1.0 x 10(3)+/-1.3 x 10(3) vs 1.4 x 10(1)+/-3.1 x 10(1); P<0.01]. Culture supernatants of all CDT(+) strains demonstrated CDT activity on HeLa cells. Mice inoculated with supernatant containing CDT activity had moderate to severe pathology in different parts of their gastrointestinal tract, with the colon being the major target. Mice inoculated with supernatant lacking CDT activity showed no significant pathology in the gastrointestinal tract. The results demonstrate that CDT(+) C. jejuni strains adhere to and invade epithelial cells more efficiently than CDT(-) strains. CDT is responsible for intestinal pathology and the colon is the major target.

Differentiation of infective from neoplastic brain lesions by dynamic contrast-enhanced MRI

IntroductionIt is not always possible to differentiate infective from neoplastic brain lesions with conventional MR imaging. In this study, we assessed the utility of various perfusion indices in the differentiation of infective from neoplastic brain lesions.Methods A total of 103 patients with infective brain lesions (group I, n=26) and neoplastic brain lesions (high-grade glioma, HGG, group II, n=52; low-grade glioma, LGG, group III, n=25) underwent dynamic contrast-enhanced MR imaging. The perfusion indices, including relative cerebral blood volume (rCBV), relative cerebral blood flow (rCBF), transfer coefficient (ktrans) and leakage (ve), were calculated and their degree of correlation with immunohistologically obtained microvessel density (MVD) and vascular endothelial growth factor (VEGF) determined. The rCBV was corrected for the leakage effect. Discriminant analysis for rCBV, rCBF, ktrans and ve was performed to predict the group membership of each case and post hoc analysis was performed to look for group differences.ResultsThe rCBV, rCBF, ktrans, ve, MVD and VEGF were significantly different (P<0.001) between the three groups. Discriminant analysis showed that rCBV predicted 73.1% of the infective lesions, 84.6% of the HGG and 72.0% of the LGG. The rCBF classified 86.5% of the HGG, 80.0% of the LGG and 65.4% of the infective lesions. The ktrans discriminated 98.1% of the HGG, 76.0% of the LGG and 88.5% of the infective lesions correctly. The ve classified 98.1% of the HGG, 76.0% of the LGG and 84.6% the infective lesions. The rCBV was correlated significantly with MVD and VEGF, while the correlation between ktrans and MVD was not significant.ConclusionPhysiological perfusion indices such as ktrans and ve appear to be useful in differentiating infective from neoplastic brain lesions. Adding these indices to the current imaging protocol is likely to improve tissue characterization of these focal brain mass lesions.

Improved bolus arrival time and arterial input function estimation for tracer kinetic analysis in DCE-MRI.

To develop a methodology for improved estimation of bolus arrival time (BAT) and arterial input function (AIF) which are prerequisites for tracer kinetic analysis of dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) data and to verify the applicability of the same in the case of intracranial lesions (brain tumor and tuberculoma).