Cerebral abscesses imaging: A practical approach.

Multiple ring-enhancing lesions in the brain

Diffusion-weighted MRI features of brain abscess and cystic or necrotic brain tumors: Comparison with conventional MRI

Tumor.

ObjectiveDiscriminating pyogenic brain abscesses from cystic or necrotic tumors is sometimes difficult with CT or conventional MR imaging. Diffusion MR imaging is a valuable diagnostic test in cases of intracranial cystic masses. MethodsThis work was conducted from July 2008 to June 2013 on 90 patients; 43 males and 47 females. Their ages range from 5 to 70years. All patients were subjected to routine MRI examination and diffusion weighted imaging using 1.5T MRI scanner. Gadolinium was given to some cases on routine MRI. Diffusion weighted imaging was performed with a single-shot spin-echo echo-planar pulse sequence (b=0–1000s/mm2). The apparent diffusion coefficient values and ratio were measured. Results and conclusionsPatients in this study were categorized into three main groups; first group is brain abscesses (36 cases), 91.6% of them showed restricted diffusion, second group is malignant cystic or necrotic brain tumors, 28 cases of high grade necrotic glioma, 60.7% of them are free diffusion, and third group is benign cystic masses, arachnoid and epidermiod cysts (11 cases); all arachnoid cysts are free diffusion. From these results diffusion-weighted imaging is playing an important role in discrimination of cystic intracranial masses.

Objective: To compare the efficacy of MR spectroscopy and diffusion-weighted imaging in discriminating between cystic or necrotic tumors and pyogenic brain abscesses.Study Design: A retrospective study design.Place and Duration of Study: The Study was conducted at the Radiology Department of Nishtar Hospital Multan and General Hospital Lahore, Pakistan, from January 2022 to January 2023. Methods: A total ten patients were included in the study. Of 10 patients, 5 had pyogenic abscesses, and 5 had tumors. Tumors were metastases (2 patients), glioblastomas (2 patients), and anaplastic astrocytoma (1 patient). Proton MR spectroscopy and diffusion-weighted imaging were performed in all patients. Results: Results showed that significant resonance lines (creatine/phosphocreatine, N-acetyl aspartate, and choline) observed in normal brain parenchyma were missing in abscesses or necrosis. MR spectroscopy of abscess showed multiple resonance peaks. Diffusion-weighted images showed that all pyogenic abscesses had lower ADC values and were hyperintense compared to normal brains. Conclusion: Diffusion-weighted imaging is more accurate and less time consuming method for discrimination of brain lesions compared to MR spectroscopy. How to cite this: Saqib HA, Asghar A, Firdous A, Zahra M, Islam Z, Mushtaq S. Discrimination of Brain Abscess and Necrotic Brain Tumor with Proton MR Spectroscopy and Diffusion Weighted Imaging. Life and Science. 2023; 4(4): 432-437. doi: http://doi.org/10.37185/LnS.1.1.431

Discrimination of an infected brain tumor from a cerebral abscess by combined MR perfusion and diffusion imaging

To retrospectively determine the value of adding perfusion-weighted (PW) and diffusion-weighted (DW) sequences to a conventional magnetic resonance (MR) imaging protocol to differentiate benign from malignant tumors. The institutional ethics committee approved this retrospective study and waived the requirement to obtain informed consent. MR images in 87 women (age range, 25-87 years) who underwent imaging before surgery for complex adnexal masses-excluding endometriomas and cystic teratomas-were analyzed. Conventional morphologic, perfusion, and diffusion MR criteria of malignancy were recorded. Three independent observers reviewed images in four steps: conventional MR images alone, conventional MR images and PW images combined, conventional MR images and DW images combined, and conventional, PW, and DW MR images combined. Receiver operating characteristic curve analysis was performed to compare the results of the readings. A recursive partitioning model was built to establish a multivariate decision tree. There was almost perfect agreement for lesion characterization regardless of the reader experiment or step considered (κ = 0.811-0.929). Area under the receiver operating characteristic curve values were higher for conventional and DW images combined, conventional and PW images combined, and conventional, DW, and PW images combined compared with conventional MR images alone (P < .05). For all readers, the accuracy of conventional, PW, and DW imaging combined was higher than that of conventional MR imaging alone for benign masses (P < .01) but not for malignant masses (P = .24). The addition of both PW and DW images led to a correct change in the diagnosis in 19% (11 of 57 patients), 23% (13 of 57 patients), and 24% (14 of 57 patients) of cases for readers 1, 2, and 3, respectively, with no incorrect changes. Conventional, PW, and DW MR imaging criteria were combined to generate a decision tree giving an accuracy of 95%. The addition of PW and DW sequences to a conventional MR imaging protocol improved the diagnostic accuracy in the characterization of complex adnexal masses.

The purpose of this study is to compare the effectiveness of relative cerebral blood volume, apparent diffusion coefficient and spectroscopic imaging in differentiating between cerebral abscesses and necrotic tumours. In the prospective study, a 3-tesla MR unit was used to perform proton MR spectroscopy, diffusion and perfusion imaging in 20 patients with cerebral abscesses and 26 patients who had solitary brain tumours (14 high-grade gliomas and 12 metastases). We found the mean apparent diffusion coefficient value at the central cavities of the cerebral abscesses to be significantly lower than in necrotic tumours. The mean relative cerebral blood volume values of the necrotic tumour wall were statistically significantly higher than the mean relative cerebral blood volume values of the cerebral abscess wall by the Student's t-test. The proton spectra obtained revealed amino acids only in the cerebral abscesses. Although the conventional MRI characteristics of cerebral abscesses and necrotic tumours may sometimes be similar, diffusion, perfusion-weighted and spectroscopic MRI enables distinction between the two.

Evaluation of cerebral abscesses by diffusion-weighted MR imaging and MR spectroscopy

• Distinguishing between cerebral abscess and rim-enhancing tumor is a problem that is encountered frequently by radiologists. Conventional contrast-enhanced MRI reveals ring enhancement of a brain abscess that is similar to the ring enhancement of a necrotic high-grade glioma or metastasis.• Advanced MRI techniques (DWI, MRS and DSC MR perfusion) may be used to differentiate between cerebral abscesses and high grade brain neoplasms.• DWI is an advanced MRI technique that provides the physiological nature of the disease based on motion of water molecules across cell membrane.• DWI allows assessment of the cellularity of the lesion non-invasively, as cellular and subcellular elements significantly impede the mobility of water molecules, thus densely cellular lesions show restricted diffusion and hence low ADC values. • Magnetic Resonance spectroscopy (MRS) is a non-invasive diagnostic test for measuring biochemical changes in the brain, it MRS is capable of differentiating normal from pathologic brain.• Dynamic susceptibility contrast (DSC) perfusion MRI is a technique that allows derivation of relative cerebral blood volume (rCBV) maps on the basis of the susceptibility effect related to passage of MRI contrast material through tissue.• It provides noninvasive physiologic measurements of tumor vascularity and relative cerebral blood volume (rCBV) maps, which can be used to identify and quantify areas of neovascularization.• We try to evaluate the role of advanced MRI techniques (DWI, MRS, DSC PERFUSION) to reach a final diagnosis in a case of brain abscess versus a cystic or necrotic tumor.

This study was undertaken to evaluate the usefulness of perfusion-weighted imaging (PWI) in the differential diagnosis of ring-enhancing cerebral lesions, including abscesses, high-grade gliomas and metastases. Nine cerebral abscesses (five pyogenic, four from Toxoplasma gondii), ten glioblastomas and five cerebral metastases in 19 patients were studied with gadolinium-enhanced magnetic resonance imaging, diffusion-weighted imaging (DWI) including calculation of mean apparent diffusion coefficient (ADC) of the lesion core, and PWI. At PWI, the mean of the maximum regional cerebral blood volume (rCBV) was calculated in the gadolinium-enhancing peripheral solid areas and compared with that of the contralateral normal-appearing white matter [ratio=rCBV (lesion)/rCBV (contralateral normal-appearing white matter)]. DWI achieved the differential diagnosis in all cases except for the four Toxoplasma abscesses. At PWI, the mean ratio of the rCBV of the capsular portion was 0.72+/-0.08 (range 0.60-0.82) in the pyogenic abscesses, 0.84+/-0.07 (range 0.75-0.91) in the Toxoplasma abscesses, 4.45+/-1.5 (range 2.9-8.0) in the high-grade gliomas and 3.58+/-0.68 (range 3.28-4.27) in the metastases. PWI seems to be useful in the differential diagnosis of ring-enhancing cerebral lesions. High rCBV values in the peripheral areas appear to indicate the possibility of a necrotic tumour, whereas low values tend to indicate an abscess.

Role of diffusion weighted imaging and proton magnetic resonance spectroscopy in ring enhancing brain lesions

Dynamic contrast agent-enhanced perfusion magnetic resonance (MR) imaging provides physiologic information that complements the anatomic information available with conventional MR imaging. Analysis of dynamic data from perfusion MR imaging, based on tracer kinetic theory, yields quantitative estimates of cerebral blood volume that reflect the underlying microvasculature and angiogenesis. Perfusion MR imaging is a fast and robust imaging technique that is increasingly used as a research tool to help evaluate and understand intracranial disease processes and as a clinical tool to help diagnose, manage, and understand intracranial mass lesions. With the increasing number of applications of perfusion MR imaging, it is important to understand the principles underlying the technique. In this review, the essential underlying physics and methods of dynamic contrast-enhanced susceptibility-weighted echo-planar perfusion MR imaging are described. The clinical applications of cerebral blood volume maps obtained with perfusion MR imaging in the differential diagnosis of intracranial mass lesions, as well as the pitfalls and limitations of the technique, are discussed. Emphasis is on the clinical role of perfusion MR imaging in providing insight into the underlying pathophysiology of cerebral microcirculation.

Whether a brain abscess is apparent by imaging depends on the stage of the abscess at the time of imaging, as well as the etiology of the infection. Because conventional magnetic resonance imaging (MRI) is limited in its ability to distinguish brain abscesses from necrotic tumors, advanced techniques are required. The management of these two disease entities differs and can potentially affect the clinical outcome. We report a case having atypical imaging features of a pyogenic brain abscess on advanced MRI, in particular, on diffusion-weighted and perfusion imaging, in a patient with osteosarcoma undergoing chemotherapy.

Cough and confusion in an elderly man with chronic lymphocytic leukemia