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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 15  |  Issue : 1  |  Page : 26-29

Role of diffusion-weighted imaging in evaluation of intracranial infections


Department of Radiology, Jawaharlal Nehru Medical College, Datta Meghe Institute of Medical Sciences (Deemed to be University), Sawangi (Meghe), Wardha, Maharashtra, India

Date of Submission27-Sep-2019
Date of Decision30-Sep-2019
Date of Acceptance10-Oct-2019
Date of Web Publication13-Oct-2020

Correspondence Address:
Dr. R P Dhande
Department of Radiology, JNMC, Sawangi, Wardha, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jdmimsu.jdmimsu_146_19

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  Abstract 


Objective: The objective is to evaluate the role of diffusion weighted imaging (DWI) in evaluation of intracranial infections. Methods: The present study was conducted in the Department of Radiology, Jawaharlal Nehru Medical College, Sawangi, Maharashtra, India. Participants after understanding the study protocol and procedure were asked to give their written consent for the study. DWI was performed on 24 patients having ring-enhancing lesions on their post-contrast brain magnetic resonance imaging scans with infective etiology. Commonly found lesions were tuberculomas, cysticercosis, pyogenic abscess, and fungal infections. Correlation of all these findings was done with histopathology obtained in all these patients. DWI and mean apparent diffusion coefficient (ADC) value were calculated. Results: Tuberculomas showed heterogeneous areas of restricted diffusion on DWI were as pyogenic abscess showed homogenous restricted diffusion, the mean ADC values from of these lesions were 0.74 × 10−3 and 0.5 × 10−3 mm2/s, respectively. Fungal abscesses were also ring enhancing. They had restricted diffusion in the central nonenhancing portions. Mean ADC for all fungal lesions was 0.33 ± 0.06 × 10−3 mm2/s, with an average ADC ratio of 0.43. However, there was no significant difference between ADC values of pyogenic abscess and fungal abscess. The vesicular cysts of NCC showed ring enhancement but no significant restriction on DWI, the ADC values from the vesicular cysticercus cysts core measured (1.66 ± 0.29) ×10 − 3 mm2/s, which was highest among the infective intracranial infection. Conclusion: DWI is noninvasive method with high sensitivity and specificity which can help in differentiation of infective ring-enhancing lesions. Fungal cerebral abscesses may have central restricted diffusion similar to that of bacterial abscesses but with histologic features of acute or chronic inflammation and necrosis rather than suppuration. Altered water diffusion in these lesions likely reflects highly proteinaceous fluid and cellular infiltration. The tuberculoma and NCC lesions showed heterogeneous and no restriction on DWI respectively with significant change in the ADC values which helped in differentiating these lesions. This modality should be read in conjunction with conventional imaging.

Keywords: Diffusion imaging, intracranial infections, magnetic resonance imaging


How to cite this article:
Dhande R P, Singhania A, Gupta A. Role of diffusion-weighted imaging in evaluation of intracranial infections. J Datta Meghe Inst Med Sci Univ 2020;15:26-9

How to cite this URL:
Dhande R P, Singhania A, Gupta A. Role of diffusion-weighted imaging in evaluation of intracranial infections. J Datta Meghe Inst Med Sci Univ [serial online] 2020 [cited 2020 Oct 28];15:26-9. Available from: http://www.journaldmims.com/text.asp?2020/15/1/26/297968




  Introduction Top


Multiple ring-enhancing lesions of the brain are one of the most commonly encountered abnormalities on neuroimaging. These can be caused by a variety of infectious, neoplastic, inflammatory, or vascular diseases. Distinguishing nonneoplastic causes from neoplastic lesions is extremely important because a misdiagnosis can lead to unwarranted neurosurgery and exposure to toxic chemotherapy or potentially harmful brain irradiation.[1]

Cerebral abscess is a well-described condition in immunocompromised patients.[2] Abscesses may be secondary to bacterial, fungal, or parasitic organisms. These lesions often produce complex clinical and radiologic findings and require prompt recognition and treatment to avoid a fatal neurologic outcome.

Magnetic resonance imaging (MRI) is a sensitive and specific technique for the diagnosis of pyogenic bacterial abscess. Typical findings are a mass lesion with a thin, smooth rim of contrast enhancement, a variable degree of surrounding vasogenic edema, and markedly restricted diffusion of water in the central nonenhancing region.[3] Abnormal diffusion-weighted imaging (DWI) findings in pyogenic brain abscess have been attributed to restricted diffusion of water due to the high viscosity and cellularity of pus.[4],[5]

DWI provides a way to assess the diffusion properties of the water molecules in tissue and has been used in clinical applications such as infection, ischemia, tumors, epilepsy, and white matter disorders.[6]

The addition of proton MR spectroscopy and magnetization transfer MRI to the brain infection protocol has improved the tissue characterization of tuberculomas and tuberculous abscesses considerably.[7],[8]

The purpose was to evaluate the usefulness of the DWI in the differential diagnosis of ring-enhancing cystic brain lesions [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5].
Figure 1: Tuberculosis. Coronal T2-weighted images (a) and postcontrast T1 weighted images (b) show a heterogeneous lesion with predominant high-signal intensity on T2-weighted images and ring enhancement, located on the right hippocampus. Not also the meningeal enhancement on the tentorium bilaterally. The diffusion-weighted imaging (c) and ADC map (d) demonstrate reduced diffusion on the center of the lesion

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Figure 2: Pyogenic abscess. Axial fluid-attenuated inversion recovery (a) demonstrates a round hypointense mass surrounded by vasogenic edema in the left frontal lobe. Postgadolinium T1weighted images (b) shows the lesion with ring enhancement. Diffusion-weighted imaging (c) and the ADC map (d) reveal reduced diffusion in abscess capsule and facilitated diffusion in the core of the lesion. The histologic evaluation defined the diagnosis of early-stage streptococcus viridans abscess

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Figure 3: Cryptococcosis. Axial T2-weighted images (a) of a patient with cryptococcal meningoencephalitis demonstrates foci of increased signal in the basal ganglia bilaterally, mainly in the left caudate. These lesions did not enhance on postcontrast T1-weighted images (b). Axial diffusion-weighted imaging (c) shows hypointense signal, and corresponding ADC map (d) reveals hyperintense signal in these lesions indicating facilitated water diffusion

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Figure 4: Toxoplasmosis. Postcontrast T1-weighted images (a) demonstrates multiple round hypointense lesions with ring enhancement. Diffusion-weighted imaging (b) shows the heterogeneity of these lesions on diffusion imaging (b, diffusion-weighted imaging and c, ADC map), with areas of reduced diffusion (arrow) and T2 shine-through effect on the wall, and facilitated diffusion on the center of the lesion

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Figure 5: Cysticercosis. Fluid-attenuated inversion recovery (a), postcontrast T1 weighted images (b), and diffusion-weighted imaging (c) show cysticercosis in different phases. A cystic-appearing lesion with a mural nodule (scolex) that has a high signal on diffusion-weighted imaging is seen in the right caudate (vesicular stage). Also, a lesion at the colloidal stage is seen on the left lentiform nucleus. This lesion has high-signal intensity on fluid-attenuated inversion recovery and ring enhancement (arrow), as well as demonstrating reduced diffusion on diffusion-weighted imaging (arrow). Another small lesion with high signal intensity on diffusion-weighted imaging is seen on the right temporal lobe

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  Methods Top


This prospective study was performed within the span of 1 year. All these patients presented to us with a varied clinical presentation such as fever, signs of mental irritation, and seizures.

The total number of patients was 24 out of which (15 males and 9 females) who suffered from infective brain lesions such as pyogenic brain abscesses, fungal brain abscess, tuberculomas, and NCC. Age range between 10 and 70 years, mean 43 years, all patients were referred from the medicine and neurosurgery department of our institution, these patients had ring-enhanced brain lesions on post-contrast T1 images and the final diagnosis was confirmed on histopathology.

Ethical clearance

Ethical clearance was obtained from the Institutional Ethical Committee of JNMC, Sawangi (Meghe), Wardha, on 10th June 2019. With ethical clearance no DMIMS(DU)/IEC/2019-20/348.

Imaging procedures

All patients showing evidence of ring-enhancing brain lesion in post-contrast T1WI of conventional MRI were examined using a 1.5T MR scanner. Conventional MR and DWI were carried out at the same time. Conventional MRI were obtained with axial T2-weighted, axial T1-weighted, coronal fluid-attenuated inversion recovery (and axial contrast-enhanced (0.1 mmol/kg of contrast agent) T1-weighted images. Contrast-enhanced images were obtained. DWIs were obtained in the axial plane using an echo-planar spin-echo pulse sequence with three b values (0, 500, 1000 s/mm2).

Postprocessing of ADC map

It was done using the standard software supplied on the machine console to obtain the ADC value and map; the ADC values were measured in the regions of interest in the center of the lesion (cavity of the abscess and necrotic portion of the tumor) and in comparable normal contralateral regions in the white and gray matter of the brain. The ADC values of the gray and white matter were 0.85 ± 0.13 · 10−3 and 0.8 ± 0.13 · 10−3 mm2/s, respectively.[3]


  Results Top


Out of 24 patients, 10 patients had pyogenic abscess, 5 of tuberculoma, 3 fungal abscess, and 6 had NCC.

All pyogenic brain abscesses showed central high-signal intensity, and low ADC values (mean, 0.52 × 103 mm2/s; range, 0.36–0.75 × 103 mm2/s) indicating restricted diffusion. All lesions had notable surroundingT2-weighted hyperintensity in a pattern consistent with that of vasogenic edema. The bacterial abscesses had restricted diffusion. These ADC values were not significantly different from those of fungal lesions.

At the time of the diagnosis, all patients with fungal infection had underlying medical conditions known to be associated with immunosuppression. Two patients had HIV infection and one patient had hematologic malignancy. All patients had neutropenia and lymphopenia. MRI demonstrated ring-enhancing lesions the lesions werelocated at the gray matter–white matter junctions and inthe basal ganglia.

On DWI, the lesions of fungal abscess had prominent central hyperintensity, and ADC maps showed hypointensity, consistent with restricted diffusion. Mean ADC for all lesions was 0.33+ −0.06 × 10 − 3 mm2/s, with an average ADC ratio of 0.43.

In patients with tuberculomas, the MRI findings showed T2 hyperintensity with heterogeneous area of restricted diffusion, the mean ADC values from the core were (1.24 ± 0.32) ×10−3 mm2. The ADC value from the core of these lesions was significantly higher compared to brain abscess.

The vesicular cysts appeared hyperintense on T2 and hypointense on T1-weighted images with scolex that appeared hypointense on T2 and iso to minimally hyperintense on T1-weighted images. ADC from the vesicular cysticercus cysts core measured (1.66 ± 0.29) ×10 −3 mm2/s, while from the degenerating cysts core it measured (1.51 ± 0.23) ×10−3 mm2/s. There was no significant difference in the ADC of the NCC. ADC values from the core of all the group of brain abscess and tuberculomas were significantly lower compared to the ADC values from the core of the NCC.


  Discussion Top


Diffusion imaging is helpful in the differential diagnosis of ring-enhancing brain lesions. Although exceptions exist, lesions such as neoplasms, subacute late ischemic infarctions, toxoplasmosis abscesses, and demyelinating plaques typically have elevated diffusion, whereas pyogenic bacterial abscesses typically have decreased diffusion in the central nonenhancing portion.[9],[10],[11],[12]

In the present study, we have observed that the tuberculomas with T2 hypointensity had higher ADC value. This is similar to what has been described in pyogenic abscesses.

Kaminogo et al.[13] have described two patients of caseating tuberculomas, where the core of the lesion showed hyperintensity on DWI. They have reported ADC values similar to pyogenic abscesses in both these patients. However, in the present study, we have seen ADC values of the tuberculoma was much higher than that of pyogenic and fungal brain abscess. The high ADC in theT2 hypointense core of the tuberculoma signifies necrosis that is seen as caseous necrosis on histopathology. This necrosis is devoid of any cellularity and is extremely viscous (solid).

It may sometimes not possible to separate cysticercus granuloma from tuberculoma especially when it shows a hyperintense core with peripheral hypointensity on T2 weighted images.[14] In such a situation, the demonstration of heterogenous restricted diffusion in tuberculoma may help to differentiate it from cysticercus granuloma. In the present study, vesicular cysticercosis showed a high ADC value consistent with cystic lesion.

In 3 patients with fungal cerebral abscesses, ring enhancement was present, and 2 had centrally restricted diffusion in a pattern similar to that seen in pyogenic abscesses. The changes in diffusion likely reflected proteinaceous fluid and cellular infiltration in the lesions. One patient had a peripheral rim of restricted diffusion with the central region of elevated diffusion, and histopathology revealed that this lesion had not yet developed a well-defined capsule, consistent with early abscess formation.[15]


  Conclusion Top


We conclude that DWI is noninvasive method with high sensitivity and specificity, which can help in the differentiation of infective ring-enhancing lesions; there is a wide spectrum of ADC values in the core of different lesions such as pyogenic abscess, fungal abscess, tuberculomas, and NCC. The tuberculoma and NCC lesions showed heterogeneous and no restriction on DWI, respectively, with significant change in the ADC values which helped in differentiating these lesions.

Fungal cerebral abscesses have decreased diffusion, similar to pyogenic abscesses. It should be included in the differential diagnosis of ring-enhancing lesions with centrally restricted diffusion, especially in immunocompromised patients.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Garg RK, Sinha MK. Multiple ring –enhancing lesions of the brain. J Postgrad Med 2010;56:307.  Back to cited text no. 1
    
2.
Guppy KH, Thomas C, Thoma K, Anderson D. Cerebral fungal infections in the immunocompromised host: A literature review and a new pathogen–Chaetomiumatrobrunneum: Case report. Neurosurgery 1992;43:1463-9.  Back to cited text no. 2
    
3.
Ebisu T, Tanaka C, Umeda M, Kitamura M, Naruse S, Higuchi T, et al. Discrimination of brain abscess from necrotic or cystic tumors by diffusion-weighted echo planar imaging. Magn Reson Imaging 1996;14:1113-6.  Back to cited text no. 3
    
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Leuthardt EC, Wippold FJ 2nd, Oswood MC, Rich KM. Diffusion weighted MR imaging in the preoperative assessment of brain abscesses. Surg Neurol 2002;58:395-402.  Back to cited text no. 4
    
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Rana S, Albayram S, Lin DD, Yousem DM. Diffusion-weighted imaging and apparent diffusion coefficient maps in a case of intracerebral abscess with ventricular extension. AJNR Am J Neuroradiol 2002;23:109-12.  Back to cited text no. 5
    
6.
Rowley HA, Grant PE, Roberts TP. Diffusion MR imaging. Theory and applications. Neuroimaging Clin N Am 1999;9:343-61.  Back to cited text no. 6
    
7.
Gupta RK, Pandey R, Khan EM, Mittal P, Gujral RB, Chhabra DK. Intracranial tuberculomas: MRI signal intensity correlation with histopathology and localized proton spectroscopy. Magn Reson Med 1993;11:443-9.  Back to cited text no. 7
    
8.
Gupta RK, Roy R, Dev R, Husain M, Poptani H, Pandey R,et al. Finger printing of Mycobacterium tuberculosis in patients with intracranial tuberculomas by using in vivo, ex vivo, and in vitro magnetic resonance spectroscopy. Magn Reson Med. 1996;36:829-33.  Back to cited text no. 8
    
9.
Toh CH, Wei KC, Chang CN, Hsu PW, Wong HF, Ng SH, et al. Differentiation of brain abscesses from necrotic glioblastoma and cystic metastatic brain tumours with diffusion tensor imaging. AJNR 2011;32:1646-51.  Back to cited text no. 9
    
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Bulakbasi N, Kocaoglu M, Ors F, Tayfun C, Uçöz T. Combination of single-voxel proton MR spectroscopy and apparent diffusion coefficient calculation in the evaluation of common brain tumors. AJNR Am J Neuroradiol 2003;24:225-33.  Back to cited text no. 10
    
11.
Hassan MA, Musa KM, Ali II, Safwat A. Role of MR spectroscopy and diffusion weighted techniques in discrimination between capsular stage brain abscesses, necrotic and cystic brain lesions. Med J Cairo Univ 2012;80:699-710.  Back to cited text no. 11
    
12.
Bryan RN, McLaughlin A. Imaging brain abscesses with diffusion-weighted and other sequences. AJNR Am J Neuroradiol 1999;20:1193.  Back to cited text no. 12
    
13.
Kaminogo M, Ishimaru H, Morikawa M, Suzuki Y, Shibata S. ProtonMR spectroscopy and diffusion-weighted MR imaging for the diagnosis of intracranial tuberculomas. Report of two cases. Neurol Res 2002;24:537-4.  Back to cited text no. 13
    
14.
Lim CC, Lee W, Chng SM, Sitoh YY, Hui F. Diffusion-weighted MR imaging in intracranial infections. Ann Acad Med Singapore 2003;32:446-9.  Back to cited text no. 14
    
15.
Jaipuriya P, Pate MY, Iratwar S, Mahakalkar CC, Chandankhede A. Clinical Study, Evaluation, and Management of Cases of Intracranial Tumors Admitted at Acharya Vinoba Bhave Rural Hospital, Sawangi (Meghe). J Datta Meghe Inst Med Sci Univ 2017;12:26-31. Available from: https://doi.org/10.4103/jdmimsu.jdmimsu_17_17. [Last accessed on 2019 Sep 02].  Back to cited text no. 15
    


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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]



 

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