British Journal of Radiology (2006) 79, e156-e161
© 2006 British Institute of Radiology
doi: 10.1259/bjr/27055708
Unusual findings in cerebral abscess: report of two cases
E J Lee, MD
1
K J Ahn, MD
2
Y S Ha, MD
3
H E Oh, MD
4
C S Park, MD
1
S-Y Song, MD
1
N H Park, MD
1 and
M S Kim, MD
1
1 Department of Radiology, College of Medicine, Myongji Hospital, Kwandong University of Korea, 2 Department of Radiology, College of Medicine, The Catholic University of Korea, 3 Department of Neurosurgery, College of Medicine, Myongji Hospital, Kwandong University of Korea, 4 Department of Pathology, College of Medicine, Myongji Hospital, Kwandong University of Korea, 697-24, Hwajung-Dong, Dukyang-Gu, Koyang-City, 412-270, Korea
 |
Abstract
|
|---|
Markedly restricted water diffusion is a characteristic of purulent fluid in brain abscesses. We report two cases of brain abscesses with unusual diffusion findings.
|
Introduction
|
|---|
Brain abscesses are potentially life-threatening conditions for which an immediate correct diagnosis is necessary in order to administer appropriate treatment. A clinical diagnosis is challenging because the signs and symptoms are often non-specific and overlap with those of other intracranial mass lesions. Uniformly thin and spherical rims are characteristic of cerebral abscesses. Nevertheless, a variety of tumours, including gliomas and metastases, can have similar appearances [1–3].
Recent reports claim that brain abscesses can be differentiated from cystic or necrotic brain tumours with diffusion-weighted imaging (DWI). Brain abscesses are usually associated with high signal intensity on DWI with a reduced apparent diffusion coefficient (ADC) value. On the other hand, low DWI signal intensity with a high ADC value is characteristic of cystic or necrotic tumours [1, 4, 5].
We report two cases of brain abscesses with unusual diffusion findings.
|
Case reports
|
|---|
Case 1
A 22-year-old female presented with a 1-month history of headache. Her medical history was acute lymphocytic leukaemia. The CT scan showed a ring-enhancing cystic lesion in the left frontal lobe (Figure 1a
). The MR images revealed a ring-enhancing cystic mass in the left frontal lobe with a significant area of diffuse oedema (Figure 1b–d). A small, lobulated, intermediate signal intensity on both T1 and T2 weighted images was observed in the dependent portion of the lesion. DWI demonstrated a markedly low signal lesion with a high ADC (Figure 1e,f). The focal gravity-dependent portion was hyperintense on the DWI and showed hypointense signal intensity on the ADC map, reflecting restricted diffusion. The patient underwent a stereotactic aspiration, and a brain abscess was confirmed histologically. The abscess culture was sterile. Unfortunately, the patient expired due to multiple medical complications.
View larger version (195K):
[in this window]
[in a new window]
|
Figure 1. A 22-year-old female with a medical history of acute lymphocytic leukaemia. (a) Post-contrast CT scan shows a ring-enhancing cystic lesion in the left frontal lobe. The lesion is hypointense on (b) the T1 weighted image and (c) hyperintense on the T2 weighted image with a focal peripheral oedema and a mild mass effect. A small pus-fluid level in the dependent portion of the lesion is shown. (d) Post-contrast T1 weighted image shows a ring-enhancing cystic lesion with several enhancing daughter nodules. With (e) the diffusion weighted image, the signal intensity of the lesion is hypointense with a corresponding marked hyperintensity on (f) the apparent diffusion coefficient (ADC) map. The small gravity-dependent portion is hyperintense on the diffusion weighted imaging (DWI) and shows hypointense signal intensity on the ADC map, indicating restricted diffusion.
|
|
Case 2
A 60-year-old male presented with a history of dysarthria and right hemiparesis for 1 week. His medical history was diabetes and hypertension. The CT scan and MR images showed a ring-enhancing cystic mass in the left temporal lobe with a large amount of adjacent oedema and a mass effect (Figure 2a–d). DWI demonstrated a heterogeneous signal intensity with an inversely heterogeneous ADC (Figure 2e,f). The patient underwent a CT-guided stereotactic aspiration, and a red-black coloured thick fluid was aspirated. The histology showed many viable inflammatory cells such as neutrophils, lymphocytes and histiocytes, with prominent necrotic cellular debris in the bloody background, which indicated a brain abscess (Figure 1g
). The Gram's stain demonstrated many gram (+) cocci. Its cultures grew Streptococcus intermedius.
View larger version (189K):
[in this window]
[in a new window]
|
Figure 2. A-60-year-old man with brain abscess in the left temporal lobe. (a) Post-contrast CT scan shows a ring-enhancing lesion in the left temporal lobe. The lesion is hypointense on (b) the T1 weighted image and (c) hyperintense on the T2 weighted image with extensive peripheral oedema and a mass effect. (d) Post-contrast T1 weighted image shows a ring-enhancing cystic lesion. The lesion shows a heterogeneous signal intensity on (e) the diffusion weighted image and inversely heterogeneous signal intensity on (f) the apparent diffusion coefficient (ADC) map. (g) Photomicrograph shows that the abscess tissues contain numerous viable inflammatory cells (white arrows), such as neutrophils, lymphocytes and histiocytes, and prominent necrotic cellular debris (black arrows) in the bloody background (Haematoxylin and Eosin, x200)
|
|
Overall, the patient recovered well after aspiration and required a 8-week course of broad-spectrum antibiotics.
|
Discussion
|
|---|
DWI is a recently developed MR technique that is widely used for diagnosing early cerebral infarctions. More recently, DWI has demonstrated significant potential in further delineating the diagnosis of ring-enhancing mass lesions [4, 6].
In 1996, Ebisu et al [7] reported the finding of restricted diffusion within the cavity of a brain abscess. Further studies confirmed the restricted diffusion in abscesses with high signal intensity in the central cavity and a correspondingly low ADC value [3, 4].
The probable factors for the restricted diffusion in brain abscesses are the microscopic organization of the tissues, the high viscosity of the pus resulting from a high protein level, different types of viable or dead cells along with necrotic tissue, bacteria and exuded plasma. Water molecules in abscesses are bound to carboxyl, hydroxyl and amino groups on the surfaces of the macromolecules, which further restricts their translational motion [5]. In contrast to purulent fluid, the necrotic areas in primary and metastatic tumours are usually more haemorrhagic, less viscous and less cellular. As a result, these necrotic areas are usually hypointense on DWI and have mean diffusion coefficients 4 to 10 times greater than those of pus [6, 8]. The ADC values of an abscess between and within reported studies varies widely. It is possible that variable concentrations of inflammatory cells and bacteria, different aetiological organisms, host immune responses and the age of the abscess with a variable viscosity of the abscess fluid were responsible for this variability in the reported studies [4].
Although a cerebral Toxoplasma abscess may have the same appearance on contrast-enhanced MRI as a pyogenic abscess, several studies have shown that water diffusion is not restricted in the centre of the Toxoplasma abscess. The core of a Toxoplasma abscess consists primarily of necrotic tissue and does not have the viscous, proteinaceous and inflammatory debris of the purulent fluid. Therefore, increased diffusion within toxoplasmosis lesions might reflect the relatively lower viscosity within their central cores. This is perhaps due to an impaired cellular immune response in these immunocompromised patients [9].
Wong et al have reported a patient with a subdural empyema of heterogeneous signal intensity on DWI. They suggested that this signal-intensity heterogeneity might have been related to three unusual clinical features. First, the patient had an unusually low white blood cell count. Second, the responsible pathogen was Escherichia coli, which can produce mixed acids and gases via anaerobic fermentation. Third, the patient had the longest disease course among the patients, which could allow for the coexistence of newly and chronically infected materials [10].
Mishra et al have reported that all patients with brain abscesses showing low ADC values had a positive culture for microorganisms. However, the pus culture from 5 out of 8 patients with high ADC values was sterile [5].
It is possible that the increased diffusion in the lesion described in case 1 might have reflected the decreased viscosity, perhaps due to an impaired cellular immune response in an immunocompromised patient and a sterile pus culture. The heterogeneous signal intensity in the DWI of case 2 is believed to be related to the prominent necrotic debris with a bloody background in the abscess tissues.
Although hyperintensity within the central portion of a ring-enhancing mass on DWI and a low ADC value suggests a cerebral abscess, these signs are not specific. Various DWI findings between brain abscesses may be related to a difference in the viscosity of the abscess fluid, which is determined by factors such as the variable concentrations of inflammatory cells and bacteria, different aetiological organisms, the host immune response, a difference of the necrotic or viable inflammatory cells and the age of the abscess.
Received for publication June 3, 2005.
Accepted for publication July 19, 2005.
|
References
|
|---|
- Lai PH, Ho JT, Chen WL, et al. Brain abscess and necrotic brain tumor: discrimination with proton MR spectroscopy and diffusion-weighted imaging. AJNR Am J Neuroradiol 2002;23:1369–77.[Abstract/Free Full Text]
- 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.[Abstract/Free Full Text]
- Guzman R, Barth A, Lovblad KO, et al. Use of diffusion-weighted magnetic resonance imaging in differentiating purulent brain processes from cystic brain tumors. J Neurosurg 2002;97:1101–7.[Medline]
- Hartmann M, Jansen O, Heiland S, Sommer C, Munkel K, Sartor K. Restricted diffusion within ring enhancement is not pathognomonic for brain abscess. AJNR Am J Neuroradiol 2001;22:1738–42.[Abstract/Free Full Text]
- Mishra AM, Gupta RK, Jaggi RS, et al. Role of diffusion-weighted imaging and in vivo proton magnetic resonance spectroscopy in the differential diagnosis of ring-enhancing intracranial cystic mass lesions. J Comput Assist Tomogr 2004;28:540–7.[CrossRef][Medline]
- Leuthardt EC, Wippold FJ, Oswood MC, Rich KM. Diffusion-weighted MR imaging in the preoperative assessment of brain abscesses. Surg Neurol 2002;58:395–402.[CrossRef][Medline]
- Ebisu T, Tanaka C, Umeda M, et al. Discrimination of brain abscess from necrotic or cystic tumors by diffusion-weighted echo planar imaging. Magn Reson Imaging 1996;14:1113–6.[CrossRef][Medline]
- Tung GA, Evangelista P, Rogg JM, Duncan JA 3rd. Diffusion-weighted MR imaging of rim-enhancing brain masses: is markedly decreased water diffusion specific for brain abscess? AJR Am J Roentgenol 2001;177:709–12.[Abstract/Free Full Text]
- Chong-Han CH, Cortez SC, Tung GA. Diffusion-weighted MRI of cerebral toxoplasma abscess. AJR Am J Roentgenol 2003;181:1711–4.[Abstract/Free Full Text]
- Wong AM, Zimmerman RA, Simon EM, Pollock AN, Bilaniuk LT. Diffusion-weighted MR imaging of subdural empyemas in children. AJNR Am J Neuroradiol 2004;25:1016–21.[Abstract/Free Full Text]
Top
Abstract
Introduction
