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AJR 2003; 180:71-75
© American Roentgen Ray Society

Original report

Diffusion-Weighted MR Imaging of Pyogenic Ventriculitis

John A. Pezzullo1, Glenn A. Tung, Sanjay Mudigonda and Jeffrey M. Rogg

1 All authors: Department of Diagnostic Imaging, Brown University School of Medicine, Rhode Island Hospital, 593 Eddy St., Providence, RI 02903.

Received February 12, 2002; accepted after revision June 13, 2002.

 
Address correspondence to J. A. Pezzullo.


Abstract
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 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
OBJECTIVE. The purpose of this study was to describe the features of pyogenic ventriculitis (ventricular empyema, pyocephalus) on diffusion-weighted MR imaging.

CONCLUSION. Markedly increased signal intensity of dependent intraventricular fluid on diffusion-weighted MR imaging and an apparent diffusion coefficient that is less than that of normal cerebral white matter indicate restricted water diffusion in purulent fluid and suggest the diagnosis of pyogenic ventriculitis.


Introduction
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 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
Ventriculitis is a rare cerebral infection that may result from the rupture of a brain abscess, the extension of meningitis into the ventricles, or a neurosurgical procedure or device [1,2,3,4]. Pyogenic ventriculitis (ventricular empyema, pyocephalus) is a subset of ventriculitis that is characterized by the presence of suppurative fluid in the ventricles. Pyogenic ventriculitis is important to recognize because its signs and symptoms may be subtle, its course can be indolent but lethal, and it may be the cause of meningitis that is difficult to eradicate [5,6,7]. Because the incidence of bacterial meningitis has increased over the last 30 years as a result of nosocomial infection, the number of cases of pyogenic ventriculitis is likely to increase [7]. However, given its rarity, the diagnosis of pyogenic ventriculitis on CT and MR imaging has not been widely reported [8,9,10,11].

The value of diffusion-weighted MR imaging for the diagnosis of a brain abscess has been described in a series of case reports [12,13,14,15]. In the purulent center of a brain abscess, water diffusion is restricted; this finding is indicated by markedly increased signal intensity on diffusion-weighted MR images and decreased signal intensity on apparent diffusion coefficient map images. However, restricted water diffusion in a rim-enhancing mass is not specific for a brain abscess [16]. In this report, we present three patients with pyogenic ventriculitis that were diagnosed prospectively as a result of signs of marked restricted water diffusion on diffusion-weighted MR imaging.


Subjects and Methods
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 Subjects and Methods
Results
 Discussion
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Pyogenic ventriculitis was diagnosed prospectively in three patients during a 5-month period from May 2001 to September 2001. All patients underwent MR imaging of the brain. These examinations were performed on a 1.5-T magnet (Vision; Siemens, Erlangen, Germany). Specific sequences included axial and parasagittal spinecho T1-weighted MR imaging before and after the administration of 0.1 mmol/kg of gadopentetate dimeglumine (Magnevist; Schering, Berlin, Germany), axial turbo spin-echo T2-weighted MR imaging, and fluid-attenuated inversion recovery (FLAIR) imaging.

The specific parameters for conventional spin-echo T1-weighted MR imaging were a TR/TE of 600/14 with 3 signals acquired, 6-mm section thickness, 220 x 256 matrix, and 230 x 230 field of view. For turbo spin-echo T2-weighted MR imaging, the parameters were a TR range/effective TE of 5000-6000/128 with 1 or 2 signals acquired, 6-mm section thickness, echo-train length of 23, 192 x 256 matrix, and 230 x 230 field of view. For FLAIR imaging, the parameters were a TR/TE of 9000/105, an inversion time of 2500 msec, 5-mm slice thickness, 173 x 230 field of view, 154 x 256 matrix, and an interslice gap of 2 mm.

Diffusion-weighted MR imaging was performed with an axial single-shot echoplanar spin-echo sequence (TR/TE, 4000/110; 5-mm section thickness; 96 x 200 matrix; 230 x 230 field of view; three b values of 0, 500, and 1000 mm2/sec). Diffusion gradients were applied in three standard orthogonal planes to generate three sets of orthogonal trace diffusion-weighted images. The apparent diffusion coefficient was quantified from the mean of three circular region-of-interest measurements, each of which was 2-3 mm in diameter, on the apparent diffusion coefficient map image.

Clinical information and laboratory data were obtained through a retrospective review of the hospital medical records.


Results
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 Subjects and Methods
 Results
Discussion
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All three patients were male: patient 1 was 14 days old; patient 2, 32 years; and patient 3, 50 years. In patient 1, a ventriculoperitoneal shunt catheter was placed on the second day of life for management of congenital hydrocephalus. Both patients 2 and 3 had a history of von Hipple—Lindau disease and presented with hydrocephalus due to compression of the fourth ventricle by hemangioblastoma. All three patients became febrile and showed neurologic deterioration an average of 8 days (range, 4-12 days) after ventricular shunt placement. Results from blood tests in patients 1 and 2 revealed peripheral leukocytosis with a left shift.

In all three patients, cerebrospinal fluid obtained from the ventriculostomy catheter was turbid and had elevated protein and reduced glucose concentrations. In the cerebrospinal fluid of patient 1, the protein concentration was 237 mg/dL, the glucose concentration was 3 mg/dL, and Enterococcus faecalis was cultured. Cerebrospinal fluid from patient 2 had protein and glucose concentrations of 129 mg/dL and 26 mg/dL, respectively, and coagulase-negative Staphylococcus aureus was cultured. In patient 3, the protein concentration in the cerebrospinal fluid was 85 mg/dL, the glucose concentration was 20 mg/dL, and Serratia marcescens was cultured.

On MR imaging, intraventricular debris was shown in the dependent occipital horn of the lateral ventricles in all patients (Figs. 1A,1B,1C and 2A,2B,2C,2D). Relative to cerebrospinal fluid, this debris was irregular and slightly hyperintense on T1-weighted images, slightly hypointense on T2-weighted images, and hyperintense on FLAIR images. Hyperintense signal was also noted on FLAIR images in the subependymal white matter in two patients and in the ventricular ependymal in one patient. After gadodiamide contrast medium was administered, diffuse ependymal enhancement was noted in all three patients. No evidence of brain abscess, meningitis, or parameningeal infection was detected.



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  		Fig. 1A. —50-year-old man with purulent ventriculitis after resection of cerebellar hemangioblastoma and ventricular shunt placement. Fluid-attenuated inversion recovery image (TR/TE, 9000/105; inversion time, 2500 msec) shows ventricular debris in dependent part of occipital horns (straight arrows) has higher signal intensity than cerebrospinal fluid in nondependent parts of lateral ventricles. Hyperintense signal around ventricles (curved arrow) is consistent with ependymitis and periventricular inflammation.

 


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  		Fig. 1B. —50-year-old man with purulent ventriculitis after resection of cerebellar hemangioblastoma and ventricular shunt placement. Contrast-enhanced T1-weighted MR image (650/17) shows irregular ventricular debris with curved and oblique layering (arrows) in occipital horns. This nonlinear fluid—fluid interface is consistent with pus. Faint linear ependymal contrast enhancement is also present.

 


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  		Fig. 1C. —50-year-old man with purulent ventriculitis after resection of cerebellar hemangioblastoma and ventricular shunt placement. Tensor diffusion-weighted MR image (4000/110; b value, 1000 m2/sec) shows pus in dependent position of occipital horns and marked hyperintense signal (arrows) compared with cerebrospinal fluid and brain.

 


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  		Fig. 2A. —32-year-old man with purulent ventriculitis after resection of cerebellar hemangioblastoma. Fluid-attenuated inversion recovery (FLAIR) image (TR/TE, 9000/105; inversion time, 2500 msec) shows hyperintense debris (arrow) in occipital horns of both lateral ventricles and hyperintense signal around ventricles.

 


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  		Fig. 2B. —32-year-old man with purulent ventriculitis after resection of cerebellar hemangioblastoma. Tensor diffusion-weighted MR image (4000/110; b value, 1000 m2/sec) shows greater relative hyperintensity in intraventricular pus (arrow) than on FLAIR image (A).

 


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  		Fig. 2C. —32-year-old man with purulent ventriculitis after resection of cerebellar hemangioblastoma. Magnified apparent diffusion coefficient map of left lateral ventricle shows that pus in more dependent position has lower apparent diffusion coefficient (33.1 x 10-3 mm2/sec) than pus in more anterior, less dependent position (97.6 x 10-3 mm2/sec). Circular regions of interest are outlined and numbered (1-4).

 


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  		Fig. 2D. —32-year-old man with purulent ventriculitis after resection of cerebellar hemangioblastoma. In contrast to C, this image, which is same apparent diffusion coefficient map image as that shown in C, shows normal-appearing cerebrospinal fluid and much higher apparent diffusion coefficient values; in addition, no position-dependent gradation is visible. Circular regions of interest are outlined and numbered (1-4).

 

In all patients, tensor diffusion-weighted imaging showed hyperintense signal in the dependent intraventricular debris but hypointense signal in the nondependent cerebrospinal fluid. The measured apparent diffusion coefficient values of dependent intraventricular fluid were lower than that of normal-appearing white matter and much lower than that of nondependent cerebrospinal fluid in the frontal horns. The apparent diffusion coefficient (mean x 10-3 mm2/sec ± SD) for dependent intraventricular debris, nondependent cerebrospinal fluid, and normal white matter was 0.44 ± 0.03, 3.16 ±0.17, and 0.75 ± 0.06, respectively, in patient 1; 0.69 ± 0.1, 2.99 ± 0.09, and 1.09 ± 0.04, respectively, in patient 2; and 0.66 ± 0.05, 3.43 ± 0.17, and 0.8 ± 0.06, respectively, in patient 3. Expressed as a percentage of normal white matter, the apparent diffusion coefficient for dependent intraventricular debris was 57% in patient 1, 63% in patient 2, and 83% in patient 3. In addition, there was a gradation of apparent diffusion coefficient values in dependent intraventricular debris: the smallest apparent diffusion coefficient values were measured in the most dependent intraventricular fluid and decreased in less dependent fluid (i.e., more rostral in the supine patient). This gradation was not observed in nondependent cerebrospinal fluid.


Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
Pyogenic ventriculitis is a rare intracranial infection that most often occurs as a complication of brain abscess rupture into the ventricles. Fukui et al. [11] recently described the MR and CT imaging features of 17 patients with pyogenic ventriculitis. An irregular configuration of ventricular debris, hydrocephalus, periventricular hypointensity, ependymal contrast enhancement, and signs of meningitis were reported in many, but not all, patients. In the three patients we presented, each of these features was present with the exception of hydrocephalus, which was absent because shunt catheters had been placed. Diffusion-weighted MR imaging findings notwithstanding, these MR imaging signs are important because they serve to distinguish an intraventricular hemorrhage from pyogenic ventriculitis. In particular, periventricular hyperintensity on FLAIR images and ependymal contrast enhancement on MR images would not be expected in cases of intraventricular hemorrhage, and marked signal loss in blood products would be expected on gradient-echo T2*-weighted MR imaging in cases of intraventricular hemorrhage [17, 18].

With respect to diffusion-weighted MR imaging findings, Fukui et al. [11] reported that diffusion in purulent intraventricular fluid was not restricted in two cases; however, these researchers did not report the apparent diffusion coefficient values for these cases. The diffusion-weighted MR images in these cases showed hyperintense signal in the layering intraventricular debris, which may have resulted in increased conspicuity.

We report markedly restricted diffusion in dependent purulent intraventricular fluid in three patients with pyogenic ventriculitis. The mean apparent diffusion coefficient, based on three region-of-interest measurements, of intraventricular pus in each patient was less than that of cerebral white matter, four to seven times lower than that of normal-appearing cerebrospinal fluid, and in the range of reported values for suppurative fluid in brain abscesses (i.e., 0.3-0.7 x 10-3 mm2/sec) [12,13,14,15,16].

Diffusion-weighted MR imaging can be used to evaluate the composition of fluid in brain cystic masses, and restricted diffusion has been used to discriminate brain abscess from cystic brain neoplasm [19]. Pus is a viscous fluid that consists of mucoproteins, bacteria, inflammatory cells, and cellular debris. The relatively high viscosity, hypercellularity, and binding of water to macromolecules have been suggested as explanations for the restricted water diffusion observed in the purulent core of a pyogenic brain abscess [12,13,14,15,16,17,18,19,20]. We report a position-dependent reduction in measured apparent diffusion coefficient values of intraventricular purulent fluid that was not observed for nonsuppurative cerebrospinal fluid. When the MR images were obtained with the patient in the supine position, the apparent diffusion coefficient was about four times lower in pus located in the dependent posterior part of the occipital horn than that located more anteriorly. This discrepancy in apparent diffusion coefficient values suggests that the dilution of purulent fluid by nonsuppurative cerebrospinal fluid may explain the slightly greater apparent diffusion coefficient in nondependent intraventricular pus, as has been suggested in a case reported by Rana et al. [21]. Thus, the two cases of pyogenic ventriculitis that were described by Fukui et al. [11] in which the diffusion of purulent fluid was not restricted might be explained by relatively small amounts of intraventricular pus.

In conclusion, the finding of restricted diffusion in patients with pyogenic ventriculitis suggests the presence of intraventricular pus. Although an apparent diffusion coefficient value of ventricular fluid that is less than that of normal-appearing white matter is consistent with suppuration, higher apparent diffusion coefficient values might be observed when pus is diluted by nonpurulent cerebrospinal fluid.


References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

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  13. Desprechins B, Stadnik T, Koerts G, Shabana W, Breucq C, Osteaux M. Use of diffusion-weighted MR imaging in differential diagnosis between intracerebral necrotic tumors and cerebral abscesses. AJNR 1999;20:1252 -1257[Abstract/Free Full Text]
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