Introduction

Neuroimaging is crucial in clearly depicting pyogenic ventriculitis. Moreover, both CT and MR imaging can reliably contribute to the diagnosis of this life-threatening cerebral infection. In this illustrative report, we demonstrate the classical and complementary imaging findings on both CT and many MRI sequences.

Case History

A 49-year-old man with an unremarkable previous medical history was admitted with a right hemiplegia and a Glasgow Coma Scale (GCS) of 7/15 (E1, M5,V1). A non-contrast computed tomography (CT) of the brain showed an intraparenchymal hematoma involving the left thalamus and mesencephalon, with extension of blood into the ventricles. CT angiography revealed a cluster of dilated serpiginous vessels behind the mesencephalon, indicating a vascular malformation. The patient was referred for catheter cerebral angiography. Contrast injection into the left vertebral artery confirmed the presence of a dural arterio-venous fistula (AVF) fed by the left superior cerebellar artery. There was early venous drainage into the left tectal and tectogeniculate veins and into the great cerebral vein. Endovascular occlusion of the AVF could not be safely performed, nor was neurosurgical resection an option, due to the local and intraventricular bleeding. The persistence of intraventricular blood with accompanying hydrocephalus necessitated long term placement of an external ventricular drain (EVD) for drainage of cerebrospinal fluid (CSF). On day 22 after admission, the patient developed fever accompanied by a rise of the inflammatory parameters (i.e., increase of C-reactive protein up to 20 mg/dl). Empirical broad-spectrum antibiotic treatment was started. However, as the CSF analysis yielded an increase in the cell index and Enterococcus faecalis was cultured from the CSF, vancomycin was administered for 10 days both intravenously and intrathecally (10 mg once daily) through the EVD. Moreover, the EVD was replaced. On day 23 after admission, a contrast-enhanced CT scan of the brain indeed showed slight hydrocephalus, irregular debris in the dependent part of the occipital horns and periventricular hypodensities (Fig. 1). These findings suggested a diagnosis of pyogenic ventriculitis. The next day, an MRI scan confirmed the characteristic hallmarks of pyogenic ventriculitis on the T2-weighted, Fluid Attenuated Inversion Recovery (FLAIR), diffusion-weighted and contrast-enhanced T1-weighted images (Fig. 2). The clinical condition as well as the inflammatory markers improved gradually and the patient was discharged to an intermediate unit with a GCS of 8/15 on day 35 after admission.

Fig. 1
figure 1

a, b Contrast-enhanced CT scan of the brain on day 23 after admission. A right frontal ventriculo-peritoneal shunt is present. The ependymal lining of the occipital horns of the lateral ventricles shows thick-walled contrast enhancement, consistent with ependymitis. Confluent hypodense margins around the ventricles indicate periventricular inflammation. In the dependent part of the occipital horns there is intraventricular debris, which has a higher density than the cerebrospinal fluid in the non-dependent parts of lateral ventricles

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Fig. 2
figure 2

MRI of the brain on day 24 after admission confirms pyogenic ventriculitis. Axial T2-weigthed (a), fluid attenuated inversion recovery FLAIR (b), diffusion-weighted (c), and contrast-enhanced T1-weighted (d) images. The intraparenchymal hematoma in the left thalamus/mesencephalon is hyperintense on all sequences and shows diffusion restriction, consistent with clotted blood. The periventricular inflammation is easily identified on T2-weighted (a) and FLAIR (b) images as a hyperintense halo in the subependymal white matter surrounding the occipital horns. The thick-walled ependymal enhancement in the occipital horns (d) indicates ependymitis. The ventricular debris in the occipital horns has high signal intensity on the FLAIR images (b), and shows diffusion restriction (c); this finding is consistent with pus

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Discussion

Pyogenic ventriculitis is an uncommon but severe intracranial infection that can lead to serious sequelae and even death. The possible routes through which a pathogen might enter the intraventricular system include the hematogenous spread to the subependyma of the choroid plexus, contiguous extension from a brain abscess or direct implantation secondary to trauma or a ventricular catheter placement. The latter was most likely the mechanism involved in our patient. The incidence of infectious complications due to EVD is reported to range from 4% up to more than 20%, with a mean value of approximately 10% [1].

Neuroimaging is crucial in clearly depicting inflammatory lesions of the brain and the spine. In bacterial meningitis and ventriculitis, a contrast-enhanced CT scan may show beginning meningeal enhancement, while parenchymal lesions are not easily visualized, except for areas of ischemia due to secondary vasculitis [2]. Parenchymal abnormalities on a scan correlate with neurological signs and a worse prognosis. Undoubtedly, MR imaging is complementary and superior to CT in demonstrating parenchymal lesions due to meningoencephalitis or vasculitic complications on FLAIR sequences. MR imaging is the only tool to reliably diagnose this life-threatening ventriculitis. Characteristic MR findings of ventriculitis are intraventricular debris and pus, abnormal ependymal signal intensity, and enhancement of the ventricular lining: a high signal on FLAIR images, ependymal enhancement, and in most cases also pial or dura-arachnoid pathology is seen. The most common sign of ventriculitis is irregular intraventricular debris and pus [2–4]. Diffusion-weighted imaging is particularly useful because of the conspicuity of the lesions, followed by abnormal periventricular intensities or enhancements on FLAIR and contrast-enhanced T1-weighted images. The lower apparent diffusion coefficient (ADC) values of the hyperintense lesions on diffusion-weighted images, might suggest the presence of material with restricted water diffusion in the periventricular space [5]. FLAIR had the highest detectability for depicting the periventricular abnormalities. Choroid plexitis is another MR finding which can be associated with ventriculitis.