Meningoencephalitis with Streptococcus equi Subspecies equi Leading to a Dural Arteriovenous Fistula

Abstract

Invasive infection with Lancefield group C streptococci in humans is extremely rare, with the vast majority of clinical isolates belonging to Streptococcus dysgalactiae subsp. equisimilis. We report a case of meningoencephalitis in a 69-year-old man caused by Streptococcus equi subsp. equi, a microbe that causes strangles in Equus caballus (i.e., the horse). This is only the fourth infection with this subtype of the central nervous system (CNS) reported in humans. The invasiveness of these bacteria, known to be capable of releasing strongly immunogenic exotoxins, is illustrated by white matter lesions that are present in the acute phase. This patient initially recovered well after treatment with antibiotics and glucocorticoids. However, the patient was readmitted 5 months later with multiple intraparenchymatous cerebral haemorrhages. Cerebral angiography confirmed the presence of a suspected superficial dural arteriovenous fistula (DAVF), which is seldom reported after CNS infection. The invasiveness of these bacteria was illustrated by white matter lesions present in the acute phase and the occurrence of a de novo dural arteriovenous fistula in the follow-up period.

Figure 1

Fluid-attenuated inversion recovery images (FLAIR) showed a “dirty CSF” appearance in the right parietal region ((a), white arrow). Axial (b) and sagittal (c) T1-weighted images after the intravenous administration of gadolinium-chelate revealed a focal area of superficial contrast enhancement overlying the cerebral cortex, presumably representing a thickened pia mater.

Figure 2

During readmission five months after the initial referral, consecutive CT scans showed multiple right-sided cerebral haemorrhages, the largest being located precentrally in the frontal lobe ((a), para-axial nonenhanced). CT angiography examination ((b), para-axial MPR) showed multiple tortuous, engorged pial veins of the right hemisphere. Cerebral angiography confirmed the presence of a suspected superficial dural arteriovenous fistula ((c), lateral projection of right internal carotid artery injection, large black arrow) in the right parietal region. The arterial feeders were mainly meningeal branches originating from the right ophthalmic artery and transosseous feeders from the right superficial temporal and occipital arteries ((d), lateral projection right external carotid artery injection); in addition, there was limited arterial supply to the fistula from the left middle meningeal artery, across the midline (not shown). Venous drainage was through a large, right temporal draining vein (large white arrow), with reflux into multiple tortuous, superficial frontotemporal veins, as shown in Figure 2(b), indicating a fistula with a high risk of haemorrhage. Comparison of axial T2-weighted images of MRI examinations at initial admittance (e) and at the second admission (f) showed the new finding of dilated pial veins (encircled), demonstrating the de novo development of the dural AV fistula.

Figure 3

Histopathology of the excised dura with lymphocytic inflammatory remnants around a damaged venous sinus (a). In the upper part of the vessel wall (see also insert (b)) there is granulation tissue with many newly formed capillaries, lymphocytes, macrophages (thick arrow), a few eosinophils (thin black arrow) and some iron debris (thin open arrow). (Haematoxylin-Eosin Staining, bar = 1 mm; asterisk = peripheral blood).