The authors report the cases of four patients who presented with progressive myelopathy (one patient had been asymptomatic for 25 years) due to spinal epidural arteriovenous fistulas (AVFs). Clinical symptoms and magnetic resonance imaging findings were similar to those of dural AVFs. In contrast to dural AVFs, angiography showed that the lesions were fed by multiple vessels and drained in one case in multiple veins. Perimedullary venous drainage was visible in three of the four cases. All fistulas were cured by embolization; arterial access was used in two cases and venous in two. The authors' aim in this paper is to emphasize the differences between dural and epidural AVFs in terms of their physiopathology and angioarchitecture as well as the therapeutic strategy.

✓The authors report the cases of four patients who presented with progressive myelopathy (one patient had been asymptomatic for 25 years) due to spinal epidural arteriovenous fistulas (AVFs). Clinical symptoms and magnetic resonance imaging findings were similar to those of dural AVFs. In contrast to dural AVFs, angiography showed that the lesions were fed by multiple vessels and drained in one case in multiple veins. Perimedullary venous drainage was visible in three of the four cases. All fistulas were cured by embolization; arterial access was used in two cases and venous in two. The authors' aim in this paper is to emphasize the differences between dural and epidural AVFs in terms of their physiopathology and angioarchitecture as well as the therapeutic strategy.

The CEO of Embraer, reflects on his company's dramatic ascent to its position as the world's leading regional aircraft manufacturer. Since becoming a private company, Embraer had successfully introduced seven commercial aircraft models to the market, including its latest, the 118-seat EMBRAER 195. Now, he is concerned because Embraer does not know what to expect from Bombardier, Boeing, and Airbus regarding their competitive response to his company's recent attacks on the commercial aircraft market. How would they respond to Embraer's successful launch of its recent family of jets? Would Bombardier really follow through with its launch of the CSeries? Would Airbus and Boeing perceive the latest attacks by Embraer and Bombardier as attacks on its own family of jets? Most importantly, given Embraer's expectations of rivals' future competitive moves, what should it do next to protect its position and influence its competitors' actions?

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