F Jebali1, S Lejri2, A B Salem3, L Grati2. 1. Anesthesiology Department, University of Monastir, 5000 Monastir, Tunisia. Electronic address: fethijeb@yahoo.fr. 2. Anesthesiology Department, University of Monastir, 5000 Monastir, Tunisia. 3. Radiology Department, University of Monastir, 5000 Monastir, Tunisia.