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Congenital middle ear malformations are rare. Most part of them are usually associated with other malformations, such as aural atresia, microtia, and dysmorphic craniofacial features. A clinical case of a 24-year-old male with a right-sided conductive hearing loss since his childhood, without craniofacial malformation, is presented. He was proposed for exploratory tympanotomy under the suspicious diagnosis of otosclerosis. The surgery revealed an abnormal location of stapes' superstructure, which was attached to the promontory and had an isolated and mobile osseous footplate in the oval window. A stapes prosthesis was inserted and resulted in closure of the air-bone gap by 25 dB. A review of the literature was also performed using MEDLINE. Two theories diverge on the embryologic origin of the stapes. Our findings seem to be in favour of the theory that defines two different embryologic origins to the stapes.

In this work highly dispersed Ru-Sn bimetallic catalysts have been prepared from organobimetallic Cp(PPh 3 ) 2 Ru-SnX 3 (X = Cl or Br) complexes. These single source precursors can be easily impregnated in high surface area supports, such as activated carbon and sol-gel SiO 2 , and upon controlled thermal treatment the ligands are released as volatile products resulting in the formation of the bimetallic system Ru-Sn. Catalytic reactions, such as hydrodechlorination of CCl 4 and chlorobenzene and TPR (Temperature Programmed Reduction) experiments carried out with these RuSn catalysts suggested a strong interaction between Ruthenium and Tin. Mössbauer measurements showed that these materials when exposed to air are immediately oxidized to form Sn (IV). It was shown that upon controlled reduction conditions with H 2 it is possible to reduce selectively Sn to different oxidation states and different phases. The Sn oxidation state showed significant effect on the catalytic hydrogenation of 1,5-cyclooctadiene. The use of these single source precursors with a controlled decomposition/reduction procedure allows the preparation of unique catalysts with an intimate interaction between the components ruthenium and tin and the possibility of varying the Sn oxidation state around the Ru metal. Keywords: bimetallic catalyst, rutheniun, tin, hydrogenationsults in selectivity for the carbonyl hydrogenation, what has been explained in terms of a strong interaction between the C=O group with the tin oxide 15 . Therefore, two factors are essential to produce an active and selective catalyst: (i) the proximity of Sn to the noble metal and (ii) the Sn oxidation state. The bimetallic system Ru and Sn has been pointed out recently as one of the most active and selective catalyst for these hydrogenation 17 . These catalysts have been prepared by the co-impregnation of two different ruthenium and tin precursors, typically RuCl 3 and SnCl 4 . However, the co-impregnation method produces mostly the segregation of the metals resulting in a poor interaction of Ru and Sn.In this work, Ru-Sn catalysts have been prepared from a single source precursor containing both metals Cp(PPh 3 ) 2 Ru-SnX 3 (X = Cl or Br). The Ru-Sn chemical bond in the precursor should result in a close proximity of the two metals throughout the catalyst preparation steps lead-