Wednesday, July 15, 2009

Embryology of nose and paranasal sinuses

Anatomically nose and paranasal sinuses are highly variable. Developmentally nose and paranasal sinuses are interlinked. They are always considered together developmentally. Developmentally the various sinuses may follow different calenders, their orgin is the same.

Development of head and neck along with face, nose and paranasal sinuses takes place simultaneously in a short window span. At the end of 4th week of development branchial arches, branchial pouches and primitive gut makes their appearance. This is when the embryo gets its first identifiable head and face with an orifice in its middle known as the stomodeum.
The stomodeum (primitive mouth) is surrounded by mandibular and maxillary prominences bilaterally. These prominences are derivatives of first arch. This arch will give rise to all vascular and neural supply of this area. The stomodeum is limited superiorly by the presence of frontonasal eminence and inferiorly by the mandibular arch.
The frontonasal process inferiorly differentiates into two projections known as “Nasal Placodes”. These nasal placodes will be ultimately invaded by growing ectoderm and mesenchyme. These structures later fuse to become the nasal cavity and primitive choana, separated from the stomodeum by the oronasal membrane. The primitive choana forms the point of development of posterior pharyngeal wall and the various paranasal sinuses.
The oronasal membrane is fully formed by the end of 5th week of development. It gives rise to the floor of the nose (palate develops from this membrane).

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