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Embryology of nose and paranasal sinuses
Dr. T. Balasubramanian M.S. D.L.O.
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.
Figure showing development of nose and pns
At about 25 – 28 weeks of gestation, three medially directed projections arise from the lateral wall of the nose. This serves as the beginning of the development of paranasal sinuses. Between these projections small lateral diverticula invaginate into the primitive choana to eventually form the meati of the nose.
Figure showing infundibulum, and meati of nose developing
The middle meatus invaginates laterally to form the embryonic infundibulum and uncinate process. During the 13th week of development the embryonic infundibulum grows superiorly to form the frontal recess area.
Development of frontal sinus: The frontal sinus may develop as a direct continuation of embryonic infundibulum and frontal recess superiorly during the 16th week. It can also develop by upward migration of anterior ethmoidal air cells to penetrate the inferior aspect of the frontal bone between its outer and inner tables. Pneumatization of frontal bone is a very slow process. The frontal sinus infact remains as a small blind sac within the frontal bone till the child is about 2 years of age, then secondary pneumatization begins. From the age of 2 till the child becomes 9 years old secondary pneumatization of frontal bone proceeds. When the child reaches the age of 9, the development of the frontal sinus has reached completion. Sometimes frontal sinus may be asymmetrical / aplastic as well.
Figure showing development and enlargement of frontal sinus. The numbers indicate the size of frontal sinus at that corresponding age.
The embryonic infundibulum may also invade the mesenchyme in the maxillary process forming the primitive maxillary sinus. Pneumatization of maxillary sinus is faster than that of frontal sinus. Pneumatization occurs at the expense of erupting upper dentition. Abnormalities of maxillary pneumatization is associated with anomalies of upper dentition.