Early development of the nose in human embryos: A stereomicroscopic and histologic analysis

Objectives/Hypothesis: To analyze the morphologic features of the nose in the human embryo from the 4th to 8th developmental week according to Carnegie stage. Study Design: Stereomicroscopic and histologic analysis of the morphology of the human embryo. Methods: A total of 27 cases of embryos, ranging from Carnegie stage 13 to 23, were analyzed. The external morphology was observed with a stereomicroscope, photographed, and analyzed. The histologic features were observed with a light microscope in the horizontally transected specimens stained with hematoxylin-eosin. Results:The nasal placode was observed in stage 13, and it became flat or even concave in stage 14. In stage 15, the nasal pit was formed. In stage 16, the nasal sac and nasal fin were observed. In stage 17, the oronasal membrane was formed by thinning of the nasal fin. In stage 18, the primitive choana was established by a rupture of the oronasal membrane. In stage 19, the lateral palatine process projected vertically below the level of the tongue. The cartilaginous nasal capsule was formed in stage 20. In stage 21, the olfactory area was localized to the upper portion of the lateral nasal wall and the nasal septum. In stage 22, the lateral palatine process developed in a somewhat horizontal orientation. In stage 23, the premaxilla and primitive choana were formed. Conclusions. The development of the nose is most active from Carnegie stage 13 to 19, which corresponds to the end of the fourth embryonic week to the end of the seventh week. Thus, this period is considered to be the most important period in human nasal embryonic development.