Describe the development of the nose and its congenital anomalies.

Development of the Nose and Sinuses

• The external nose and nasal cavity form from the frontonasal process with the medial and lateral nasal processes, and from the maxillary processes of the first branchial arch
• The nasal placodes sink to form the nasal pits, which deepen to form the nasal sacs, separated from the oral cavity by the OROnasal (bucconasal) membrane
• Rupture of the oronasal membrane creates the primitive choanae — and failure of this rupture causes choanal atresia.

Congenital Anomalies

• Choanal atresia — failure of canalisation of the posterior choana, which is bony in the majority or mixed, rarely purely membranous
• Bilateral choanal atresia is a neonatal emergency.
• Immediate management — an oral airway (a McGovern nipple or a modified teat) to maintain mouth breathing, feeding by tube, then definitive repair
• Diagnosis — failure to pass a fine catheter through either nostril, confirmed by endoscopy and CT.
• Unilateral atresia presents late, in childhood or even adulthood, with unilateral obstruction and persistent unilateral mucoid discharge, and is frequently mistaken for a foreign body or chronic rhinitis
• Look for the charge association — Coloboma, Heart defects, Atresia of choanae, Retardation of growth and development, Genital and Ear anomalies — which is present in a substantial proportion and requires cardiac and ophthalmic assessment
• Treatment — endoscopic transnasal repair with removal of the atretic plate and the posterior vomer, with or without stenting; restenosis is the principal problem and may require revision
• Midline nasal masses — the group that must never be biopsied or excised before imaging.
• Nasal dermoid — a midline pit or swelling, classically with a hair protruding, which may have a tract extending to the dura
• Encephalocele — herniated brain and meninges.
• Nasal glioma — ectopic glial tissue.
• The rule IS absolute: MRI (with CT) before any biopsy or excision of a midline nasal mass in a child. Biopsy of an encephalocele causes CSF leak and meningitis
• Other anomalies — pyriform aperture stenosis, which mimics choanal atresia in a neonate and is associated with a single central megaincisor and with holoprosencephaly; congenital nasolacrimal duct cyst (dacryocele), which may obstruct the nose; bifid nose and arhinia; and thornwaldt cyst in the nasopharynx
• Failure of the oronasal membrane to rupture causes choanal atresia, which is the key developmental fact of this answer
• The neonate is an obligate nose-breather, which is why bilateral atresia is an immediate emergency