What is the embryology and first radiology appearance of each paranasal sinus?

From the Guidelines

The paranasal sinuses develop at different stages of embryonic and fetal life, with each having distinct timelines for appearance on radiological imaging, and understanding this timeline is crucial for interpreting pediatric sinus imaging and distinguishing between normal developmental variations and pathological conditions. The development of the paranasal sinuses can be summarized as follows:

• Maxillary sinuses: appear first during the 10th week of gestation as outpouchings from the middle meatus of the nasal cavity, and can be visualized radiologically at birth as small bilateral air-filled spaces 1.
• Ethmoid sinuses: begin development around the 12th week of gestation as evaginations from the lateral nasal wall, with anterior ethmoid cells visible on imaging by 3-6 months of age and posterior cells by 1-2 years 1.
• Sphenoid sinuses: start as invaginations of the sphenoethmoidal recess at approximately 3-4 months of gestation, but are typically not pneumatized until 3-5 years of age and thus not radiologically apparent until then 1.
• Frontal sinuses: develop last, originating from anterior ethmoid cells that migrate superiorly into the frontal bone around the 16th week of gestation, but are generally not visible on imaging until 6-8 years of age 1.

The first radiology appearance of each paranasal sinus can be summarized as follows:

• Maxillary sinuses: visible on imaging at birth as small bilateral air-filled spaces 1.
• Ethmoid sinuses: anterior ethmoid cells visible on imaging by 3-6 months of age, and posterior cells by 1-2 years 1.
• Sphenoid sinuses: not radiologically apparent until 3-5 years of age, when they become pneumatized 1.
• Frontal sinuses: generally not visible on imaging until 6-8 years of age 1.

It is essential to note that the diagnosis of uncomplicated acute sinusitis is based on clinical criteria alone, and radiographic imaging is not recommended in children as the initial diagnostic tool 1. However, when a complication of ABRS or an alternative diagnosis is suspected, imaging studies such as CT or MRI may be obtained 1.

From the Research

Embryology of Paranasal Sinuses

• The embryonic development of paranasal sinuses is not yet fully understood, but studies suggest that all four pairs of paranasal sinuses are developed from the cartilaginous nasal capsule 2.
• The outpouching of the nasal mucous membranes is a secondary phenomenon, rather than the primary force in the development of paranasal sinuses 2.
• The development of human nasal mucosa was studied in 20 fetal heads between 8 and 24 weeks of gestation, and it was found that the nasal cavity is initially lined by a single layer of flattened cells, which produces two to three layers of undifferentiated spherical cells 3.

First Radiology Appearance of Paranasal Sinuses

• There is limited information available on the first radiology appearance of paranasal sinuses in the provided studies.
• However, it is known that the paranasal sinuses are complex anatomical structures, and their development and growth have been investigated utilizing various methods, including cadaveric analysis and modern cross-sectional imaging with 3D modeling 4.

Development of Each Paranasal Sinus

• Maxillary Sinus: The maxillary sinus is developed from the cartilaginous nasal capsule, and its development is associated with the uncinate process 2.
• Frontal Sinus: There is limited information available on the embryology and first radiology appearance of the frontal sinus in the provided studies.
• Ethmoid Sinus: The ethmoid sinus is developed from the cartilaginous nasal capsule, and its development is associated with the formation of pseudostratified ciliated cuboidal or columnar epithelium 3.
• Sphenoid Sinus: There is limited information available on the embryology and first radiology appearance of the sphenoid sinus in the provided studies.

Clinical Relevance

• Understanding the embryology and development of paranasal sinuses is important for the diagnosis and treatment of congenital conditions and sinusitis 2, 4.
• Functional endoscopic sinus surgery (FESS) is becoming increasingly common, and an understanding of sinus anatomy and development is important for clinicians 4.