Overview
This lecture covers the anatomy of the paranasal sinuses, their spatial relationships with the nasal cavity, their drainage pathways, and nearby critical structures relevant for radiology and surgery.
Paranasal Sinuses Identification
- The four paranasal sinuses are frontal, maxillary, ethmoidal, and sphenoidal.
- On coronal CT, identify frontal sinuses in the frontal bone, maxillary sinuses below the orbits, ethmoid sinuses between the orbits, and sphenoid sinus posteriorly.
Nasal Cavity Boundaries and Anatomy
- The floor of the nasal cavity is the hard palate; lateral walls are the medial walls of the maxillary sinuses.
- The roof consists of parts of the ethmoid bone including crista galli, horizontal lamella, and fovea ethmoidalis.
- Three turbinates (superior, middle, inferior) are visible per side, each with a corresponding meatus (aerated space).
Sinus Drainage Pathways
- Frontal, maxillary, and anterior ethmoidal sinuses drain into the middle meatus.
- Sphenoid and posterior ethmoidal sinuses drain into the superior meatus.
- Frontal sinus drainage is via the frontal recess.
- Maxillary sinus drains through the osteomeatal complex, involving the maxillary ostium, infundibulum, and hiatus semilunaris.
- The incinent (uncinate) process diverts airflow away from the maxillary sinus.
Imaging and Clinical Relevance
- CT is the gold standard for evaluating paranasal sinuses.
- Blockage of sinus drainage can lead to fluid buildup and infection.
- Fractures or masses may block drainage pathways.
Structures Surrounding the Sinuses
- Lamina papyracea forms the thin lateral wall of the ethmoid sinus near the orbit; fractures can connect the sinus to the orbit.
- The optic nerve and carotid artery are adjacent to the sphenoid sinus; surgical injury here can be dangerous.
- The pituitary gland lies just above the sphenoid sinus within the sella turcica.
Additional Drainage: Inferior Meatus
- The nasolacrimal duct drains into the inferior meatus, explaining why crying can cause a runny nose.
Key Terms & Definitions
- Paranasal sinuses — Air-filled spaces in the skull around the nasal cavity.
- Meatus — Passageways under each turbinate in the nasal cavity.
- Frontal recess — Drainage pathway from the frontal sinus to the middle meatus.
- Osteomeatal complex — Area where maxillary sinus drains into the middle meatus.
- Lamina papyracea — Thin bone separating ethmoid sinus and orbit.
- Incinate (uncinate) process — Hook-shaped bone affecting airflow into the sinuses.
Action Items / Next Steps
- Review paranasal sinus CT anatomy and practice identifying key structures and drainage pathways.
- Be aware of critical surrounding anatomy when reviewing imaging or preparing for surgery.