Sinus Anatomy & Pathology Quiz
Normal Sinus Anatomy:
What are the borders of the ethmoid sinuses?
Answer: Nasal cavity medially, lamina papyracea laterally, and the fovea ethmoidalis and cribriform plate superiorly
What structure separates the anterior ethmoid air cells from the posterior ethmoid air cells?
Answer: Basal Lamella of middle turbinate
What structures do the basal lamella of the middle turbinate attach to?
Answer: Vertically to the cribriform plate, laterally to the lamina papyracea and posteriorly to the perpendicular plate of the palatine bone. The coronal view is best for looking at the vertical attachment and the sagittal view for looking at the lateral and posterior attachments.
The anterior ethmoid air cells drain into which meatus?
Answer: Middle meatus
The posterior ethmoid air cells drain into which meatus?
Answer: Superior meatus
Which artery do the ethmoidal arteries originate from?
Answer: Opthalmic artery
Into what space does the sphenoid sinus drain?
Answer: First into the sphenoethmoidal recess, then into the superior meatus and finally into the nasopharynx
What are the boundaries of the sphenoethmoidal recess?
Answer: Superior turbinate bone, posterior wall of the ethmoid sinus and anterior wall of the sphenoid sinus
What structures make up the posterior sinus drainage?
Answer: Posterior ethmoid air cells, sphenoid sinus, sphenoethmoidal recess and the superior meatus
What structures make up the OMU?
Answer: Frontal sinus ostium, frontal recess, maxillary sinus ostium, infundibulum, bulla ethmoidalis and middle meatus
Where does the maxillary sinus drain into?
Answer: Maxillary sinus ostium, infundibulum, hiatus semilunaris and middle meatus
What three structures are seen if the middle turbinate is removed?
Answer: Uncinate process, hiatus semilunaris and bulla ethmoidalis
What are the boundaries of the infundibulum?
Answer: Inferomedial orbit laterally, hiatus semilunaris and ethmoid bulla superiorly, uncinate process medially and maxillary sinus ostium inferiorly
What are the boundaries of the hiatus semilunaris?
Answer: Ethmoid bulla superiorly, medial bony orbit laterally, uncinate process inferiorly and middle meatus medially
If the anterior portion of the uncinate process attaches to the skull base then what structure makes up the inferior compartment of the FSDP?
Answer: Ethmoid infundibulum
If the anterior portion of the uncinate process attaches to the lamina papyracea then what structure makes up the inferior compartment of the FSDP?
Answer: Middle meatus
What structure does the nasolacrimal duct drain into?
Answer: Inferior meatus
What are two important anatomic relationships between the paranasal sinuses and adjacent structures for inflammatory sinus disease and sinus endoscopy?
Answer: Bulging of the carotid artery into the sphenoid sinus which can have bony dehiscence in 4-8% of cases. The optic canal and nerve which courses along the superolateral sphenoid sinus wall, forming the optic eminence. Complete bony dehiscence of the optic canal can be present in 3-4% of cases.
Variant Sinus Anatomy:
In paradoxical curvature of the middle turbinate which direction is the curvature?
Answer: The convexity of the bone is directed laterally toward the lateral sinus wall
What type of epithelium lines the air cavity in a concha bullosa?
Answer: Ciliated pseudostratified columnar cells which is the same type of epithelium lining the nasal cavity
What significance do infraorbital ethmoid air cells (Haller Cells) play in inflammatory sinus disease?
Answer: Can cause narrowing of the infundibulum and maxillary sinus ostium resulting in OMU pattern of inflammatory sinus disease
What is the clinical significance of an enlarged ethmoid bulla?
Answer: May contribute to sinus disease by obstructing the infundibulum or middle meatus resulting in OMU inflammatory disease pattern
What is an Onodi air cell?
Answer: Contigous extension of the posterior ethmoid air cells into the sphenoid sinus and closely associated with the optic nerve. They can also be a potential cause of incomplete sphenoidectomy
Why is pneumatization of the sphenoid sinus involving the anterior clinoid processes important to know prior to sinus surgery?
Answer: Due to the close anatomic relationship between the optic nerves and carotid canals which are both vulnerable during sinus surgery
Inflammatory Sinus disease
What are the 5 recurring inflammatory sinus disease patterns?
Answer: Infundibular, OMU, sphenoethmoidal recess, sinonasal polyposis and sporadic (unclassifiable)
What is obstructed in the infundibular pattern?
Answer: Obstruction of the maxillary sinus ostium and ethmoid infundibulum
What is obstructed in the OMU pattern?
Answer: Ipsilateral involvement of the maxillary, frontal and ethmoidal sinuses due obstruction of the middle meatus
What is obstructed in the sphenoethmoidal recess pattern?
Answer: Obstruction of the sphenoethmoidal recess resulting in sphenoid and/or posterior ethmoid sinus disease
What pattern does sinonasal polyposis have?
Answer: Extensive polyps occupying the paranasal sinuses and nasal cavity can result in widespread obstruction.
What is the most common expansile lesion to develop in the paranasal sinus?
Answer: Mucocele. Most common in the frontal sinuses. Less commonly they occur in the ethmoid and maxillary sinuses and rarely in the sphenoid sinus.
How does a mucus retention cyst differ from a mucocele on imaging?
Answer: A MRC is usually spherical in shape, usually surrounded by sinus air and is typically not expansile compared to a mucocele which completely fills the sinus cavity, absent sinus air and expansile with bony remodeling of the sinus walls.
What radiologic signs may be present with a frontal mucocele?
Answer: Inferolateral proptosis of the globe, frontal bossing, nasal obstruction and intracranial extension.
What three clinical scenarios result in the CT finding of central areas of high attenuation separated by the sinus walls by a peripheral rim of mucoid attenuation material?
Answer: Inspissated secretions, mycetoma (aspergillosis) or sinus hemorrhage.
What structure do antrochoanal polyps widen?
Answer: Maxillary infundibulum
Where do antrochoanal polyps commonly extend?
Answer: Nasal fossa and posterior nasopharynx. If they are large enough they may also cause air way obstruction.
What adjacent structure can ethmoid sinus disease spread to?
Answer: The orbit resulting in orbital cellulitis, subperiosteal abscess, retrobulbar abscess, optic neuritis and venous thrombosis of the opthalmic veins. Orbital extension can occur due to the valveless ethmoidal veins and thin lamina papyracea which occasionally may be dehiscent. Clinical distinction between pre-septal and post-septal orbital infections are important because they are managed and treated differently.
What are the intracranial complications of sinus infections?
Answer: Meningitis, subdural and epidural empyema, brain abscesses, and venous sinus thrombosis.
What is the most common benign bone lesion to occur in the sinuses?
Answer: Osteoma which most often occurs in the frontal sinuses. If large enough they can result in an obstructive sinusitis with secondary mucocele formation or encroach into adjacent structures like the orbit.