--- title: "Anatomy of Paranasal Sinuses" description: "ENT notes on Anatomy of Paranasal sinuses - drainage, relations, and clinical aspects - for medical students and ENT residents." source: "The ENT Resident" author: "Dr. Mausumi Das" canonical_url: "https://www.theentresident.com/ent-notes-lectures/paranasal-sinus-anatomy" categories: ["Rhinology"] video: "https://www.youtube.com/watch?v=Ex3u3Lfkx2o" image: "https://media.theentresident.com/og-images/paranasal-sinus-anatomy.png" --- # Anatomy of Paranasal Sinuses ENT notes on Anatomy of Paranasal sinuses - drainage, relations, and clinical aspects - for medical students and ENT residents. Watch the full video lecture on YouTube: https://www.youtube.com/watch?v=Ex3u3Lfkx2o ## Anatomy of the Paranasal Sinuses In this post, we'll cover the **paranasal sinuses** — their anatomy, drainage, relations, variations, and clinical significance. --- ### 🌬 What Are Paranasal Sinuses? Paranasal sinuses are **air-filled cavities** located within the bones of the skull. There are **four paired sinuses**: - **Maxillary Sinus** - **Frontal Sinus** - **Ethmoidal Sinuses** - **Sphenoidal Sinus** --- ### 🔺 Maxillary Sinus (Antrum of Highmore) - **Largest** of all sinuses - **Shape**: Pyramidal - **Location**: Occupies the **body of the maxilla** - **Capacity**: ~15 ml **📍 Orientation:** - **Base**: Faces the lateral nasal wall - **Apex**: Directed towards the **zygomatic process** **📤 Drainage:** Drains into the **middle meatus** via its **ostium** #### **🔄 Maxillary Ostia:** There are 2 maxillary Ostium - Natural Ostium and Accessory Ostium. >What are the differences between **Natural Ostium** and **Accessory Ostium**? **🧭 Relations of Maxillary Sinus:** - **Anterior Wall**: Facial surface of maxilla, cheek soft tissue - **Posterior Wall**: Infratemporal and pterygopalatine fossa - **Medial Wall (Base)**: Middle and inferior meatus; often thin - **Floor**: Alveolar & palatine processes; related to roots of 2nd premolar and 1st molar - **Roof**: Orbital floor — traversed by **infraorbital nerve and vessels** --- ### 🔺 Frontal Sinus - Located in between **inner and outer tables** of frontal bone - Often **asymmetrical** - Divided by a thin or absent bony septum **📤 Drainage:** Via **frontal ostium** into **frontal recess**, then into **middle meatus** **🧭 Relations of Frontal Sinus:** - **Anterior Wall**: Skin of forehead - **Inferior Wall**: **Orbit** and its contents - **Posterior Wall**: **Meninges** and **frontal lobe** --- ### 🔺 Ethmoidal Sinuses - Numerous thin-walled air cells (3–18) - Located in the **lateral masses of the ethmoid bone** - Separated into: - **Anterior group** → Middle meatus - **Posterior group** → Superior meatus - Divided by **ground lamella** (basal lamella of middle turbinate) >What are the relations of Ethmoidal sinuses? #### **Anterior Ethmoid Cells** - **Agger Nasi Cell**: Anterior-most cell; affects uncinate process position - **Ethmoidal Bulla**: Most constant anterior cell - **Supraorbital Cell**: Lies over orbit → can mimic frontal sinus >What is the surgical importance of Supraorbital cells? - **Suprabulla or Frontal Bulla Cells** - **Frontoethmoidal Cells** - situated in area of Frontal Recess and may encroach Frontal sinus. >What is Kuhn's Classification of Frontoethmoidal Cells? - **Haller Cells**: Infraorbital; can obstruct maxillary drainage >What is the surgical importance of Haller cells? #### Posterior Ethmoid Cells - Drain into **superior meatus** - **Onodi Cell**: - Most posterior cell - May be confused with sphenoid sinus - Lies close to **optic nerve** and **carotid artery** >What is the surgical importance of Onodi cell? --- ### 🔺 Sphenoid Sinus - Located in the **body of sphenoid bone** - Rarely symmetrical; separated by a thin septum **📤 Drainage:** - Into **sphenoethmoidal recess** >What is the location of sphenoid ostium in relation to Posterior Choana? >What are the different types of pneumatization patterns of Sphenoid sinus? **🧭 Relations of Sphenoid Sinus:** - **Lateral Wall**: - Optic nerve, carotid artery, opticocarotid recess - Maxillary nerve (lower lateral wall) - **Roof**: - Olfactory tract, optic chiasma, frontal lobe (anterior) - Pituitary gland, cavernous sinus (posterior) - **Floor**: Vidian nerve - **Posterior Wall**: Contributes to clivus --- ### �� Drainage Summary | Sinus | Drains Into | | --- | --- | | Maxillary Sinus | Middle Meatus (via infundibulum) | | Frontal Sinus | Middle Meatus (via frontal recess) | | Anterior Ethmoidal | Middle Meatus | | Posterior Ethmoidal | Superior Meatus | | Sphenoid Sinus | Sphenoethmoidal Recess | --- ### 🔬 Mucosal Lining of Sinuses - **Thinner and less vascular** than nasal mucosa - **Epithelium**: Ciliated columnar with **goblet cells** - **Cilia** are denser near the ostia → **assist mucus drainage** --- ### 📌 Clinical Points to Remember - **Accessory ostia** can hinder natural drainage - **ONODI cells** pose a risk during endoscopic surgery due to proximity to optic nerve - **Supraorbital cells** may obstruct frontal recess and confuse surgical orientation - **Frontal cell classification** prevents incomplete dissection during FESS - **Sphenoid sinus** relations are vital during skull base or pituitary surgeries --- ## About This Note This free ENT note on Anatomy of Paranasal Sinuses was written by Dr. Mausumi Das and is paired with a corresponding video lecture. 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