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M01.02.037 The Paranasal Sinuses
The paranasal sinuses are air-filled extensions of the nasal cavity, playing critical roles in physiology and pathology. Understanding their anatomy, drainage, innervation, and clinical relevance is essential for medical students.
Anatomy of Paranasal Sinuses
General Features
- Location: Found in paired formations within specific cranial bones.
- Structure: Lined by ciliated pseudostratified epithelium interspersed with goblet cells.
- Sinuses:
- Maxillary
- Frontal
- Sphenoidal
- Ethmoidal
| Sinus | Bone | Drainage | Innervation | Blood Supply |
|---|---|---|---|---|
| Maxillary | Maxilla | Hiatus semilunaris (middle meatus) | Maxillary nerve | Infraorbital and superior alveolar |
| Frontal | Frontal | Frontonasal duct (middle meatus) | Supraorbital nerve | Anterior ethmoidal artery |
| Sphenoidal | Sphenoid | Sphenoethmoidal recess | Posterior ethmoidal and maxillary nerves | Pharyngeal branches of the maxillary artery |
| Ethmoidal | Ethmoid | Hiatus semilunaris or lateral walls | Anterior and posterior ethmoidal nerves | Anterior and posterior ethmoidal arteries |
Functions of the Paranasal Sinuses
The exact functions remain debated. Proposed roles include:
- Lightening the skull: Reducing overall weight.
- Immune defense: Supporting nasal cavity protection.
- Humidification: Conditioning-inspired air.
- Voice resonance: Enhancing vocal tone and clarity.
Clinical Correlations
1. Sinusitis
- Definition: Infection leading to inflammation of the sinus mucosa.
- Common Symptoms: Pain, swelling, nasal congestion, and toothache (maxillary sinus involvement).
- Pansinusitis: Involvement of multiple sinuses.
| Sinus | Associated Symptom |
|---|---|
| Maxillary | Toothache due to maxillary nerve supply |
| Frontal | Headache near the forehead |
| Ethmoidal | Pain between the eyes |
| Sphenoidal | Deep-seated headache or orbital pain |
2. Transsphenoidal Surgery
- Indication: Used for treating pituitary adenomas.
- Procedure: Endoscopic instruments pass through the sphenoid sinus to access the pituitary gland.
- Advantages: Minimally invasive compared to craniotomy.
Points to Remember
- The paranasal sinuses develop by erosion of the nasal cavity into adjacent bones.
- All sinuses drain into the nasal cavity through openings on the lateral nasal walls.
- Sinusitis can mimic dental or orbital pain depending on the sinus involved.
- Transsphenoidal surgery highlights the clinical relevance of the sphenoidal sinus.