Monday, June 4, 2012

Anatomy of the paranasal sinuses

The paranasal sinuses are a set of 8 aerial cavities or sinuses, four on each side of the nose in the frontal, sphenoid, ethmoid and superior maxillary bones, covered by a fine mucosa of ciliated epithelium and which communicate with the nasal fossae.
The bones that surround the nasal fossae are pneumatised (hollow and containing air). They are coated by a wet mucosa that constantly produces a lubricating mucus that drains through the nasal fossae apertures. They are involved in breathing, phonation, heating and olfaction.

Frontal sinus
These two cavities separated by the interfrontal septum are linked through the back with the anterior cranial fossa and through the bottom with the orbits and the nasal fossae.

Ethmoid sinus
The labyrinth or ethmoidal cells are located on each side of the half and upper third of the nasal and medial cavity to the orbit bone. They are clustered and are closely connected at the side with the orbital content and at the rear with the sphenoidal sinus.

 Maxillary sinus
The Maxillary sinus or antrum of Highmore is the largest of the paranasal sinuses. It has the form of an irregular pyramid with the base towards the nasal fossa and the vertex towards the zygomatic or pyramidal process of the maxillary.

Sphenoidal sinus
This is the farthest anterior and usually septated by 1 or 2 osseous septums. It is located in the body of the sphenoid, hence its size and shape are variable. Each sphenoidal sinus communicates with the superior nasal meatus through small apertures that drain into the sphenoethmoidal recess.

Opening of the sinuses 
The sinuses of each bone open out into a meatus through the ostium, a conduct through which they drain any unnecessary content, this structure is called Ostiomeatal Complex (OMC).

Attic: leads to the sphenoidal sinus, the attic is the area above the superior meatus.
  •  Superior meatus: leads to the posterior ethmoid sinus.
  •  Middle meatus: leads to various paranasal sinuses as the anterior ethmoid sinus, superior maxillary sinus, frontal sinus.
  •  Inferior meatus: lead to the nasolacrimal duct.
  •  Mucosa of the paranasal sinuses
The mucosa of the paranasal sinuses is of the same histological type as that of the nasal fossae, as it is a continuation of the latter. It is different from the nasal mucosa in that it is far less vascularised and is slimmer and more fragile. The epithelium is of the stratified cylinder type and ciliated with muciparous cells. The chorion contains blood vessels, nerves and seromucous glands. The conjunctive tissue is condensed, and there is continuity between the chorion and the periosteum.

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