Paranasal Sinuses – Frontal, Maxillary, Sphenoid, Ethmoidal Sinuses

August 17, 2012 | By | Reply More

Paranasal Sinuses – Frontal, Maxillary, Sphenoid, Ethmoidal Sinuses

Four air-filled extensions of the respiratory part of the nasal cavity; named according to the bones in which they reside; frontal, ethmoidal, sphenoidal & maxillary bones.

They are lined with mucous membrane which is continuous with that of the nasal cavity through the sinus apertures in the lateral wall of the nose.

The maxillary sinus is well developed at birth, the frontal & sphenoidal exhibit a definite cavity at the 7th year of life while the ethmoidal develop late at puberty.

The definite function of the PNS is not well known, functions include acting as resonating chambers for the voice, warming and humidifying air, decreasing the weight of the skull, and adding contours to the face .

The frontal sinuses:

These two sinuses are located on each side of the midline in the frontal bone behind the superciliary ridges.
They are rarely symmetrical.
They are roughly triangular in sagittal section with a maximum vertical length of 2.5 cm & maximum AP depth of 2 cm in the orbital plate of the frontal bone.

  • vital anatomical structures – depending on its size, its roof may form the floor of the orbit and its roof may form the floor of the anterior cranial fossa
  • drainage – via frontonasal duct into ethmoidal infundibulum, which opens into the semilunar hiatus of the middle meatus
  • innervation – branches of the supraorbital nerves (CNV1)
  • arterial supply – supraorbital artery of ophthalmic artery

Maxillary Sinus:

largest of the paranasal sinuses; pyramid-shaped cavities occupy the body of the maxillae and its apex can extend into zygomatic bone, the base forms the inferior part of the nasal cavity, the roof is formed by the floor of the orbit, and the floor is formed by the alveolar part of the maxilla. The sinus opens in the posterior part of hiatus semilunaris. The big opening in the lateral nasal wall produced by the maxillary sinus is blocked for most of its size by the overlapping inferior concha.

  • vital anatomical structures – infraorbital nerve (off of CNV2) and vessels, roots of maxillary molar teeth, and superior alveolar nerves.
  • drainage – via maxillary ostium into semilunar hiatus of the middle meatus
  • innervation – anterior, middle, and posterior superior alveolar nerves – branches of the maxillary nerve (CNV2)
  • arterial supply – mainly from superior alveolar branches of the maxillary artery; branches of the greater palatine artery supply the floor of the sinus

Clinical Notes

1) Unfortunate placement of maxillary ostium (located high on the superomedial walls) leads to poor drainage with the consequent accumulation of secretion in the sinus & superadded infection resulting in sinusitis. So this condition could not be treated unless the draining system is restored & normal physiology of its cilia is resumed either medically or surgically.

2) When maxillary molar teeth are removed, a communication between the sinus and the oral cavity may result and an infection can occur.

3) The maxillary teeth and the mucosa of the maxillary sinus have the same innervation (sup. alveolar nerve), so inflation of the sinus mucosa can lead to sensation of a toothache in the molar teeth.

4)The root of the upper second premolar tooth sometimes perforates the floor of the maxillary sinus & its extraction may lead to oro-antral fistula.

Sphenoid Sinus-

These two sinuses are located on each side of the midline in the body of sphenoid separated from each other by thin plate of bone and may extend into the wings of this bone. They lie behind the posterior ethmoidal cells, in front of the dorsum sellae, inferior to the hypophyseal fossa superior to the nasopharynx & bounded on each side by the MCF.

  • vital anatomical structures – the optic nerves, the optic chiasm, the pituitary gland, the internal carotid arteries, and the cavernous sinuses
  • drainage – into sphenoethmoidal recess above superior nasal conchae
  • innervation – posterior ethmoidal nerve (off CNV1)
  • arterial supply – posterior ethmoidal artery

Ethmoidal Sinuses

comprise several cavities; These three groups of sinuses are located in the lateral mass of the ethmoid in its labyrinth. They are named; anterior, middle & posterior sinuses (air cells). The walls of these spaces are very thin & completed by other bones like the lacrimal, sphenoid, palatine, frontal & maxillae. Innervated by the anterior and posterior ethmoidal branches of the nasociliary nerves.

  • anterior ethmoidal cells – drain directly or indirectly through the ethmoidal infundibulum into the semilunar hiatus of the middle meatus. supplied by anterior ethmoidal vessels & nerves.
  • middle ethmoidal cells – open directly into the middle meatus and are sometimes called “bullar cells” because they form the ethmoidal bulla, a swelling on the superior border of the semilunar hiatus. supplied by anterior ethmoidal vessels & nerves.
  • posterior ethmoidal cells – open directly into the superior meatus. posterior ethmoidal vessels & nerves.

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Category: Anatomy, Medical

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