Brief about Maxillary sinus

Maxillary Sinus

- Also known as Antrum of Highmore.

- Maxillary sinus are two in number, one on either side pf the maxilla, and they are the largest of the paranasal air sinuses.

- It can be described as pyramidal in shape, consisting of base, an apex and four sides.

- Base is formed by the lateral wall of nose.

- Apex projects laterally to the zygomatic process of maxilla.

-The four walls of pyramid are formed by;

1. The roof of antrum or the floor of orbit
2. The anterior wall
3. The posterior wall;Infra temporal surface of body of maxilla.
4. The alveolar process of maxilla which is the floor of sinus.

- Roof is formed by thin orbital plate.

Blood supply 

- Blood supply to the mucous membrane is from arteries which pierce the bone, and are derived from facial, maxillary, infraorbital and greater palatine arteries.
- Veins accompany the arteries and drain into anterior facial vein and then to pterygoid plexus of veins.
- The lymphatics drainage of maxillary sinus is through the infraorbital foramen or through the ostium and then to submandibular and deep cervical lymph nodes.

Nerve supply
- It is derived from all the branches of v2(maxillary division of trigeminal nerve)- infraorbital, anterior, middle and posterior superior alveolar nerves.

Functions

- Impart resonance to the voice.
- Increase the surface area and lighten the skull.
- Moisten and warm the inspired air.
- Filter the debris from the inspired air.
- Create ‘air padding’ to provide the thermal insulation.

Developmental anomalies
- Hypoplastic or underdeveloped maxillary sinus is present in:
- Crouzon syndrome.
- Treacher collins syndrome.
- Binder syndrome.

Classification of disease/pathologies of maxillary sinus.

- Developmental anomalies
- Agenesis
- Aplasia
- Hypoplasia
- Supernumerary maxillary sinus.

Inflammatory diseases
- Mucositis
- Maxillary sinusitis
- Empyema
- Antral polyps
- Antroliths

Cysts of maxillary sinus
- Odontogenic cysts
- Non odontogenic cysts

Traumatic diseases
- Oroantral fistula(OAF)
- Fractures
- Pneumocele
- Foreign bodies/ teeth root jn maxillary sinus 

Tumors of the maxillary sinus: Benign and malignant tumors

Other diseases involvement
- Fibro-osseous lesions.
- Granulomatous diseases.

Applied Anatomy.
Root anatomy: 
- Approximately, 1-1.25 cm between the floor of the sinus and apices of maxillary posterior teeth.
- Most common teeth whose roots are in close approx to the maxillary sinus are 2nd maxillary molar followed by 1st and 3rd premolar,  1st premolar and canine.

Maxillary sinus in children
- The maxillary sinus reaches its normal adult size by the age of 15 years. Hence, the risk of creating oral antral fistula is less in children and young adults.

Oro antral fistula and maxillary sinus
- Large sinus may pose risk of sinus wall fracture if the force used during maxillary posterior extraction results in an oro antral fistula.
- The presence of unerupted tooth in the maxillary tuberosity is a potential line of weakness.

Periapical involvement
- Periapical involvement, in the form of acute or chronic abscess in teeth related to floor of sinus, may secondarily involve maxillary sinus. The pus may discharge into sinus producing a fluid level.
- The extraction of such a tooth, results in blood clot getting infected, and results in creation of oroantral fistula.

Tumors developing in maxillary antrum
- The tumors which develop in maxillary sinus may erode these walls and present as swellings of cheek.
- Tumors may also penetrate floor of maxillary sinus and present as a palatal lump or a swelling in buccal sulcus.
- In case, tumor erodes the posterior wall, the PSA nerves may be destroyed and patient may complain of anesthesia of gingiva or teeth in maxillary molar area.

Antral puncture intranasal antrostomy
- It can be carried out by puncturing into the sinus cavity through the middle meatus in children and the inferior meatus in adults creating a point of dependent drainage. In the case of acute sinusitis, pus is formed inside the antrum which in turn increases intraantral pressure because of occlusal lining mucosa.

Canine fossa
- The wall of the sinus is very thin in the area of the canine fossa. It can be used for following:

1. Diagnostic aspiration.
2. The site for caldwell- luc operation.
3. For the entry of the endoscope.

Fractures of the middle 3rd face
- The thin walls of maxillary sinus get easily fractured as a result of trauma. The fractures of middle third of face involve maxillary sinus. Fractures of zygomatic bone show the zygomatic buttress pushed into the sinus; Fractures of middle third of the maxilla causes Lefort I, II and lII fractures.

Foreign bodies in the sinus.
- Various foreign bodies have been reported in the maxillary sinus.
- They gain entry via oroantral communication and others through a tooth socket. Foreign bodies can be through broken burs, dental impression material, root canal filling materials, implant, match sticks, bullets,bony fragments etc.

Classification of maxillary sinusitis according to duration of its course.

1) Acute maxillary sinusitis: Has a sudden onset and duration of 4 weeks or less.
2) Sub acute maxillary sinusitis: Has a duration of 4-12 weeks
3) Recurrent subacute maxillary sinusitis: Occurs at least four times per year with each episode lasting 7-10 days. The symptoms are completely absent in between the episode.
4) Chronic maxillary sinusitis: Has duration of at least 12 weeks.