Sinusitis is an inflammation of the paranasal sinuses, which may or may not be as a result of infection, from bacterial, fungal, viral, allergic or autoimmune issues.

Newer classifications of sinusitis refer to it as rhinosinusitis, taking into account the thought that inflammation of the sinuses cannot occur without some inflammation of the nose as well (rhinitis).

Recent theories of sinusitis indicate that it often occurs as part of a spectrum of diseases that affect the respiratory tract (i.e. - the "one airway" theory) and is often linked to asthma.

All forms of sinusitis may either result in, or be a part of, a generalized inflammation of the airway so other airwaysymptoms such as cough may be associated with it.

Classifications by Location

Sinusitis can be classified by the sinus cavity which it affects:

• Ethmoid sinusitis - can cause pain or pressure pain between/behind eyes, headache.
• Frontal sinusitis - can cause pain or pressure in the frontal sinus cavity (located behind/above eyes), headache.
• Maxillary sinusitis - can cause pain or pressure in the maxillary (cheek) area (e.g., toothache, headache).
• Sphenoid sinusitis - can cause pain or pressure behind the eyes, but often refers to the vertex of the head

Sinusitis can be acute (going on less than four weeks), subacute (4-12 weeks) or chronic (going on for 12 weeks or more).

All three types of sinusitis have similar symptoms, and are thus often difficult to distinguish.

Acute Sinusitis

• Acute sinusitis is usually precipitated by an earlier upper respiratory tract infection, generally of viralbacteria, most commonly Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis and Staphylococcus aureus. Other bacterial pathogens include other streptococci species, anaerobic bacteria and, less commonly, gram negative bacteria.
  
• Another possible cause of sinusitis can be dental problems that affect the maxillary sinus. 
• Acute episodes of sinusitis can also result from fungal invasion. These infections are most often seen in patients with diabetes or other immune deficiencies (such as AIDS or transplantpatients on anti-rejection medications) and can be life threatening. In type I diabetes, ketoacidosis causes sinusitis by Mucormycosis.

• Chronic sinusitis is a complicated spectrum of diseases that share chronic inflammation of the sinuses in common.
  
• The causes are multifactorial and may include allergy, environmental factors such as dust or pollution, bacterial infection, or fungus* (either allergic, infective, or reactive).
  
• Non allergic factors such as Vasomotor rhinitis can also cause chronic sinus problems.
  
• Abnormally narrow sinus passages, which can impede drainage from the sinus cavities, can also be a factor.
• Symptoms include: Nasal congestion; facial pain; headache; fever; general malaise; thick green or yellow discharge; blurred vision, feeling of facial 'fullness' worsening on bending over; aching teeth.