Paranasal Air Sinuses - Functions, Diseases, Diagnostic Procedures
Know your Body

Paranasal Air Sinuses - Part I

Dr.Surya Rao Poodipeddi profile Authored by Dr.Surya Rao Poodipeddi on 1 Apr 2014 - 15:55.

The nose is the main drainage system consisting of two cavities called the nasal cavities, one for each side of the face into which all other cavities in and around the nose drain their contents. These cavities surrounding the nose called Paranasal Air Sinuses are hollow chambers with openings for drainage into the nasal cavities of the corresponding side.

These air sinuses, four on each side are cavities (hollow spaces) in the bones that are adjacent to the nose. They are the outgrowths from the nasal cavity and communicate with it by means of openings for drainage. The openings are known as ostia.

These four pairs of Paranasal air sinuses are named according to the bones in which they are located and are known as Frontal, Ethmoidal, Sphenoidal and Maxillary sinuses respectively.

Like the nasal cavities the Para nasal air sinuses are lined with mucous membrane composed of cells that produce mucus and have tiny hair like projections called Celia.
The mucus traps the incoming dirt particles and the cilia help in moving these collections into the nasal cavities from where the mucus drains out or when the quantity is more is sneezed out.
 The functions of these air sinuses include:

  • They make the skull bone lighter and help reducing the bony part by virtue of being hollow.
  • They provide resonance to the voice.  
  • They help in increasing the surface area for easy eruption of the teeth.
  • They aid and facilitate rapid growth of the bones in the face after birth  mainly the maxillary bone that gives the face its shape.
  • Whenever the drainage system is blocked, the sinuses tend to get inflamed and become vulnerable to infections leading to a common disease entity called Sinusitis which again is named as per the sinus involved, like maxillary sinusitis and frontal sinusitis etc.
  • These sinuses are air-filled, mucosal-lined cavities that develop in the bones of the face and cranium. All the four sinuses communicate with the nasal airways without exception.

They frequently become infected due to obstruction of normal drainage and lead to a negative pressure in the affected sinus causing intense headache. It is important to know that the four pairs of sinuses are differently named in accordance with the bones in which they are situated namely:

  • Frontal: The frontal pair occupies the frontal bone. They are usually asymmetrical and occasionally absent.
  • Maxillary: These are paired and occupy most of the maxilla bone. The floor of the corresponding orbit binds the top wall. The outer wall of the nose acts as the inner wall of the sinus. The teeth-bearing area of the maxilla acts as the lower boundary of the sinus.
  • Ethmoid: Numerous cells in the lateral walls of the nose and the inner walls of the orbit account for this pair of sinuses.
  • Sphenoid: These are paired and situated in the sphenoid bones.

All four pairs of the Paranasal air sinuses are endowed with rich blood supply, venous drainage, lymphatic drainage and nerve supply. Of these sinuses the Maxillary sinus is the largest air sinus and is pyramidal in shape. This pyramid shaped sinus is bound by several small bones on the floor, roof and the base on the face.

Several diagnostic procedures play their role in detecting diseases of the sinuses, namely:

  • Eliciting sinus tenderness by pressing the finger on the corresponding sinus suspected to be involved. For example the frontal sinuses can be palpated by pressing the finger top and inner side of the superior orbital margin. The maxillary sinuses are palpated by pressing the thumb over the bony projections by the side of the nose. The ethmoidal sinuses can be palpated by pressing the thumb in the inner canthus of one eye and the index finger on the other and gently pushing inside backwards.
  • Tranillumination in maxillary and frontal sinusitis with a torch light.
  • Radiological examination through an X-ray of the PNA sinuses (Para Nasal Air Sinuses) to detect the presence of haziness in the respective sinus.
  • ​Diagnostic puncture and sending the sample for bacterial examination.
  • ​Sinoscopy a method involving the use of fibre-optic sinoscope to detect early pathology, particularly malignancy and the procedure requires intranasal approach called anterostomy. 

CT Scan is considered as a confirmatory procedure.

Conditions affecting the paranasal air sinuses will be covered separately in Part II of the article of the same name.

*Disclaimer: This is not medical advice. The content is for educational purposes only. Please contact your doctor for any health care issues.