Thursday, August 23, 2012

Causes of sinusitis: problems in OMC

There are a number of causes of sinusitis. One of the anatomical causes is the ostiomeatal complex (OMC), which is referred to as “the key to the sinuses.” The term ostiomeatal unit was coined by Naumann. The words “ostio” and “meatus” mean “passage.” The unit, located on the lateral nasal wall, consists of the maxillary sinus’ ostium, frontal recess (frontonasal duct), infundibulum, middle turbinate, middle and anterior ethmoidal cells, bulla ethmoidalis, hiatus semilunaris and uncinate process.

Within the complex, the slim channels connect the paranasal sinuses to the nasal cavities. The ethmoid, frontal and maxillary sinuses drain into the complex. If the mucosa of the complex swells, both the cavities and sinuses will be obstructed. The blocked complex interferes with mucus drainage, creating a suitable environment for the growth of bacteria and consequent inflammation. The infection or blockage of any part of the complex can thus lead to sinusitis. For instance,
  • Anatomic anomalies within the middle nasal meatus region, located in the complex, may disrupt ventilation and mucocillary clearance of the sinuses. The pathways facilitating mucocillary clearance for the ethmoid, frontal and maxillary sinuses open into the complex.

  • Structural problems in the anterior ethmoid sinus may block the complex, and thereby adversely affect the maxillary or frontal sinuses.
  • Structural problems, including tumor, foreign bodies, polyps, deviation of the septa, concha bullosum, unusually big uncinate process, abnormally large extramural ethmoid cells may also obstruct the complex.

  • Edema of the mucosa due to allergy, infection, exposure to chemicals, air pollutants and cigarette smoke reduces distance between the mucosa because the OMC is a narrow area, and thus it impairs mucociliary function.
  • The uncinate process’ deviation may impair sinus drainage.

A thorough examination of the OMC will help in finding the causes of sinusitis. Computed tomography (CT) of the sinonasal tract in coronal plane shows the complex clearly and the mucosa inflammation. If the OMC is blocked, it needs to be opened. In case of mechanical factors responsible for the obstruction, functional endoscopic sinus surgery (FESS) is required to open the complex. If pathology in the complex is unclear, the surgeon may prefer rigid endoscope to flexible one because the former unfolds a good view of the area.

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