Pathophysiology of Chronic Paranasal Sinusitis

財團法人仁愛綜合醫院 耳鼻喉科 朱敬中

        To understanding sinus disease, it is important to have a clear knownledge of the basic pathophysiology of the sinuses. The three factors essential to normal physiology of the paranasal sinuses are patency of the ostia, function of the cilia, and the quality of the nasal glandular secretions.

        Cilia require a fluid medium in which to beat and function normally; therefore, the sinus and nasal secretions are critical for normal nasal function. The normal ciliary environment is composed of a doube layer of mucus: a superficial viscid gel layer and an underlying serous or sol layer.

        The primary and most significant pathophysiology that produces sinusitis is a mucosal edema in and around the sinus ostium. The obstruction of the sinus ostium produces hypooxygenation of the involved sinus. When ciliary function is disturbed, the mucus blanket does not function normally. Local host resistance factors are diminished. Secretions are retained within the sinus as a result of ostial obstruction. Initially, there is a transient increase in intrasinal pressure follow by a negative intrasinal pressure with a result of hypoxia within the sinus. Nasal breathing is decreased as a result of various factors causing mucosal edema and further hypoxia results. With sneezing, sniffing, or nasal blowing, bacteria may enter the sinus ostium and further retention of secretions occurs. Ciliary function is impaired. A change in the viscosity of nasal secretions occurs, providing an ideal culture medium for bacteria.

        Our understanding of what allows bacterial sinusitis to occur has improved because of our recognition of predisposing factors. The epithelium that lines the nose and paranasal sinuses is pseudostratified columnar-ciliated epithelium. It is known that mucociliary transport function is important in the normal nasal and sinus function, so understanding the factors that impaire mucociliary transport is critical to understanding bacterial sinusitis. In treating a person with sinusitis, it is important to try to determine whether the presence of a local, regional, or systemic factor predisposes to the development of sinusitis. Upper respiratory tract infections usually also involve the sinus mucosa because the epithelium of the sinus is contiguous with the epithelium of the nose.

        Local predisposing causing of secondary bacterial invasion into the sinus are related to an important of the mucociliary transport function.

        Inspiration of cold or dry air can result in alterations in the mucociliary transport function and lead to sinus infection. Medications and drugs may also adversely affect mucociliary transport.

        The major regional cause that predisposes to suppurative sinusitis is an apical dental infection. Or there may be local causes, such as initial trauma, which may alter the anatomy of the ostiomeatal complex. Mechanical obstruction secondary to significant septal pathology may be present. Choanal atresia, which interfers with the drainage of the nose, may also be a significant predisposing factor. Edema secondary to an upper respiratory tract infection can obstruct the ostium of sinus, and bacteria can gain entrance into the sinus and produce suppurative sinusitis. Barotrauma (pressure changes ) during air travel or swimming or diving can produce edema of the sinus ostium, and swimming in contaminated water can allow bacteria into the nose and sinuses and produce suppurative sinusitis. Nasal polyps, foreign bodies, or nasal packing may alter the ventilation of the sinuses and produce sinusitis. Nasal tumors also be a predisposing factor in the development of bacterial sinusitis. The immotile cilia syndrome or ciliary dyskinesia, a congenital disorder that involves disorientation of the cilia and abnormalities of the dynein arms, may produce sinusitis and bronchitis due to a loss of mucociliary clearance.

        Systemic factors predisposing to the development of rhinosinusitis are general debilitating conditions such as malnutrition, long-term steroid therapy, uncontrolled diabetes, blood dyscrasias, chemotherapy, and other factors that contribute to states of metabolic depletion. Sinusitis may also be a manifestation of serious immune deficiencies such as IgG deficiency. Deficiencies should be considered in all cases of recurrent sinus infections. Sinusitis may also occur as a manifestation of acquired immunodeficiency disease ( AIDS ). It has been reported that at least 80% of AIDS patients have some symptoms of sinusitis. In fact, the otorhinolaryngologist may see the AIDS patient with recurrent sinusitis as one of the first manifestations of AIDS. Regardless of the cause, various systemic factors may predispose to the development of bacterial sinusitis.

        Consequently, it is mandatory to identify the predisposing factors not only to effect proper management but also to remove this predisposing cause, especially if it occurs locally in the nose or regionally in the teeth.

        Thus, in the long-term management of recurrent rhinosinusitis it is important to control any predisposing factor.