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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Eye, Ear, and Sinus Infections

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Sinus Infections

The paranasal sinuses (ethmoid, frontal, and maxillary) all communicate with the nasal cavity. In healthy individuals, these sinuses are air-filled cavities lined with ciliated epithelium and are normally sterile.

SINUS INFECTIONS

The paranasal sinuses (ethmoid, frontal, and maxillary) all communicate with the nasal cavity. In healthy individuals, these sinuses are air-filled cavities lined with ciliated epithelium and are normally sterile. They are poorly developed in early life and, in con-trast to otitis media, sinus infections are a rare problem in infancy. The pathogenesis of sinus infection can involve several factors, most of which act by producing obstruction or edema of the sinus opening, impeding normal drainage. Consequently, bacterial infec-tion and inflammation of the mucosal lining tissues develop. Predisposing factors may be (1) local, such as upper respiratory infections producing edema of antral tissues, mu-cosal polyps, deviation of the nasal septum, enlarged adenoids, or a tumor or foreign body in the nasal cavity; or (2) systemic, such as allergy, cystic fibrosis, or immunodefi-ciency. Occasionally, maxillary sinusitis can result from extension of a maxillary dental infection.

MANIFESTATIONS

Signs and symptoms vary according to which sinuses are affected and whether the illness is acute or chronic. Fever is sometimes present. In addition, nasal or postnasal discharge, daytime cough that may become worse at night, fetid breath, pain over the affected sinus, headache, and tenderness to percussion over the frontal or maxillary sinuses are all fea-tures that may appear in different combinations and suggest the diagnosis. Complications of sinusitis can include extension of infection to nearby soft tissues, such as the orbit, and occasionally spread, either directly or via vascular pathways, into the CNS.

COMMON ETIOLOGIC AGENTS

Table 61 – 3 summarizes the usual etiologies of sinus infections. Respiratory viruses are also occasional direct causes but are most important as predisposing factors to bacterial superinfection of inflamed sinuses and their antral openings. Together, S. pneumoniae and H. influenzae account for more than 60% of cases of acute sinusitis. Opportunistic, sapro-phytic fungi, such as Mucor, Aspergillus, and Rhizopus species, are being increasingly seen in compromised hosts, such as those with severe diabetes mellitus or immunodefi-ciency. These have a particular tendency to spread progressively to adjacent tissues and to the CNS and are very difficult to treat.


DIAGNOSTIC APPROACHES

Radiographic studies of the sinuses confirms the diagnosis. If it becomes necessary to de-termine the specific infectious agent, fluid should be obtained directly from the affected sinus by needle puncture of the sinus wall or by catheterization of the sinus antrum after careful decontamination of the entry site. Gram smears and cultures are then made. Cul-tures of drainage from the antral orifices or nasal secretions are unreliable because of con-taminating aerobic and anaerobic normal flora.

MANAGEMENT PRINCIPLES

In uncomplicated acute sinusitis, prompt antimicrobial therapy is initiated. The choice of antimicrobics is usually empirical, based on the most likely bacterial causes and their usual susceptibility. For example, amoxicillin is effective against most strains of S. pneu-moniae and H. influenzae. Severe, complicated acute infections and chronic sinusitisoften require otolaryngologic consultation. In such cases, it is often necessary to obtain cultures directly from the sinuses to select specific antimicrobial therapy, consider the need for surgical procedures to adequately remove the pus and inflammatory tissues, and correct any anatomic obstruction that may exist.


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