Chapter 2-5-2. Anaerobic infections (individual fields): anaerobic infections of the head and neck.

The region ranging from the base of the skull to the clavicle includes many organs: the oral cavity, pharynx (epipharynx, oropharynx and hypopharynx), nasal cavity, paranasal sinuses, larynx, esophagus, thyroid gland, salivary glands (sublingual, submandibular, and parotid glands), blood vessels (cervical arteries and veins), nerves (cranial and spinal nerves), muscles, and bones (facial bones, mandible, hyoid bone and vertebra). Each tissue of the neck is demarcated by the thick fibrous connective tissue known as fascia. These interfascial spaces, which are filled with coarse connective tissue (areolar tissue), are called fascial spaces. Once an infection reaches the fascial spaces, it spreads to remote sites, thereby leading to an increasingly severe infection because these spaces are sparse and continuous. Infections of these spaces in cervical tissues are known generically as deep neck infections [1]. Most of the deep neck infection cases are derived from dental or otorhinolaryngological infections. Classification of deep neck infections is slightly confusing because of coexisting anatomical or pathological classification schemes. In the anatomical classification, the infections are generally named according to the tissue spaces in which the infections are located. The main tissue spaces are submandibular, sublingual, masticatory, para-pharyngeal, retropharyngeal, danger, and carotid spaces. The infections are referred to as abscesses of the para-pharyngeal space, submandibular space, etc. according to tiers localizations [2]. When deep neck infections progress to the mediastinum, prognoses are poor. An infection showing mediastinal development, which is called ‘‘descending necrotizing mediastinitis’’, is frequently dealt with as an independent disease, because the morbid conditions and therapeutic methods differ considerably from those for deep neck infections. Deep neck infections are occasionally classified into the aerosis type and the non-aerosis type according to the associated morbid conditions. Infections of the aerosis type are traditionally called ‘‘gas gangrene’’. Gas gangrene is classified into the clostridial type and the non-clostridial type. Clostridial gas gangrene is generally believed to progress faster and to be more severe than the non-clostridial type. At present, infections of the neck involving Clostridium are uncommon, and the significance of actual classification of aerosis-type infections of the neck according to Clostridium is low. There is a morbid condition called ‘‘necrotizing fasciitis’’ among these infections, which are severe as regards the degree of infectious progression. This indicates an infection with a poor prognosis, which includes inflammation of the fascia and progresses rapidly. This disorder is differentiated from abscess-forming diseases. This section deals with deep neck infections, necrotizing fasciitis, descending necrotizing mediastinitis and Lemierre syndrome among anaerobic infections of the head and neck.