Infections of the deep neck tissues are complicated, in diagnosis, localization, access, and management. The anatomy of the neck is complex with critical structures of the airway, gastrointestinal system, and major vessels and nerves. The affected tissues may be deep and impossible to palpate or visualize externally. Nearby structures can become involved in the inflammation and lead to neurovascular, bony, or airway issues. It is crucial to understand different neck abscesses and how they may present, as well as the best ways to treat them. ,,
Historically, before antibiotics, tonsillitis and pharyngitis were the most frequent causes of deep neck space infections. Tonsillitis remains the most common cause of deep neck space infection in children, but in adults, an odontogenic origin is the most common. Other causes include oral surgical procedures, salivary gland infection or obstruction, trauma to the oral cavity or pharynx, instrumentation, foreign body aspiration, intravenous drug use, cervical lymphadenitis/suppuration of malignant lymph node or mass, branchial cleft anomalies, thyroglossal duct cyst, and others. There may be no clear source for 20% to 50% of deep neck infections. It is important to consider immunocompromise due to HIV/AIDS, chemotherapy, or immunosuppressant medications in these infections. 
Deep neck infections are common. As they comprise many discrete entities, it is difficult to accurately estimate the number of deep neck space infections in the United States or worldwide. It would be reasonable to assume that incidence in the United States is lower than in countries where immunizations and/or early medical intervention for more superficial infections is unavailable. A study in 2009 by Adeil et al. estimated more than 3400 U.S. pediatric hospital admissions per year for deep neck space infection.
Peritonsillar abscess is most common in 20- to 40-year-olds. Children are not often affected by a peritonsillar abscess but can be if they are immuno-compromised. Females and males are affected equally. Chronic tonsillitis or multiple rounds of oral antibiotics may predispose a person to the formation of a peritonsillar abscess.
Parapharyngeal abscesses can develop in any age patient but are most common in children and adolescents. Immunocompromised adults are also at increased risk. 
There are different potential paths of infection in the neck. Oral cavity/face/superficial neck infection can spread via the lymphatic system to the deep tissues of the neck. Lymphadenopathy may cause suppuration and then focal abscess formation. Direct communication between tissues in the neck may occur. Finally, penetrating trauma can introduce infection to the deep tissues.
After the spread of infection, either local inflammation or phlegmon may develop, or a fulminant abscess may form with a purulent collection of fluid. Signs of neck abscess in the deep tissues may result from either mass effect of inflamed tissue or abscess on the surrounding structures or from direct involvement of those structures with the infection. Examples of different types of spread include the following:
This can lead to mediastinitis or empyema. Neck abscess can include peritonsillar infections, retropharyngeal infections, submandibular infections, buccal infections, parapharyngeal space infections, and canine space infections. The retropharyngeal, retroesophageal, and posterior mediastinum are all a continuous space for the spread of infection.
Causative organisms for deep neck infections include gram-positive organisms, including but not limited to Streptococcus viridans, Staphylococcus epidermidis, and Staphylococcus aureus; and gram-negative organisms, including but not exclusively Escherichia coli, Klebsiella oxytoca, and Haemophilus influenza. In studies of retropharyngeal abscess, polymicrobial results were found in almost 90% of patients. Aerobes were found in all patients and anaerobes found in more than half. Anaerobes may include Peptostreptococcus, Fusobacterium, Prevotella, and Actinomyces. Other bacteria may include Lactobacillus, Bacteroides, and Propionibacterium, among others.
Some studies show cultures with an average of at least five isolates. There have been studies showing an association between the presence of biofilm and abscess development. 
Deep neck space abscess should be considered when patients describe any or many of the following: severe pain, recent dental procedures, upper respiratory infection, neck or mouth trauma, respiratory distress, dysphagia or dysphonia, immunosuppression, the rapid rate of onset, or prolonged duration of symptoms. Particular red flags include asymmetry of the neck, neck masses, lymphadenopathy, trismus, medial displacement of the lateral pharyngeal wall and tonsil, torticollis, cranial nerve involvement, spiking fevers, and tachypnea/shortness of breath.
CT imaging of the neck can offer help with confirming and localizing the presence of a deep neck infection. However, patients are often either too unstable for CT imaging or unable to lie flat on the CT table to have the CT performed. There may be situations where only a portable lateral soft tissue neck x-ray can be obtained, and this can help support the diagnosis of neck abscess without much help in localization.
In cases where an early neck abscess is suspected, an otolaryngologist may be called upon to perform direct laryngoscopy to ascertain the presence of swelling. 
Treatment involves adequate drainage of the abscess in the operating room. Also, antibiotic therapy is paramount. Because cultures are not available at the time of presentation, empiric antibiotics are started at presentation. A study in 2008 by Yang et al. found three comparable antibiotic regimens: (1) ceftriaxone and clindamycin (2) ceftriaxone and metronidazole, or (3) penicillin G and gentamicin and clindamycin.
In a 2015 Iranian study by Motahari, et al., 815 of 428 cases were managed surgically while the rest were managed medically. Tracheostomy was performed in five cases. One 15-year-old with symptoms suggestive of mediastinitis died of airway compromise a day after undergoing surgical management of parapharyngeal abscess. The study concluded that if medical management fails after 24 to 48 hours, or if fluctuance or any complications are present, prompt surgical management is indicated.
It is important to determine the underlying cause of the problem and to address that specifically. For example, with odontogenic infections, early dental extraction is crucial. Airway management must always be a consideration, as there is often swelling and distortion of anatomy, the surgical airway may be preferable. Certainly, in cases of deep neck infection, early notification of otolaryngology and anesthesia for airway backup is wise. For patients presenting with a compromised airway, prompt transfer to the operating room for simultaneous evaluation, airway management, and treatment may be life-saving. ,
The anatomy of the neck is quite complex. Terms of review include:
The two main fascial planes are (1) superficial cervical fascia and (2) deep cervical fascia.
The deep neck spaces include the following:
Deep neck infections are not uncommon in clinical practice. The problem is that they are sometimes missed, and this can have an enormous morbidity on the patient. Deep neck infections cannot only compromise the airways but also spread vertically to the brain, spinal cord, and the mediastinum. Because the majority of patients initially present to the primary care worker, it is important to have a streamlined process to ensure that the diagnosis is made promptly and the condition treated. Data from infections in the pediatric population reveal that by following clinical guidelines one can achieve a very low morbidity. While there are no universal guidelines in the management of deep neck infections, current expert opinion reveals that an interprofessional group of health professionals can help achieve excellent outcomes. Once a deep neck infection is suspected, the following healthcare workers need to be involved:
Since most deep neck infections are considered surgical emergencies, there are no randomized trials to determine the best procedure, antibiotic, or duration of treatment. The only definitive data is that surgery is recommended in almost all patients with neck abscess. The earlier the surgery, the better the outcomes.  [Level III]