Deep Neck Infections

Etiology

Deep neck space infections are almost uniformly polymicrobial, originating from the normal oral cavity flora and upper respiratory tract. The most common source of deep neck infections among adults is the dental and periodontal structures, with the second most common source being the tonsils. Tonsil and pharyngeal sources are the most common etiologies in children. Streptococcus pyogenes, Streptococcus viridans, Staphylococcus aureus, Klebsiella, gram-negative rods, anaerobes, and Fusobacterium species are frequently encountered microorganisms, representing pathologic overgrowth of expected oropharyngeal flora. Actinomyces, Mycobacterium, and fungi are also potential causative organisms but are rarer. The presence of risk factors such as immunocompromised state, diabetes mellitus, intravenous (IV) drug use, and the site of origin of infection influences the type of causative organism.[7][8]

Epidemiology

Retropharyngeal and parapharyngeal abscesses are prevalent types of deep neck infections. Retropharyngeal abscesses develop from infections within the potential space between the pharyngeal constrictor muscles and the posterior vertebral fascia. At the same time, parapharyngeal abscesses typically arise from infections that spread directly through the pharyngeal wall. Although these infections are relatively uncommon, with an annual incidence of approximately 0.22 cases per 10,000 individuals, they pose a significant risk to children. Alarmingly, research indicates a rising incidence rate over the past 10 years.[9]

Retropharyngeal and parapharyngeal abscesses predominantly affect children younger than 5 years old, often following respiratory tract infections that extend to the retropharyngeal and parapharyngeal lymph nodes. These infections are primarily observed in young children as these lymph nodes typically regress by age 5.[10] Common symptoms of retropharyngeal and parapharyngeal abscesses include difficulty swallowing (i.e., dysphagia), neck stiffness, fever, painful swallowing (i.e., odynophagia), and respiratory distress. Deep neck infections are particularly hazardous due to their proximity to and potential communication with the posterior mediastinum and cervical vessels, which can lead to severe complications such as airway obstruction, sepsis, necrotizing mediastinitis, carotid artery aneurysm, and occlusion of cervical vessels.

Pathophysiology

To understand the pathophysiology of deep neck infections, a thorough understanding of the cervical compartments and interfacial spaces is essential. The cervical fascia can be divided into superficial and deep fascia. The superficial fascia is the subcutaneous tissue of the neck and contains the platysma. This layer completely envelops the head and neck. The deep fascia of the neck is divided into superficial, middle, and deep layers. The superficial layer of the deep fascia covers the submaxillary and parotid glands, the trapezius, sternocleidomastoid, and strap muscles. It is also termed the investing layer. Infections of odontogenic and submandibular origin affect this space, which includes the submandibular and masticator spaces. The middle layer encloses vital parts of the neck, including the pharynx, larynx, trachea, upper esophagus, thyroid, and parathyroid glands.

Infections of pharyngeal, tonsillar, and laryngeal origin affect this space, which includes the parapharyngeal and retropharyngeal spaces. This space can also become involved by odontogenic infections of the 2nd and 3rd molars, where infection can spread inferior to the dentate line of the mandible to penetrate the middle layer of deep cervical fascia. The deep cervical fascia's deep layer, also called prevertebral fascia, covers the vertebral column and muscles of the spine. An alar fascia in this space forms the terminus of the retropharyngeal space and lies between the middle layer of deep cervical fascia and the prevertebral fascia proper. The space between this alar layer and the prevertebral fascia is the "danger space," as it is in continuity with the mediastinum, and infections of upper aerodigestive origin can spread freely to cause mediastinitis. Actual retropharyngeal infections can involve the deep layer of cervical fascia. Still, the hematogenous spread of other infections (eg, in IV drug users) can lead to vertebral and prevertebral abscesses.

Infections in these spaces can lead to clinical lymphadenopathy in the appropriate lymphatic chains, most commonly in the anterior and posterior cervical lymphatic chains. Host factors such as an immunocompromised state, the presence of comorbid conditions (eg, diabetes), trauma, recent instrumentation in the area (eg, surgery or dental work), and IV drug abuse can further influence the spread of infection to deeper layers.[11][12][13][14][15]

Lemierre syndrome occurs when bacteria invade the pharyngeal mucosa, weakened by an earlier viral or bacterial pharyngitis, spreading to the lateral pharyngeal space. This leads to internal jugular vein septic thrombophlebitis and subsequent metastatic infections. Fusobacterium necrophorum is the most frequently identified pathogen in Lemierre syndrome, with Fusobacterium nucleatum also being a notable cause. The most common metastatic infection associated with this syndrome is pneumonia or pleural empyema. Septic syndrome, along with ear, neck, and pulmonary empyema, is a rare but increasingly recognized condition. Given the rapid and often severe progression of the disease, early diagnosis and immediate antibiotic treatment are crucial.[16]

History and Physical

Clinical presentation of these infections is variable based on the primary site of infection, the fascial plane involved, the extent of inflammation and disease, the presence of abscess and local pressure effects, and other systemic conditions. Most patients present with fever and neck pain. Associated symptoms such as dental pain, dysphagia, stridor, dysphonia, trismus, pain in neck movements, and respiratory distress can provide clues regarding the potentially affected facial plane. Predisposing factors such as immunocompromised state, recent oral or dental procedures, recent neck or oral trauma, recent neck surgery or radiation, IV drug use, or diabetes mellitus should be sought.

Patients may be febrile and appear ill and toxic. Inspection of the neck may reveal asymmetry, redness, swelling, induration, and regional lymphadenitis. Torticollis may be present. Abscesses in this area are more complex to diagnose clinically due to the frequent absence of fluctuance due to the taut fascia, overlying muscles, and deep location. However, they are easily demonstrated on computed tomography (CT). Physicians should have a low threshold to obtain such imaging so patients can lie supine and protect their airways.

Proximal deep neck (peritonsillar, parapharyngeal, parotid, and submandibular) infections and abscesses tend to present with a sore throat and sometimes trismus. Trismus occurs due to the local inflammation of the muscles of mastication or the infection’s direct involvement of these muscles. A physical exam may reveal neck or lower facial swelling, local erythema, tenderness, and regional lymphadenitis. Medial displacement of the uvula in conjunction with tonsillar asymmetry suggests peritonsillar abscess, whereas medial displacement of the pharyngeal wall suggests parapharyngeal space infection.[17] Local pressure may result in dysphagia or odynophagia and may have associated inflammation in the cricoarytenoid joints. If the vagus nerve is affected, dysphonia and hoarseness, or “hot potato” voice, can occur. Infections in the submandibular space may occur after spreading from dental abscesses, sublingual or submaxillary salivary glands, or oral infections following trauma. Cellulitis in this space is also known as Ludwig angina if it originates from the 3rd molars, which can lead to life-threatening airway obstruction if untreated. Ludwig angina presents with drooling, inability to swallow, trismus, induration, and elevation of the floor of the mouth.

A peritonsillar abscess is a pus collection in the space between the superior constrictor muscle and the tonsillar capsule. Common symptoms include a sore throat, swallowing pain, high fever, and drooling. It can lead to upper airway obstruction and complicated intubation due to jaw muscle spasms (trismus). While group A beta-hemolytic streptococci (Streptococcus pyogenes) is the most frequently cultured bacterium from these abscesses, identifying the specific organism is generally not required for diagnosis or treatment planning.[18]

Parapharyngeal and retropharyngeal space infections are more common in children and usually follow an upper respiratory infection. They often present with dysphagia, drooling, and stridor and can lead to airway compromise or spread into the chest to cause mediastinitis. Infections in the danger space, located posterior to the retropharyngeal space and anterior to the prevertebral space, with loose areolar tissue, facilitate the rapid spread of disease to surrounding regions and often present with complications (eg, mediastinitis, empyema, and sepsis).[19]

Parapharyngeal abscess can lead to severe complications such as jugular vein thrombosis (Lemierre syndrome), venous septic embolus, disseminated intravascular coagulopathy, and carotid artery pseudoaneurysm or rupture. Cervical nervous and bone structures can also be affected, resulting in conditions like epidural abscess, atlanto-axial subluxation, cervical osteomyelitis, spinal cord abscess, and meningitis.[17] 

André Lemierre observed that septicemia and distant septic emboli can originate from various sites, including the nasopharynx, mouth, jaws, middle ear infections (otitis media), urinary passages, as well as during conditions like mastoiditis, purulent endometritis, and appendicitis. The bacterium Fusobacterium necrophorum is most commonly responsible for Lemierre syndrome and shows intrinsic resistance to several antibiotics, including macrolides, fluoroquinolones, tetracyclines, and aminoglycosides. Therefore, early diagnosis and appropriate antibiotic treatment are essential for a favorable outcome of this syndrome.[20] Lung lesions often manifest as necrotic cavitary lesions but can also present as infiltrates, pleural effusions, empyema, lung abscesses, and necrotizing mediastinitis. Patients with pulmonary involvement may exhibit pneumonia or empyema and could develop acute respiratory distress syndrome, sometimes necessitating mechanical ventilation. Other less common manifestations of metastatic disease include soft tissue abscesses, pyomyositis, abscesses in the spleen and liver, osteomyelitis, endocarditis, pericarditis, renal abscesses, and brain abscesses.[16]

Evaluation

Biomarkers play a crucial role in assessing inflammatory activity during acute infections. Neutrophilia and systemic neutrophil activation can cause organ damage in cases of sepsis. The characteristic rise in neutrophil counts and the reduction in lymphocyte counts have led to the proposal of various leukocyte ratios as indicators of infection and potential immune dysfunction. Several inflammatory biomarkers have been suggested as prognostic indicators in sepsis and infections, including C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), neutrophil to lymphocyte ratio (NLR), mean platelet volume (MPV), and platelet to lymphocyte ratio (PLR). Studies have identified an NLR cut-off value of over 8.02 as a predictor for the necessity of incision and drainage in managing deep neck infections (DNI). Other significant factors include elevated CRP levels (above 41.25 mg/L) and higher ESR values (above 56.6 mm/h).[21]

A complete blood count (CBC) usually shows leukocytosis, often with a left shift, and chemistry may reveal evidence of dehydration if the patient’s fluid intake is poor due to pain. A blood culture should be obtained if the patient demonstrates clinical features of sepsis, and cultures should be obtained of any purulent discharge in the affected region.

In the past, lateral neck radiographs were commonly employed in diagnosing deep neck infections (DNIs). However, their use has significantly declined as modern radiological techniques have demonstrated much higher diagnostic sensitivity and provide more reliable information for determining the need for surgical intervention. Plain radiography of the neck in children may suggest retropharyngeal abscess when the prevertebral soft tissue shadow is >7 mm at the C2 level or >14 mm at the C6 level. The soft tissue shadow is >22 mm among adults at the C6 level.[22] Additionally, plain radiographs may reveal a foreign body or subcutaneous air when present. They can importantly rule out such entities in the pediatric population, where accurate history can be challenging to obtain. Despite this shift, chest X-rays remain crucial when complications such as mediastinitis, pneumomediastinum, lower airway foreign bodies, or empyema are suspected.[17]

Intraoral or transcervical ultrasonography (US) is often ideal for assessing superficial lesions, such as cervical adenitis and peritonsillar abscess (PTA), and performing percutaneous image-guided aspiration or drainage of pus. This method provides the advantage of immediate use, facilitating quick decisions regarding further diagnostics and appropriate therapy initiation. Additionally, the US reduces the need for contrast-enhanced computed tomography (CECT) scans, minimizing children’s exposure to ionizing radiation. However, the US has several limitations. It is less effective for visualizing deeper neck spaces, which restricts its diagnostic utility in many deep neck infections (DNIs). Furthermore, the success of the US heavily depends on the operator’s skill, making the expertise of the physician performing the ultrasound crucial for accurate diagnosis and treatment decisions.[23] If the ultrasound results are questionable, a CT scan should be obtained if the patient has no contraindications.[24] 

CT with contrast is the gold-standard imaging modality for diagnosing the source and extent of deep neck infection. Contrast-enhanced CT (CECT) is essential, as non-contrast CT scans are much less effective at distinguishing between cellulitis and abscesses. Additionally, CECT provides detailed information about the abscess’s relationship with nearby structures, such as major neck vessels, which is crucial for safely performing abscess drainage and reducing surgical risks.[25]

Magnetic resonance imaging (MRI) may also be considered, though logistically more challenging. MRI offers superior soft-tissue characterization compared to ultrasound (US) and CT, enabling more accurate differentiation between abscesses, cellulitis, and lymphadenomegaly in children and adults. MRI is valuable for diagnosing life-threatening complications non-invasively, and its findings often have significant prognostic implications. Additionally, MRI is associated with low radiation exposure. However, MRI is less frequently used as the primary imaging modality in emergencies due to limited availability, longer scanning times, reporting challenges, higher costs, and sedation issues in children.[26][25][27][25] 

Treatment / Management

Directed antimicrobial coverage, surgical drainage for discrete abscesses, and aggressive supportive care are the main management options. Empiric regimens based on the expected microbiology and local resistance data should be initiated and adjusted appropriately once the organism and its sensitivities become available. Clinical trials have not established the optimal antimicrobial regimen for treating deep neck space infections. However, IV nafcillin or vancomycin plus gentamycin or tobramycin combination, ampicillin/sulbactam, or clindamycin are generally accepted initial choices. For methicillin-resistant Staphylococcus aureus (MRSA) infections, vancomycin or linezolid plus cefepime may be utilized. Alternative medications include metronidazole, imipenem, meropenem, and piperacillin-tazobactam. MRSA coverage must be included as part of the initial treatment regimen for patients who are at high risk for being MRSA carriers or having MRSA infection, including those with comorbid disease (eg, diabetes mellitus), a history of IV drug use and in communities or hospitals where MRSA incidence is substantial.

For most deep neck infections, especially parapharyngeal, retropharyngeal, or prevertebral space infections, antibiotic treatment should generally be continued for 2 to 3 weeks, and longer courses may be required when complications are present. Antibiotics can be switched to the oral route once there is significant clinical improvement and the patient can tolerate oral intake. Consultation with head and neck surgeons is recommended, as surgical drainage may become necessary if no improvement is noted after 48 hours of antibiotic therapy. All but the smallest deep neck abscesses typically warrant surgical drainage, while small or questionable abscesses and phlegmon often respond well to appropriate aggressive medical management.[28]

Treating Lemierre syndrome requires a multidisciplinary approach involving infectious disease specialists, pharmacologists, radiologists, otolaryngologists, and thoracic surgeons to ensure timely diagnosis and effective treatment. This typically includes appropriate antibiotics and surgical drainage of any abscesses. Antimicrobial regimens should include a β-lactamase inhibitor due to the presence of β-lactamase-producing strains of Fusobacterium necrophorum and other co-infecting pathogens. Metronidazole is the most frequently prescribed antibiotic for this condition, known for its bactericidal properties and excellent tissue penetration, including into the cerebrospinal fluid. It can be administered orally without losing effectiveness. Studies have shown that metronidazole or carbapenem is more effective against Fusobacterium necrophorum than clindamycin. The recommended duration for antimicrobial therapy is typically between 3 to 6 weeks. A review of 100 Fusobacterium necrophorum isolates from 1990 to 2000 found that all strains were susceptible to metronidazole, clindamycin, imipenem, amoxicillin-clavulanate, and cefoxitin. Only 2% of the strains resisted penicillin, and 15% were resistant to erythromycin.[16][16][16]

Nonetheless, in the acute setting, the airway is always prioritized. Patients with deep neck infections, particularly those with submandibular or odontogenic infections and those with any airway symptoms or difficulty handling their oral secretions, should have their airways adequately secured first and foremost via elective intubation. This frequently requires awake fiberoptic intubation. The use of glucocorticoids for symptomatic relief in patients with acute airway obstruction remains controversial due to the lack of supporting evidence. Therefore, any patient with a deep neck abscess and even minimal airway symptoms should be electively intubated and the abscess drained.[4](A1)

Differential Diagnosis

Differential diagnosis of deep neck infections is variable based on presenting symptoms. Neck pain with fever can be caused by meningitis, apical pneumonia, or subarachnoid hemorrhage. Acute neck pain, especially with asymmetry, can be a result of trauma causing cervical fractures or dislocations, neck muscle hematomas, or neck muscle strains. Among patients presenting with stridor, acute epiglottitis, bacterial tracheitis, and the croup should be considered, and those with significant odynophagia or dysphagia, foreign body ingestion, and acute esophagitis should be considered. Astute clinicians should consider the malignancy amount in the differential diagnoses of a patient with neck swelling or mass.

Prognosis

Prognosis is variable depending on the immunological status of the host and the severity and location of the infection. Mortality rates range between 1% and 25%.

Complications

Lateral pharyngeal space infections can spread to the carotid sheath and cause septic thrombophlebitis (eg, Lemierre syndrome) and erosion. Retropharyngeal or danger space infections can spread to the mediastinum and cause acute mediastinitis, which may further spread and cause empyema and pericarditis. Respiratory failure can occur from an obstructed airway and spread into the systemic circulation, resulting in sepsis and intracranial infections.