CHAPTER 14 Deep Neck Space Infections
Infections of the deep spaces of the neck often present a true clinical challenge. Although antibiotics have reduced their incidence, deep neck space infections remain a relevant health problem. The complex anatomic organization of the neck makes diagnosis and precise localization of deep infections difficult. Clinical suspicion remains critical in that many deep neck infections are not evident on palpation or visual inspection. Although improved imaging and medical protocols exist, surgical intervention remains a critical component of successful management.
Infectious and inflammatory conditions of the upper aerodigestive tract are the primary instigators of deep neck infections. Multiple retrospective studies have revealed dental infections as the most common starting point, followed by oropharyngeal infections.1–7 Acute bacterial tonsillitis and pharyngitis remain as leading causes in children. Suppuration of lymph nodes after an episode of cervical lymphadenitis may progress to a neck abscess. In the pediatric population, acute rhinosinusitis is a common cause of retropharyngeal lymphadenitis. Oral surgical procedures and endoscopic instrumentation may iatrogenically incite an upper airway infection or traumatize the pharyngoesophageal lumen. Sialadenitis, with or without ductal obstruction, can precipitate infectious spread. A foreign body trapped within the upper aerodigestive tract may initiate infection, while penetrating cervicofacial trauma can both introduce pathogens and serve as a conduit between adjacent spaces. Superficial infections, such as skin cellulitis, may spread along fascial planes. Needle injection associated with intravenous drug use introduces pathogens to the neck in a similar fashion as penetrating trauma. Congenital or acquired lesions such as branchial cleft cysts, thyroglossal duct cysts, or laryngoceles may become infected, with resulting spread. Acute mastoiditis may progress to a Bezold abscess with subsequent spread. Necrotic malignant lymph nodes can form an abscess. Immunocompromised patients must raise the index of suspicion for more virulent or atypical pathogens. Although the etiologic factors are many, a thorough search for the cause often reveals no clear source.
Wherever the starting point, the infection may spread from its portal of entry to other regions of the neck through the lymphatic system, arterial or venous channels, or direct extension between spaces and along fascial planes. The inflammatory process may plateau as a soft tissue phlegmon upon presentation, or culminate in a deep focal abscess, which usually demands surgical intervention.
The microbiology of deep neck space infections most often yields a mixture of aerobic and anaerobic organisms, usually representative of the oropharyngeal flora. Retrospective microbiologic analyses consistently demonstrate polymicrobial isolates.2,7–11 The commonly cultured organisms, which often reflect the microbiology of odontogenic infections, are Streptococcus viridans, Staphylococcus epidermidis, Staphylococcus aureus, group A beta-hemolytic Streptococcus (Streptococcus pyogenes), Bacteroides, Fusobacterium, and Peptostreptococcus species. Cultures occasionally reveal Neisseria, Pseudomonas, Escherichia, and Haemophilus species. The proportion of community-acquired methicillin-resistant Staphylococcus aureus (MRSA)-associated neck space infections is significantly increasing in some regions of the United States, especially in pediatric populations.12,13 One retrospective review concluded that MRSA is more likely to infect younger patients, but that a medial abscess location was less likely for both MRSA and methicillin-sensitive S. aureus infections.13
Atypical organisms may also initiate a deep neck infection. Actinomyces are endogenous saprophytic organisms of the oral cavity and tonsil. The most common site of cervicofacial actinomycosis is in the vicinity of the angle of the mandible, and this pathogen may cross fascial planes in its route of spread. A granulomatous reaction with central abscess formation and necrosis with “sulfur granules” is characteristic. Tuberculous and nontuberculous infection of the head and neck most commonly presents with cervical lymphadenopathy. Histopathologically, caseating necrotizing granulomatous inflammation is present. Cat scratch disease, caused by the pleomorphic gram-negative bacillus Bartonella henselae, manifests with large, tender cervical lymph nodes. Late lesions may form an abscess. Management of atypical neck space infections often leans toward nonsurgical management, because incision and drainage procedures may result in a chronic wound or fistulous tract.
Accurate diagnosis and application of timely treatment requires an understanding of the complex anatomic organization of the neck spaces. Fascial planes divide the neck into true and potential spaces. The two main fascial divisions of the neck are the superficial cervical fascia and the deep cervical fascia, which further divides into three layers.
The superficial cervical fascia, deep to the dermis, envelops the platysma and muscles of facial expression. It incorporates the superficial musculoaponeurotic system and extends from the zygoma to the axillae, clavicles, and deltopectoral region. Deep to the platysma, a potential space separates the superficial and deep cervical fasciae. This space houses adipose tissue, sensory nerves, and blood vessels, such as the anterior and external jugular veins, and facilitates free movement of the skin.
The deep cervical fascia is divided into three layers: the superficial, middle, and deep. The superficial layer of deep cervical fascia, or investing fascia, surrounds the neck. Posteriorly it attaches to the superior nuchal line, the ligamentum nuchae of the cervical vertebrae, and the mastoid process. As it transmits anteriorly, it splits and re-fuses to surround the trapezius and sternocleidomastoid muscles. Anterosuperiorly, this layer attaches to the inferior zygomatic arch. As it proceeds inferiorly, it splits to enclose the parotid gland, forming the parotid fascia superficially, and extends along the temporal bone to the carotid canal deeply. It envelops the muscles of mastication and covers the submandibular gland. This layer also forms the stylomandibular ligament, which separates the parotid from the submandibular gland. Inferiorly the investing fascia attaches to the hyoid, clavicle, acromion, and spine of the scapula, but first splits to encompass the intermediate tendon of the omohyoid and form the suprasternal space. The superficial layer of deep cervical fascia contributes to the lateral aspect of the carotid sheath.
The middle layer of deep cervical fascia, or visceral fascia, is composed of a muscular and visceral division. The muscular division surrounds the strap muscles (sternohyoid, sternothyroid, thyrohyoid, omohyoid). The visceral division surrounds the buccinator, pharyngeal constrictor muscles, larynx, trachea, esophagus, thyroid, and parathyroid glands. The visceral division forms a pretracheal fascia that overlies the trachea. The visceral division also contributes the buccopharyngeal fascia posterior to the esophagus, which separates the esophagus from the deep layer of deep cervical fascia and forms the anterior border of the retropharyngeal space. The buccopharyngeal fascia forms two raphae: (1) one in the posterior midline that adheres to the alar layer of the deep layer, and (2) the pterygomandibular raphe of the lateral pharynx. The middle layer also contributes to the medial aspect of the carotid sheath.
The deep layer of deep cervical fascia, or prevertebral fascia, divides into two layers: the prevertebral and alar layers. The prevertebral layer envelops the paraspinous muscles and cervical vertebrae, lying anterior to the vertebral bodies from the skull base to the coccyx, and attaching laterally to the transverse processes. It covers the scalene muscles and forms the floor of the posterior triangle. As it courses anteromedially, it contributes to the posterior carotid sheath and splits to form the alar layer. The alar layer lies between the prevertebral layer and the buccopharyngeal fascia of the visceral middle layer. The alar fascia separates the retropharyngeal and danger spaces and covers the cervical sympathetic trunk.
The carotid sheath extends from the skull base to the thorax, and is a confluence of each layer of deep fascia. The sheath contains the common carotid artery, internal jugular vein, vagus nerve, and ansa cervicalis.
The above fasciae and the structures within the neck form real and potential spaces. Many of these compartments openly communicate with each other, and some spaces are contiguous with distant regions of the body, offering a route of rapid transit for infections. The neck spaces can be organized by their location: the face (buccal, canine, masticator, parotid), suprahyoid neck (peritonsillar, submandibular, sublingual, parapharyngeal), infrahyoid neck (anterior visceral), and along the length of the neck (retropharyngeal, danger, prevertebral, carotid).
Also called the lateral pharyngeal or pharyngomaxillary space, the parapharyngeal space is an inverted pyramid with its superior base at the skull base and its inferior apex at the junction of the posterior belly of the digastric muscle and greater cornu of the hyoid bone. The pterygomandibular raphe and medial pterygoid muscle bound the space anteriorly, while the prevertebral fascia bounds it posteriorly. The superior constrictor, tensor, and levator veli palatini muscles form the medial boundary, and the parotid gland, mandible, and lateral pterygoid muscle bound it laterally.
The styloid process divides the space into two compartments: the prestyloid compartment, which is anterior to the styloid process, and the post-styloid compartment, which is posterior to the process. The prestyloid compartment contains fat, muscle (styloglossus and stylopharyngeus), lymph nodes, deep lobe of the parotid, internal maxillary artery, inferior alveolar, lingual, and auriculotemporal nerves. The post-styloid compartment contains neurovascular structures: carotid artery, internal jugular vein, sympathetic chain, and cranial nerves IX, X, XI, and XII.
The parapharyngeal space provides a central connection for the major deep neck spaces. It connects posteromedially with the retropharyngeal space, inferiorly with the submandibular space, and laterally with the masticator space. The carotid sheath courses through the space into the mediastinum. Lateral extension from the peritonsillar space directly invades the parapharyngeal space.
These two spaces are best discussed together, because they functionally comprise a single space. The mucosa of the floor of the mouth forms the superior border of the submandibular space, and the digastric muscle and hyoid bone form the inferior. Anteriorly, the mylohyoid muscle and anterior belly of digastric bound the submandibular space, with the posterior belly of the digastric and stylomandibular ligament serving as its posterior borders. The hyoglossus, mylohyoid, styloglossus, genioglossus, and geniohyoid muscles are medial, with the platysma and mandible being lateral.
The mylohyoid muscle divides the submandibular space into a superior sublingual compartment and an inferior submaxillary compartment. This sublingual compartment is also called the sublingual space, and contains the sublingual gland and Wharton’s duct. The supramylohyoid sublingual space is lateral to the geniohyoid and genioglossus muscles. The sublingual space openly connects to the submaxillary compartment around the free posterior edge of the mylohyoid. The inframylohyoid submaxillary compartment, sometimes itself called the submandibular space, connects to its corresponding space contralaterally and contains the submandibular gland and lymph nodes.
The relationship of the mylohyoid to the tooth apices, the mylohyoid line, determines the most likely route of odontogenic infectious spread. The teeth apices anterior to the second molar lie superior to the mylohyoid line and thus involve the sublingual space. Infections of the second and third molars initially involve the submandibular or parapharyngeal space, because their roots extend below the mylohyoid line.
The retropharyngeal space, extending from the skull base to the mediastinum at the tracheal bifurcation, refers to the lymph node and connective tissue containing potential space between the middle and deep layers of deep cervical fasciae. The space lies anterior to the alar fascia of the deep layer and posterior to the buccopharyngeal fascia of the middle layer that lines the posterior pharynx and esophagus. The carotid sheath is lateral to the space. It typically becomes involved by direct spread from the parapharyngeal space, or lymphatic spread from the paranasal sinuses or nasopharyngeal region, primarily in children.
The danger space, so named because of the potential for rapid inferior spread of infection to the posterior mediastinum through its loose areolar tissue, extends from the skull base to the diaphragm. This potential space lies between the retropharyngeal and prevertebral spaces. The deep layer of deep cervical fascia subdivisions bound this space. The alar layer forms its anterior border, and the prevertebral layer forms its posterior border. Laterally, the transverse processes of the vertebrae enclose the danger space. The sympathetic trunk courses through this space. Infectious infiltration from the retropharyngeal, parapharyngeal, or prevertebral spaces are the primary routes to the danger space.
The prevertebral space is enclosed by the prevertebral fascia, vertebral bodies and transverse processes, and extends from the clivus of the skull base to the coccyx. It is a compact potential space that contains dense areolar tissue and lies posterior to the danger space. In addition to the paraspinous, prevertebral, and scalene muscles, it contains the vertebral artery and vein, brachial plexus, and phrenic nerve. The main pathways of spread to the prevertebral space are from infection of the vertebral bodies and penetrating injuries. Tuberculosis of the spine may breach the space and form a Pott’s abscess.
The superficial layer of deep cervical fascia defines the masticator space upon splitting at the inferior border of the mandible to cover the medial pterygoid and masseter muscles. Next, the fascia continues superiorly to cover the inferior tendon of the temporalis muscle and incorporate with the superficial temporalis fascia. It contains the mandible and muscles of mastication (masseter, temporalis, medial pterygoid, lateral pterygoid). The masticator space also contains the third portion of the trigeminal nerve, which enters through the foramen ovale, the internal maxillary artery, and much of the buccal fat pad. This space occupies a position anterolateral to the parapharyngeal space.
The masticator space is also further divided into subspaces: the masseteric space between the masseter muscle and ramus of mandible, the pterygoid space between the pterygoid muscles and ramus, the superficial temporal space between the superficial temporal fascia and temporalis muscle, and the deep temporal space between the deep temporal fascia and temporal bone. Transmission of infection into the masticator space is most commonly from the third mandibular molars.
The peritonsillar space consists of loose connective tissue between the capsule of the palatine tonsil and the superior constrictor muscle. The anterior and posterior tonsillar pillars contribute to its anterior and posterior borders, respectively. The posterior tongue forms the inferior boundary. Peritonsillar infections may readily spread to the parapharyngeal space.
The superficial layer of deep cervical fascia forms the parotid space as it splits to surround the parotid gland. However, the fascia, which does not enclose the superomedial aspect of the gland, permits communication with the prestyloid compartment of the parapharyngeal space. The space also contains the facial nerve, external carotid artery, and posterior facial vein. It occupies a position lateral to the parapharyngeal space.
The carotid, or visceral vascular, space is the potential space within the carotid sheath containing the carotid artery, internal jugular vein, vagus nerve, and sympathetic plexus. Infection from the surrounding parapharyngeal space, penetrating trauma, or intravenous drug use may potentiate spread into this space.
The visceral division of the middle layer of deep cervical fascia encloses the anterior visceral space, or pretracheal space, which lies immediately anterior to the trachea. It extends from the thyroid cartilage to the superior mediastinum. It contains the pharynx, esophagus, larynx, trachea, and thyroid gland. Perforation of the anterior esophageal wall by endoscopic instrumentation, foreign bodies, or trauma may introduce infection to this space.
The symptoms of deep neck space infection are determined by both the generalized inflammatory process as well as localizing symptoms at the site of infection. Inflammatory symptoms such as pain, fever, swelling, and redness are common. Symptoms such as dysphagia, odynophagia, drooling, “hot potato” voice, hoarseness, dyspnea, trismus, and ear pain offer further clues about the location of the inflammatory process as well as its potential severity. The onset and duration of symptoms should be elicited. Recent events such as dental work, upper airway surgery or intubation, intravenous drug use, sinusitis, pharyngitis, otitis, or blunt or penetrating soft tissue trauma that preceded worsening symptoms should be identified in order to formulate a differential of likely microorganisms and common pathways of spread.
The past medical history should be reviewed to account for antibiotic allergies and immunodeficiency status. Patients with a history of human immunodeficiency virus, hepatitis, diabetes, collagen vascular diseases, hematologic malignancy, and recent chemotherapy or steroid use are at increased risk of atypical pathogens and rapidly progressive disease.