**1. Introduction**

The goal of this chapter is to present the basis for correct diagnosis and management of severe odontogenic infections. The knowledge of the anatomy of fascial spaces is essential for the correct diagnosis and treatment of head and neck infections, because both facial and cervical fasciae work as an effective barrier against the spread of infections in this region[1, 2]. Once these infections occur, they are often difficult to assess accurately by clinical examinations and conventional radiographic techniques, and the outcome may be serious and potentially lifethreatening[3]

The fasciae of the neck are glossy and divided into two separated layers: the superficial fascia and the deep fascia. The superficial fascia is actually a component of the fatty subcutaneous tissue while the deep cervical fascia is divided into three layers: the superficial layer, the visceral or middle layer, and the pre vertebral or deep layer. The deep cervical fascia plays an important role in determining the location and course of spread of infections within the soft tissues of the neck. The infections that commonly affect head and cervical areas are frequently from odontogenic origin and to a lesser frequency, proceeding from foreign bodies or trauma to this region[4]. An impacted mandibular third molar is one of the most frequent causes of odontogenic infection[5-7]. Moreover, an semi-impacted third molar results in odontogenic infection more commonly than fully erupted or completely impacted molars [7].

Odontogenic infections occasionally spread beyond the barriers of the fascial spaces, which are formed, as seen, by the deep cervical fascia of the suprahyoid regions of the neck[2]. Among various spaces, the submandibular space is one of the first to be involved in odontogenic

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infections, similar to the masticatory space[2]. As infection may spread along deep cervical facial planes and neck cavities, widespread cellulitis, necrosis, abscess formation, and sepsis may occur in these cases[4]. Therefore, it is important to understand the anatomy, rate of progression and potential for airway compromise of an infection[7].Spontaneous dissemina‐ tion of an odontogenic infection is however, very rare in immunocompetent patients[8, 9]. In patients with anatomical abnormalities, systemic diseases or immunosuppression, bacteremia caused by dental procedures may lead to generalized or metastatic systemic infection com‐ plications leading to hospital care[10, 11]. In particular, patients with poorly controlled diabetes mellitus are more susceptible to bacterial infections[12-14]. However, death from odontogenic infection is quite rare [9, 15, 16].

Despite being rare, facial and neck fasciae spaces involved by infections from odontogenic origin may lead to a very morbid condition. The diagnosis delay and late or wrong therapeutic approachs to deep infections in these areas are the main causes of high mortality rate in this life-threatening situation.[4] Dentistry has made great progress in prevention and early intervention of odontogenic infection. The introduction of antibiotics reduced significantly the mortality and morbidity of these infections, however, even in this contemporary postantibiotic era, serious infections such as a descending necrotizing mediastinitis still have a high mortality rate with a fulminating course, leading frequently to death.[17-20]

#### **2. Facial and cervical space anatomy**

The knowledge of the relevant facial and cervical anatomy of the face is essential for todays clinical practice, allowing precise and successful diagnosis. Figure 1 describes the principal anatomic structures and spaces of the face.

**Figure 1.** Anatomy of the fascial spaces in axial (A) and coronal (B) images. SMS: submandibular space; SLS: sublin‐ gual space; PPS: parapharyngeal space; CS: carotid space; MS: masticatory space. SMG: submandibular gland; GGM: genioglossus muscle; MHM: mylohyoid muscle; MM: masseter muscle; MPM: medial pterygoid muscle; LPM: lateral pterygoid muscle; TM: temporal muscle.

The superficial fascia a component of the fatty subcutaneous tissue and the deep cervical fascia is an important anatomic structure, determining the location and course of spread within the soft tissues of the neck.

#### **2.1. Deep cervical fascia**

infections, similar to the masticatory space[2]. As infection may spread along deep cervical facial planes and neck cavities, widespread cellulitis, necrosis, abscess formation, and sepsis may occur in these cases[4]. Therefore, it is important to understand the anatomy, rate of progression and potential for airway compromise of an infection[7].Spontaneous dissemina‐ tion of an odontogenic infection is however, very rare in immunocompetent patients[8, 9]. In patients with anatomical abnormalities, systemic diseases or immunosuppression, bacteremia caused by dental procedures may lead to generalized or metastatic systemic infection com‐ plications leading to hospital care[10, 11]. In particular, patients with poorly controlled diabetes mellitus are more susceptible to bacterial infections[12-14]. However, death from

Despite being rare, facial and neck fasciae spaces involved by infections from odontogenic origin may lead to a very morbid condition. The diagnosis delay and late or wrong therapeutic approachs to deep infections in these areas are the main causes of high mortality rate in this life-threatening situation.[4] Dentistry has made great progress in prevention and early intervention of odontogenic infection. The introduction of antibiotics reduced significantly the mortality and morbidity of these infections, however, even in this contemporary postantibiotic era, serious infections such as a descending necrotizing mediastinitis still have a high mortality

The knowledge of the relevant facial and cervical anatomy of the face is essential for todays clinical practice, allowing precise and successful diagnosis. Figure 1 describes the principal

**Figure 1.** Anatomy of the fascial spaces in axial (A) and coronal (B) images. SMS: submandibular space; SLS: sublin‐ gual space; PPS: parapharyngeal space; CS: carotid space; MS: masticatory space. SMG: submandibular gland; GGM: genioglossus muscle; MHM: mylohyoid muscle; MM: masseter muscle; MPM: medial pterygoid muscle; LPM: lateral

odontogenic infection is quite rare [9, 15, 16].

342 A Textbook of Advanced Oral and Maxillofacial Surgery Volume 2

**2. Facial and cervical space anatomy**

anatomic structures and spaces of the face.

pterygoid muscle; TM: temporal muscle.

rate with a fulminating course, leading frequently to death.[17-20]

The deep cervical fascia is divided into three layers: the superficial layer, the visceral or middle layer, and the pre-vertebral or deep layer.

**The superficial layer** of the deep cervical fascia encircles the neck, enveloping the sternoclei‐ domastoid and trapezius muscles and the muscles of mastication, along with the submandib‐ ular and parotid salivary glands. It extends from the nuchal line of the skull, mastoid processes, and mandible inferiorly to the scapula, clavicle, and lower cervical vertebrae.

**The middle layer** of the deep cervical fascia encloses the anterior viscera of the neck (thyroid gland, larynx, trachea, and pharynx) and the strap muscles. It attaches to the skull base and extends into the mediastinum.

**The deep layer** of the deep cervical fascia is divided into the pre-vertebral and alar divisions. The pre-vertebral division tightly encloses the spine and paraspinous muscles. Ventrally, it lies immediately anterior to the vertebral bodies, forming the anterior wall of the pre-vertebral space. It extends from the base of the skull to the coccyx.

**The alar division** of the deep layer of the deep cervical fascia lies between the pre-vertebral division and the middle layer of the deep cervical fascia. It extends from the skull base to the mediastinum. The carotid sheath is made of contributions from all three layers of the deep cervical fascia and envelops the carotid artery, jugular vein, and vagus nerve.[21, 22]

#### **2.2. Fascialspaces**

**The parapharyngeal space** fascia is in an area of fatty areolar tissue with complex fascial margins that lies in a central location in the deep face. It extends from the skull base to the hyoid bone, containing only fat tissue, branches of the trigeminal nerve, and the pterygoid venous plexus. Posterior to the parapharyngeal space is the carotid space. All three layers of deep cervical fascia contribute to the carotid sheath that circumscribe this space.

**The carotid space** extends from the skull base to the aortic arch. Its suprahyoid contents include the internal carotid artery, jugular vein, cranial nerves IX–XII, and deep cervical lymph node chain.

**The retropharyngeal space** is a posterior midline space that has the middle layer of deep cervical fascia as its anterior margin and the deep layer of deep cervical fascia as its posterior and lateral margins. It extends from the skull base to the level of the T3 vertebral body.[21, 23]

**The danger space** lies posterior to the retropharyngeal space and is separated from the retropharyngeal space by the alar fascia. The posterior margin of the danger space is the prevertebral division of the deep layer of the deep cervical fascia. The importance of the danger space, and the reason for its name, is that it extends from the skull base to the level of the diaphragm, providing a pathway into the posterior mediastinum and pleural spaces. Infec‐ tions of danger space most commonly occurs when an abscess in the retropharyngeal space ruptures through the alar fascia.[21, 23-31]
