9.1 Introduction

The PPS is a fibrofatty fascial compartment encapsulating major structures of suprahyoid anatomy. Both infectious and neoplastic pathologies that occupy this space tend to represent secondary spread from neighboring fascial compartments. Knowledge of the intricate anatomy of cervical fasciae and the compartments that they form is thus key to the understanding PPS pathology.

The cervical fasciae traverse between and around organs of the neck, tying them in distinct fascial compartments (▶ Fig. 9.1). The superficial cervical fascia lies directly beneath the dermis. The more complex deep cervical fascia divides into three layers: superficial (investing), middle (pretracheal), and deep (prevertebral).

The subcutaneous tissues of the head and neck, including the platysma muscles, subcutaneous fat and lymph nodes, superficial veins (e.g., the external jugular vein), and neurovascular supply to the skin, are encompassed between the superficial cervical fascia and the superficial (investing) layer of the deep cervical fascia.

The superficial (investing) layer of the deep cervical fascia forms a tube shape around the entire neck circumference. It splits to envelope the trapezius, sternocleidomastoid (SCM), and muscles of facial expression. Its leaflets also surround the submandibular and parotid salivary glands, as well as the muscles of mastication (the masseter, pterygoid, and temporalis muscles), forming the parotid, masticator, and buccal spaces.

The middle (pretracheal) layer of the deep cervical fascia divides into two components: muscular and visceral. The muscular portion encloses the strap muscles (sternohyoid, sternothyroid, and thyrohyoid) and omohyoid muscle. The visceral portion forms the visceral compartment of the neck. It surrounds the pharynx, larynx, trachea, esophagus, thyroid, parathyroids, buccinators, and constrictor muscles of the pharynx. The mucosa lining these structures, lymphoid tissue of Waldeyer’s ring (adenoids, tonsils), and minor salivary glands are all included within the visceral compartment.

The deep (prevertebral) layer of the deep cervical fascia surrounds the paraspinous muscles and cervical vertebrae. The prevertebral compartment spans the space between the prevertebral fascia anteriorly and the vertebral bodies and longus-colli muscle posteriorly.

The retropharyngeal space forms between the visceral fascia anteriorly and the prevertebral fascia posteriorly. The alar fascia, a subdivision of the prevertebral fascia, splits the retropharyngeal space into anterior and posterior compartments. The posterior retropharyngeal compartment extends inferiorly to the posterior mediastinum at the level of the diaphragm. It is commonly referred to as the “danger space,” signifying the risk for spread of infection through this space from the neck into the mediastinum. These fascial compartments are especially important in cases of infectious-inflammatory disease.

As mentioned above, the PPS, the focus of the current chapter, is yet another fibrofatty fascial compartment within the neck. It has the shape of an inverted teepee, extending from the base of the skull superiorly to the greater cornu of the hyoid bone inferiorly. All three layers of the deep cervical fascia contribute to the formation of the PPS. Its anatomical borders span the nasopharynx and oropharynx medially, the masticator space anterolaterally, the deep lobe of the parotid gland posterolaterally, and the retropharyngeal space posteromedially.

The PPS divides into pre-styloid and post-styloid compartments by the fascia running from the styloid process to the tensor veli palatini muscle (▶ Fig. 9.2). The contents of the pre-styloid compartment include the deep lobe of the parotid gland, minor salivary glands, lymph nodes, and parapharyngeal fat. The post-styloid compartment, also known as the carotid space, consists of lymph nodes and glomus tissue and is traversed by major blood vessels and nerves, including the internal carotid artery, internal jugular vein, cranial nerves IX–XII, and the cervical sympathetic chain.

In pathology, however rare, the PPS may accommodate congenital, infectious, or neoplastic disease. Pathologic processes can inhabit the space via:

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  Direct spread from neighboring compartments: Primary pathologies of the PPS are rare. As mentioned above, most pathological processes are found to involve the PPS stem, in fact, from adjacent fascial compartments, and are therefore secondary. The central anatomic location of the PPS, surrounded by the peritonsillar, retropharyngeal, submandibular, parotid, and masticator spaces (see ▶ Fig. 9.1), dictates possible routes of direct spread, both for infection and neoplastic processes.

  
  
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  Local malformation/transformation: The diverse, naturally populating, structures within the PPS may give rise to tumors or congenital lesions.

  
  
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  Distant hematogenous, lymphatic, or perineural seeding.

9.2 Infectious Disease of the PPS

In the pediatric population, parapharyngeal pathology is dominated by infection. Deep neck infections (DNIs) are more common in children than in adults. ¹ They may involve the parapharyngeal space (PPDNI), and in some cases, evolve into full-blown parapharyngeal abscess (PPA). In the United States, the incidence of deep neck space infections (including both retropharyngeal and parapharyngeal abscesses) was estimated to be 4.6 per 100,000 children. ² For PPA specifically, estimated incidence ranged between 1.29 and 1.49 per 100,000 children during the years 2003 to 2012, with skewed tendency toward younger (<5-year-old), male patients.

Unlike in the adult population, where the odontogenic route of infection prevails, pediatric DNIs are commonly acquired through the spread of tonsillitis, pharyngitis, deep cervical lymph-node suppurative adenitis, or hematogenous dissemination. DNIs are notoriously known for their ability to cross the fascial planes and potential spaces of the neck. The submandibular, retropharyngeal, parotid, and masticator spaces all neighbor the PPS and thus serve as potential sources of infection ³ (▶ Fig. 9.1).

Most cases of PPDNI are of bacterial etiology; cultures of aspirated fluid are often polymicrobial. The most commonly isolated microorganisms in pediatric DNI are Staphylococcus aureus and group A Streptococcus. Anaerobic species include Fusobacterium, Peptostreprococcus, and Porphyromonas. ³

PPDNIs have a rapidly progressive nature, their complications may be life-threatening, including airway obstruction, infectious internal jugular vein thrombosis (Lemmier syndrome), carotid artery aneurism or rupture, mediastinitis, and sepsis. ^{3 , 4} Ipsilateral Horner syndrome and cranial nerve IX–XII palsies might also result from PPDNI involving the post-styloid compartment. ³ The incidence of DNI’s life-threatening complications is reported to be 2.2%. ³ Nonetheless, in light of these possible complications, early diagnosis and assertive management are required.

High index of suspicion is crucial for early detection of PPDNI in younger children, because symptoms are not verbalized and clinical signs might be subtle at first, overlapping with other common childhood diseases, such as tonsillitis and lymphadenitis. ⁴ The most prevalent clinical manifestations of DNI in children are fever (83%), odynophagia (67%), pharyngeal bulging (67%), adenomegaly (53%), and neck mass (40%). ⁴ Neck pain, torticollis, reduced motion range, dysphagia, trismus, and drooling should also raise suspicion.

PPDNI localized to the pre-styloid compartment will commonly present with fever, neck pain, trismus, and medial displacement of the ipsilateral palatine tonsil. Infections localized to the post-styloid compartment are both more common in children and more difficult to diagnose. Their initial presentation is subtler, and is often devoid of pain, trismus, or obvious swelling; however, the potential for serious complications is significant, due to the richness of vital structures populating the poststyloid compartment. ³

Respiratory distress is not common at the presentation of PPDNI, but impending risk for airway compromise should always be evaluated and addressed at first priority upon suspicion of DNI. Airway obstruction or edema, suggestive of unstable airway patency, may necessitate prompt intubation or surgical tracheostomy. ³

Workup should consist of complete history, physical examination, and blood tests. Signs of bacterial infection such as leukocytosis (elevated WBC) and elevated inflammatory markers (such as C-reactive protein) are most commonly evident in blood tests.

Imaging should be carried out in all cases where the suspicion of PPA is high. Imaging, especially computed tomography (CT), is utilized to predict the risk of impending airway and to delineate the presence of abscess or inflammatory collection, its size, and the involvement of other cervical compartments. These findings may crucially affect the decision for surgical intervention as well as surgical approach and extent of surgery.

The mainstays of treatment include: (1) appropriate antibiotic therapy; (2) surgical drainage; and (3) management of complications. There is lack of consensus regarding the role surgery should play in the management of these patients. Advocates of the conservative approach favor an empiric trial of intravenous antibiotics, reserving surgery for cases that fail to clinically improve. Others reckon that a more aggressive approach, with immediate surgical drainage, is justified, given the rapidly progressive nature of DNIs and the risk of hazardous complications. Children with complicated or unstable presentation should with no doubt be treated with immediate surgical drainage. Younger children (<51 months) and children with larger abscesses (>2 cm in diameter) are less likely to sufficiently improve under conservative therapy, and will likely require surgery. ^{3 , 4} Airway compromise, complications, septicemia, progressive infection, or the lack of clinical improvement within 48 hours of appropriate empiric intravenous antibiotics are all definite indications for surgery.

Empiric antibiotic treatment should be administrated in all PPDNI cases and may be adjusted according to culture and sensitivity results when these become available. The empiric regimen should effectively target both aerobic and anaerobic bacteria. An amoxicillin with clavulanic acid preparation, or β-lactamase-resistant antibiotics, such as cefuroxime, imipenem, or meropenem, in combination with an agent that is highly effective against anaerobes, such as clindamycin or metronidazole, is recommended as an empiric treatment.

9.2.2 Surgical Technique

Surgical planning must rely on high-quality imaging studies, and should aim to provide good access to all of the involved cervical compartments. High-resolution preoperative CT scan can sufficiently delineate the anatomy, enabling the informed choice of surgical approach.

Access to the PPS may be gained either via an external transcervical approach or through a transoral route (▶ Fig. 9.3). Endoscopic transoral techniques for PPA drainage, employing endoscopes and image guidance, have also been described. ³

The transcervical approach is the most robust. It allows for excellent visualization and control of the major vessels and nerves, suits both pre-styloid and retro-styloid PPAs, and permits the placement of a drain. It is thus the surgical procedure of choice in most cases.

The intraoral approach is appealing for its less extensive nature; however, cases treated with this approach must be chosen carefully. Small, pre-styloid PPAs, that are located medial to the great vessels may be attempted transorally. Intraoral drainage of deeply situated abscesses, which are not directly facing the pharynx or oral cavity, poses risk for neurovascular damage. ³ Moreover, such abscesses might be impossible to fully drain intraorally.

The Transcervical Approach for PPS Surgery

As mentioned above, the transcervical approach is utilized to drain most PPAs, including the more challenging ones, i.e., larger or more deeply situated abscesses. ⁵

The patient should be positioned supine on the operating table with his head supported by a soft ring-shaped holder. A slight head-up tilt of the table is preferable to minimize intraoperative bleeding. It is recommended to mark the skin incision on a slightly flexed neck. In this position skin tension is relaxed, allowing identification of the natural skin creases. Incision should be planned to a natural skin crease at Level 2a of the neck, about two fingers below the mandible, to protect against injury to the marginal mandibular branch of the facial nerve (▶ Fig. 9.3 and ▶ Fig. 9.4a). Finally, a roll should be placed under the patient’s shoulders to hyperextend the neck, and the head should be rotated toward the contralateral side.

Skin incision is executed with a #15 blade. Subsequently, delicate electrocautery, using the lowest effective setting, is utilized for subcutaneous and platysmal dissection. Subplatysmal flaps are elevated superiorly, leaving the superficial layer of the deep cervical fascia intact on the submandibular gland. This protects the marginal mandibular branch of the facial nerve, which runs within the fascia superior to the submandibular gland. Dissection then proceeds, using electrocautery, to divide the superficial (investing) layer of the deep cervical fascia along the anterior border of the sternocleidomastoid (SCM) muscle. The superior two-thirds or the SCM are treated first, approaching from its anterior border. Small vessels interconnecting the superficial and deep borders of the SCM are cauterized with bipolar electrocautery. Care is taken to avoid injury to the spinal accessory nerve, as we approach its entry point at the deep aspect of the SCM, which occurs at the junction of the muscle’s upper and middle third and lateral to its medial border. Major anatomic structures are now identified and preserved, including the spinal accessory nerve, posterior belly of the digastric muscle, internal jugular vein, common carotid artery and its branches, and the vagus nerve. Dissection continues from below toward the exposed digastric muscle, making a point to identify and preserve the hypoglossal nerve. The hypoglossal nerve should be visible inferior to the posterior belly of the digastric muscle, superficial to the internal and external branches of the carotid artery, and anterior to the distal part of the internal jugular vein. Anterior branches of the Ansa Cervicalis are also helpful in tracing the nerve.

The abscess is now approached through blunt dissection—a finger is passed deep to the posterior belly of the digastric muscle, dissecting bluntly along the carotid sheath and up to the tip of the styloid (▶ Fig. 9.4b). Loculations are thoroughly broken using blunt dissection. Any pus encountered is aspirated, in attempt to achieve adequate drainage. A sample of the aspirate is sent for culture. Finally, the cavity is scooped gently to remove necrotic debris.

Irrigation, using at least 1 L of warm saline, and hemostasis of the wound are carefully executed as indicated. Sufficient hemostasis should be confirmed with adequate blood pressure.

A drain should be left in the surgical bed. Usually, a Penrose drain is placed into the abscess cavity and exits through the incision. A “ghost” stitch may be placed where the Penrose drain exists to reapproximate the skin once the drain is removed. The Penrose itself is sutured to the skin with 4.0 nylon suture. A balled-up super-sponge gauze is placed around the Penrose drain and covered with clear dressing.

The platysma is sutured with absorbable sutures and the skin with 5.0 nylon sutures. Depending on the need for additional drainage, the surgical incision may also be left partially open.

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