55 Neck Space Infection
To understand deep neck space infection, it is important to have a clear understanding of the anatomy of the numerous fascial spaces within the neck. The spaces are interconnected, and so infection can spread from one space to another. Nerves and blood vessels pass through the spaces and the bones of the skull base, vertebrae and mandible are in close proximity. A delay in diagnosis or treatment can result in significant complications including osteomyelitis, vascular erosion or thrombosis. The management principles common to all neck space infections include the early identification and immediate management of any airway compromise, early use of empirical parenteral broad-spectrum antibiotics (while waiting for culture and sensitivity), drainage of any abscess (surgical or by aspiration) and management of any complications.
The superficial fascia of the neck is deep to the dermis and encloses the platysma muscle. The space deep to this contains superficial blood vessels and lymph nodes as well as the cutaneous nerves. The deep cervical fascia forms three distinct fibrous layers, the investing layer, the pretracheal layer and the prevertebral layer, in addition to the carotid sheath. The deep cervical fascia supports the viscera, muscles and vessels of the neck (Fig. 55.1, Fig. 55.2).
55.2.1 Investing Layer
Attached posteriorly to the ligamentum nuchae, the superior nuchal line, occipital protuberance and the mastoid process, the investing layer encloses the anterior and posterior triangles of the neck. It splits to enclose trapezius and sternomastoid. Anteriorly, it is attached to the hyoid bone and splits to enclose the submandibular glands. Superiorly, it is attached to the mandible; it splits to enclose the parotid glands in a dense fascia and attaches to the zygomatic arch and skull base superiorly to the parotid gland. The stylomandibular ligament is formed by a condensation of the fascia between the styloid process and the angle of the mandible. Inferiorly, the fascia is attached to the clavicle and the manubrium.
55.2.2 Pretracheal Layer
Superiorly attached to the thyroid and cricoid cartilages, the fascia ensheaths the thyroid and parathyroid glands and invests the infra-hyoid muscles. Inferiorly, the fascia extends into the mediastinum and blends with the fibrous pericardium. Laterally, the fascia blends with both the investing layer deep to sternomastoid and the carotid sheath.
Fig. 55.2 Coronal view of fascial spaces. TS, temporal space; MS, masticator space; PMS, pharyngeal mucosal space; PS, parotid space; PPS, parapharyngeal space; SM, submandibular space.
55.2.3 Prevertebral Layer
Attached to the ligamentum nuchae, the pre-vertebral fascia invests the prevertebral muscles and forms the floor of the posterior triangle. Superiorly, it is attached to the base of the skull, in front of the atlas. Inferiorly, the fascia extends into the thorax and attaches to the anterior longitudinal ligament of the vertebral column, at the level of T3. An abscess behind this fascia cannot extend below T3 unless the fascia is breached.
55.3 Retropharyngeal Space
Immediately anterior to the prevertebral fascia is a potential space extending from the skull base to the diaphragm. That portion behind the pharynx is the retropharyngeal space. There is no anatomical barrier preventing an abscess tracking inferiorly into the superior and posterior mediastinum, although the inflammatory reaction usually localises the abscess to the retropharyngeal space. The retropharyngeal space communicates laterally with the parapharyngeal space.
55.4 Parapharyngeal Space
The parapharyngeal space is a potential space immediately lateral to the oropharynx and nasopharynx, the styloid process dividing it into an anterior or pre-styloid and a posterior or post-styloid compartment. The latter contains the carotid sheath, which is firmly attached on its lateral aspect to the investing layer of deep fascia on the deep aspect of sternomastoid but has only loose areolar tissue lying medially and posteriorly. Infection may therefore spread from the pre-styloid to the post-styloid compartment by passing medial to the carotid sheath or from the retropharyngeal space to the post-styloid compartment (and vice versa) by passing posterior to the carotid sheath. An abscess in the post-styloid compartment may track further laterally to point just behind the posterior aspect of sternomastoid. In the pre-styloid compartment, a collection may extend as far forwards as the fascia surrounding the submandibular gland, just anterior to the sternomastoid but above the hyoid bone.
55.5 Infra-Temporal Fossa
The infra-temporal fossa lies beneath the base of skull between the sidewall of the pharynx and the ascending ramus of the mandible. It is bounded posteriorly by the styloid process and the anterior wall of the carotid sheath, anteriorly by the posterior wall of the maxilla and superiorly by the infra-temporal surface of the greater wing of the sphenoid. The infra-temporal fossa therefore is equivalent to the pre-styloid compartment of the parapharyngeal space.
55.6 Submandibular Space
The submandibular space is bound by the mucosa of the floor of the mouth superiorly and by the mylohyoid muscle and deep fascia investing the submandibular gland inferiorly.
55.7 Clinical Presentation
The clinical features of deep neck space infections are variable; while some patients will present in extremis with severe pain, dysphagia, stertor, stridor and obvious neck swelling, others may have little or no temperature, no neck swelling but a sore throat and some neck stiffness. It is important to have a high index of suspicion and take a thorough history.
55.8 Common Symptoms and Signs
Reduced/painful neck movement.
Patients should have routine blood tests looking specifically for raised inflammatory markers, septic patients should have blood sent for culture. Pus should be sent for aerobic and anaerobic culture. In immunocompromised patients fungal and tuberculosis (TB) culture should also be requested.
In the past, lateral plain X-rays of the neck were the standard initial investigation. While ultrasound can be effective in differentiating an abscess from cellulitis, CT with contrast is now regarded as the imaging investigation of choice. CT is helpful both in determining the presence and location of neck infections in children; it is less helpful in differentiating abscess from lymphadenitis and cellulitis. Magnetic resonance imaging (MRI) gives improved soft tissue definition without the use of radiation, but its use is limited due to time constraints especially in children, for whom general anaesthesia is often required. MR angiography may be needed if there is suspicion of the involvement of major neck vessels. Both CT and ultrasound can be used to assist in the aspiration of abscesses and so may prevent the need for open incision and drainage.
Any pus from aspiration or drainage should be sent for culture and the determination of antibiotic sensitivities. The organisms which may be responsible are numerous, including both aerobic and anaerobic organisms. Both gram-positive and gram-negative organisms can be cultured.
Patients with a small collection (< 2.2 cm on computed tomography [CT]), without airway compromise who are otherwise fit and well, may respond to a period of medical management with appropriate broad-spectrum antibiotics. However, septic patients, those with airway compromise or complications, need surgical intervention. Surgery is also indicated for those who have failed to respond to antibiotics after 48 hours or with progressive symptoms in spite of antibiotics. Ultrasound-guided drainage can be effective for patients with well-defined unilocular abscesses in the absence of airway compromise. Whilst parapharyngeal and retropharyngeal abscesses, which are pointing in the pharynx, may be drained intra-orally, an external approach is required for most cases.
55.11 Specific Neck Space Infections
Citelli’s abscess and Bezold’s abscess, both complications of acute suppurative otitis media and peritonsillar abscess have been described earlier (see Related Topics of Interest).
55.12 Prevertebral Abscess
This is seen in adults, usually associated with cervical spinal tuberculosis. A prevertebral abscess may also be a consequence of iatrogenic trauma. The attachment of the fascia limits the inferior extent to the vertebral body of T3. The usual presentation is with a progressively painful and tender neck with limitation of movement. Occasionally, collapse will cause acute spinal cord compression, requiring urgent drainage of the abscess and cord decompression.
A contrast-enhanced CT scan of the neck is the investigation of choice (Fig. 55.3). Aspirating the abscess allows a sample to be subjected to a Z–N stain. A positive result does not distinguish between tuberculosis and atypical mycobacterial infection, but it may allow empirical anti-tuberculosis treatment to be instigated while the culture and sensitivity result is awaited.