Clinical Radiology 66 (2011) 876e885
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Pictorial Review
A pain in the neckdImaging in neck sepsis N.J. Lyle*, E.E. Rutherford, V.B. Batty Department of Diagnostic Imaging, Southampton General Hospital, Southampton, UK
article in formation Article history: Received 29 December 2010 Received in revised form 22 March 2011 Accepted 25 March 2011
Deep neck infection has a high morbidity and mortality and the extent of infection is often difficult to estimate clinically. The complex anatomy and the communication between neck spaces means that infection can spread along fascial planes leading to life-threatening complications such as airway compromise, vascular erosion/thrombosis, neural dysfunction, and ultimately descending necrotizing mediastinitis. Imaging has an important role to play in identifying the extent of infection and the presence of complications. Ó 2011 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.
Introduction Deep neck infection has a high morbidity and mortality, mainly due to the life-threatening complications that can arise.1 Neck sepsis is commonly poly-microbial and the most common sources are odontogenic or oropharyngeal infection.1e3 Less common causes include suppurative lymphadenitis, salivary gland infections, penetrating injuries of the pharynx or cervical oesophagus, and spondylodiscitis. Imaging is important in assessing disease extent, identifying complications, and planning the surgical approach.2 Presenting features of neck sepsis include fever, pain, swelling, sore throat, dysphagia, odynophagia, trismus, or stridor.4 Ultrasound can be used as a first-line investigation, particularly for superficial infection5 and in children. Contrast-enhanced computed tomography (CT) is useful for delineation of abscesses, assessing the spaces involved, and identifying the presence of complications.2,6,7 MRI has better soft tissue resolution and can be used in imaging deep neck infection if the patient’s condition allows.6 MRI is also essential in assessing patients with suspected spondylodiscitis, especially if they present with a prevertebral abscess.
Neck infection may begin with cellulitis, which causes inflammatory stranding and loss of fat planes on CT. An enhancing inflammatory phlegmon can then form, which may progress to abscess formation. On CT, an abscess has been defined as a focal area of low attenuation surrounded by an enhancing rim within an inflammatory mass.8,9 Although early studies indicated that CT had a 100% accuracy using this definition,8 recent studies have revealed that fluid collections without wall enhancement can also yield pus on surgical exploration.10e12 The various layers of the deep cervical fascia of the neck divide the complex anatomy of the neck into a number of spaces. Familiarity with these spaces is essential in understanding and describing the location and extent of neck infection.13,14 It is interesting to note that the detailed anatomy of the fascia and spaces of the neck was first described by surgeons seeking ways to predict the spread of neck infection prior to the antibiotic era.15 The fascial layers and spaces in the neck are described below, together with the relevant pathology and imaging findings:
Anatomy of the neck The fascial layers (Fig 1)
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The fascial layers are condensed sheaths of connective tissue which surround muscles, forming planes that separate
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N.J. Lyle et al. / Clinical Radiology 66 (2011) 876e885
various spaces.2,13 These layers consist of the superficial and deep cervical fascia. The superficial cervical fascia is a fibrofatty layer lying just deep to the subcutaneous tissue, surrounding the whole neck and enveloping the plastysma. The deep cervical fascia consists of three layers, all of which contribute to the carotid sheath: (1) a superficial (Investing) layer, which surrounds the entire neck enveloping the sternocleidomastoid and trapezius muscles. It divides to form the capsules of the submandibular and parotid glands. The superficial layer extends from the nuchal ridge and mandible superiorly, to the clavicles, sternum and scapulae inferiorly. (2) A middle layer, which extends from the skull base into the thorax and blends with the pericardium and is divided into the visceral division, which surrounds the pharynx, larynx,
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trachea, oesophagus, thyroid and parathyroid glands; and the muscular division, which surrounds the strap muscles. (3) A deep layer, which surrounds the spine and paravertebral muscles. Anteriorly it divides into (a) the prevertebral fascia, which lies posteriorly extending from the skull base to the coccyx and envelops the vertebral bodies and the deep muscles of the neck and (b) the alar fascia, which lies anteriorly between the prevertebral fascia and the visceral division of the middle layer. It extends from the skull base to the upper mediastinum at T2.
The fascial spaces The deep neck spaces are areas of loose connective tissue or potential spaces between the layers of deep cervical fascia. These spaces can be divided into three main groups1: (1) spaces above the hyoid: masticator space, sublingual space, submandibular space, parotid space, pharyngeal mucosal space, and parapharyngeal space; (2) spaces spanning the entire length of the neck: retropharyngeal space, danger space, carotid space, and prevertebral space; and (3) spaces below the hyoid: the visceral space.
Anatomy of the masticator, sublingual, submandibular and parotid spaces Masticator space (Fig 2) The masticator space is formed as the superficial layer of deep cervical fascia splits around the mandible. It encloses
Figure 1 Axial (a) and Sagittal (b) diagrams illustrating the anatomy of the fascial layers. 1. Superficial cervical fascia; 2a. superficial layer of deep cervical fascia; 2b. middle layer of deep cervical fascia; 2c. deep layer of the deep cervical fascia, which divides anteriorly to form the alar fascia (red).
Figure 2 An axial, T2-weighted MR image at the level of C2 illustrates the masticator space (blue), the parotid space (pink), the parapharyngeal space (yellow) and the carotid space (green).
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Figure 3 A coronal, T1-weighted MR image illustrates the right submandibular (blue) and sublingual (SLS) spaces. The mylohyoid muscle is indicated by white arrowheads. The sublingual space lies superiorly between the tongue and the mylohyoid muscle with the submandibular space more inferiorly between the mylohyoid muscle and superficial layer of deep cervical fascia.
the muscles of mastication, mandible and inferior alveolar vessels/nerves and extends from the skull base to mandible.
Submandibular and sublingual spaces (Fig 3) These spaces lie between the floor of the mouth and the superficial layer of deep cervical fascia. The oblique line of the mandible (origin of mylohyoid) separates the sublingual space superiorly from the submandibular space inferiorly; these communicate around the free posterior margin of mylohyoid. The sublingual space contains: the sublingual gland, hypoglossal nerve and Wharton’s duct. The submandibular space contains: the anterior belly of digastric, submandibular glands, facial vessels and hypoglossal nerve.
Parotid space (Fig 2) Formed as the superficial layer of deep cervical fascia splits around the parotid gland, the parotid space contains the parotid gland, facial nerve, external carotid artery, retromandibular vein, auriculotemporal nerve and lymph nodes.
Infections in the sublingual, submandibular, parotid and masticator spaces
Figure 4 Odontogenic abscess. An orthopantomogram (a) and an axial CT image on bony windows (b) show established osteomyelitis of the left side of the mandible arising from a dental infection with alveolar bone destruction, a sinus track running through the inferior alveolus (long arrows) and periosteal reaction along the lingual cortex (short arrows).
reaction. Alternatively there may be extra-osseous extension with diffuse cellulitis or abscess formation6 (Fig 5). The oblique line of the mandible is important as infections that start in tooth roots superior to this line (incisors to first molar) present in the sublingual space first, while those in the roots of the molar teeth present in the submandibular space.6,16 The parapharyngeal, submandibular and masticator spaces are often involved, particularly in the diabetic patient.
Odontogenic infection
Salivary gland infection
The majority of deep neck infections in adults are odontogenic in origin. Odontogenic infections arise from dental caries invading the dental pulp and extending into the tooth root to form a periapical abscess. This can remain localized within the mandible causing osteomyelitis (Fig 4), which can be identified as alveolar bone destruction or periosteal
Acute suppurative sialadenitis most commonly involves the parotid gland. Sialadenitis can also occur in the submandibular gland, particularly if related to stone disease17 (Fig 6). Ultrasound is often the first-line investigation, revealing heterogeneous glandular architecture or an abscess. CT findings include glandular enlargement and
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Figure 5 Odontogenic abscess. Axial, contrast-enhanced CT image shows a poorly defined ring-enhancing mass adjacent to the lingual cortex of the mandible in the region of the left lower eight tooth (long arrow) where a small breach in the bony cortex was seen on bone windows. The mass extends medially displacing the pharyngeal wall and effacing the parapharyngeal fat plane.
enhancement with surrounding inflammatory change. An area of low density within the gland with surrounding enhancement suggests abscess formation and duct dilatation may also be observed. The fascia medial to the parotid gland is thin and a parotid abscess can easily spread into the parapharyngeal space.
Ludwig’s angina Ludwig’s angina is a serious, acute cellulitis, which is generally due to infected mandibular molars. It involves the sublingual, submandibular, and submental spaces bilaterally with an infiltrative phlegmonous infection, which can progress rapidly and lead to airway compromise.16e18 It is characterized by thickening of the skin and subcutaneous tissues with increased attenuation of subcutaneous fat. Abscess is generally not a common feature but CT may be indicated if a patient’s condition deteriorates.
Necrotizing fasciitis Necrotizing fasciitis of the head and neck is an uncommon and life-threatening condition, which is often secondary to pharyngeal infection. Clinical distinction from cellulitis can be difficult at an early stage so imaging is important to make the diagnosis and allow early surgical treatment. The CT features associated with necrotizing fasciitis include thickening and enhancement of the cervical fascia, thickening of the cervical muscles, with or without myonecrosis and fluid collections affecting multiple neck spaces.19 Gas collections may or may not be seen.
Figure 6 Submandibular abscess. (a) Ultrasound image showing a heterogeneous, low-reflectivity area (arrows) in the region of the right submandibular gland with posterior acoustic enhancement. (b) Axial, contrast-enhanced CT image in the same patient demonstrates an area of low attenuation with a poorly enhancing rim in the region of the right submandibular gland (long arrow), which is closely related to a 16 mm submandibular calculus (short arrow).
Anatomy of the pharyngeal mucosal space The pharyngeal mucosal space lies lateral to and posterior to the nasopharynx and oropharnyx. The middle layer of the deep cervical fascia forms its posterior and lateral borders. It contains the pharyngeal mucosa, lymphoid tissue of Waldeyer’s ring (including
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tonsils and adenoids), pharyngobasilar fascia and constrictor muscles. It extends inferiorly to the level of the piriform sinuses.
sepsis. Infection commonly spreads from odontogenic or tonsillar infection.16 Cross-sectional imaging is essential to determine the origin of the infection, extent of spread and proximity to the carotid sheath contents.
Pharyngeal mucosal space infection Tonsillitis is the commonest infection to occur in the pharyngeal mucosal space. It is usually treated empirically, but imaging is indicated if there is failure to respond to treatment, clinical evidence of spread, or airway compromise.17 CT may be helpful to differentiate between uncomplicated tonsillitis (enlarged mass-like tonsils) and an abscess (central low density). A peritonsillar abscess (Fig 7) may extend into the retropharyngeal or parapharyngeal spaces.
Anatomy of the retropharyngeal space (Fig 8) The retropharyngeal space lies between the pretracheal (visceral) fascia anteriorly and the alar fascia posteriorly. It extends from the skull base to the carina (T2), where these two layers fuse, and contains the retropharyngeal lymph re) on either side. nodes (of Rouvie
Retropharyngeal space infection Anatomy of the parapharyngeal space (Fig 2)
Infection does not arise primarily within the parapharyngeal space but it becomes secondarily infected as a result of adjacent neck space infection. The parapharyngeal space communicates with most of the other neck spaces, so a thorough search should be made for a potential source of
Retropharyngeal space infection occurs mainly in children due to suppuration of retropharyngeal lymph nodes, which are present up to 5 years of age. It is commonly secondary to infection in the nasopharynx, oropharynx, or paranasal sinuses.16 In adults, instrumentation, foreign body, and trauma are the common causes of retropharyngeal space infection (Fig 9). Findings on CT may include mild fat stranding with linear fluid and effacement of the tissue planes. Abscesses in this location do not always demonstrate classical ring-enhancement, which can make them difficult to differentiate from non-infected fluid collections, seen in conditions such as internal jugular vein thrombosis or post chemoradiotherapy (Fig 10). The retropharyngeal space is the most common route by which neck infections track into the posterior mediastinum (above the level of the carina).
Figure 7 Peritonsillar abscess. An axial, contrast-enhanced CT image shows an irregular low attenuation collection centred on the right tonsil (arrowheads), with airway compromise of the oropharynx. Peripheral enhancement is difficult to appreciate on this image due to poor contrast opacification.
Figure 8 A diagram showing the retropharyngeal space (turquoise) between the visceral fascia (purple) and the alar fascia (red). The danger space (grey) is posterior to this between the alar fascia (red) and the prevertebral fascia (orange).
The parapharyngeal space is an inverted pyramid between the layers of deep cervical fascia, with the pharynx medial, carotid sheath posterior and mandible, pterygoid muscles and parotid gland laterally. It extends from the skull base to the hyoid and contains the internal maxillary artery, inferior alveolar, lingual and auriculotemporal nerves.
Parapharyngeal space infection
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Figure 10 Non-infected retropharyngeal fluid collection. This axial, contrast-enhanced CT image demonstrates a non-infected retropharyngeal fluid collection (arrows) in a patient undergoing treatment for squamous cell carcinoma. (Note the large right level II lymph node.)
Danger space infection The alar fascia can be eroded by infection from the retropharyngeal space, which penetrates into the danger space. Prevertebral and parapharyngeal abscesses can also spread to the adjacent danger space. As it is not possible to demonstrate the alar fascia radiologically, the only way of distinguishing between retropharyngeal and danger space infection is the extent of inferior spread, which should be fully demonstrated with cross-sectional imaging. The danger space is aptly named as it contains loose areolar tissue and provides a direct pathway for head and neck infection to spread into the posterior mediastinum and pleural spaces resulting in mediastinitis and empyema (Fig 11).
Anatomy of the carotid space (Fig 2) Figure 9 Retropharyngeal abscess. (a) Lateral neck radiograph clearly demonstrates prevertebral swelling with a gas collection in the retropharyngeal soft tissues. (b) Axial, contrast-enhanced CT image confirms a large, retropharyngeal, peripherally enhancing collection. It is predominately gas-filled but also contains fluid and debris.
The carotid space lies within the carotid sheath, lateral to the retropharyngeal and prevertebral spaces, posterior to the parapharyngeal space and medial to the parotid space. It contains the internal jugular vein, carotid artery, vagus nerve, and cervical sympathetic chain and extends from the skull base to the pericardium.
Anatomy of the danger space (Fig 8) Carotid space infection The danger space lies between the retropharyngeal and prevertebral spaces and is separated from them by alar fascia anteriorly and prevertebral fascia posteriorly. It extends from the skull base to the diaphragm, allowing infection to spread the entire length of the neck and torso.
The carotid space is an enclosed fascial compartment and infection arising within it is rare unless there is direct inoculation (intravenous access).4 Infection in the parapharyngeal space can encroach on the carotid sheath and lead to internal jugular vein thrombosis (Fig 12),
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Figure 11 Retropharyngeal abscess with mediastinal extension. (a) Axial, contrast-enhanced CT image demonstrating a right retropharyngeal gas collection (arrow) with an associated radio-opaque foreign body extending through the oesophageal wall. (b) This gascontaining collection extends into the visceral space and down into the mediastinum (arrowheads).
haemorrhage/mycotic aneurysm of the internal carotid artery or Horner’s syndrome. Carotid sheath infection spreads readily into the mediastinum causing pericardial and pleural involvement.1
Lemierre’s syndrome Lemierre’s syndrome is a rare condition characterized by oropharyngeal infection, septic thrombophlebitis of the internal jugular vein, and multiple metastatic abscesses. It is caused by Fusobacterium necrophorum and typically affects previously healthy infants and adolescents.21 The metastatic infection commonly involves the lungs (septic pulmonary emboli) and large joints, but hepatic and splenic abscesses have also been reported. The condition has a high morbidity and mortality, often due to delayed diagnosis. It is important for the radiologist to be aware of this condition as the clinical presentation may be nonspecific and the radiological findings are integral to the diagnosis.
Figure 12 Tuberculous abscess with internal jugular vein (IJV) thrombosis. (a) An ultrasound image shows a mixed reflectivity collection deep to the sternocleidomastoid muscle (arrows) with a central necrotic component and IJV thrombosis (v). (b) Axial, T2-weighted MR image confirms a poorly defined heterogeneous inflammatory mass, which encases the left internal jugular vein with loss of the flow void (arrow) indicating IJV thrombosis.
Anatomy of the prevertebral space The prevertebral space is a potential space posterior to the prevertebral fascia, which contains the vertebral bodies, intervertebral discs, prevertebral muscles, vertebral artery, and phrenic nerve. It extends the whole length of the vertebral column.
Prevertebral space infection Infection in the prevertebral space is largely of spinal origin, such as pyogenic/tuberculous discitis or vertebral osteomyelitis.6 Gadolinium-enhanced MRI with fatsuppression should be performed to detect an epidural abscess/phlegmon in these cases (Fig 13). An abscess can be localized to the prevertebral space as it displaces the prevertebral muscles anteriorly.22 In contrast to the danger space, the prevertebral space contains dense fibrous attachments, which tend to contain prevertebral infections.
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Figure 13 Prevertebral abscess. A sagittal, gadolinium-enhanced, fat-saturated, T1-weighted MR image demonstrates an avidly enhancing prevertebral phlegmon secondary to spondylodiscitis at the C5/6 level. There is no evidence of a fluid collection to suggest a drainable abscess. There is also spinal canal stenosis due to epidural phlegmon anterior and posterior to the cord (arrows).
Bezold’s abscess Bezold’s abscess is a rare complication of acute coalescent mastoiditis in which pus erodes through the tip of the mastoid bone and extends into the neck (Fig 14). These abscesses are not strictly within the prevertebral space but have been included here for completeness. They lie deep to the superficial layer of the deep cervical fascia, in the perivertebral spaces making them difficult to palpate.23 Extension medially into the carotid, prevertebral, danger, and retropharyngeal spaces is not uncommon. Enhanced imaging of the neck and brain, together with highresolution imaging of the temporal bones is essential if this diagnosis is considered.24
Anatomy of the visceral space The visceral space is confined by the middle layer of the deep cervical fascia. It surrounds the trachea and contains the oesophagus, thyroid, and parathyroids. It extends from the thyroid cartilage down to the superior mediastinum (T4).
Visceral space infection An abscess in the visceral space may result from traumatic perforation of the anterior oesophageal wall. This can lead to potentially life-threatening complications with
Figure 14 Bezold’s abscess. (a) Axial CT image reconstructed on a bone algorithm demonstrates opacification of the left mastoid air cells due to acute coalescent mastoiditis, with a bleb of gas seen extending into the surrounding soft tissues. (b) Axial, contrastenhanced CT in this patient shows a gas and fluid collection, which arises from the mastoid tip and extends inferiorly into the posterior triangle and perivertebral space (black arrows).
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What the surgeon needs to know
Figure 15 Infected thyroglossal duct cyst. Transverse midline image of the neck shows a well defined, low-reflectivity structure with multiple reflective foci, closely related to the hyoid and distorting the overlying strap muscles (arrow). It was aspirated and proven to be an infected thyroglossal duct cyst.
Airway management, intravenous antibiotics, and surgical drainage are the mainstays of treatment for deep neck abscesses. Recent studies, however, have found that conservative management in patients (particularly children) with no clinical evidence of severe symptoms or airway compromise can be successful25 and does not increase mortality or length of hospital stay.26 In deep neck infection, CT or MRI assessment is essential for surgeons as urgent surgical intervention for deep neck abscesses may be appropriate if: (1) there is impending airway compromise; (2) there is a vascular complication; (3) there is evidence of descending infection into the mediastinum;2,20 (4) the abscess is greater than 3 cm in size;20 (5) the abscess involves the prevertebral, visceral or carotid spaces;20 and (6) the abscess involves more than two spaces.20 Although practice varies, it has been suggested20 that a “watch and wait” policy with 48 h of intravenous antibiotics may be adopted if none of these criteria apply. CT or MR assessment is also important in the early detection of complications.
Conclusion infection spreading into the anterior mediastinum.2,16 Other sources of infection in this space include an infected laryngocoele or thyroglossal duct cyst (Fig 15).
Routes of spread of infection The fascial layers limit the spread of infection in the neck to some degree but there is a complex communication between the fascial spaces, forming avenues by which infection can spread. It is important to note that the centrally placed parapharyngeal space is intimately related to most of the other neck spaces, including the danger space, retropharyngeal space, and carotid sheath, which provide pathways for infection to descend into the mediastinum. The flow diagram (Fig 16) illustrates the routes of spread of infection between the fascial spaces of the neck.
Submandibular/ Sublingual
Parotid
Carotid
Masticator
Pharyngeal mucosal
Parapharyngeal
Retropharyngeal
Danger
Prevertebral
Visceral
Mediastinum
Figure 16 Routes of spread of infection between the fascial spaces of the neck.
Head and neck infection has a high morbidity and mortality due to complications such as airway compromise, vascular complications, and necrotizing descending mediastinitis. There is a tendency to underestimate the severity and extent of infection clinically and imaging may be required out-of-hours as it has an important role to play in guiding further management. It is, therefore, important for the general radiologist to have an overview of the anatomy of the fascial spaces and routes of spread of infection as well as knowledge of the more common causes of neck sepsis.
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