Emergency Head and Neck Radiology: Neck Infections

Jason A. McKellop, MD; Suresh K. Mukherji, MD, FACR


Appl Radiol. 2010;39(7):23-29. 

In This Article

Neck Infections

Retropharyngeal Space Infections

In adults, infection of the retropharyngeal space is usually due to a penetrating injury. Gram-positive cocci are the most common pathogen implicated in such cases.[6] In children, however, retropharyngeal space infections are most commonly due to an upper respiratory tract infection. Acute pharyngitis is common in childhood and affects children usually <3 years of age. The causal organism is usually Hemophilus influenzae. From the pharynx, microorganisms can spread to the retropharyngeal nodes resulting in suppurative adenitis. If treatment is delayed, suppurated lymph nodes may rupture and result in the formation of retropharyngeal abscess or retropharyngeal cellulitis. Clinically, patients with retropharyngeal space infection often present with fever, neck pain, sore throat and neck mass.[7] The patients may also complain of a choking feeling and difficulty in swallowing. Inspection of the pharynx will reveal edema and redness.

On imaging, plain film typically demonstrates thickening of the soft tissues in the prevertebral space. This is a nonspecific finding and may be seen in retropharyngeal cellulitis, retropharyngeal suppurative adenitis, or retropharyngeal abscess.

On CT, retropharyngeal cellulitis is identified by symmetric low attenuation in the retropharyngeal space (Figure 6). There is some anterior displacement of the posterior wall of the pharynx from the prevertebral muscles. However, the symmetric displacement does not exceed more than a few millimeters. Retropharyngeal suppurative adenitis is identified by enlarged paramedian retropharyngeal lymph nodes that contain a low-attenuation center (Figure 7). A retropharyngeal abscess is identified by a low-attenuation fluid collection that causes substantial anterior displacement of the posterior wall of the pharynx from the prevertebral muscles (Figure 8). This collection may be asymmetric. Retro-pharyngeal abscesses usually do not have a thick enhancing wall.

Figure 6.

Retropharyngeal space edema. There is symmetric low attenuation in the retropharyngeal space (arrows) without evidence of a focal fluid collection.

Figure 7.

Suppurative adenitis of a retropharyngeal lymph node. Axial contrastenhanced CT shows a suppurative retropharyngeal lymph node (large arrow) with surrounding phlegmon (large arrow). The low attenuation in the retropharyngeal space (small arrow) is edema and not a retropharyngeal space abscess.

Figure 8.

Retropharyngeal space abscess. Contrast-enhanced CT shows fluid (large arrow) and gas (small arrow) in the retropharyngeal space.

On MR, enlarged retropharyngeal nodes show intermediate signal intensity on T1W images and strong contrast enhancement. Rim enhancement indicates the presence of suppurative lymphadenitis. On T2W images, the inflamed nodes show high signal intensity. Soft-tissue thickening, as a result of cellulitis, also shows strong contrast enhancement and high signals on T2W images.

Tonsillar Abscess

In contrast to acute tonsillitis, which is more common in children, a tonsillar abscess is more common in young adults. The average age is 25 years with >65% of patients falling between 20 and 40 years of age. The most common symptoms are sore throat, dysphagia, fever and trismus. Almost all patients have a history of recurrent pharyngitis. Management typically includes incision and drainage with antibiotic coverage.[8]

CT should be used to evaluate a suspected tonsillar abscess because it is quicker and cheaper than MRI. CT shows an enhancing mass in the tonsillar fossa that may or may not show pus formation (Figure 9). Extension into the parapharyngeal space may involve the medial pterygoid muscles (leading to trismus). In extensive disease, the inflammatory process may spread posterolaterally to involve the carotid sheath. It is important to evaluate this entity for possible jugular vein thrombosis or carotid artery erosion.

Figure 9.

Tonsillar abscess. Contrastenhanced axial CT demonstrates an abscess involving the left tonsil (arrow).

Parapharyngeal Abscess

The parapharyngeal space is the area within the deep neck medial to the masseter muscle and lateral to the superior pharyngeal constrictor. It is divided into anterior and posterior compartments by the styloid process, the latter of which contains the carotid artery and internal jugular vein. An abscess in this space may arise from direct extension of infection from the pharynx through the pharyngeal wall, as a consequence of odontogenic infection, local trauma, and occasionally peritonsillar abscess.[9] Diabetes is the most common systemic condition predisposing one to parapharyngeal abscess.

Patients with parapharyngeal abscess often present clinically with fever, sore throat and neck swelling. Erythema, odynophagia, and dysphagia often accompany such infections.[10] Trismus is most commonly associated with anterior compartment abscesses.

On imaging, plain film findings are typically nonspecific and include thickening of the soft tissues in the prevertebral space and loss of cervical lordosis. Contrast-enhanced CT is the examination of choice to diagnose parapharyngeal abscess. CT shows a single or multiloculated low-density lesion with an air and/or fluid center (Figure 10). Contrast-enhanced sequences may occasionally demonstrate enhancement of the abscess wall.

Figure 10.

Parapharyngeal abscess. Contrast-enhanced CT shows a low-attenuation fluid collection deep to the left tonsil located in the parapharyngeal space.

Necrotizing Fasciitis

Cervical necrotizing fasciitis is a rapidly spreading bacterial infection of the soft tissue that can quickly become a life-threatening condition. It is commonly caused by either streptococcal or polymicrobial infections. However, methicillin-resistant S. aureus (MRSA) species have been seen with increasing prevalence.[11] Patients commonly present with high fevers and appear acutely ill. The overlying skin of the affected tissue may be erythematous and tender. One might appreciate crepitus with gas-producing bacterium. Patients with necrotizing fasciitis are best managed in the ICU and are typically treated with parenteral antibiotics and frequent surgical debridement.[12]

CT imaging will reveal nonspecific findings of diffuse reticulation of subcutaneous fat along with thickening and enhancement of the platysma. One may also find multiple abscesses extending along the fascial planes. Presence of gas within the soft tissue in the absence of prior surgery or radiation therapy is pathognomonic for necrotizing fasciitis (Figure 11).

Figure 11.

Cervical necrotizing fasciitis. Contrast-enhanced CT scan showing diffuse thickening of the soft tissues of the neck associated with small fluid collection (large arrow). The presence of air (small arrows) in a patient with fever who has never had surgery or radiation therapy is strongly suggestive of necrotizing fasciitis..

Bezold's Abscess

A Bezold's abscess is a rare complication of otomastoiditis characterized by necrosis of the mastoid tip and spread of infection from bone to the adjacent soft tissue. Inflammatory collections form inferior to the mastoid process and may course along the plane of the sternocleidomastoid muscle to the lower neck. If left untreated, the abscess may spread as far as the larynx and mediastinum which results in poor prognosis. Clinically, patients present with fever, neck pain, restricted neck motion, and otalgia. Since the secondary abscesses lie deep to the superficial fascial planes surrounding the sternocleidomastoid and trapezius muscles, the fluctuance and contours may be difficult to palpate, clinically.[13]

On CT imaging, one can appreciate unilateral opacification of the middle ear and mastoid cavities, often associated with bone erosion especially of the mastoid tip (Figure 12A). The abscess involves the adjacent musculature surrounding the mastoid and extends inferiorly (Figure 12B).[9,14] Surrounding the abscess, one may notice obliteration of the fat planes, reticulation of the subcutaneous tissues and thickening of the overlying skin.

Figure 12.

Bezold's abscess. Axial contrast-enhanced CT shows opacification of the mastoid air cells with associated bone erosion and aggressive inflammatory process. The soft tissue algorithm demonstrates a multiloculated abscess involving the paraspinal musculature.


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