Emergency Head and Neck Radiology: Neck Infections

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

Disclosures

Appl Radiol. 2010;39(7):23-29. 

In This Article

Infections of the Lymph Node

In children, enlarged cervical lymph nodes are most commonly due to an associated infectious process rather than malignancy. A variety of infectious and non-infectious processes may cause enlargement of the cervical lymph nodes. The stimulated node is often referred to as "reactive." Ongoing and untreated infection may eventually result in necrosis of the node leading to suppurative adenitis.

Cervical Adenitis

The term cervical adenitis denotes an inflammation of the lymph nodes due to an infectious process (Figure 1A) Suppurative adenitis indicates an infected node which has undergone liquefaction necrosis (Figure 1B). The likelihood of developing cervical adenitis, especially suppurative forms, decreases with age, although, the incidence of suppurative adenitis is increasing in older patients.

Figure 1.

Cervical and suppurative adenitis. Axial contrast-enhanced CT (A) shows homogeneous enlargement of multiple various-sized lymph nodes (arrows) in a patient with neck pain due to cervical adenitis. Axial contrast-enhanced CT (B) shows a suppurative cervical lymph node (large arrow) with surrounding phlegmon.

The most common cause of lymph node enlargement in children is a benign viral infection of the upper respiratory tract.[1] Young adults with infectious mononucleosis, also present with generalized lymphadenopathy, along with complaints of weakness, fever and malaise. Another noteworthy viral infection is the acquired immunodeficiency syndrome (AIDS), which is caused by human T-cell lymphotropic virus type III (HTLV-III), and is a potentially devastating disease of childhood. Symptoms include localized or generalized lymphadenopathy, thrush, parotid swelling, interstitial pneumonitis, hepatosplenomegaly, and diarrhea.

Bacterial infections are the most common cause of suppurative cervical adenitis with staphylococcus aureus (S. aureus) and group A streptococcus bacterium (Streptococcus pyogenes) being the most common etiologic agents.[2,3] Infected patients typically present with fever and upper respiratory tract infections. Early in the course of infection, discrete nodes are palpated. With uncontrolled infection, the firm nodes are replaced by a palpable fluctuant mass (suppurative adenitis), which may require drainage.

Computed tomography (CT) is the preferred modality to evaluate patients suspected of having cervical lymphadenitis. Early involvement by infection is characterized by homogeneous enlargement, loss of the fatty hilum and increased enhancement of the involved lymph node on CT. Reticulation of the adjacent fat surrounding a suppurative lymph node, or the presence of a circumferential rim of soft tissue, may be indicative of an inflammatory etiology as the cause of the abnormal node—as opposed to metastases.

Cat-scratch Disease

Cat-scratch disease (CSD) is a very common cause of enlarged cervical lymph nodes in the pediatric age group and has been reported to be the cause of ≤73% of head and neck masses in children in which the diagnosis was subsequently confirmed by biopsy. The disorder is caused by the bacteria Bartonella henselae and usually presents within 3 to 10 days following contact. A prior history of a cat scratch is present in 72% of cases. Clinically, these patients present with tender, enlarged cervical lymph nodes, fever, and malaise. Approximately 10% of patients develop overlying erythema and fluctuant lymph nodes that require drainage.

The typical findings on CT are a unilateral clumped group of enlarged lymph nodes clustered in the primary echelon drainage of the site of contact. Central areas of decreased attenuation within the lymph nodes are rare (Figure 2). There may be some subtle reticulation of the fat surrounding the lymph nodes, however, gross findings of extracapsular extension are rare. On magnetic resonance imaging (MRI), the signal characteristics are nonspecific and can be seen in a variety of disorders. The nodes typically enhance with contrast and contain high T2 signal.

Figure 2.

Axial contrast-enhanced CT shows enlarged level-2 and level-5 lymph nodes in a patient with pathologically proven cat scratch disease (arrows).

Tuberculous Lymphadenitis

There is a dramatic rise in the prevalence of tuberculosis in industrialized countries due to the AIDS epidemic, drug abuse and increased migration. The most common form of head and neck tuberculosis is lymphadenitis. Cervical lymphadenopathy is usually painless. Involvement is commonly bilateral and most frequently involves the internal jugular, posterior triangle and supraclavicular nodes. In advanced stages, the overlying skin may be inflamed and sinus tracts may appear.

Pathologically, tuberculosis typically shows tubercles with marked fibroblastic response. These tubercles show characteristic amorphous caseating necrosis which may rupture into surrounding structures, such as the airway and blood stream, causing endobronchial or hematogenous dissemination.

CT imaging of the early stages of tuberculous lymphadenitis reveals nodes with homogeneous contrast enhancement. As the disease evolves, central necrosis can be detected as foci of low density associated with rim enhancement (Figure 3). Healed lesions and nodes undergoing chemotherapy may show calcifications.

Figure 3.

Tuberculous lymphadenitis. Axial contrast-enhanced CT shows a necrotic suppurative lymph node in a patient with tuberculosis (arrow).

MR imaging shows nonspecific homogeneous enhancement on T1-weighted (T1W) images and high signals on T2-weighted (T2W) images. In nodes undergoing necrosis, contrast-enhanced MR imaging shows rim enhancement with a central area of no enhancement representing caseating necrosis. These nodes typically show high signal intensity on T2W images. MR imaging, although helpful in demonstrating lymphadenitis, cannot detect nodal calcifications.

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