Metastatic cervical lymph nodes are common in patients with head and neck [1] and non–head and neck [2] cancers. In patients with squamous cell carcinoma in the head and neck, the presence of a metastatic node reduces the 5-year survival rate to 50%, and the presence of another metastatic node on the contralateral side further reduces the 5-year survival rate to 25% [3]. Therefore, evaluation of cervical lymph nodes is important in patients with cancers because it aids in the assessment of patient prognosis and helps in planning treatment. Cervical lymph nodes are also common sites of involvement of lymphoma; tuberculous lymphadenitis; and other benign lymphadenitis such as Kikuchi's disease, Kimura's disease, and Rosai-Dorfman disease [4, 5].

Sonography is a useful imaging tool in the assessment of cervical lymph nodes. Gray-scale sonography is widely used in the evaluation of the number, size, site, shape, borders, matting, adjacent soft-tissue edema, and internal architectures of cervical lymph nodes. Although both color and power Doppler sonography are routine, 3D sonography is not commonly used to assess the intranodal vascular distribution. With the use of spectral Doppler sonography, the vascular resistance of lymph nodes can also be measured. The purpose of this article is to briefly reiterate and illustrate the sonographic features of normal and abnormal cervical lymph nodes.

In sonography examinations, cervical lymph nodes are usually classified into eight regions (Fig. 1). Normal and reactive lymph nodes are usually found in submandibular, parotid, upper cervical, and posterior triangle regions. On gray-scale sonography, normal and reactive nodes tend to be hypoechoic compared with adjacent muscles and oval (short axis–to–long axis ratio [S/L] < 0.5) except for submandibular and parotid nodes, which are usually round (S/L ≥ 0.5), and to have an echogenic hilus [6] (Fig. 2A, 2B). The upper limit in minimal axial diameter of normal and reactive nodes is 9 mm for subdigastric and submandibular nodes and 8 mm for other cervical nodes [7].

On color Doppler, power Doppler, and 3D sonography, normal cervical nodes show hilar vascularity or appear avascular, and reactive nodes predominantly show hilar vascularity [6] (Fig. 3A, 3B, 3C). On spectral Doppler sonography, normal and reactive nodes usually show low vascular resistance (resistive index [RI] and pulsatility index [PI]) [6] (Fig. 4A, 4B). Inflammation causes vasodilatation, which increases blood flow velocity in reactive lymph nodes. It may explain the low vascular resistance in reactive lymph nodes given that high blood flow velocity is always associated with a lower vascular resistance.

Malignant lymph nodes include metastatic and lymphomatous nodes. On grayscale sonography, metastatic nodes are usually hypoechoic, round, and without echogenic hilus (Fig. 5A). Coagulation necrosis, which appears as a demarcated echogenic focus, may be found in metastatic nodes (Fig. 5A). Eccentric cortical hypertrophy is a useful sign to indicate focal tumor infiltration (Fig. 5B). Lymph nodes with cystic necrosis are suggestive of malignancy, and intranodal cystic necrosis is common in metastatic nodes from squamous cell carcinomas (Fig. 5C).

A proven metastatic lymph node with illdefined borders may suggest extracapsular spread and patients may have a poor prognosis (Fig. 5D). Metastatic nodes from papillary carcinoma of the thyroid may be hyperechoic compared with adjacent muscles and have punctate calcifications [8] (Fig. 5E). In Hodgkin's lymphoma and non-Hodgkin's lymphoma, lymph nodes tend to be round, hypoechoic, and without echogenic hilus and tend to show intranodal reticulation [9] (Fig. 6).

On color Doppler, power Doppler, and 3D sonography, metastatic and lymphomatous nodes usually show peripheral (Fig. 7A, 7B, 7C) or mixed (Fig. 8A, 8B) vascularity. On spectral Doppler sonography, malignant lymph nodes tend to have high RI and PI values [8] (Fig. 9). In metastatic nodes, blood vessels within the nodes are compressed by tumor cells, which grow and spread and replace a large portion of the lymph node, resulting in an increase in vascular resistance.

Gray-scale sonography has a sensitivity of 95% and a specificity of 83% in differentiating metastatic and reactive nodes [10]. Color or power Doppler sonography is essential and useful to patients when gray-scale sonography is equivocal. In one study, power Doppler sonography aided in the diagnosis of 5% of patients with metastatic nodes and 17% of patients with reactive nodes [10].

On gray-scale sonography, tuberculous nodes tend to be hypoechoic, round, and without echogenic hilus and tend to show intranodal cystic necrosis, nodal matting, and adjacent soft-tissue edema [8] (Fig. 10A, 10B). On color Doppler, power Doppler, and 3D sonography, the vascular distribution of tuberculous nodes is varied and simulates benign and malignant nodes. However, displacement of hilar vascularity is common in tuberculous nodes and is due to the high incidence of intranodal cystic necrosis, which displaces the vessels, in tuberculous nodes [11] (Fig. 11A, 11B, 11C).

Diseases such as Kikuchi's disease (histiocytic necrotizing lymphadenitis), Kimura's disease (eosinophilic hyperplastic lymphogranuloma), and Rosai-Dorfman disease (sinus histiocytosis with massive lymphadenopathy) may show benign and inflammatory lymphadenopathy in the neck. Kikuchi's disease is a self-limiting and benign lymphadenitis in which cervical nodes are usually affected. Kimura's disease is an autoimmune eosinophilic granulomatous disorder with generalized lymphadenopathy. Rosai-Dorfman disease is a rare idiopathic benign histiocytic proliferation, and massive lymphadenopathy is usually found in the neck region with predominant sinusoidal histiocyte infiltration.

On sonography, lymph nodes involved with Kikuchi's and Kimura's diseases have an appearance similar to that of reactive nodes, which tend to be hypoechoic, and have an echogenic hilus. In patients with Kikuchi's disease, lymph nodes are usually oval (Fig. 12A), whereas lymph nodes in patients with Kimura's disease are usually round (Fig. 13A). On power Doppler sonography [12, 13], lymph nodes in patients with Kikuchi's disease and Kimura's disease tend to show hilar vascularity [12, 13] (Figs. 12B and 13B). In patients with Rosai-Dorfman disease, involved lymph nodes appear similar to malignant nodes, which are hypoechoic, round, and without echogenic hilus (Fig. 14A). On power Doppler sonography, involved lymph nodes in Rosai-Dorfman disease also have an appearance similar to that of malignant nodes and show peripheral or mixed vascularity [12] (Fig. 14B). Because the sonographic appearance of these unusual lymphadenopathies is similar to that of reactive or malignant nodes, the diagnosis is still based on histology.

Address correspondence to M. Ying.