Preglandular, postglandular, prevascular, postvascular, and intravascular. The preglandular and prevascular groups are located anterior to the submandibular gland and facial artery, respectively. The postglandular and postvascular groups are posterior to these structures. Differing from the parotid gland in embryological development, there is no true intraglandular node; however, occasionally, a node has been identified inside the capsule of the gland. The submandibular nodes drain the ipsilateral upper and lower lip, cheek, nose, nasal mucosa, medial canthus, anterior gingiva, anterior tonsillar pillar, soft palate, anterior two thirds of the tongue, and submandibular gland. The efferent vessels drain into the internal jugular nodes. For the submental nodes, 2-8 nodes are located in the soft tissues of the submental triangle between the platysma and mylohyoid muscles. These nodes drain the mentum, the middle portion of the lower lip, the anterior gingiva, and the anterior third of the tongue. The efferent vessels drain into both the ipsilateral and contralateral submandibular nodes or into the internal jugular group.

The internal jugular chain consists of a large system covering the anterior and lateral aspects of the internal jugular vein, extending broadly from the digastric muscle superiorly to the subclavian vein inferiorly. As many as 30 of these nodes may exist, and they have been arbitrarily divided into upper, middle, and lower groups. The efferents of these nodes eventually pass into the venous system via the thoracic duct on the left and multiple lymphatic channels on the right. These nodes drain all the other groups mentioned. Direct efferents may be present from the nasal fossa, pharynx, tonsils, external and middle ear, Eustachian tube, tongue, palate, laryngopharynx, major salivary glands, thyroid, and parathyroid glands. Although fairly consistent, these drainage patterns are subject to alteration with malignant involvement or after radiotherapy. In such cases, rerouting is possible, with metastases arising in unusual sites. Metastases have also been shown to skip first-echelon nodes and manifest in the lower internal jugular group.

The nodes found in level II are located around the upper third of the internal jugular vein, extending from the level of the carotid bifurcation inferiorly to the skull base superiorly. The lateral boundary is formed by the posterior border of the SCM muscle; the medial boundary is formed by the stylohyoid muscle. Two subzones are also described; nodes located anterior to the spinal accessory nerve are part of level IIa, and those nodes posterior to the nerve are located in level IIb. The middle jugular lymph node group defines level III. Nodes are limited by the carotid bifurcation superiorly and the cricothyroid membrane inferiorly. The lateral border is formed by the posterior border of the SCM muscle; the medial margin is formed by the lateral border of the sternohyoid muscle. Level lV contains the lower jugular group and extends superiorly from the omohyoid muscle to the clavicle inferiorly. The lateral border is formed by the posterior border of the SCM muscle; the medial margin is formed by the lateral border of the sternohyoid muscle. The lymph nodes found in level V are contained in the posterior neck triangle, bordered anteriorly by the posterior border of the SCM muscle, posteriorly by the anterior border of the trapezius, and inferiorly by the clavicle. Level V includes the spinal accessory, transverse cervical, and supraclavicular nodal groups. Level VI lymph nodes are located in the anterior compartment. These nodes surround the middle visceral structures of the neck from the level of the hyoid superiorly to the suprasternal notch inferiorly.

Furthermore, the presence of cervical adenopathy has been correlated with an increase in the rate of distant metastasis. Unfortunately, clinical palpation of the neck demonstrates a large variation of findings among various examiners. Although both inexpensive to perform and repeat, palpation findings are generally accepted as inaccurate. Both the sensitivity and specificity are in the range of 60-70%, depending on the tumor studied. Because of the known low sensitivity and specificity of palpation, a neck side without palpable metastases is at risk of harboring occult metastasis, with the risk determined by the characteristics of the primary tumor. The incidence of false-negative (occult) nodes based on physical examination findings varies in the literature from 16-60%. Before the introduction of diagnostic imaging, particularly CT scan, clinical palpation was shown to be inadequate for detecting cervical metastasis. Soko et al reported that only 28% of occult cervical metastases were found by clinical palpation. Martis reported a 38% prevalence of occult metastasis based on clinical examination findings

Ultrasound : Ultrasound is reported superior to clinical palpation for detecting lymph nodes and metastases. The advantages of ultrasound over other imaging modalities are price, low patient burden, and possibilities for follow-up. Sonographs of metastatic lymph node disease characteristically find enlargement with a spherical shape. Commonly, nodes are hypoechoic, with a loss of hilar definition. In cases of extranodal spread with infiltrative growth, the borders are poorly defined. Common findings of metastases from squamous cell carcinoma are extranodal spread and central necrosis together with liquid areas in the lymph nodes. Lymph node metastases from malignant melanoma and papillary thyroid carcinoma have a nonechoic appearance that mimics a cystic lesion. Sonography also is useful for assessing invasion of the carotid artery and jugular vein. Because lymph nodes of borderline size cannot be reliably diagnosed using ultrasound alone, ultrasound-guided fine-needle aspiration and cytologic examination of the nodes in question can be easily performed. The result of the aspirate examination depends on the skill of the ultrasonographer and the quality of the specimen (ie, harboring an adequate number of representative cells). Using this technique, most studies report that a sensitivity of up to 70% can be obtained for the N0 neck.

Magnetic resonance imaging: The value of MRI is its excellent soft tissue resolution. MRI has surpassed CT scanning as the preferred study in the evaluation of cancer at primary sites such as the base of the tongue and the salivary glands. The sensitivity of MRI exceeds that of clinical palpation in detecting occult cervical lymphadenopathy. Size, the presence of multiple nodes, and necrosis are criteria shared by CT scanning and MRI imaging protocols. Most reports indicate that CT scanning still has an edge over MRI for detecting cervical nodal involvement. Advances in MRI technology (e.g., fast spin-echo imaging, fat suppression) have not yet surpassed the capacity of CT scanning to identify lymph nodes and to define nodal architecture. Central necrosis, as evaluated by unenhanced T1- and T2-weighted images, has been shown to provide an overall accuracy rate of 86-87% compared with CT scanning, which has an accuracy rate of 91-96%. The use of newer Contrast media, especially supramagnetic contrast media agents, hopefully will improve the sensitivity of MRI.

8.Van den Brekel MW: Lymph node metastases: CT and MRI. Eur J Radiol 2000 Mar; 33(3): 230-8[Medline].

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