Suspicious (malignant) sonographic features of cervical lymph nodes:

1. Size and shape
   • Round shape with a high short-to-long axis ratio (S/L ratio > 0.5) is suggestive of malignancy (though some benign nodes, e.g., submandibular, can also be round).
   • Large lymph nodes raise suspicion, but size alone is not diagnostic. Serial growth in a patient with known malignancy is highly suggestive of metastatic involvement.
     

     Fig 2: A - Normal cervical lymph node with an elongated shape and a well-defined echogenic hilum. B - Hypoechoic, round (S/L ratio > 0.5) lymph node in left level V, consistent with B-cell lymphoma persistence/recurrence. © Department of Radiology, Centro Hospitalar Universitário de São João, Porto/Portugal.
2. Borders
   • Sharp borders are more commonly seen in metastatic lymph nodes (due to the difference in acoustic impedance caused by tumor infiltration).
   • Ill-defined borders may indicate extracapsular spread of malignancy, which is associated with a worse prognosis.
     

     Fig 3: A - (Ultrasound). Heterogeneous, hypoechoic solid mass in the right level III/IV with irregular margins, suspicious for lymph node metastasis with possible extracapsular spread. B - (CT). Contrast-enhanced scan at the transition from right level III to IV shows the same nodular lesion with spiculated borders and loss of the normal plane with the sternocleidomastoid muscle. Biopsy results confirm persistent metastatic adenopathy in a patient with squamous cell carcinoma of the tongue. © Department of Radiology, Centro Hospitalar Universitário de São João, Porto/Portugal.
3. Echogenic Hilus
   • Malignant nodes typically lack a normal echogenic hilus.
   • However, the presence or absence of an echogenic hilus alone cannot definitively distinguish benign from malignant nodes.
4. Echogenicity
   • Most malignant nodes are hypoechoic compared with adjacent muscles.
   • Papillary thyroid carcinoma metastases can be hyperechoic and often show punctate calcifications.
5. Intranodal Necrosis
   • Cystic necrosis presents as an anechoic (or very hypoechoic) area within the node.
   • Coagulation necrosis may appear as an isolated echogenic focus within the node, not continuous with surrounding fat.
   • Any form of intranodal necrosis is considered pathologic and is frequently seen in metastatic or tuberculous nodes.
     

     Fig 4: A - (Ultrasound). Right level IIA lymph node with a heterogeneous echotexture and multiple anechoic foci representing necrosis, biopsy-confirmed as metastatic squamous cell carcinoma. B - (CT) The same lesion showing focal low attenuation foci on CT. © Department of Radiology, Centro Hospitalar Universitário de São João, Porto/Portugal.
6. Calcifications
   • Punctate or peripheral calcifications are particularly common in metastatic nodes from papillary thyroid carcinoma.
   • Calcifications within a node are otherwise uncommon. 
     

     Fig 5: A - (Ultrasound). Left level IIA–IIB lymph node with extensive hyperechoic foci corresponding to dystrophic calcifications. B - (CT). Axial contrast-enhanced image of the same node demonstrating prominent calcifications). Despite the suspicious appearance, no evidence of malignancy was identified on histopathology (non-specific necrotizing inflammatory process). © Department of Radiology, Centro Hospitalar Universitário de São João, Porto/Portugal.
7. Vascular Pattern (Color Doppler)
   • Peripheral or mixed vascularity (both central and peripheral flow) on Doppler evaluation is highly suggestive of malignancy. 
     

     Fig 6: A - (Ultrasound). Heterogeneous hypoechoic mass showing peripheral vascularization on Doppler - an appearance suspicious for metastatic involvement. B - (CT). The same lesion appears as a partially necrotic lymph node measuring. Fine-needle biopsy confirmed a squamous cell carcinoma in this case of hypopharyngeal origin. © Department of Radiology, Centro Hospitalar Universitário de São João, Porto/Portugal.

These ultrasound characteristics should be interpreted in clinical context, and histopathological examination remains the gold standard for definitive diagnosis.

Suspicious (malignant) CT features of cervical lymph nodes:

1. Size
   • Nodes ≥ 1 cm in short-axis diameter on axial imaging are generally considered suspicious.
   • No absolute size cutoff guarantees malignancy or benignity. Small (< 1 cm) nodes may still harbor metastases, especially if other worrisome features are present. Large nodes can occasionally be reactive or inflammatory.
2. Shape
   • Rounded or spherical nodes raise suspicion for malignancy.
   • Clustered or conglomerate lymph nodes are also more suspicious than a solitary lymph node.
     

     Fig 7: (CT). Large, conglomerate lymph node mass at left level IIB with loss of the normal interface with the sternocleidomastoid muscle, indicating possible extracapsular extension. Given the rounded, bulky appearance and clustered nature, this lymphadenopathy is highly suspicious for malignancy. Fine-needle aspiration and immunohistochemistry confirmed a well-to-moderately differentiated squamous cell carcinoma, consistent with a primary hypopharyngeal carcinoma. © Department of Radiology, Centro Hospitalar Universitário de São João, Porto/Portugal.
3. Margins and extracapsular spread
   • Irregular or ill-defined nodal margins are suggestive of extracapsular spread of tumor.
   • Imaging signs of extracapsular spread include:
     1. Irregular nodal capsule with spiculated or blurred borders.
     2. Surrounding fat stranding or infiltration of adjacent tissues.
     3. Loss of normal tissue planes or fascial planes.
        

        Fig 8: A - (Axial CT). Extensive necrotic lymph node measuring approximately 62 mm at the transition from right level II to level III, with irregular margins and loss of the normal interface to the adjacent musculature, suggesting extracapsular spread. B - (Coronal CT). Coronal reconstruction of the same nodal mass. Biopsy confirmed keratinizing squamous cell carcinoma. © Department of Radiology, Centro Hospitalar Universitário de São João, Porto/Portugal.
4. Internal architecture: necrosis and cystic change
   • Central or focal necrosis is highly specific for malignancy in the presence of a known head and neck primary.
     1. Appears as focal low attenuation on CT with an enhancing peripheral rim.
   • Cystic nodal metastases have:
     1. Homogeneous fluid density, a thin smooth capsule, and no complex internal enhancement.
     2. Commonly associated with p16-positive oropharyngeal carcinomas and papillary thyroid carcinoma.
5. Calcifications
   • Calcifications within a cervical node are suspicious, most often seen with:
     1. Papillary thyroid carcinoma.
     2. Medullary thyroid carcinoma (less common than papillary).
   • Less frequently, calcified nodes may be seen in treated head and neck cancers, mucinous adenocarcinoma, or tuberculous lymphadenitis.
   • Combination of cystic changes and calcification in a neck node strongly points toward papillary thyroid carcinoma.
     

     Fig 9: A - (CT). Axial image of a lymph node showing both cystic changes and peripheral calcification, strongly indicative of metastatic papillary thyroid carcinoma. B - (Ultrasound). The same node demonstrates a peripheral calcified rim. Histopathology confirmed the diagnosis of papillary thyroid carcinoma. © Department of Radiology, Centro Hospitalar Universitário de São João, Porto/Portugal.
6. Enhancement pattern (hypervascular metastases)
   • Hypervascular LN metastases are seen with tumors that characteristically have a rich blood supply (e.g., thyroid papillary or medullary carcinoma, renal cell carcinoma, neuroendocrine tumors).
   • Appear as markedly enhancing nodes on contrast-enhanced CT, often with intense enhancement and possible small feeding vessels.
     

     Fig 10: (CT). Axial image demonstrating a markedly enhancing lymph node at left level IIA, consistent with hypervascular metastasis from papillary thyroid carcinoma. © Department of Radiology, Centro Hospitalar Universitário de São João, Porto/Portugal.
7. Location and distribution
   • Asymmetric prominence of cervical nodes or a cluster of three or more contiguous lymph nodes in a known drainage chain is a red flag. 
     

     Fig 11: (CT). Axial image demonstrating a cluster (conglomerate) of right level IIB lymph nodes (43 × 36 mm) that raises suspicion for recurrent or metastatic disease. © Department of Radiology, Centro Hospitalar Universitário de São João, Porto/Portugal.

Ultrasound vs CT sensitivity in depicting suspicious feature:

Ultrasonography (US) generally demonstrates higher sensitivity than CT in depicting subtle changes in cervical lymph node morphology, particularly for superficial nodes. Multiple studies have shown that US excels in identifying features such as nodal shape and cortical thickening, as well as intranodal vascular patterns via Doppler imaging - all of which serve as strong indicators of malignancy.. Because US is performed in real time, it allows more precise, dynamic evaluation of lymph node borders and vascular flow. This makes it especially useful when investigating smaller, superficial nodes, which may be missed or appear indeterminate on CT.

CT, by contrast, provides a more comprehensive overview of the head and neck region, enabling easier assessment of deeper or complex node stations that can be challenging to visualize on ultrasound. Moreover, CT’s high spatial resolution facilitates the detection of nodal necrosis and other structural details that can impact staging and treatment decisions. However, CT often relies primarily on size-based criteria for nodal characterization, which can lead to underestimation of metastatic disease if the node does not meet the conventional dimensional threshold..

Because each imaging modality has distinct strengths and limitations, combining US and CT can improve diagnostic accuracy. US more readily detects smaller pathological changes and vascular abnormalities, while CT better evaluates deeper nodes and the overall extent of disease. Utilizing both modalities provides a more complete picture of nodal involvement and helps guide timely and appropriate treatment planning.