Ultrasound Findings Pertinent to Head and Neck Lymphoma
Lymphoma nodes characteristically appear as round, hypoechoic, homogeneous masses with absent fatty hilum, often showing multiple confluent lobulated patterns and minimal internal vascularity on ultrasound. 1, 2, 3
Key Sonographic Features of Lymphomatous Nodes
Shape and Size Characteristics
- Round morphology with short-to-long axis ratio >0.5 is highly suspicious, as virtually all longitudinal nodes are benign while 80% of round nodes demonstrate malignancy 1
- Nodes exceeding 20 mm in axial diameter, particularly when round or oval-shaped, are strongly associated with malignancy 1
- Multiple nodes often appear as confluent lobulated masses rather than discrete nodules 2
Internal Architecture
- Homogeneous hypoechoic echotexture is the hallmark finding, appearing darker than adjacent muscle tissue 2, 3, 4
- Complete absence of echogenic fatty hilum is critical—the hilus is a linear echogenic structure continuous with perinodal fat that disappears in malignant infiltration 3, 4
- Lymphoma nodes typically lack the punctate bright echogenic spots seen in 78% of metastatic carcinoma nodes, helping differentiate these entities 3
- Homogeneous internal echo pattern without cystic necrosis distinguishes lymphoma from squamous cell carcinoma metastases (which show cystic changes in 19% of cases) 3
Border and Margin Features
- Sharp, well-defined borders are typical, contrasting with the ragged, irregular borders of some metastatic nodes 4
- Loss of normal fascial planes and adjacent soft tissue edema may occur in aggressive cases 4
- Matted nodes (clumped together without intervening soft tissue) suggest extensive disease 4
Vascular Patterns
- Minimal or absent intranodal vascularity on Doppler is characteristic of lymphoma, contrasting with the increased peripheral and hilar vascularity of reactive nodes 5
- Venous invasion can occur, demonstrated as loss of echogenicity in vessel walls, particularly in the internal jugular vein 2
- Contrast-enhanced ultrasound shows reduced parenchymal perfusion compared to reactive nodes 5
Critical Diagnostic Pitfalls
Size Thresholds
- While nodes <10 mm in short axis are generally benign, lymphoma can present with nodes ≤15 mm that appear reactive 6
- Do not rely solely on size criteria—internal architecture is more specific 1, 3
Distinguishing from Other Pathology
- Tuberculosis lymphadenitis may mimic lymphoma with hypoechoic appearance but often shows cystic necrosis and calcification 2, 4
- Metastatic squamous cell carcinoma shows punctate bright echogenic spots (78% of cases) and cystic necrosis (19%), features absent in lymphoma 3
- Reactive nodes maintain oval shape, preserved fatty hilum, and increased hilar vascularity 5, 3
Tissue Confirmation Requirements
Core needle biopsy is mandatory for definitive diagnosis, as ultrasound alone cannot reliably distinguish lymphoma from other pathologies 7, 8
- Core biopsy provides superior diagnostic accuracy (88% sensitivity) compared to fine needle aspiration (74% sensitivity) and yields tissue for immunohistochemistry essential for lymphoma subtyping 6
- Ultrasound-guided FNA is acceptable when anticoagulation cannot be discontinued, with 52-79% sensitivity when combined with ultrasound guidance 6
- Never rely solely on imaging to exclude malignancy when clinical suspicion exists, as physical examination findings of hard, fixed nodes override reassuring ultrasound features 8
Red Flags Requiring Immediate Biopsy
- Progressive enlargement to >15 mm in short axis on serial imaging 6
- Development of irregular borders, necrosis, or extranodal extension 6
- Loss of fatty hilum on follow-up imaging (90-93% positive predictive value for malignancy) 6
- Cortical thickness >3 mm 6
- Hard, fixed consistency on palpation regardless of ultrasound appearance 8