Plain CT Detection of Lymph Nodes in Non-Hodgkin's Lymphoma
Plain (non-contrast) CT has poor sensitivity for detecting lymph node involvement in non-Hodgkin's lymphoma and should not be used as the primary staging modality. While it can identify grossly enlarged nodes based on size criteria alone, it misses a substantial proportion of nodal disease and provides inadequate soft tissue characterization for accurate staging 1.
Why Plain CT is Inadequate
Limited Sensitivity for Nodal Disease
- CT relying on size criteria alone (typically >1 cm short axis) has a sensitivity of only 51-58% for detecting lymph node metastases, meaning it misses nearly half of involved nodes 1
- Small lymph nodes may harbor metastatic disease while enlarged nodes may be reactive, and plain CT cannot distinguish between these scenarios without contrast enhancement 1
- CT cannot detect microscopic tumor metastases in non-enlarged lymph nodes, which is a critical limitation in lymphoma staging 1
Poor Soft Tissue Characterization
- Plain CT provides very poor soft tissue characterization in the abdomen and pelvis, making it difficult to distinguish lymph nodes from adjacent vessels and small bowel loops 1
- Without IV contrast, the anatomic localization and significance of abnormal findings become difficult to interpret 1
- The lack of contrast enhancement reduces the ability to assess nodal architecture and internal characteristics that may suggest malignancy 1
Recommended Imaging Approach
PET-CT is the Gold Standard
- PET-CT from skull base to mid-thigh is now the preferred modality for staging FDG-avid lymphomas including most non-Hodgkin's lymphomas, with sensitivity of 82-96% and specificity of 95-98% 2, 3
- PET-CT detects additional disease sites in 15-20% of patients and changes treatment decisions in approximately 8% of cases 1
- Low-dose non-enhanced PET-CT has been shown to be more sensitive and specific than routine contrast-enhanced CT alone for evaluating lymph node and organ involvement in high-grade NHL 1
Contrast-Enhanced CT When PET-CT Unavailable
- If PET-CT is not available, contrast-enhanced CT is strongly preferred over plain CT for nodal assessment 1
- Contrast enhancement improves detection of enlarged lymph nodes by approximately 11%, particularly in critical stations like the right upper paratracheal region 4
- Contrast-enhanced CT allows better differentiation of lymph nodes from vessels and provides information about nodal enhancement patterns and necrosis that suggest malignancy 5
Critical Pitfalls to Avoid
- Do not rely on plain CT for staging decisions in non-Hodgkin's lymphoma, as it will understage a substantial proportion of patients 1, 6
- Avoid delaying appropriate imaging (PET-CT or contrast-enhanced CT) in favor of plain CT, as tissue diagnosis and accurate staging are rate-limiting steps for treatment 7
- Do not assume that normal-sized lymph nodes on plain CT exclude lymphomatous involvement, as microscopic disease is common 1
- Be aware that lesions smaller than 1 cm are not reliably visualized even with optimal imaging techniques 1