MRI of lymph nodes

Principles and limitations of diagnostic imaging

Traditional tomographic methods (CT and MRI) diagnose lymph node involvement primarily based on their size. The main problem with this approach is the high risk of diagnostic errors. About 4% of patients have micrometastases in completely normal-sized nodes (false-negative result). On the other hand, node enlargement is often caused by reactive hyperplasia in response to primary tumor necrosis (false-positive result).

Overall, when searching for lymphogenic metastases, MRI offers no significant advantages over CT. For more precise diagnostics, particularly of micrometastases, FDG-PET is used, with a sensitivity reaching up to 100%. Nevertheless, in massive pelvic involvement, MRI serves as the method of choice for a detailed assessment of tumor conglomerate spread and its degree of impact on adjacent organs.

Evaluation of lymph nodes in carcinomas

Staging of lymphogenic metastasis (category N) has specific features depending on the location of the primary tumor:

• Gastric cancer: The stage depends strictly on the number of involved nodes rather than their anatomical region. Metastases in 1–2 nodes correspond to stage N1, in 3–6 to N2, and in 7 or more to N3 (subdivided into N3a and N3b). Regional nodes include perigastric nodes as well as those along the celiac, left gastric, and common hepatic arteries. Involvement of non-regional nodes (para-aortic, retropancreatic) is considered distant metastasis (stage M1).
• Renal cell carcinoma: When staging RCC, the overall accuracy of imaging is 83–89%. Single lymph node involvement (N1) and multiple involvement (N2) are distinguished.
• Cervical cancer: Lymphadenopathy is not part of the classical FIGO staging system. However, the detection of distant lymph node metastases (e.g., supraclavicular) immediately upgrades the process to terminal stage IVB and radically alters the treatment plan. The maximum standardized uptake value (SUV) in pelvic nodes serves as an accurate biomarker of response to therapy.

Specific involvement patterns in lymphomas

The radiologic semiotics of lymphomas include involvement of characteristic lymph node groups that require the radiologist's targeted attention:

1. Node of the omental foramen (portacaval node): Located between the portal vein and the inferior vena cava. Normally, it has a triangular shape (up to 3 cm in length and 1 cm in thickness). It is frequently overlooked during image analysis.
2. Splenic hilum: Involved in approximately 30% of patients. This involvement is almost always combined with diffuse tumor infiltration of the spleen itself.
3. Mesenteric lymph nodes: In massive involvement of the retroperitoneum and mesentery, the “hamburger sign” (hamburger sign) develops—a specific pattern where a loop of the bowel is compressed between two large tumor masses. Multiple mesenteric nodes (even if not enlarged) are suspicious for lymphoma and are also the cause of the “misty mesentery” sign.
4. Mediastinum: In Hodgkin lymphoma, involvement of the internal mammary lymph node chain is frequently detected, while primary B-cell lymphoma is typically characterized by massive involvement of the anterior and middle mediastinum.

Differential diagnosis and contrast enhancement

Upon intravenous contrast administration, involved lymphomatous nodes generally enhance uniformly. This is a crucial diagnostic criterion: if multilocular (heterogeneous) enhancement is identified within a node, it is atypical for lymphoma. In such cases, alternative causes should be sought, such as tuberculosis or atypical infections.

Non-Hodgkin lymphomas are characterized by the formation of massive coalescing nodes (bulky disease) and a non-contiguous spread pattern. At the same time, in Hodgkin lymphoma, enlargement of inguinal or femoral lymph nodes is rarely recorded—in less than 20% of cases, which requires extremely careful evaluation of all pelvic structures.

Class and exam questions

What else to study on this topic

• Criteria for invasion into adjacent organs (T4b) and gastric cancer staging
• Prognostic significance of FDG-PET: SUVmax evaluation
• Local staging of cervical cancer: the role of MRI
• Differential diagnosis of mediastinal masses
• Radiologic semiotics of cystic and medullary renal cell carcinoma

Other topics in the section "Diagnostic Radiology of the Abdominal Organs"

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