Staging features and pathways of spread
Parenchymal involvement in lymphomas can be classified as primary, secondary (in the setting of extrathoracic disease), and associated with pre-existing intrathoracic lymph node involvement. Post-transplant lymphoproliferative disorders and AIDS-related lymphomas are also distinguished.
Secondary involvement often represents direct tumor extension from lymph nodes into the adjacent tissue (perihilar or paramediastinal zones). Such local extension is designated by the index "E" (extranodal involvement) and does not upstage the overall disease stage.
There are important differences between the two main types of lymphomas:
- Hodgkin Lymphoma (HL): extremely rarely presents with intrapulmonary nodules without concomitant mediastinal lymphadenopathy. Exceptions include relapses after radiation therapy to the lung roots or mediastinum, where the process may be confined strictly to the parenchyma.
- Non-Hodgkin Lymphoma (NHL): in half of the patients with lung or pleural involvement, intrathoracic lymph nodes remain unaffected.
As the disease progresses or in cases of relapse, the frequency of pulmonary involvement increases (in patients with HL, this indicator eventually reaches 30–40%).
Computed tomography (CT) findings
Radiological patterns are extremely variable. Most lesions of diffuse large B-cell lymphoma (DLBCL) and HL show avid radiopharmaceutical (FDG) uptake on PET/CT.
Main visualization patterns:
- Isolated nodules. The most frequent sign. This is a single nodule or multiple foci that may undergo breakdown (cavitation). Unlike carcinoma metastases, their margins are usually less distinct.
- Peribronchial nodularity. The tumor spreads along lymphatic pathways, affecting follicles along the bronchovascular bundles. On CT, this appears as linear strands or nodules radiating from the lung roots.
- Consolidation. Lymphomatous cells may fill the acini, forming rounded or segmental opacity areas with the "air bronchogram" sign.
- Rare forms. These include a lymphangitic pattern (interstitial reticulonodular shadows) and atelectasis (more often due to endobronchial tumor growth rather than extrinsic compression).
Primary pulmonary lymphoma
This extremely rare pathology (less than 1% of all lymphomas) is represented by three main variants:
- Low-grade B-cell NHLs. Originating from mucosa-associated lymphoid tissue (MALT/BALT). Typical for patients aged 50–60 years, frequently with an autoimmune history (e.g., Sjögren's syndrome). The clinical course is indolent, with a 5-year survival rate exceeding 80%. CT shows long-standing nodules or consolidation areas.
- High-grade NHLs. Account for up to 20% of primary pulmonary lymphomas (most commonly DLBCL). Manifest as rapidly growing pulmonary nodules. Unlike MALT lymphomas, the chest wall and lymph nodes are more frequently involved here.
- Primary pulmonary HL. Extremely rare, typically manifesting as nodules in the upper lobes.
Pleural and thymic involvement
The pathological process in lymphomas frequently extends beyond the lung parenchyma:
Pleural effusion: Observed in 50% of patients with mediastinal lymphadenopathy. This is usually an exudate resulting from venous or central lymphatic obstruction. Concomitant involvement of the lungs themselves is not mandatory. There is also a specific primary effusion lymphoma affecting mesothelial spaces (associated with HIV and human herpesvirus type 8).
Thymus: Involvement of the thymus gland is observed in 30% of patients with HL at presentation. For staging purposes, the thymus is equated to a lymph node. Its involvement is also typical for primary mediastinal large B-cell lymphoma (PMBL), which frequently occurs in young women (25–40 years). This form rapidly forms a massive mass, causing superior vena cava syndrome in 40% of cases.
Important: following successful chemotherapy, a benign "rebound" thymic hyperplasia may develop, which is difficult to distinguish from recurrence even with PET/CT.
Briefly: answers to topical questions
What are the pathogenetic mechanisms of pleural effusion formation in intrathoracic lymphomas?
Pleural effusion in intrathoracic lymphomas results from the obstruction of central lymphatic pathways or veins. By its nature, such effusion is typically an exudate. It is detected on CT in half of patients with mediastinal lymph node involvement and resolves rapidly upon treatment of this lesion. Concomitant lung parenchymal involvement is not required for its development.
By what radiological features are pulmonary lymphoma nodules differentiated from hematogenous carcinoma metastases?
Pulmonary lymphoma nodules are differentiated from carcinoma metastases primarily by the margins of the nodules.
| Sign | Lymphoma nodules | Carcinoma metastases |
|---|---|---|
| Nodule margins | Less distinct | More distinct |
| Overall CT picture | Similar to metastases | Similar to lymphoma |
Otherwise, isolated pulmonary lymphoma nodules (with or without cavitation) are visually similar to metastatic carcinoma. Due to the lack of histological specificity on CT, endobronchial metastases and lymphoma may present with a similar appearance.
What are the CT findings and characteristic clinical complications of primary mediastinal large B-cell lymphoma (PMBL)?
Primary mediastinal large B-cell lymphoma (PMBL) presents as a rapidly growing massive mass (bulky disease) involving the thymus. On CT, it is frequently impossible to differentiate enlarged mediastinal lymph nodes from involvement of the thymus itself.
- Cystic changes may be initially detected, persist, or enlarge following treatment.
- Calcifications may be present initially or appear during the course of treatment.
- Pericardial effusion frequently accompanies the disease.
A clinical complication is superior vena cava syndrome, which occurs in up to 40% of patients and is rarely observed in other lymphomas.
Class and exam questions
How to distinguish pulmonary lymphoma from infectious pneumonia on CT?
In lymphomatous consolidation with the air bronchogram sign, a specific differential feature is often revealed—nodularity along the bronchial walls, which is atypical for infectious inflammation.
Does tumor invasion from a lymph node into the lung affect the stage?
No, direct secondary extension from an intrathoracic lymph node into the adjacent lung parenchyma is designated as extranodal involvement (stage "E") and does not alter the baseline disease stage.
What is rebound thymic hyperplasia?
This is a benign enlargement of the thymus gland that occurs after the completion of chemotherapy courses. It has a typical triangular shape but can mimic tumor recurrence on PET/CT.
What else to study on this topic
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- Differential diagnosis of chest wall lesions using MRI
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