Lymphomas arising in the thorax vary significantly by type; they are more common in Hodgkin's disease (ranging from 31% to 71%) than in non-Hodgkin's lymphoma (ranging from 13% to 23%) (1) , with HL demonstrating a predilection for young adults and NHL showing a broader age distribution. While HL classically originates in the lymph nodes, NHL often arises from extranodal sites, including the lungs, pleura, and mediastinal structures. The clinical presentation varies: HL may manifest with constitutional “B symptoms” (e.g., fever, night sweats), whereas NHL can present with nonspecific respiratory symptoms such as cough or dyspnea, complicating early diagnosis.

Imaging serves as the cornerstone of evaluation, bridging the gap between clinical suspicion and histopathological confirmation. Accurate staging, guided by the Lugano classification system, hinges on radiological findings to determine disease extent, prognosis, and therapeutic strategies, including chemotherapy, radiation, or immunotherapy.

A-Radiological Modalities: Strengths and Applications

1. Computed Tomography (CT)

CT remains the primary modality for initial assessment due to its superior spatial resolution and ability to delineate anatomical details. Contrast-enhanced CT excels in identifying lymphadenopathy, parenchymal lesions, and complications such as airway compression or superior vena cava syndrome. In HL, contiguous mediastinal lymph node enlargement is characteristic, often involving the anterior and middle compartments. NHL, conversely, may present with non-contiguous nodal disease or extranodal masses, such as solitary pulmonary nodules or diffuse infiltrates mimicking pneumonia.

Limitations include inadequate differentiation between active lymphoma and post-treatment fibrosis, as well as difficulty distinguishing lymphoma from metastatic carcinoma or granulomatous diseases.

2. Positron Emission Tomography (PET)/CT

Integrated PET/CT combines metabolic and anatomical data, revolutionizing lymphoma management. Fluorodeoxyglucose (FDG) avidity, quantified via standardized uptake values (SUVs), reflects tumor aggressiveness and guides biopsy targeting. In HL, PET/CT detects subcentimeter nodes missed by CT alone, while in NHL, it identifies extranodal sites such as pericardial or chest wall involvement (2).

The Deauville 5-point scale is pivotal for post-treatment response assessment, distinguishing residual active disease from inflammation. However, false positives may arise from infectious or inflammatory processes, and indolent NHL subtypes (e.g., marginal zone lymphoma) often exhibit low FDG avidity, reducing sensitivity.

3. Magnetic Resonance Imaging (MRI)

MRI’s superior soft-tissue contrast makes it invaluable for evaluating chest wall invasion, spinal involvement, or pericardial disease. Diffusion-weighted imaging (DWI) and dynamic contrast-enhanced sequences provide functional insights, aiding in the detection of early treatment response. Nevertheless, motion artifacts from respiration and cardiac pulsation limit its utility in lung imaging.

4. Ultrasound

Ultrasound plays a niche role in assessing pleural effusions and guiding thoracentesis. Complex septated effusions, often exudative, may suggest lymphoma involvement, though cytological confirmation remains necessary.

B-Hodgkin vs. Non-Hodgkin Lymphoma: Distinct Imaging Phenotypes

1.Hodgkin Lymphoma (HL): Radiologic Hallmarks

a) Lymph Node Involvement: A Topographic Signature

HL is characterized by contiguous, predictable spread along lymphatic chains. Imaging typically reveals enlargement of anterior mediastinal and paratracheal lymph nodes, a near-pathognomonic feature [Figure 1]. At diagnosis, 67% of patients exhibit intrathoracic lymphadenopathy, with a predilection for the superior mediastinum (99% of cases). Isolated hilar involvement is rare, and nodal calcifications—exceptional prior to treatment—may emerge post-radiotherapy (3).

The Ann Arbor-Cotswolds staging system guides prognosis: localized stages (IA-IIA) may be managed with radiotherapy alone, while advanced disease requires combination chemotherapy.

Fig 1: Computed tomography images of a 21-year-old patient presenting with marked mediastinal and bilateral hilar lymphadenopathy at different lymph nodes groups (blue arrows). Notably, there was right upper paratracheal lymphadenopathy causing external compression of the superior vena cava (SVC), marked by a red arrow. The prevascular lymph nodes exhibited heterogeneous enhancement following contrast administration (yellow arrow). The findings are indicative of Hodgkin lymphoma, as confirmed by biopsy.

b) Pulmonary Parenchymal Involvement: Three Dominant Patterns

.         Multiple Nodules: Present in 70% of cases, these ill-defined opacities, often associated with hilar lymphadenopathy, reflect direct tumor infiltration or lymphatic dissemination [Figure 2].

Fig 2: A computed tomography scan of a 50-year-old patient revealed perilymphatic micronodules in the middle lobe (yellow arrows) associated with mediastino-hilar lymphadenopathy (blue arrows), bilateral axillary lymphadenopathy (red arrows), and retroperitoneal lymphadenopathy (green arrows). The biopsy confirmed the diagnosis of Hodgkin lymphoma.

.         Septal Reticulations:  Secondary to lymphatic or venous obstruction by enlarged nodes, these interlobular lines may mimic pulmonary edema (4).

.         Alveolar Consolidations [Figure 3]: Air bronchograms within consolidated areas can resemble bacterial pneumonia, necessitating biopsy for confirmation (4).

Fig 3: A computed tomography scan of a 66-year-old male revealed persistent consolidation (indicated by green arrows) accompanied by air bronchograms (shown by the blue arrow) in the lingula. Additionally, ground-glass opacities were observed in the left ventro-basal and bilateral postero-basal segments (marked with red arrows). A biopsy confirmed the diagnosis of primary Hodgkin lymphoma. Furthermore, a left pleural effusion was noted (indicated by the yellow arrow).

c) Thoracic Complications

Pleural effusions, resulting from lymphatic obstruction rather than direct pleural invasion, are common. Bulky mediastinal disease may cause superior vena cava syndrome, tracheal compression, or chest wall masses (e.g., within pectoral muscles) (5).

 2.Non-Hodgkin Lymphoma (NHL): Radiologic Heterogeneity

a) Histologic Diversity and Imaging Implications

Unlike HL, NHL comprises a broad spectrum of subtypes (low- to high-grade), each dictating distinct presentations. Only 43% of patients present with thoracic involvement at diagnosis, with mediastinal lymphadenopathy in fewer than 50% of cases. Aggressive NHLs (e.g., diffuse large B-cell lymphoma) manifest as bulky mediastinal masses (>10 cm) causing compression [Figure 4], while indolent forms (e.g., follicular lymphoma) favor isolated lymphadenopathy.

Large lymph node masses may exhibit heterogeneity with complex low attenuation, indicative of necrosis, hemorrhage, or cystic degeneration (2).

Fig 4: A computed tomography scan of a 23-year-old female revealed a large necrotic mediastino-parenchymal mass in the left upper lobe (yellow stars), exerting a mass effect on the mediastinum, which is displaced to the right side and compressing vascular structures, notably the aorta (purple arrow) and left pulmonary artery (green arrow). This was associated with a moderate-sized right pleural effusion (blue arrow) and hypodense cortical-medullary renal nodules on the right side (red arrows). The biopsy confirmed the diagnosis of diffuse large B-cell lymphoma.

b) Parenchymal Involvement: A Polymorphic Spectrum

Though rare (<5% of cases), pulmonary infiltration may occur without associated lymphadenopathy, particularly in primary pulmonary lymphomas. Patterns include:

• Cavitary Nodules [Figure 5]: Characteristic of angiocentric lymphoma (formerly lymphomatoid granulomatosis), these lesions occur in 25% of cases (6).

Fig 5: A computed tomography scan of a 54-year-old male revealed an excavating lung mass in the dorsal segment of the right upper lobe(indicated by arrows) . There were also mediastinal lymphadenopathy located in the superior and inferior right paratracheal chains (marked with green arrows). Additionally, a solid pulmonary nodule was identified in the ventral segment of the right upper lobe. A biopsy of the mass confirmed the diagnosis of primary low-grade B-cell non-Hodgkin lymphoma of follicle cell type.

• Alveolar Masses: Seen in mucosa-associated lymphoid tissue (MALT) lymphomas, these slow-growing lesions carry a favorable prognosis (5-year survival >80%) (7).
• Reticulonodular Infiltrates: Associated with peribronchovascular thickening, these often result from direct extension from hilar nodes.

c) Complications and Rare Involvement

Pleural effusions typically coexist with mediastinal lymphadenopathy [Figure 6]. Thoracic wall invasion, more common in recurrent disease, presents as infiltrative masses with osseous or muscular destruction.

Fig 6: A computed tomography scan of a 53-year-old female patient being followed for primary low-grade B-cell non-Hodgkin lymphoma of mucosa-associated lymphoid tissue (MALT) revealed a large right pleural effusion (orange star) with associated passive collapse of the lung. The scan also showed mediastinal lymphadenopathy (green arrow), bilateral axillary lymphadenopathy (red arrows), right external iliac lymphadenopathy (blue arrow), and lumbar-aortic lymphadenopathy (yellow arrow).

C- Clinical Implications and Therapeutic Considerations

1. Staging and Prognostication

Imaging determines disease stage, which directly impacts therapy. For example, localized HL (stage I–II) may be treated with abbreviated chemotherapy and involved-site radiation, while advanced disease requires multi-agent regimens. In NHL, PET/CT findings influence the International Prognostic Index (IPI), guiding risk-adapted therapies.

2. Treatment Response Assessment

Interim PET/CT after 2–4 chemotherapy cycles predicts long-term outcomes. A Deauville score of 4–5 necessitates treatment escalation, whereas scores of 1–3 may permit de-escalation to reduce toxicity. Post-treatment surveillance imaging, however, remains controversial due to radiation exposure and cost-effectiveness concerns.

3. Complications and Follow-Up

Imaging detects therapy-related complications, such as radiation pneumonitis or chemotherapy-induced cardiomyopathy. Late relapses, particularly in NHL, require long-term monitoring via low-dose CT.