Epidemiology and the impact of antiretroviral therapy
Before the widespread introduction of combination antiretroviral therapy (cART), the incidence of primary CNS lymphoma (PCNSL) and Burkitt lymphoma in HIV-infected individuals exceeded that of the general population by 1000-fold. Modern therapy has significantly reduced these risks, yet it has revealed new patterns.
The overwhelming majority of HIV-associated lymphomas are aggressive B-cell variants. There is a clear correlation between the degree of immunodeficiency and the histological subtype of the tumor:
- Diffuse large B-cell lymphoma (DLBCL) manifests during severe suppression (CD4 count < 100 cells/µL).
- Burkitt lymphoma develops with a less profound decline in immunity.
- Hodgkin lymphoma (HL) demonstrates a paradoxical dynamic: its incidence has actually increased against the background of cART use.
Additionally, the Epstein-Barr virus (EBV) is a critical pathogenetic factor. It is detected in nearly 100% of HIV-associated Hodgkin lymphoma cases and in more than 90% of PCNSL cases.
Clinical presentation and patterns of involvement
Tumors in the context of HIV are characterized by a high degree of aggressiveness and are usually diagnosed at advanced stages. They are typically characterized by the formation of massive tumor conglomerates (bulky disease) and elevated blood lactate dehydrogenase (LDH) levels.
The primary distinctive feature of HIV-associated lymphomas is the propensity for extranodal dissemination. It occurs in more than 75% of cases (unlike in immunocompetent patients). The tumor primarily affects the gastrointestinal tract, central nervous system, liver, and bone marrow. At the same time, classic peripheral lymphadenopathy is uncommon in such patients.
Unusual localizations may also occur. For example, epidural lymphoma appears on contrast-enhanced CT as a contrast-enhancing mass in the paraspinal soft tissues. It rapidly spreads into the spinal canal and musculature, causing compression of the dural sac.
Imaging features
The radiological semiotics of lymphomas in HIV have specific features that require careful differential diagnosis, primarily with opportunistic infections.
Chest CT Respiratory tract involvement is usually extranodal in nature. Imaging visualizes pleural effusion, pulmonary nodules, as well as acinar and interstitial opacities. Enlargement of intrathoracic lymph nodes is mildly expressed. Important: If CT reveals cavitation (decay cavities), small nodules up to 1 cm in diameter, and signs of lymph node necrosis, this points to a mycobacterial infection (tuberculosis or mycobactereiosis) rather than lymphoma.
Abdominal CT In the abdomen, the gastrointestinal tract, liver, kidneys, adrenal glands, and lower urinary tract are most frequently affected. In this case, the CT picture does not fundamentally differ from that in HIV-negative patients.
Primary CNS lymphoma (PCNSL) Interestingly, ring-like contrast enhancement and multifocality of brain lesions are more commonly observed in individuals with normal immunity. In HIV patients, PCNSL tends to localize in the deep white matter. The primary differential diagnosis is made with cerebral toxoplasmosis and progressive multifocal leukoencephalopathy (PML). For accurate verification without biopsy, quantitative FDG-PET and MR spectroscopy are used.
Staging and response assessment principles
As with conventional lymphomas, staging utilizes the Lugano classification (Lugano classification). The main factor determining treatment tactics for non-Hodgkin lymphomas (which constitute the majority of HIV-associated tumors) is their histological subtype.
FDG-PET/CT has become the gold standard for staging and monitoring treatment response. It is capable of detecting tumor involvement in normal-sized lymph nodes, leading to an upstaging of the disease in 10–30% of patients. Contrast-enhanced CT remains the modality of choice only for evaluating lymphomas with initially low or variable radiopharmaceutical uptake. A complete response (Complete response, CR) to therapy confirmed by imaging methods is a critical predictor of long-term survival.
Briefly: answers to topical questions
How does primary CNS lymphoma differ from cerebral toxoplasmosis on MRI in HIV patients?
A distinguishing MRI feature of primary CNS lymphoma (PCNSL) from cerebral toxoplasmosis is its localization in the deep white matter.
| Sign | Primary CNS lymphoma |
|---|---|
| Localization | Deep white matter |
| T1- and T2-WI | Usually isointense |
| Contrast enhancement | Homogeneous (atypical ring-enhancing possible in AIDS) |
For definitive differentiation of these conditions, quantitative FDG-PET (FDG-PET) and MR spectroscopy are additionally employed.
To remember the association of lymphomas with CD4 levels: "DLBCL — Deep" (occurs with a deep drop in CD4 < 100), and "Burkitt — Bigger" (at higher counts). Meanwhile, Hodgkin paradoxically grows against the background of Good therapy.
Class and exam questions
How to differentiate lymphoma from mycobacterial infection on chest CT in an HIV patient?
The presence of decay cavities (cavitation), multiple small nodules (less than 1 cm), and necrotic changes in lymph nodes favor mycobacterial infection. Pleural effusion and interstitial opacities without pronounced lymph node enlargement are more characteristic of lymphoma.
What conditions must primary CNS lymphoma be differentiated from?
The main differential diagnosis includes cerebral toxoplasmosis and progressive multifocal leukoencephalopathy. A distinguishing feature of lymphoma is the involvement of the deep white matter; MR spectroscopy and FDG-PET are used to clarify the diagnosis.
Which imaging modality is the gold standard for assessing lymphoma treatment response?
Fluorodeoxyglucose (FDG) PET/CT has become the gold standard. It allows for accurate assessment of the metabolic activity of the tissue, whereas conventional CT may visualize inactive residual masses (e.g., in the mediastinum) for years.
What else to study on this topic
- Clinical and radiological variants of Burkitt lymphoma (endemic, sporadic).
- Lugano classification in lymphoma staging.
- MALT lymphomas and their pathogenetic association with autoimmune processes.
- Post-transplant lymphoproliferative disorders (PTLD).
- The role of interim PET/CT in assessing chemotherapy efficacy.
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