Urinary system
Renal involvement (Renal Lymphoma) is most often secondary in nature. There are several types of involvement:
- Direct infiltration: Occurs in 25% of cases. The tumor from retroperitoneal lymph nodes encases the renal vessels and extends into the sinus, which can strongly mimic transitional cell carcinoma on imaging.
- Perirenal space involvement: Tumor masses wrap around the kidney without invading the parenchyma itself.
- Diffuse infiltration: A rare variant typical of aggressive forms (e.g., Burkitt lymphoma). Leads to total enlargement of the organ.
On ultrasound, affected kidneys appear hypoechoic. Contrast-enhanced CT reveals multiple hypodense nodules or diffuse replacement of normal tissue. PET/CT is useful in complex cases, showing focal or diffuse FDG uptake.
The urinary bladder is predominantly involved by direct extension from pelvic nodes (up to 15% of cases). Primary bladder tumors are extremely rare, more commonly presenting as a MALT lymphoma in the form of a large submucosal mass.
Reproductive organs
Male genital system: Lymphoma accounts for about 5% of all primary testicular tumors and is the most common neoplasm of this localization in men over 60 years old (usually DLBCL). In 20% of cases, the process is bilateral. The ultrasound appearance is non-specific, so the staging protocol always includes examination of the contralateral testis. Primary lymphoma of the prostate, unlike the bladder, is associated with a very poor prognosis.
Female genital system: Isolated involvement is rare (about 1% of extranodal NHLs), predominantly in postmenopausal women.
- Uterus: The cervix is most frequently affected. On MRI, the myometrium may be diffusely enlarged with lobulated contours mimicking a myoma, but the mucosa and junctional zone remain intact. The prognosis is favorable in this case.
- Ovaries: The prognosis is extremely unfavorable. Tumors are often bilateral and large (10–15 cm). Unlike ovarian cancer, calcification and hemorrhage are atypical here.
Bone marrow
The bone marrow is frequently involved, which automatically upstages the disease to stage IV. In non-Hodgkin lymphomas (NHL), this occurs in 20–40% of cases at initial presentation.
Historically, bilateral trephine biopsy was the staging standard, but modern imaging modalities have higher sensitivity:
- MRI: Detects pathology in 30% of patients with a negative biopsy. The typical pattern is low signal on T1-weighted imaging and high signal on STIR. Positive MRI indicates a worse prognosis regardless of histology results.
- FDG PET/CT: Also effectively upstages the disease. However, the method has nuances: diffuse tracer uptake is often a result of reactive hyperplasia (especially following colony-stimulating factors), yielding a false-positive result. False-negative findings are possible with microscopic infiltration (less than 5%).
Musculoskeletal system
Primary bone lymphoma (almost always NHL) is a rare diagnosis. It is established if only a single bone is involved and distant metastases are absent for at least 6 months. Secondary skeletal involvement is more common and has distinct features:
- Non-Hodgkin lymphoma (NHL): Lesions are usually osteolytic and permeative in nature.
- Hodgkin lymphoma (HL): In 86% of patients, lesions are mixed or sclerotic. A classic radiological phenomenon in HL is pronounced sclerosis of a vertebral body, the so-called ivory vertebra sign.
CT excellently visualizes bone destruction, but MRI remains the method of choice for assessing the extraosseous soft tissue component and precise local staging.
Briefly: answers to topical questions
What patterns of renal involvement are detected on contrast-enhanced CT in lymphoma?
Contrast-enhanced CT reveals multiple hypodense lesions or homogeneous hypodense tissue, corresponding to the three main types of involvement.
- Direct infiltration (Direct infiltration) — the result of contiguous spread from retroperitoneal lymph nodes with encasement of renal vessels, and involvement of the hilum and sinus.
- Perirenal space involvement (Perirenal space) — soft tissue masses that can encase the kidney without invasion into the parenchyma itself.
- Diffuse infiltration (Diffuse infiltration) — total enlargement of the organ, in which normal parenchymal enhancement is replaced by homogeneous hypodense tissue.
For quick memorization of bone lesion patterns: Hodgkin lymphoma = Dense/sclerotic lesions (ivory vertebra). Non-Hodgkin = Destructive/lytic lesions.
Class and exam questions
Why perform an ultrasound of the second testis if only one is enlarged?
In testicular lymphomas, the risk of bilateral involvement reaches 20%, and relapse frequently occurs in the contralateral side. Therefore, staging always includes evaluation of both testes.
How to differentiate uterine involvement from a myoma on MRI?
Lymphoma causes diffuse enlargement with a lobulated contour, while the mucosal membrane and underlying junctional zone remain intact.
What is an "ivory vertebra"?
This is a classic sign of secondary bone involvement in Hodgkin lymphoma, manifested by pronounced osteosclerosis of a vertebral body on radiography or CT.
Why can PET/CT yield a false-positive result in the bone marrow?
Diffuse or heterogeneous FDG uptake is frequently the result of reactive bone marrow hyperplasia, especially following the administration of colony-stimulating factors (G-CSF) during treatment.
What else to study on this topic
- Differential diagnosis of renal lymphoma and transitional cell carcinoma.
- Primary CNS lymphoma (PCNSL): association with immunodeficiency and "butterfly" patterns.
- Application of DWIBS (diffusion-weighted whole-body imaging with background body signal suppression) for staging and monitoring.
- Adrenal gland changes in lymphomas and differentiation from metastases.
- Involvement of Waldeyer's ring and its association with testicular lymphoma.
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