Reactive lymphadenopathy is benign enlargement of lymph nodes due to infection, inflammation, or immune response. It is the most common cause of lymphadenopathy and can occur in all age groups. Histologically classified as follicular hyperplasia, paracortical hyperplasia, or sinus histiocytosis. Reactive nodes are usually tender, measure 1-2 cm, and regress when the underlying cause is treated. Bilateral and symmetric involvement suggests a systemic immune response rather than localized infection. On imaging, benign morphological features are preserved: oval shape, preserved hilar architecture, and uniform cortical thickening are characteristic.
Age Range
5-80
Peak Age
25
Gender
Equal
Prevalence
Common
In reactive lymphadenopathy, antigenic stimulation leads to cellular proliferation in lymph node compartments. In follicular hyperplasia, B-cell germinal centers expand; in paracortical hyperplasia, T-cell zones enlarge; in sinus histiocytosis, macrophage accumulation occurs. This proliferation causes cortical thickening while hilar vascular structures and fatty tissue are preserved — hence the echogenic hilum appearance persists on ultrasonography. Uniform cortical expansion reflects the homogeneous nature of the reactive process; focal asymmetric thickening suggests focal pathology. Increased blood flow occurs through hilar vascular pedicles, maintaining the hilar vascularity pattern on Doppler — distinct from the peripheral or chaotic vascularity pattern of malignant nodes.
Preservation of central echogenic hilum on ultrasonography is the most reliable morphological indicator of benign character. Intact hilar fat and vascular structures indicate patent normal lymphatic drainage pathways and absence of malignant infiltration.
Oval-shaped, well-defined lymph node. Central echogenic hilum is prominently preserved. Cortex may be uniformly thickened (3-4 mm) but is symmetric and regular. Short axis is usually <10 mm. No internal necrosis, calcification, or cystic change. No perinodal edema or matting in surrounding soft tissue.
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Oval-shaped lymph node with preserved central echogenic hilum and uniform cortical thickening, consistent with reactive lymphadenopathy.
Color Doppler shows hilar vascularity pattern — blood flow branches from hilum toward cortex. No peripheral, subcapsular, or chaotic vascularity. Power Doppler shows regular and symmetric vascular branching. Resistive index (RI) is usually <0.8. Vascularity degree may be increased (hyperreactive node) but distribution pattern remains hilar.
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Color Doppler demonstrates hilar vascularity pattern with no peripheral or chaotic vascularity detected — consistent with benign morphology.
Oval-shaped lymph node with homogeneous enhancement on contrast-enhanced CT. Central hilar fat plane is preserved and seen as a low-density central area. Short axis is usually <10 mm. No necrosis, calcification, or perinodal infiltration. Enhancement is similar to or slightly increased compared to surrounding muscle. No conglomerate lymphadenopathy.
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Oval-shaped lymph node with homogeneous enhancement and preserved central hilar fat plane, consistent with reactive lymphadenopathy.
May show mild-moderate diffusion restriction on DWI — cellular density is increased but not as pronounced as in malignant nodes. ADC values are usually >1.0 × 10⁻³ mm²/s (typically <0.8-1.0 in malignant nodes). Intermediate signal intensity on T2-weighted images, isointense to muscle on T1. Homogeneous signal pattern and preserved oval morphology are characteristic.
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Lymph node shows mild diffusion restriction on DWI with ADC value >1.0 × 10⁻³ mm²/s — malignancy is of low probability.
May show mild-moderate FDG uptake on PET-CT — SUVmax is usually <3-4. Reactive nodes can show false-positive FDG uptake especially during acute infection. Symmetric, bilateral uptake supports reactive process. Focal intense uptake (SUVmax >4-5) is suspicious for malignancy and may require biopsy. Morphological benign features (oval shape, preserved hilum) on CT component are critical in interpreting PET positivity.
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Mild FDG uptake is observed in the lymph node (SUVmax: ...) — reactive lymphadenopathy is probable in clinical context, follow-up recommended.
Oval-shaped lymph node at soft tissue density (30-50 HU) on non-contrast CT. Central low-density hilar fat may be visible. No necrosis, calcification, or perinodal stranding. Homogeneous internal structure. Similar morphology nodes may be found in multiple stations — multifocal reactive lymphadenopathy.
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Oval-shaped lymph nodes at soft tissue density with homogeneous internal structure, no necrosis or calcification detected.
Criteria
Expansion of B-cell germinal centers, characterized by tingible body macrophages in reactive germinal centers. Most common type of reactive lymphadenopathy.
Distinct Features
No specific imaging features — general reactive morphology is observed. Requires histological diagnosis. Usually associated with infections or autoimmune diseases.
Criteria
Expansion of T-cell-rich paracortical zones, particularly seen in viral infections (EBV, CMV) and drug reactions. Immunoblast increase is characteristic.
Distinct Features
Prominent cortical thickening may relatively suppress hilar structure — can mimic malignant nodes. Bilateral cervical nodes are typical in EBV mononucleosis. Usually seen in young patients.
Criteria
Histiocyte (macrophage) accumulation in lymph node sinuses, usually seen in lymph nodes draining cancer regions. Phagocytic activity is increased as part of immune response.
Distinct Features
When detected in presence of known malignancy, differentiation from metastasis is important — but histologically contains no tumor cells. Diagnosed by biopsy. Nonspecific reactive morphology on imaging.
Criteria
Regional lymph node enlargement due to skin diseases (dermatitis, psoriasis, eczema). Melanin-laden macrophages, interdigitating dendritic cells, and Langerhans cells accumulate in paracortical area.
Distinct Features
Common in inguinal and axillary nodes, in same drainage area as skin lesion. Reactive morphology on imaging — no specific findings. May be associated with mycosis fungoides — lymphoma should be excluded.
Distinguishing Feature
Hodgkin lymphoma shows intense FDG uptake (SUVmax usually >5), involvement of contiguous nodal stations, and anterior mediastinal mass is typical — reactive LAP shows mild uptake, symmetric and non-contiguous distribution.
Distinguishing Feature
Metastatic SCC shows central necrosis (ring enhancement), round morphology, hilar architecture loss, and perinodal invasion — reactive LAP preserves hilum, no necrosis, and oval shape predominates.
Distinguishing Feature
TB lymphadenitis shows peripheral rim enhancement (central caseous necrosis), matting of nodes, and calcification — reactive LAP has no necrosis, no matting, and calcification is not expected.
Distinguishing Feature
Cat-scratch disease shows focal necrosis, abscess formation, and prominent perinodal inflammatory changes — regional LAP near inoculation site with cat contact history is diagnostic. Reactive LAP shows no necrosis.
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
6-monthReactive lymphadenopathy is a benign condition that usually regresses with treatment of the underlying cause. Biopsy is not needed when short axis <10 mm, oval shape, and preserved hilum are present. Follow-up US at 4-6 weeks to assess regression. If growth, shape change, or hilum loss develops, further investigation (biopsy) should be planned. Biopsy should be considered initially when short axis >15 mm or malignancy history is present.
Reactive lymphadenopathy is the most common cause of lymphadenopathy and does not require treatment. It spontaneously regresses when the underlying infection/inflammation is treated. Regression is expected at 4-6 week follow-up. However, biopsy should be considered if >2 cm, round shape, hilar loss, or continued growth.