Orbital lymphoma is the most common primary malignant tumor of the orbit, comprising approximately 10-15% of orbital masses in adults. The most common type is MALT (mucosa-associated lymphoid tissue) lymphoma, categorized as low-grade B-cell non-Hodgkin lymphoma. The most characteristic feature of orbital lymphoma is the 'moulding' pattern, growing by conforming to orbital structures without causing bone destruction. The lacrimal gland, conjunctiva, and extraconal soft tissue are the most common sites of involvement. Bilateral involvement is seen in 10-15% of cases and requires systemic lymphoma screening. It typically presents with painless proptosis and eyelid swelling in patients over 60 years of age.
Age Range
50-80
Peak Age
65
Gender
Equal
Prevalence
Uncommon
Orbital lymphoma develops from mucosa-associated lymphoid tissue (MALT) of the conjunctiva and lacrimal gland, or as orbital involvement of systemic lymphoma. In MALT lymphoma pathogenesis, chronic antigenic stimulation (autoimmune diseases, chronic infections — especially Chlamydia psittaci association) triggers reactive lymphoid tissue hyperplasia and subsequently monoclonal B-cell proliferation. Lymphoma cells have small, uniform morphology and their loosely cohesive structure conforms to anatomic contours of orbital structures (moulding), generally without causing bone destruction; this differs from aggressive malignant tumors (carcinomas, sarcomas). Low cell proliferation index (Ki-67 <10%) explains the indolent clinical course. Restricted diffusion on MRI is due to high nuclear-to-cytoplasmic ratio and cell density resulting from dense packing of lymphoma cells.
The growth of orbital lymphoma conforming to the globe, extraocular muscles, and orbital walls without bone destruction (moulding pattern) is the most characteristic and pathognomonic growth pattern of orbital lymphoma. This pattern reflects the loosely cohesive structure and low aggressiveness of lymphoma cells.
Orbital lymphoma shows marked diffusion restriction on diffusion-weighted imaging (DWI) and appears hyperintense at high b-values (b=800-1000). Low signal on ADC map is noted and ADC values are typically in the range of 0.5-0.7 × 10⁻³ mm²/s. These low ADC values are the strongest quantitative parameter for distinguishing orbital lymphoma from other orbital masses (benign mixed tumor, cavernous venous malformation, pleomorphic adenoma, etc.). Increase in ADC values in treatment response monitoring indicates treatment efficacy.
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Marked diffusion restriction is noted in the orbital mass on DWI with low measured ADC value, consistent with orbital lymphoma.
A homogeneously enhancing mass growing by moulding to orbital structures is seen on contrast-enhanced CT. The mass grows conforming to the globe, extraocular muscles, and bony structures without causing bone destruction. This moulding pattern is the most typical growth feature of lymphoma and is distinguishing from aggressive tumors (carcinoma, sarcoma). The mass is generally of intermediate-to-high density with homogeneous structure. Calcification is rare. In lacrimal gland involvement, the gland appears diffusely enlarged and enhanced. Bilateral lacrimal gland involvement is highly typical for lymphoma.
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A homogeneously enhancing mass growing by moulding to orbital structures without bone destruction is noted on contrast-enhanced CT (moulding pattern), consistent with orbital lymphoma.
Orbital lymphoma appears as an isointense homogeneous mass relative to extraocular muscles on T1-weighted images. Mass margins are generally smooth without capsule formation. Internal necrosis or hemorrhage is rare, maintaining the tumor's homogeneous character. In lacrimal gland involvement, diffuse enlargement and loss of normal gland parenchyma are seen. The contrast difference between orbital fat and mass is clearly evaluated on T1 because fat is bright on T1 while lymphoma mass has intermediate signal.
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A homogeneous mass isointense to extraocular muscles is noted on T1-weighted images, and orbital lymphoma should be considered in the differential diagnosis.
Orbital lymphoma shows isointense or slightly hypointense signal on T2-weighted images. This T2 signal characteristic reflects the tumor's high cellularity and dense cellular packing. The degree of T2 hypointensity may correlate with tumor aggressiveness; more aggressive subtypes may show lower T2 signal. The mass has homogeneous structure and edema or necrosis is generally not associated. On fat-suppressed T2 sequences, the mass is clearly distinguished from orbital fat. This T2 signal pattern is distinguishing from benign lesions such as cavernous venous malformation (T2 hyperintense) and pleomorphic adenoma (T2 high signal).
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Isointense-to-slightly hypointense homogeneous signal in the orbital mass is noted on T2-weighted images, consistent with a highly cellular tumor (lymphoma).
FDG uptake of orbital lymphoma on FDG PET-CT varies depending on lymphoma subtype. Aggressive subtypes (diffuse large B-cell lymphoma) show high FDG uptake, while indolent subtypes (MALT lymphoma) may show low-to-moderate FDG uptake. The primary value of PET-CT is systemic staging: evaluation of cervical, axillary, mediastinal, abdominal lymph nodes, and extra-nodal involvement sites. PET-CT is the gold standard for bilateral orbital and systemic involvement evaluation. Decrease in FDG uptake in treatment response assessment indicates effective treatment.
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Increased metabolic activity in the orbital mass is noted on FDG PET-CT, and additional sites of involvement should be evaluated in systemic lymphoma screening.
Orbital lymphoma generally appears as a hypoechoic, homogeneous, well-defined mass on B-mode ultrasonography. Low-to-medium internal reflectivity and regular internal structure is characteristic on A-scan ultrasonography. The mass shows moulding to surrounding structures and absence of bone destruction can also be evaluated by ultrasonography. Low-to-moderate vascularity may be seen on Doppler ultrasonography. In lacrimal gland involvement, diffuse hypoechoic enlargement is seen. Ultrasonography is useful as a screening and follow-up tool but MRI is required for deep orbital and intracranial extension assessment.
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A well-defined, hypoechoic, homogeneous mass is noted on orbital ultrasonography with low-to-medium internal reflectivity on A-scan, consistent with orbital lymphoma.
Criteria
Most common orbital lymphoma subtype (60-80%). Low-grade B-cell non-Hodgkin lymphoma. Indolent course, low Ki-67 index (<10%). Conjunctiva and lacrimal gland are the most common sites. Chlamydia psittaci association has been demonstrated in some geographic regions.
Distinct Features
Local radiation therapy (24-30 Gy) is primary treatment with excellent local control (95%+). Risk of systemic involvement is low but long-term follow-up is required. May show low uptake on FDG PET-CT. 5-year survival is over 90%.
Criteria
Aggressive high-grade B-cell lymphoma. Rapid growth, more prominent proptosis and pain. High Ki-67 index (>40%). Risk of systemic involvement is high. Shows high FDG uptake on FDG PET-CT.
Distinct Features
R-CHOP (rituximab + cyclophosphamide, doxorubicin, vincristine, prednisone) chemotherapy is standard treatment. Radiation therapy may be added as consolidation. Imaging may show more heterogeneous appearance and necrosis areas. Bone destruction is rare but more likely compared to MALT.
Criteria
Indolent B-cell lymphoma subtype. Accounts for 10-20% of orbital lymphomas. Nodular growth pattern is histologically characteristic. Systemic involvement is more common and Ann Arbor staging is required.
Distinct Features
Treatment approach is determined by disease stage and extent of involvement. Radiation therapy for localized disease, chemoimmunotherapy for widespread disease. May show chronic relapse-remission course. Transformation risk (conversion to DLBCL) is important in long-term follow-up.
Distinguishing Feature
Idiopathic orbital inflammation is usually painful (lymphoma is painless), shows rapid response to steroid treatment, and MRI may show extraocular muscle tendon involvement (tendon sparing in lymphoma) and scleral thickening. Diffusion restriction is more prominent in lymphoma with lower ADC values.
Distinguishing Feature
IgG4-related disease frequently involves the lacrimal gland and may mimic lymphoma. However, T2 hypointense areas due to fibrosis component are more prominent in IgG4, serum IgG4 is elevated, and storiform fibrosis + obliterative phlebitis on biopsy supports the diagnosis. Diffusion restriction may be seen in both.
Distinguishing Feature
Lacrimal gland pleomorphic adenoma is seen in younger patients (lymphoma in elderly), is well-encapsulated and shows hyperintense signal on T2 (isointense-hypointense in lymphoma). CT shows lacrimal fossa widening (bone remodeling) while bone changes are not typical in lymphoma. ADC values are higher in pleomorphic adenoma.
Distinguishing Feature
In orbital metastasis, a history of known primary malignancy is present, bone destruction is common (absent in lymphoma), and imaging findings are more heterogeneous. Enophthalmos may be seen in breast carcinoma metastasis (proptosis in lymphoma), bone lytic lesions in lung carcinoma. Clinical course is faster compared to lymphoma.
Urgency
urgentManagement
medicalBiopsy
NeededFollow-up
Tanı sonrası sistemik evreleme (PET-BT, kemik iliği biyopsisi). MALT lenfomada lokal radyoterapi sonrası 3-6 aylık aralıklarla klinik ve görüntüleme takibi. DLBCL'de kemoterapi sırasında ve sonrasında yakın takip.Orbital lymphoma diagnosis requires histopathological confirmation by biopsy because imaging findings alone are not diagnostic. Incisional biopsy (not excisional) is preferred because preservation of part of the tumor is important for treatment planning. Post-diagnosis systemic staging (PET-CT, bone marrow biopsy, complete blood count, LDH) is mandatory. Local radiation therapy (24-30 Gy) is standard treatment for MALT lymphoma with 95%+ local control. Systemic R-CHOP chemotherapy is required for aggressive subtypes (DLBCL). Treatment approach is individualized in bilateral orbital involvement or presence of systemic lymphoma. Long-term follow-up is important because of risk of late relapse and aggressive transformation in indolent lymphoma.
Biopsy is mandatory for diagnosis. MALT lymphoma is low-grade and treated with radiotherapy. Systemic lymphoma staging (PET-CT) is required. Prognosis is generally good (>90% 5-year survival for MALT lymphoma).