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E2337. Extranodal Manifestations of Lymphoma on 18F-FDG PET/CT
Authors
  1. Qiubai Li; UT Southwestern Medical Center
  2. Daniella Pinho; UT Southwestern Medical Center
  3. Orhan Oz; UT Southwestern Medical Center
  4. Asha Kandathil; UT Southwestern Medical Center
Background
25 - 40% of patients with lymphoma present with involvement of anatomic sites other than lymph nodes, spleen, bone marrow and thymus. Reported sites of primary extranodal lymphoma include gastrointestinal tract (GIT), head and neck, orbit, central nervous system (CNS), lung, bone, skin, breast, testis, thyroid, and genitourinary tract (GUT). 18F FDG PET-CT is the standard for staging FDG-avid lymphomas. Identification of extranodal disease at initial diagnosis is crucial for the staging and management. A single site of extranodal lymphoma without nodal involvement is classified as Stage 1E and involvement of regional lymph nodes is classified as Stage 2E. There may be secondary extranodal involvement in later stages of primary nodal lymphoma. Histologic variants of extranodal lymphoma such as DLBCL and Burkitt’s lymphoma are FDG avid with the exception of MALT lymphoma, which involves the lungs and GI tract.

Educational Goals / Teaching Points
Aim: - To describe the spectrum of manifestations of primary extranodal lymphoma on 18F-FDG PET/CT and correlative CT and/or MRI images - To illustrate role of 18F-FDG PET/CT in staging extranodal lymphoma - To identify site-specific strengths and weakness of 18F-FDG PET/CT in evaluating extra nodal lymphoma

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Extranodal sites of involvement CNS: MR imaging is the ideal modality in the diagnosis, follow-up and monitoring treatment response of CNS lymphoma due to intense physiologic FDG uptake in the brain cortex that limits detection of primary CNS lymphoma. 18F-FDG PET/CT is often performed to assess systemic spread of primary CNS lymphoma. Head and Neck: Extranodal lymphoma can arise from the tonsils, mandible, hard palate, nasopharynx, parotid glands, nasal cavity, paranasal sinuses, pharynx, larynx, thyroid gland or ocular adnexa. It is important to differentiate physiologic FDG uptake from disease involvement. Chest: Mucosa-associated lymphoid tumor (MALT) arising from the bronchus is the most common histologic variant of primary pulmonary lymphoma. It can present as nodules, masses, endobronchial lesion, ground glass opacities or interstitial opacities with variable FDG uptake. DLBCL rarely presents as primary cardiac lymphoma. Breast: Primary extranodal NHL in the breast can mimic breast cancer. GU tract: Renal lymphoma can present as single or multiple renal lesions or involve the perinephric tissue. Rarely lymphoma can arise from the testes or ovaries. Bone: Primary bone lymphoma can present as solitary or multiple bone lesions. Skin: 18F-FDG PET/CT is very sensitive and specific in detecting both cutaneous and extra cutaneous lymphoma. GI tract: The stomach and small intestine are the most common sites of GI lymphoma. Lymphoma frequently presents with wall thickening, nodularity, luminal narrowing or aneurysmal dilatation. MALT lymphomas have low FDG avidity.

Conclusion
Awareness of common sites of involvement by primary extranodal lymphoma will help identify and stage the disease on 18F-FDG PET/CT.