18F-Fluorodeoxyglucose positron emission tomography computed tomography detection threshold in follicular lymphoma: A
Sarah Péricart1, Guillaume Martin-Blondel, Camille Franchet
1Departement de Pathologie, Institut Universitaire du Cancer Oncopole de Toulouse Institut National de la Sante et de la Recherche Médicale, U1037, Centre de Recherches en Cancérologie de Toulouse U1037 and Laboratoire d'Excellence (Labex Toucan) Université Paul Sabatier Departement des maladies Infectieuses et tropicales Service de médecine Nucléaire, Centre Hospitalier et universitaire de Toulouse Purpan, Place du Dr Baylac, Toulouse, France.
Insights
Follicular lymphoma in situ, even with few cells, can show high 18F-Fluorodeoxyglucose avidity on PET scans. This suggests the tumor microenvironment contributes to hypermetabolism, necessitating BCL2 immunohistochemistry on suspicious lymph nodes.
Area of Science:
- Oncology
- Nuclear Medicine
- Pathology
Background:
- Follicular lymphoma in situ (FLIS) is characterized by reactive germinal centers with minimal lymphoma cell infiltration.
- These lymphoma cells can exhibit significant 18F-Fluorodeoxyglucose (FDG) uptake, a marker of metabolic activity.
Observation:
- A 70-year-old patient presented with symptoms suggestive of paraneoplastic polymyalgia rheumatica.
- Positron emission tomography (PET) imaging revealed high FDG uptake in inguinal lymph nodes (SUVmax 8.6 and 5.8).
- Histological examination of the PET-positive lymph nodes confirmed subtle infiltration by FLIS with very low tumor cell volume.
Findings:
- Low-volume FLIS can demonstrate hypermetabolism detectable by FDG-PET.
- The tumor microenvironment may play a role in the observed high FDG avidity.
- Corticosteroid therapy was initiated for the patient.
Implications:
- Systematic immunohistochemistry for BCL2 should be considered for PET-positive lymph nodes with seemingly normal morphology.
- Long-term follow-up is crucial to monitor for potential clinical progression of FLIS.
- This case highlights the diagnostic utility of integrating PET imaging with histopathology for early FLIS detection.
Rationale:
Follicular Lymphoma in situ is generally identified as reactive follicular hyperplasia in which some of the hyperplastic germinal centers are colonized by few lymphoma cells. These cells can be detected through their strong 18F-Fluorodeoxyglucose avidity.
Patient Concerns:
We report the case of a 70 year-old patient with arthralgia, weight loss and chronic fever over two months. A paraneoplastic polymyalgia rheumatica was initially suspected on abnormal 18F fluoro-deoxyglucose positron emission tomography (PET) pictures in two inguinal lymph nodes with a standardized uptake value at 8.6 and 5.8.
Diagnoses:
The PET lymph nodes were removed and histological examination revealed subtle lymph nodes infiltration by follicular lymphoma in situ. The absolute number of the follicular lymphoma cells determined using virtual imaging and 3D reconstruction appeared very low with a total tumor cell volume estimated at around 0.026 mm for one lymph node and 0.041 mm for the other.
Interventions:
The patient has been treated by corticotherapy alone.
Outcomes:
A long-time follow-up should be highly suggested for this patient to avoid any risk of clinical progression to follicular lymphoma.
Lessons:
Our findings show that low amounts of follicular lymphoma cells in reactive germinal center may reach a threshold of hypermetabolism detectable with positron emission tomography imaging, suggesting that tumor microenvironment also accounts for such as strong fluoro-deoxyglucose avidity. Thus, a systematic immunohistochemistry with anti-BCL2 antibodies should be performed on PET positive lymph node with apparent normal morphological features.
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