Fluorine-18 fluorodeoxyglucose PET-CT for extranodal staging of non-Hodgkin and Hodgkin lymphoma

PURPOSE

We aimed to evaluate the role of fluorine-18 fluorodeoxyglucose positron emission tomography-computed tomography (¹⁸F-FDG PET-CT) involving care-dose unenhanced CT to detect extranodal involvement in patients with non-Hodgkin and Hodgkin lymphoma.

MATERIALS AND METHODS

Lymphoma patients (35 Hodgkin lymphoma, 75 non-Hodgkin lymphoma) who were referred for ¹⁸F-FDG PET-CT imaging, following a diagnostic contrast-enhanced CT (CE-CT) performed within the last month, were included in our study. A total of 129 PET-CT images, and all radiologic, clinical, and pathological records of these patients were retrospectively reviewed.

RESULTS

In total, 137 hypermetabolic extranodal infiltration sites were detected by ¹⁸F-FDG PET-CT in 62 of 110 patients. There were no positive findings by CE-CT that reflected organ involvement in 40 of 137 ¹⁸F-FDG-positive sites. The κ statistics revealed fair agreement between PET-CT and CE-CT for the detection of extranodal involvement (κ=0.60). The organs showing a disagreement between the two modalities were the spleen, bone marrow, bone, and thyroid and prostate glands. In all lesions that were negative at CE-CT, there was a diffuse ¹⁸F-FDG uptake pattern in the PET-CT images. The frequency of extranodal involvement was 51% and 58% in Hodgkin and non-Hodgkin lymphoma patients, respectively. There was a high positive correlation between the maximum standardized uptake values of the highest ¹⁸F-FDG-accumulating lymph nodes and extranodal sites (r=0.67) in patients with nodal and extranodal involvement.

CONCLUSION

¹⁸F-FDG PET-CT is a more effective technique than CE-CT for the evaluation of extranodal involvement in Hodgkin and non-Hodgkin lymphoma patients. PET-CT has a significant advantage for the diagnosis of diffusely infiltrating organs without mass lesions or contrast enhancement compared to CE-CT.Lymphomas are common hematological malignancies that predominantly affect the lymph nodes. However, both non-Hodgkin lymphoma (NHL) and Hodgkin lymphoma (HL) may affect any organ or tissue in the body. The lymphomatous infiltration of tissues other than the lymph nodes or lymphoid organs is described as extranodal lymphoma. The most common sites of lymphomatous infiltration are skin, stomach, spleen, Waldeyer’s ring, central nervous system, bone, and lungs. The distribution and prevalence of affected organs vary according to the histological type and stage of the disease (1–4).The presence of extranodal involvement is very important for staging NHL and HL. In general, extranodal involvement is more common in NHL than in HL, while it is frequently observed in recurrent disease and immune deficiency-related lymphomas (2–4). Moreover, primary and secondary extranodal diseases have different prognostic implications. Lymphomas that initially appear to have the bulk of the disease at extranodal sites are described in primary extranodal lymphoma and categorized as stage I or II. In secondary extranodal lymphoma, there is secondary involvement of the extranodal sites from primary nodal disease, which is categorized as stage III or IV. Except for the thymus and spleen, extranodal infiltration also indicates stage IV disease in HL. All of these data demonstrate the vital importance of diagnosis of extranodal lymphoma when designing treatment protocols at primary staging or restaging (3–5).Cross-sectional anatomical imaging techniques, particularly computed tomography (CT), have been the primary modality for the diagnosis, staging, restaging, and follow-up of patients with lymphoma. However, these modalities have several limitations when detecting nodal or extranodal disease, because CT is based only on anatomical structural changes, such as the enlargement of lymph nodes or organs, presence of masses, and abnormal contrast enhancements. In NHL or HL, these structural abnormalities are detected in 60% to 90% of patients by CT (6–8). Normal-sized organs or nodes and diffuse lymphomatous infiltrations without mass effects reduce the sensitivity of anatomical imaging modalities.Fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography-computed tomography (PET-CT) is a hybrid imaging technique that simultaneously provides functional and anatomical information. This provides a significant advantage for the evaluation of lymphoproliferative malignancies, particularly for the detection of lymphomatous involvement in organs and nodes of normal size without any mass. Several studies suggest that the sensitivity and specificity of ¹⁸F-FDG PET-CT for the assessment of nodal and extranodal involvement were higher than those of standard contrast-enhanced CT (CECT) (3, 4, 7–11). These benefits make ¹⁸F-FDG PET-CT the standard imaging technique for the initial staging, therapy response evaluation and restaging of patients with lymphoma.The aim of this study was to evaluate the utility of ¹⁸F-FDG PET-CT involving care-dose unenhanced CT for the detection of extranodal involvement in patients with NHL and HL. The ¹⁸F-FDG PET-CT results were retrospectively compared with the diagnostic CE-CT data; follow-up results were used as a reference standard.