Answer
Several studies have shown the superiority of FDG-PET scanning over 67Ga scanning in the initial diagnosis of HD and NHL, as well as in the diagnosis of recurrent HD and NHL. As many as 100% of patients with a positive PET scan after chemotherapy have an early relapse, while in more than 80% of patients with a negative PET, long-term remission occurs. Most studies indicate that FDG-PET scanning results are significantly correlated with patient outcome, whereas the correlation for CT scanning is poorer.
FDG-PET scanning does not rely entirely on lymph size, as do anatomic imaging methods, but is dependent on levels of metabolic activity, which can be high enough to visualize even some small lesions. CT scanning often cannot be used to differentiate residual disease and posttherapeutic fibrosis. On the basis of a number of clinical results, FDG-PET is gaining increasing importance for staging, restaging, and monitoring treatment responses in malignant lymphomas.
FDG-PET scanning has high sensitivity for the detection of nodal involvement in HD and NHL and generally detects activity in all abnormal lymph nodes identified on CT scans. FDG-PET scanning also has the advantage of detecting additional nodal disease, which might be missed on CT scans because of size criteria; this is particularly true for small mesenteric lymph nodes. The sensitivities reported for FDG-PET scanning in the detection of nodal disease are 62-100%; the variability is related to the fact that FDG-PET scanning's sensitivity differs according to the particular histologic grade of lymphoma that is present. Despite this range of sensitivities, FDG-PET scanning consistently has higher accuracy than CT scanning in the staging of lymphoma.
In a retrospective study of 56 patients (42 with mediastinal Hodgkin lymphoma and 14 with primary mediastinal B-cell lymphoma) to assess differences in clinical, laboratory, and FDG PET/CT metrics, lactate dehydrogenase (LDH) levels and several FDG PET/CT findings (tumor size, presence of necrosis, and degree of FDG uptake) were found to be helpful in discriminating mediastinal Hodgkin lymphoma from primary mediastinal B-cell lymphoma (PMBCL). [31]
However, another reretrospective study of FDG PET to assess response to therapy in 36 consecutive patients treated for PMBCL found that a positive interim FDG-PET/CT did not reflect persistence of active disease in the vast majority of PMBCL cases. The relapse rates were similar regardless of interim FDG-PET/CT results and interpretation criteria. [32] In NHL, extranodal disease generally worsens the prognosis. FDG-PET scanning detected 57% more extranodal sites of disease than can CT scanning.
A small study at 2 treatment sites found that coregistering FDG-PET and CT scans on treatment planning for lymphoma patients yielded changes in management, volume definition, and normal tissue dosimetry for a significant number of patients. [4]
F18 FDG-PET uptake variability within the liver and mediastinum during chemotherapy should be taken into account when this parameter is used to score the interim PET scans and to make decisions in defining response-adapted therapeutic strategies. The liver uptake increases in the interim period in comparison to a baseline study. Conversely, the stability of mediastinal uptake activity during therapy provides a more reliable benchmark for the response assessment. Finally, the intersubject’s variability of both parameters should be considered when point score models perform the visual evaluation of the interim PET. [16]
A study by Albano et al found that pulmonary MALT lymphoma is 18F-FDG avid in most cases, 18F-FDG avidity is correlated with tumor size, and single or multiple areas of consolidation are the most common pattern of presentation of lung MALT lymphoma on CT. [2]
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Posteroanterior (PA) chest radiograph in a man with thoracic non-Hodgkin lymphoma (NHL) shows mediastinal widening due to grossly enlarged right paratracheal and left paratracheal nodes.
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Posteroanterior (PA) chest radiograph in a 16-year-old male adolescent with thoracic non-Hodgkin lymphoma (NHL) shows subtle enlargement of the lower paratracheal lymph nodes.
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Nonenhanced CT scan through the mediastinum shows multiple enlarged lymph nodes in the prevascular space, in the right and left paratracheal region. Nodes in the left paratracheal region cause the trachea to be indented and narrowed on the left side. Note the small, bilateral pleural effusion.
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Nonenhanced CT scan through the mediastinum at the level of the carina shows enlarged tracheobronchial and subcarinal nodes. Note the small bilateral pleural effusion.
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Image shows gross enlargement of subcarinal lymph nodes, which causes the tracheal bifurcation to become splayed, and large hilar nodes. Small bilateral pleural effusions are present.
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Contrast-enhanced axial CT scan in a child shows hypoattenuating, enlarged, subcarinal lymph nodes with splaying of the tracheal bifurcation.
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Posteroanterior (PA) chest radiograph shows a large mass in the right parahilar region extending into the right upper and middle zones, with silhouetting of the right pulmonary artery. Smaller mass is seen in the periphery of the right lower zone. The masses did not respond to a trial of antibiotics. Core-needle biopsy of the larger lesion revealed NHL deposits in the lung.
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Lateral image shows a large mass in the anterior aspect of the right upper lobe of the lung.
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Image shows a normal mediastinum and lungs, destruction of the posterior aspect of the right seventh rib, and soft tissue swelling.
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Radiograph of a patient with non-Hodgkin lymphoma (NHL) of the ribs shows destruction of the rib and soft-tissue mass.
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Tomogram of the right lower chest wall demonstrates the lesion better than previous image in this patient with non-Hodgkin lymphoma (NHL) of the ribs.
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Anteroposterior (AP) view shows a collapsed vertebra in a patient with non-Hodgkin lymphoma (NHL) of the thoracic vertebrae.
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Lateral myelogram shows abrupt tapering of thecal sac caused by compression of soft tissue associated with the lymphomatous deposit in the thoracic vertebrae.
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Posterior bone scan shows no abnormally increased uptake in the thoracic vertebrae. Image shows an unusual pattern of non-Hodgkin lymphoma (NHL) of the upper thoracic vertebra.
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Image shows a right-sided, hemorrhagic pleural effusion. Cytologic and pleural biopsy results confirmed non-Hodgkin lymphoma (NHL).
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Nonenhanced axial CT scan shows biopsy-proved non-Hodgkin lymphoma (NHL) of the thymus, which appears as a hypoattenuating mass in the anterior mediastinum. Note the tracheal displacement to the right.
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This 28-year-old man was being evaluated for fever of unknown origin. Gallium-67 study shows extensive uptake in the mediastinal lymph nodes due to non-Hodgkin lymphoma (NHL).
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T1-weighted coronal MRIs of the thorax in a 55-year-old woman with lower dorsal pain. Note the signal-intensity changes in the body of D12; these are associated with a right-sided, large, paravertebral soft-tissue mass involving the psoas muscle. Biopsy confirmed non-Hodgkin lymphoma (NHL).
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T1-weighted coronal MRIs of the thorax in a 55-year-old woman with lower dorsal pain (same patient as in the previous image). Note the signal-intensity changes in the body of D12; these are associated with a right-sided, large, paravertebral soft-tissue mass involving the psoas muscle. Biopsy confirmed non-Hodgkin lymphoma (NHL).
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Positron emission tomography (PET) CT in an 80-year-old woman with diffuse, large B-cell NHL of the skin and subcutaneous tissues that recently transformed from prior low-grade non-Hodgkin lymphoma (NHL). CT scan of the lower neck shows several subcutaneous nodules of varying size with variable uptake on PET (arrows).
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Positron emission tomography (PET) CT in an 80-year-old woman with diffuse, large B-cell NHL of the skin and subcutaneous tissues that recently transformed from previous low-grade non-Hodgkin lymphoma (NHL) in the same patient as in the previous image. PET shows high level of uptake in the anterior subcutaneous nodule in the chest (white arrows). CT scan of similar nodules (arrowheads) on the anterior left chest does not show PET uptake; these may represent regions of lower-grade NHL. PET image of posterior lesions shows only mild uptake (gray arrow).
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Contrast enhanced axial CT showing extensive right hilar and posterior mediastinal lymphadenopathy due to thoracic NHL.
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Gallium-67 (67Ga) scan shows the intrathoracic lymphoma to be 67Ga avid.
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A PA chest radiograph in a 28-year-old woman who presented with weight loss, showing a cavitating lesion (mimicking tuberculosis) in the left midzone adjacent to the left hilum. Histology confirmed a large-cell NHL.
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An axial CT scan showing an intraparenchymal cavitating lung lesion adjacent to the anterior thoracic wall.
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Axial CT scans showing superior vena caval obstruction secondary to lymphadenopathy from NHL.
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Axial CT scans showing superior vena caval obstruction secondary to lymphadenopathy from NHL.
