Many lymphomas are potentially curable with their prognosis depends on the stage and histological type [5]. CT scan used to be the cornerstone of imaging in lymphoma and was playing a crucial role in staging. Currently, the advances in molecular imaging with18F-FDG PET/CT scan have facilitated the diagnosis, staging, and response assessment in lymphoma patients [3]. Integrated PET/CT offers the advantage of combining functional and anatomical information and better attenuation correction [4]. The purpose of this study is to evaluate and compare the diagnostic performance of18F-FDG-PET/CT and CECT in the initial assessment of nodal and extra-nodal lymphomatous lesions. For this purpose, 100 patients diagnosed as lymphoma, which proved and classified by histopathology, were initially assessed and staged by CECT and 18F-FDG PET/CT (Figs. 8, 9, 10, 11, 12, 13, 14, 15, 16, and 17).
Regarding demographic data
In this study, the percent of patients having NHL 66% was higher than those having HL 34%; this was agreed with Raanani P et al. [15] whose study stated that the incidence of NHL 68% was higher than that of HL 35%. Also, Mozaffer R and Sadiqa S’s [16] study stated that 81.6% of their patients had NHL compared to 18.4% had HL. The same lymphoma type predilection was resulted by Roman E and Smith A [17]., while the study of Ricard F et al. [18] was carried out on 50.8% of cases with NHL and 49.2% with HL. In our study, NHL patients showed higher percent of males 39% than females 27%, also HL patients showed higher percent of males 22% than females 12% which emphasizes that male affection by both types of lymphoma is higher than female affection. The same sex predilection was resulted by Roman E and Smith A [17]. In our study, the higher percent 27% of cases was at the age group 50–< 60 years distributed as 24% had NHL and 3% had HL, while the lower percent 16% was at the age group of 20–< 30 years distributed as 12% had HL and 4% had NHL. This was agreed with Rodriguez B et al. [19] who stated that mean age of NHL 52± 15 while for HL the mean age was 31 ± 12.
Regarding total lesions
In our study, PET/CT diagnosed a total number of 545 involved regions with sensitivity 96.6%, specificity 98.8%, and accuracy 99% which was higher than those diagnosed by CECT; 439 involved regions with sensitivity 87.5%, specificity 85.7%, and accuracy 88%; la Fougere C et al.’s [20] study showed that PET/CT sensitivity 97% was higher than that of CECT 87.5%, also PET/CT specificity 99% was higher than that of CECT 85.5% as follows.
Regarding lymph nodal involvement
Our study resulted that PET/CT detected 312 true positive nodal group involvement with sensitivity 97.5%, specificity 94%, and accuracy 98% which was higher than CECT that detected 266 true positive nodal group involvement with sensitivity 83.1%, specificity 94%, and accuracy 89.6%, denoting significant difference (P > 0.005). Also, there were 46 false negative lymph node groups on CECT that decreased to only 3 groups by PET/CT. This was in agreement with Ricard F et al. [18] who stated that the sensitivity of PET/CT 99% was higher than the sensitivity of CECT 85% and also detected in their study 32 false negative lymph node groups by CECT that was corrected to 3 groups by PET/CT. Kwee T et al. [21] mentioned that some subtypes of lymphoma, namely small cell lymphocytic lymphoma/chronic lymphocytic leukemia may manifest as an increased number of small LNs, which declares that the size criteria used for the morphological assessment of lymph nodes in onco-hematology is insufficient and the metabolic status of lymph nodes by PET scan should be integrated even if their size seems to be normal on CT. The most common involved lymph node group, in this study, was the abdomino-pelvic group, while the least common was inguinal group. In agreement with our study, the most common affected LN group in Mozaffer R and Sadiqa S’s [16] study was the abdominopelvic group and the least common was the inguinal group, while the most common affected LN group in Rodriguez B et al.’s [19] study was the mediastinal group and the least common was the abdominal group.
Regarding splenic involvement
In this study, splenic involvement was truly positive in 79% of the patients by PET/CT with sensitivity 95.2%, specificity 98%, and accuracy 99% which was higher than CECT that detected true positive lesions in 47% of the patients with sensitivity 87.6%, specificity 86.6%, and accuracy76%. There were 22% of the patients with false negative results when assessed by CECT alone that was corrected to zero% by PET/CT. Close results were concluded by De Jong P et al. [22] who stated that PET/CT sensitivity and specificity in detecting splenic involvement were 100% and 95% versus 91% and 96% for CECT and confirmed the importance of metabolic status shown on PET/CT to discover splenic lesions with density similar to splenic tissue that could not be differentiated by CECT alone.
Regarding bone marrow involvement
In our study, bone marrow involvement was truly positive in 54% of the patients by PET/CT with sensitivity 93.7%, specificity of 96%, and accuracy 99% which was higher than CECT that detected true positive lesions in 41% of the patients with sensitivity 88.6%, specificity 86.2%, and accuracy 75%. There were 13% of the patients with false negative bone marrow involvement when assessed by CECT alone that was corrected to zero% by PET/CT. Also, the axial skeleton was the most commonly involved. In agreement with our results, Kwee T et al. [21] who mentioned that PET/CT is more sensitive 95% than CECT 86%. Othman A et al. [23] detected that bone marrow lymphoma mainly affecting the axial skeleton more than the appendicular skeleton.
Regarding other extranodal organ involvement
In our study, PET/CT detected 100 true positive extranodal organ involvements with sensitivity 94%, specificity 96.2%, and accuracy 99.5% which was higher than CECT that detected 85 true positive extranodal organ involvements with sensitivity 80%, specificity 88.6%, and accuracy 95.9%. There were 25 false negative extranodal organ involvements when assessed by CECT alone that was corrected to zero% by PET/CT. In agreement with our results, Ricard F et al. [18] stated that PET/CT sensitivity in detection of extranodal lymphomatous involvement 88% was higher than that of CECT alone 78% and that 9 false negative extranodal results by CECT were corrected to 5 by PET/CT. The most common involved extranodal organs in our study were lung 19%, GIT (mainly the stomach) 16%, liver 14% and renoadrenal 12%. In Das J et al. [22], the most frequently involved extranodal organs were GIT 14.8% (stomach is commonest site), followed by head and neck region 10% (including tonsils, pharynx, tongue, and orbit), lung 8%, and liver 5%, while Othman A et al.’s [23] study stated that the most common involved extranodal organs were head and neck 18% and GIT 15%. In this study, the organs showing the highest SUV max by PET/CT were lung 44.0, GIT (stomach) 33.4, head and neck (submandibular glands) 32.7, and renoadrenal (kidney) 30.8, while the organs showing the lowest SUV max were chest (thymus 2.80), chest (pleura 5.50), GIT (peritoneum 6.50), and liver 7.00. Othman A et al.’s [23] study resulted that the organs showing the highest SUV max were kidney 73.0, oropharynx 60.0, tonsils 40, and thyroid 37.0, while organs showing the lowest SUV max were pancreas 6.0, peritoneum 8.2, and suprarenal 9.0.
Regarding lymphoma staging according to Lugano classification
Differences in staging by PET/CT and CECT were found in our study. Discordant staging by both modalities was found in 23% of the patients. Lymphoma was upstaged by PET/CT in 17% of patients; with major changes in 12% (i.e., upstaging from stages I or II to stages III or IV) and downstaged in 6%. In agreement with our results, Ricard F et al. [18] who stated changes in the staging of 20% of the patients with upstaging in 17% and downstaging in 3% with major changes in 10%. Also, Othman A et al.’s [23] study mentioned that 10% of the patients were upstaged while 5% were downstaged after PET/CT. Luminari et al. [24] resulted that PET/CT helped in upstaging of 11% and downstaging of 1% of patients, while Raanani P et al.’s [15] study revealed changes in staging of 39% of the patients after PET/CT with 33% upstaging and 6% downstaging. This change in staging was explained by the higher ability of PET/CT over CECT in detection of involved sites either with normal morphology; as normal-sized lymph nodes or hidden and missed by its isodensity in extra nodal sites, by detection of increased activity in the form of high FDG uptake.