By the advantage of PET/CT to demonstrate the biological function of the tumor before anatomical changes took place, a PET/CT scan enables physicians to more accurately diagnose and stage patients with esophageal cancer thus changing in clinical management of a significant number of patients avoiding unnecessary surgery [7].
In the current study, PET/CT had changed the stage group of 8 patients out of 19 (40%). Six of 8 patients were upstaged while 2 of 8 were downstaged; this was achieved by its greatest ability to detect distant metastases in 6 patients with esophageal cancer missed by CECT. This results led to the upstaging of these patients from stage III to stage IV.
As a general rule, all stage 0, I, and II are considered resectable. Most stage III cancer, which was the commonest stage for presentation of esophageal cancer in this study, are potentially resectable, even when they have spread to the nearby lymph nodes as long as cancer has not grown into important adjacent structures such as the lung, trachea, heart, aorta and spine. Cancer that has spread into these nearby important structures or that has spread to the distant lymph nodes is considered unresectable, so treatment other than surgery is usually the best option [8].
The aforementioned results are in accordance with those previously concluded that the ability of PET/CT to identify otherwise occult metastases has led to alter staging in up to 30% of esophageal cancer cases [9, 10].
The statistical parameters of the current study displayed sensitivity, specificity, PPV, NPV, and accuracy of PET/CT were 100%, 83%, 96%, 100%, and 96%, while those of CECT were 73%, 100%, 100%, 50%, and 79%, respectively in detecting distant metastatic diseases.
As regards the regional lymph node, no significant statistical differences could be detected in the current study between both modalities. This may be due to the small study sample.
The current study showed sensitivity, specificity, PPV, NPV, and accuracy for PET/CT were 68%, 82%, 68%, 82%, and 79% while those of CECT were 53%, 95%, 82%, 80%, and 82%, respectively.
These do not correspond with the previous studies done by [11, 12] as the authors concluded that PET/CT has similar specificity but significantly greater sensitively and accuracy than CECT for detection of LN metastases in staging esophageal cancer.
PET/CT sensitivity, specificity, and accuracy for metastatic LN detection were 52%, 94%, and 84%, respectively comparing to 15%, 97%, and 77% of CECT, respectively.
Limitations of the study
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1.
This study has its limitations as the staging of esophageal cancer was adapted only on patients with stage T3 which was the commonest stage group of presentation of esophageal cancer in this study.
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Small sample size which limits its statistical power.
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Due to limited spatial resolution, PET/CT could result in false negative of regional lymph nodes which are in direct vicinity of the tumor, as the avid uptake by the tumor may obscure the peritumoral node. However, the utility of PET/CT over CECT in regional LN detection needs further studies to improve its diagnostic accuracy.
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4.
High cost of PET/CT scan.
In addition to PET/CT scans, MRI with the functional feature of diffusion-weighted imaging (DWI) is another advancing imaging technology, which has current and future potential to overcome the limitations of conventional staging methods in patients with esophageal carcinoma [13].
MRI possessed the advantage including multiparameter imaging, lack of ionizing radiation, safer contrast agent, and the ability to determine the functionality of tumors with DWI. The technique is applied in whole-body MRI (WBMRI) DWI. Compared with PET/CT, WBMRI has similar accuracy in detecting the primary tumor, nodal deposits, and metastatic disease. In a study done by [14], the PET-CT and WBMRI detected the primary tumor in 46 of 49 (94%) and 48 of 49 (98%) patients, respectively. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of nodal metastasis detection in patients undergoing surgery (n = 18) were 27%, 100%, 100%, 47%, and 56% for PET-CT compared with 30%, 100%, 100%, 53%, and 61% for WBMRI.
The investigation of WBMRI in esophageal carcinoma is still limited and it is still early to derive a conclusion. However, the use of WBMRI in systemic evaluation of esophageal cancer has gradually increased [15].