SPN are rare, with approximately 2744 reported cases . US and CT are the most used imaging methods for diagnosis and represent approximately 80% of imaging studies for the diagnosis of SPN. In the past few decades, the use of MRI has increased substantially, as has EUS, but it still accounts for only 5% of the imaging methods used for the diagnosis of SPN. In addition, there are few studies that determine the additional benefit offered by the EUS-FNA to imaging tests such as CT and MRI . The benefit in the use of EUS in patients with solid and cystic pancreatic tumors with a yield approaching 78.8% and 71.4%, respectively, has been proven [17, 18]. Therefore, the inclusion of EUS-FNA increases the diagnostic accuracy of this type of tumor.
The results of this study highlight the difficulty of CT, MRI and EUS in correctly classifying the SPN using only the image resources, with a diagnostic performance of 21.95%, 28.88%, 64.71% respectively. These results are similar to another recent study, which was 23.5% and 41.2% for CT and EUS, respectively . When we include the results of EUS-FNA, there is an increase in the diagnostic performance of CT (72.16%) and MRI (65.23%), rising up to 94.11% in both methods.
Classically, SPN are described as circumscribed, hypoechoic, solid, heterogeneous masses and eventually with a cystic component. However, this appearance presents in just 60% of patients, with a predominantly solid lesion found in 32% of cases, suggesting a more classic appearance associated with a neuroendocrine tumor . In our series, the solid, solid/cystic, and cystic morphology was 52.9%, 41.1% and 7.8% respectively. SPN can mimic other pancreatic tumors, which can lead to diagnostic challenges .
This fact can be observed in our study, as CT and EUS suspected the presence of NF-NET in (9.75%) and (7.8%), respectively, since the injuries identified by these exams had a predominantly solid component. When microcystic, SPN are similar to serous cystadenoma and can cause diagnostic confusion, which occurred in 4% of the cases examined by CT, MRI and EUS. The microcystic pattern must be recognized as part of the morphological spectrum of the SPN, which can lead to confusion regarding the presence of a serous cystadenoma . Previous CT and EUS studies, in which SPN was identified as other cystic lesions in the pancreas in up to 50% of cases, including benign lesions such as serous cystadenoma, confirm the findings of our study [13, 21, 22].
Some cases were interpreted as pseudocysts, highlighting the difficulty in determining the etiology of a cystic lesion based only on morphological characteristics of the image. This occurred in 7.31% and 15.55% of CTs and MRIs, respectively. Therefore, the importance of correctly classifying SPN is emphasized in this study, where 8 (33.3%) cysts were erroneously classified by CT, as pseudocysts (2), unspecific pancreatic cystic lesion (2), unspecific pancreatic cystic lesion with calcification (2), hematoma (1) and serous cystadenoma (1), all which have prognosis and management completely different from those adopted in SPN. The same happened with MRI / MRCP which was normal in 3 patients and identified unspecific pancreatic cystic lesion in 4 and pseudocyst in 3 patients.
In the literature, rupture of the SPN is associated with abdominal trauma or may be spontaneous, which is rare. To date, there have been only 3 cases of SPN with spontaneous rupture reported worldwide . In our series, we had two young patients with blunt abdominal trauma who underwent imaging exams that suspected hematoma (1) and pseudocyst (1). In these two cases, the EUS-FNA was crucial for the diagnosis of SPN, changing the management of these patients.
The aim of this study was to confirm the benefit of performing the EUS-FNA to increase the diagnostic performance of other conventional imaging tests such as CT and MRI. The EUS-FNA association increased diagnostic yield by almost 72.16% for CT and 65.23% for MRI. The results are similar to previous studies, which report a low sensitivity rate and absence of adverse events as in the current series . Regarding the adverse events resulting from the EUS-FNA, the first case of neoplastic cell implantation in the stomach was recently described . In our series, even after prolonged follow-up and interviews with patients and attending physicians, we did not observe this type of complication.
In the present series we found 2 cases of interest, as they had a strong suspicion of SPN on imaging exams. In the first, CT and MRI confirmed the diagnosis of pseudocyst, the EUS suspected SPN, and the EUS-FNA revealed NF-NET, which was confirmed by uncinate process resection. The second had CT, MRI and EUS image exams with SPN morphology (solid-cystic), the McH obtained by EUS-FNA confirmed the presence of SPN, but the operative piece confirmed NF-NET. In this case, the diagnosis by McH confirming SPN was performed only by HE, as there was not enough material to perform the IHC. These findings corroborate those found in the literature where the EUS-FNA performed on suspected SPN has excellent positive and negative predictive value, however the most common classification errors were with NF-NET which presents no clinical impact, just as it was observed in our series . In addition, in 177 patients studied by the EUS-FNA with suspected NF-NET, discrepancies were reported in 14 patients. In 4 of them the erroneous diagnosis was SPN. Accordingly, it is concluded that when an adequate sample is obtained, the most significant error is the incorrect classification, which is more often associated with SPN, but the damage associated with this diagnostic error is minimal .
The authors conclude that the isolated CT, MRI and EUS have low rates of correct diagnosis, but the association with EUS-FNA increases preoperative diagnosis and should be considered to rule out other pancreatic diseases such as NF-NET and SCA. These results suggest that patients who do not have a clear diagnosis of SPN, as is usually the case, should undergo EUS-FNA.