....Bondeson et al.[10] were the first to correctly diagnose SPT by preoperative transabdominal FNA. Subsequently, SPTs have also been studied by preoperative, sonographically guided, percutaneous aspiration.[11] However, SPT has not been diagnosed previously by EUS-FNA, as in the 2 cases presented.
The cytologic features of SPT of the pancreas are distinctive and allow differentiation from other lesions.[11] These include highly cellular aspirates composed of small, uniform epithelial cells with oval nuclei, fine chromatin, and small nucleoli. The cells are arranged as papillary structures with delicate fibrovascular cores, and there may be a layer of myxoid material between the core and lining epithelial cells. Cytologic features were diagnostic in each of these 2 cases and were confirmed by surgical resection.
By immunohistochemistry, SPTs are usually positive for vimentin, alpha-1-antitrypsin, alpha-1-antichymostrypsin, and neuron specific enolase. Approximately one third are keratin positive, whereas some express other neuroendocrine markers such as synaptophysin. Chromogranin has been consistently reported as negative. Recently, SPTs have been described that also stain positive for beta catenin.[12] In both cases, there was a pattern consistent with SPT, although in the second case, there were reportedly rare cells positive for chromogranin.
There is no known correlation between tumor size and metastatic potential. However, in tissue sections, the presence of venous invasion and large necrotic clusters may be indicative of an increased risk of malignancy.[13] SPTs have an excellent prognosis with a low potential for local invasion or metastasis. At presentation, approximately 85% are limited to the pancreas with metastases in only 10% to 15% of cases.[8] [14] Over 95% of SPTs limited to the pancreas may be cured by complete surgical resection. [15] Long-term survival with a 15-year follow-up has been reported after surgical resection of both primary tumors and metastatic disease that is primarily found in the liver.[16] Long-term survival has also been noted for patients with residual disease.[13] [17]
A common reason for performing EUS-FNA of small or incidentally found pancreatic lesions is that most patients with such lesions are reluctant to undergo major pancreatic surgery, and most community surgeons hesitate to consider such an operation without a preoperative diagnosis of a potentially malignant lesion, as was the situation in Case 1. This is especially the case for patients who are poor candidates for surgery. In addition, EUS-FNA can guide surgical management, because a potentially benign tumor (e.g., neuroendocrine, SPT) may be treated by local excision, in contrast to an adenocarcinoma, which would require a more extensive resection. This was also the result in Case 1, as the patient underwent a central pancreatectomy.
EUS features alone cannot reliably distinguish between benign and malignant cystic lesions of the pancreas, making preoperative FNA desirable.[18] There is increasing evidence that EUS-FNA may help to distinguish benign from potentially malignant pancreatic cysts through analysis of cyst fluid, not only cytologic evaluation, but also for amylase, lipase, and CEA.[19] This was the situation in Case 2 in which there was a question whether the lesion might be a pseudocyst from previous clinically silent pancreatitis.
EUS-FNA is not always needed for evaluation of potentially resectable pancreatic masses. When there is an obvious large mass lesion, enlargement of a lesion demonstrated by serial imaging studies, a lesion that is clearly the cause of symptoms, or when the patient and the surgeon are comfortable with resection based on imaging characteristics alone, the diagnostic information provided by EUS-FNA ultimately may not change the need for surgical resection. Also, EUS-FNA has potential complications (1% complication rate for solid lesions, 14% for cystic lesions), which could make subsequent surgery more difficult or even impossible.[20]
In summary, solid-pseudopapillary neoplasm of the pancreas should be considered in young, asymptomatic women with incidentally detected pancreatic body masses. EUS-FNA can accurately diagnose SPTs of the pancreas and may help guide surgical management.
Acknowledgment
Cynthia Behling, MD, PhD, for pathology and manuscript review.
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