Positive somatostatin receptor scintigraphy in accessory spleen mimicking recurrent neuroendocrine tumor

Impact of PET data driven respiratory motion correction and BSREM reconstruction of 68Ga-DOTATATE PET/CT for differentiating neuroendocrine tumors (NET) and intrapancreatic accessory spleens (IPAS)

To evaluate whether quantitative PET parameters of motion-corrected ⁶⁸Ga-DOTATATE PET/CT can differentiate between intrapancreatic accessory spleens (IPAS) and pancreatic neuroendocrine tumor (pNET). A total of 498 consecutive patients with neuroendocrine tumors (NET) who underwent ⁶⁸Ga-DOTATATE PET/CT between March 2017 and July 2019 were retrospectively analyzed. Subjects with accessory spleens (n = 43, thereof 7 IPAS) and pNET (n = 9) were included, resulting in a total of 45 scans. PET images were reconstructed using ordered-subsets expectation maximization (OSEM) and a fully convergent iterative image reconstruction algorithm with β-values of 1000 (BSREM₁₀₀₀). A data-driven gating (DDG) technique (MOTIONFREE, GE Healthcare) was applied to extract respiratory triggers and use them for PET motion correction within both reconstructions. PET parameters among different samples were compared using non-parametric tests. Receiver operating characteristics (ROC) analyzed the ability of PET parameters to differentiate IPAS and pNETs. SUVmax was able to distinguish pNET from accessory spleens and IPAs in BSREM₁₀₀₀ reconstructions (p < 0.05). This result was more reliable using DDG-based motion correction (p < 0.003) and was achieved in both OSEM and BSREM₁₀₀₀ reconstructions. For differentiating accessory spleens and pNETs with specificity 100%, the ROC analysis yielded an AUC of 0.742 (sensitivity 56%)/0.765 (sensitivity 56%)/0.846 (sensitivity 62%)/0.840 (sensitivity 63%) for SUVmax 36.7/41.9/36.9/41.7 in OSEM/BSREM₁₀₀₀/OSEM + DDG/BSREM₁₀₀₀ + DDG, respectively. BSREM₁₀₀₀ + DDG can accurately differentiate pNET from accessory spleen. Both BSREM₁₀₀₀ and DDG lead to a significant SUV increase compared to OSEM and non-motion-corrected data.

Spleen Scan for 68Ga-DOTATOC PET-Positive Pancreatic Tail Lesion: Differential Diagnosis of Neuroendocrine Tumor from Accessory Spleen

⁶⁸Ga-DOTATOC PET/CT is widely used as a functional imaging technique in the detection and characterization of neuroendocrine tumors (NETs). Pancreatic NET and intrapancreatic accessory spleen (IPAS) have similar radiologic characteristics in anatomical imaging and usually show high uptake of ⁶⁸Ga-DOTATOC. Thus, it is challenging to make a differential diagnosis between NET and IPAS when the tumor-like lesion is located in the pancreatic tail. Here, we present a case of ⁶⁸Ga-DOTATOC PET-positive pancreatic tail lesion with high arterial enhancement on CT and MRI. Since ^99mTc-labeled damaged red blood cell does not accumulate on NET, a negative spleen scan finding was a crucial diagnostic step to decide surgical resection, which was histologically proven as insulinoma. Our case shows a promising role of additional use of spleen scan with SPECT/CT for the differential diagnosis of ⁶⁸Ga-DOTATOC PET-positive pancreatic NET from the accessory spleen.

[Intrapancreatic accessory spleen]

BACKGROUND

Accessory spleen is the human growth anomaly, which appears in embryogenesis and frequently becomes an accidental finding during prophylactic medical examination. Pancreatic tail - the second frequent localization after the splenic hilus. Intrapancreatic accessory spleen can mimic the pancreatic tumor.

AIM

To demonstrate case series of intrapancreatic accessory spleen in course of differential diagnostic with pancreatic neuroendocrine tumor and metastasis of renal - cell cancer.

MATERIAL AND METHODS

Three patients with intrapancreatic accessory spleen were observed in abdominal department #1 A.V.Vishnevsky Institute of Surgery, - two females and one male.

RESULTS

Two patients were surgically treated: in the first case basing on preoperative anamnesis and diagnostic data diagnosis of renal - cell cancer metastasis was established, in the second case - nonfunctional pancreatic neuroendocrine tumor. In both cases robotic distal pancreatectomy was performed. There were no conversions. Postoperative recovery was accompanied by clinicaly not relevant pancreatic fistulas, which didn't increase length of hospitalization. In the third case during CT and MRI diagnosis of intrapancreatic accessory spleen was determined. Surgical treatment wasn't performed. Control examination showed an absence of dynamic of characteristics and growth.

CONCLUSION

Described cases demonstrate difficulty of differential diagnostics of tumor - like mass. Neuroendocrine tumors, renal - cell cancer metastases, solid pseudopapillary neoplasms and accessory spleen can have similar CT-characteristics. In appearance of differential diagnostic difficulties minimally invasive surgical treatment has to be performed.