Further Discussion
The definitive feature is the enhancement kinetics on CEUS. Both Intrapancreatic Accessory Spleen (IPAS) and Pancreatic Neuroendocrine Tumors (PNETs) are hypervascular. However, IPAS has a unique sinusoidal vasculature identical to the main spleen. On CEUS, this manifests as enhancement that is perfectly synchronous with the splenic parenchyma in the arterial phase and persists without any washout throughout the late vascular phases (often beyond 5-10 minutes), a "mirror" or "shadow" pattern. PNETs, while hypervascular, typically show early arterial enhancement followed by late (>60-90 seconds) and progressive washout. Pancreatic adenocarcinoma is characteristically hypovascular. Solid pseudopapillary neoplasms often show heterogeneous enhancement with cystic/necrotic components. The MRI findings (T2 hyperintensity, T2 "shine-through" on DWI, and subtle persistent enhancement) are also highly consistent with splenic tissue. Therefore, the CEUS pattern is pathognomonic for IPAS.
Considering the coexistent simple pancreatic cyst found incidentally, what is the most appropriate clinical management for this patient?
Additional Discussion:
The simple pancreatic cyst is a common, incidental finding with a very low malignant potential, especially when sub-centimeter and without worrisome features. The solid lesion has CEUS features diagnostic for IPAS, a benign congenital anomaly. Therefore, the combination does not signify a complex neoplasm but two separate, incidental, and benign findings. Aggressive management (options 1 and 2) is not indicated and would be invasive and unnecessary. Somatostatin receptor imaging (option 4) is not indicated without clinical or laboratory suspicion of a PNET. The recommended management is conservative follow-up to document stability, which reinforces the benign diagnosis and provides reassurance.
Conclusion:
This case highlights the critical role of CEUS in characterizing incidental pancreatic lesions. The hallmark of an Intrapancreatic Accessory Spleen is its enhancement kinetics, which are perfectly synchronous and identical to the main splenic parenchyma on all vascular phases, including the very late phase (up to 9 minutes in this case). This pattern reliably distinguishes it from hypervascular neoplasms like PNETs, which exhibit late washout. Recognizing this pattern can prevent misdiagnosis, unnecessary invasive procedures, and anxiety for the patient.
Conflicts of Interest:
Meloni MF reports honorary lectures for Bracco. The other authors declare no conflict of interest.
References
- Kim SH, Lee JM, Han JK, Kim KW, Cho KC, Choi BI. Intrapancreatic Accessory Spleen: Findings on MR Imaging, CT, US and Scintigraphy, and Pathological Analysis. Korean J Radiol. 2008;9(2)162-174
- Munk-Madsen MZ, Zakarian K, Oturai PS et al. Intrapancreatic accessory spleen mimicking malignanttumor: three case reports. Acta Radiol Open 2019;8:2058460119859347
- Fujimoto T. Letter to the Editor: Usefulness of contrast-enhanced ultrasound-Intrapancreatic accessory spleen mimicking malignant tumor. Acta Radiol Open 2020; 9(1):2058460120902311.
- Ota T, Ono S. Intrapancreatic accessory spleen: diagnosis using contrast-enhanced ultrasound. Br J Radiol 2004;77 (915):148-149
- Makino Y, Imani Y, Fukuda K, et al. Sonazoid-enhanced ultrasonography for the diagnosis of an intrapancreatic accessory spleen: a case report . J Clin Ultrasound 2011;39: (6):344-347
Additional Discussion:
The simple pancreatic cyst is a common, incidental finding with a very low malignant potential, especially when sub-centimeter and without worrisome features. The solid lesion has CEUS features diagnostic for IPAS, a benign congenital anomaly. Therefore, the combination does not signify a complex neoplasm but two separate, incidental, and benign findings. Aggressive management (options 1 and 2) is not indicated and would be invasive and unnecessary. Somatostatin receptor imaging (option 4) is not indicated without clinical or laboratory suspicion of a PNET. The recommended management is conservative follow-up to document stability, which reinforces the benign diagnosis and provides reassurance.
Conclusion:
This case highlights the critical role of CEUS in characterizing incidental pancreatic lesions. The hallmark of an Intrapancreatic Accessory Spleen is its enhancement kinetics, which are perfectly synchronous and identical to the main splenic parenchyma on all vascular phases, including the very late phase (up to 9 minutes in this case). This pattern reliably distinguishes it from hypervascular neoplasms like PNETs, which exhibit late washout. Recognizing this pattern can prevent misdiagnosis, unnecessary invasive procedures, and anxiety for the patient.
Conflicts of Interest:
Meloni MF reports honorary lectures for Bracco. The other authors declare no conflict of interest.
References
- Kim SH, Lee JM, Han JK, Kim KW, Cho KC, Choi BI. Intrapancreatic Accessory Spleen: Findings on MR Imaging, CT, US and Scintigraphy, and Pathological Analysis. Korean J Radiol. 2008;9(2)162-174
- Munk-Madsen MZ, Zakarian K, Oturai PS et al. Intrapancreatic accessory spleen mimicking malignanttumor: three case reports. Acta Radiol Open 2019;8:2058460119859347
- Fujimoto T. Letter to the Editor: Usefulness of contrast-enhanced ultrasound-Intrapancreatic accessory spleen mimicking malignant tumor. Acta Radiol Open 2020; 9(1):2058460120902311.
- Ota T, Ono S. Intrapancreatic accessory spleen: diagnosis using contrast-enhanced ultrasound. Br J Radiol 2004;77 (915):148-149
- Makino Y, Imani Y, Fukuda K, et al. Sonazoid-enhanced ultrasonography for the diagnosis of an intrapancreatic accessory spleen: a case report . J Clin Ultrasound 2011;39: (6):344-347
