Solid Pseudopapillary Neoplasm of the Pancreas Showing Spontaneous Regression Followed by Regrowth: A Case Report

Solid pseudopapillary neoplasm (SPN) of the pancreas is a rare, low-grade malignant tumor. Although SPNs generally exhibit indolent behavior, spontaneous regression detected on CT imaging is exceedingly rare, and to the best of our knowledge, regrowth following regression has not been previously reported.

A 33-year-old woman was referred to Kansai Medical University following the detection of liver dysfunction during a routine medical checkup. Imaging revealed a well-demarcated 20-mm mass in the pancreatic body, and an endoscopic US-guided biopsy confirmed SPN. Surgical resection was initially planned but postponed because of a COVID-19 infection in a fellow inpatient. During follow-up, the tumor showed spontaneous regression and became undetectable on imaging at 4 months. However, MRI at 16 months revealed tumor regrowth, which became clearly visible on T2-weighted imaging by 23 months, measuring 15 mm. At 24 months, a laparoscopic spleen-preserving distal pancreatectomy was performed. Histopathology confirmed SPN with intratumoral hemorrhage and characteristic pseudopapillary architecture. Complete resection was achieved, and the patient's postoperative course was uneventful.

This case illustrates that SPN can regress spontaneously, yet subsequently regrow, underscoring the need for careful long-term imaging surveillance even after apparent tumor shrinkage.