A 67-year-old woman in Japan had a CT scan because doctors wanted a closer look at an abnormal spot on her lung. The scan turned up something nobody was looking for: a mass measuring 31 by 23 millimeters, a little over an inch across, in her pancreas.
Its appearance pointed doctors toward a pancreatic neuroendocrine tumor, a type of growth that can be cancerous. After surgery, the real answer turned out to be far rarer. It was a schwannoma, a usually benign tumor of the sheath that wraps around nerves, and extensive bleeding inside it had made it look like something else.
The case, from gastrointestinal surgeons and a pathologist at Kameda Medical Center in Kamogawa, Chiba, was published online Oct. 5, 2026, as a clinical image report in Oxford Medical Case Reports. The title spells out the twist: a hemorrhagic pancreatic schwannoma mimicking a pancreatic neuroendocrine tumor.
A Mass That Looked Like Something Else
On contrast-enhanced CT, the growth had sharp, well-defined borders. Inside, it looked patchy, with darker areas mixed throughout. Its edges picked up more contrast dye as the scan went on, and a few small spots inside lit up about as brightly as nearby blood vessels.
That picture fits a pancreatic neuroendocrine tumor, or pNET, a growth that arises from the hormone-producing cells of the pancreas. The National Cancer Institute describes these tumors as uncommon cancers, with about 1,000 new cases a year in the United States, accounting for less than 2% of pancreatic malignancies.
The report does not describe any symptoms tied to the mass. The woman came to medical attention only because of the lung finding, and the authors did not say what that lung spot turned out to be.
Ruling Out the Usual Suspects
Before operating, the team ran two specialized nuclear medicine scans to narrow the possibilities. A somatostatin receptor scan, which often lights up neuroendocrine tumors because many carry receptors for the hormone somatostatin, came back negative.
That result helps but does not settle the matter. The National Cancer Institute notes that this type of scan is less useful for finding insulinomas, a pNET subtype that often has few of those receptors.
The second test, a scan using a tracer called MIBG, showed only faint uptake. The NCI describes the MIBG scan as a tool for finding neuroendocrine tumors such as paragangliomas, some of which release excess adrenaline and noradrenaline. After an endocrinology consultation, a hormone-producing paraganglioma was considered unlikely.
Together, the scans made both pNET and paraganglioma less likely, but they did not provide a firm diagnosis. The surgeons went ahead with laparoscopic enucleation, a minimally invasive operation that removes the tumor itself while sparing the surrounding pancreas.
The Microscope Delivered the Real Diagnosis
Once the tumor was out, the explanation became clear. The well-defined mass contained extensive internal bleeding and degeneration. Under the microscope, pathologists saw wavy, spindle-shaped cells arranged in alternating dense and loose patterns, known as Antoni A and Antoni B areas, a classic signature of schwannoma. The cells showed no significant atypia or signs of rapid division.
Special stains confirmed it. The tumor tested positive for S100, a protein found in Schwann cells, and negative for synaptophysin, chromogranin A, and INSM1, markers commonly used to identify neuroendocrine tumors.
Schwannomas grow from Schwann cells, which form the protective sheath around nerves. Mayo Clinic describes schwannoma as the most common type of benign peripheral nerve tumor in adults and notes that these tumors are rarely cancerous.
The woman recovered without complications and went home seven days after the operation.
Why a Rare Tumor Is Easy to Mistake
In the pancreas, schwannoma is a true outlier. The authors call it an extremely rare tumor, accounting for about 0.03% of all pancreatic tumors.
That rarity is part of the diagnostic trap. The authors wrote that “the preoperative diagnosis of PS is challenging because it frequently mimics other pancreatic neoplasms,” using PS as shorthand for pancreatic schwannoma. They pointed to a 2019 review by Zhang and colleagues in the journal Pancreatology, which reported that 29% of patients with pancreatic schwannoma had been diagnosed with a pNET before surgery.
The authors explained the mix-up in this case this way: schwannomas can bleed or form fluid-filled cysts as they degenerate, while pNETs can contain areas of dead tissue. In this woman’s tumor, the heavy internal bleeding produced an uneven appearance that resembled a pNET with dead tissue at its core.
One case can only show so much. This is a single patient described in a short image-focused report, and it does not establish how often bleeding leads doctors to misread schwannomas or how imaging practice should change. What it does show is why examining the tissue after removal can remain the final word for some pancreatic masses, even after advanced scans.
For readers, the takeaway is not that a pancreatic mass is likely to be harmless. Pancreatic growths have many possible causes, some of them serious, and the right workup depends on each patient. Anyone told about an unexpected finding on a scan should ask their clinician what it might mean and what follow-up makes sense.
Key Questions Answered
How was the pancreatic mass discovered? By chance. The 67-year-old woman had a CT scan to evaluate an abnormal lung opacity, and the images also showed a 31-by-23-millimeter mass in her pancreas.
What did the tumor turn out to be? A pancreatic schwannoma, a tumor that arises from the Schwann cells that sheathe nerves. Pathologists confirmed it through its classic cell patterns and a positive S100 stain, while neuroendocrine markers were negative.
Why did doctors first suspect a neuroendocrine tumor? Extensive bleeding inside the tumor gave it a patchy, uneven look on CT, with enhancement around its edges. The authors said this resembled a pancreatic neuroendocrine tumor with internal necrosis, or dead tissue.
Are schwannomas cancerous? Rarely, according to Mayo Clinic, which calls schwannoma the most common type of benign peripheral nerve tumor in adults. Finding one in the pancreas, however, is extremely unusual.
How was the woman treated, and how did she do? Surgeons removed the tumor through laparoscopic enucleation, which spares the rest of the pancreas. She had no complications and was discharged seven days after surgery.
Does this mean an unexpected pancreatic mass is probably harmless? No. This is one rare case, and pancreatic masses have many possible causes, some of them serious. Anyone with an incidental finding should discuss next steps with their clinician.
Published by Medicaldaily.com
