Incidental schwannoma of the pancreatic tail mimicking a solid pseudopapillary tumor: A case report

Abstract

BACKGROUND

Pancreatic schwannomas are extremely rare benign neurogenic tumors, with nonspecific clinical and imaging features leading to frequent preoperative misdiagnosis as other pancreatic neoplasms. This case report clarifies its diagnostic process and clinical management.

CASE SUMMARY

A 58-year-old asymptomatic woman was found to have a 27 mm × 19 mm well-encapsulated hypovascular mass in the pancreatic tail on routine imaging, which was misdiagnosed as solid pseudopapillary tumor preoperatively. She received open distal pancreatectomy with splenectomy. Pathological and immunohistochemical (S-100, SOX10SRY-related high-mobility group-box 10 positive) results confirmed pancreatic schwannoma. The patient recovered smoothly with no recurrence at 12-month follow-up.

CONCLUSION

Pancreatic schwannoma, a rare hypovascular mass mimicking solid pseudopapillary tumor, requires surgical resection for cure with excellent prognosis.

Key Words: Pancreatic schwannoma; Pancreatic neoplasms; Preoperative diagnosis; Distal pancreatectomy; Case report

Core Tip: Pancreatic schwannoma is a rare benign tumor that often mimics solid pseudopapillary tumor on imaging. This case highlights the diagnostic challenge and emphasizes that complete surgical resection is curative. Definitive diagnosis requires immunohistochemical confirmation with S-100 and SRY-related high-mobility group-box 10 positive positivity.

INTRODUCTION

Schwannomas are encapsulated, typically benign neoplasms arising from the Schwann cells of peripheral nerve sheaths. Although they can occur at nearly any anatomical site, pancreatic involvement is extremely rare, accounting for only a small proportion of all pancreatic neoplasms and gastrointestinal schwannomas[1,2]. These tumors usually grow slowly and indolently, resulting in an often-asymptomatic clinical course; thus, most pancreatic schwannomas are incidentally detected on imaging studies for unrelated indications[3,4]. When present, symptoms are nonspecific and related to tumor size and location, mainly including vague abdominal or back pain, and rarely obstructive jaundice if the pancreatic head is affected[5].

The major clinical challenge is that imaging features of pancreatic schwannomas overlap significantly with solid pseudopapillary neoplasm solid pseudopapillary tumors (SPTs), pancreatic neuroendocrine tumors (PNETs), and other common benign or malignant pancreatic lesions on computed tomography (CT) and magnetic resonance imaging (MRI), leading to considerable preoperative diagnostic uncertainty[6-9]. Definitive diagnosis therefore depends on postoperative histopathological and immunohistochemical examination, supported by characteristic Antoni A/B patterns and diffuse strong expression of S-100 protein and SRY-related high-mobility group-box 10 positive (SOX10)[10,11].

Owing to their rarity and diagnostic difficulty, clinical experience remains limited. This case report presents an incidentally discovered pancreatic tail schwannoma mimicking SPT, aiming to summarize its imaging, pathological, and therapeutic features, and to strengthen the evidence for differential diagnosis and clinical management of this rare tumor.

CASE PRESENTATION

Chief complaints

A 58-year-old female patient was referred to our hospital for further evaluation and management of a pancreatic mass incidentally discovered during a routine health examination.

History of present illness

The lesion had been identified half a month earlier on an abdominal ultrasound performed at an outside hospital, where it was localized to the tail of the pancreas. The patient was previously healthy and asymptomatic, with no abdominal pain, bloating, diarrhea, nausea, vomiting, or weight loss.

History of past illness

She denied any history of chronic diseases, previous abdominal surgery, or trauma.

Personal and family history

She denied any long-term alcohol consumption or smoking. There was no family history of pancreatic diseases, neural tumors, or hereditary conditions such as neurofibromatosis.

Physical examination

Physical examination upon admission revealed stable vital signs. The abdomen was flat, soft, nontender, and without rebound tenderness. No palpable masses or hepatosplenomegaly were detected. Vascular bruits were absent, shifting dullness was negative, and bowel sounds were normal.

Laboratory examinations

The results of laboratory tests, including complete blood count, hepatic and renal function, electrolytes, and coagulation profile, were all within normal ranges. Tumor marker assays, including alpha-fetoprotein, carcinoembryonic antigen, carbohydrate antigen 125, and carbohydrate antigen 19-9, were negative, ruling out the elevation of common pancreatic malignancy markers.

Imaging examinations

To characterize the lesion further, a detailed radiological evaluation was performed. An abdominal CT scan without contrast agent revealed a well-defined, round, slightly hypodense mass measuring approximately 27 mm × 19 mm in the pancreatic tail, with homogeneous density and no evident calcification, necrosis, or hemorrhage. Following intravenous contrast agent administration, the lesion showed gradual, mild heterogeneous enhancement during the arterial, portal venous, and delayed phases. Specifically, it enhanced less than the surrounding pancreatic parenchyma in the arterial phase, with progressively increasing but still lower enhancement in later phases, suggesting a hypovascular or mesenchymal origin. The mass was well encapsulated and clearly demarcated from adjacent pancreatic tissue, without signs of invasion, compression of the splenic vein, or pancreatic duct dilation (Figure 1).

Figure 1 Preoperative computed tomography findings of the pancreatic schwannoma. A: Plain computed tomography (CT) scan showing a well-marginated, slightly hypodense mass (arrow) in the pancreatic tail; B: Contrast-enhanced CT scans in the arterial phase demonstrating inhomogeneous mild enhancement of the lesion; C: Contrast-enhanced CT scans in the arterial phase demonstrating inhomogeneous mild enhancement of the lesion; D: Contrast-enhanced CT scan in the parenchymal phase showing progressive enhancement of the mass.

MRI of the upper abdomen was subsequently conducted for better soft tissue characterization. The mass appeared homogeneously hypointense on T1-weighted imaging and slightly hyperintense on T2-weighted imaging. The tumor capsule was clearly visualized on magnetic resonance images and appeared as a hypointense rim on T1-weighted imaging and a hyperintense rim on T2-weighted imaging (Figure 2), a feature that may suggest a neurogenic origin, such as a schwannoma. On diffusion-weighted imaging, the lesion exhibited high signal intensity (Figure 2C), suggesting high cellularity or restricted diffusion. Dynamic contrast-enhanced MR image revealed mild progressive enhancement of the mass after gadolinium administration (Figure 2D), which was consistent with its hypovascular nature. On the basis of the combined CT and MRI findings, a SPT was considered the most likely diagnosis due to its well-encapsulated appearance and progressive enhancement pattern. However, PNET could not be entirely excluded, although the hypovascular enhancement was atypical for PNET.

Figure 2 Preoperative magnetic resonance imaging findings of the pancreatic schwannoma. A: T1-weighted image showing a hypointense mass (arrow) in the pancreatic tail; B: T2-weighted image showing a slightly hyperintense mass; C: Diffusion-weighted imaging showing increased signal intensity of the lesion; D: T1 fat saturation postcontrast image showing mild enhancement of the mass after gadolinium administration.

FINAL DIAGNOSIS

Gross examination of the resected specimen revealed a solid tumor measuring 3.2 cm × 3.0 cm × 2.5 cm. The mass was well encapsulated, and the cut surface presented a whorled pattern with intermixed grayish-white and pale-yellow areas that were firm in consistency. Focal cystic and myxoid changes were observed internally, without significant hemorrhage or necrosis. Microscopically, the tumor was composed of spindle-shaped cells with bland, elongated, and wavy nuclei. These cells were densely arranged in classic fascicular, interlaced, or whorled patterns. In cellular areas (Antoni A areas), nuclear palisading and characteristic Verocay bodies were noted (Figure 3A). In hypocellular regions (Antoni B areas), the stroma was loose and edematous, with myxoid changes and hyalinized blood vessels. No significant cellular atypia or mitotic activity was observed.

Figure 3 Histopathological and immunohistochemical features of the pancreatic schwannoma. A: Hematoxylin and eosin staining (× 200) showing tumor cells arranged in palisades and whorls, with spindle-shaped nuclei, fine chromatin, and absence of mitosis; B: Immunohistochemical staining (× 100) showing negative expression of smooth muscle actin; C: Immunohistochemical staining (× 100) showing diffuse strong positivity for S-100 protein.

Immunohistochemically, the tumor cells showed strong and diffuse positivity for the S-100 protein and SOX10, confirming the neural sheath origin. Staining for smooth muscle actin (SMA), CD117 (c-kit), discovered on gastrointestinal stromal tumor 1 (DOG1), CD34, and cytokeratin was negative, ruling out gastrointestinal stromal tumors, smooth muscle tumors, and epithelial neoplasms (Figure 3B and C). The Ki-67 proliferation index was very low (< 1%), suggesting a benign nature. The negative staining for SMA, CD117, DOG1, CD34, and cytokeratin effectively ruled out gastrointestinal stromal tumor, leiomyoma, and epithelial neoplasms, reinforcing the diagnosis of schwannoma. On the basis of these gross, microscopic, and immunohistochemical features, the final pathological diagnosis was a schwannoma of the pancreatic tail.

TREATMENT

Following multidisciplinary discussion and thorough communication with the patient and her family, open exploration and resection of the pancreatic body and tail were performed. Under general anesthesia, intraoperative exploration revealed a firm, well-circumscribed, round mass approximately 3 cm in diameter located near the junction of the pancreatic body and tail adjacent to the splenic hilum. The mass was encapsulated, with smooth margins and an expansile growth pattern, displacing but not invading the surrounding pancreatic parenchyma. It is closely related to the splenic artery and vein but remains clearly separable. No evidence of tumor metastasis or invasion was found in the liver, stomach, intestines, or peritoneum. A distal pancreatectomy with splenectomy was performed, and the specimen was sent intact for pathological examination. The procedure was uneventful with minimal blood loss.

OUTCOME AND FOLLOW-UP

The patient’s postoperative recovery was uneventful, with no complications, such as pancreatic fistula, abdominal infection, or hemorrhage. She was able to ambulate on the first postoperative day and gradually resumed oral intake. After one week of hospitalization, she was discharged in good condition. The patient was placed on a surveillance protocol with contrast-enhanced CT scans at 6 months and 12 months postoperatively, and will undergo annual imaging thereafter. At 12 months, she remains asymptomatic with no evidence of recurrence.

DISCUSSION

Pancreatic schwannomas are exceptionally rare, accounting for approximately 0.2% of all non-epithelial pancreatic tumors[12]. Our 58-year-old asymptomatic female patient, with an incidentally detected, well-encapsulated hypovascular mass in the pancreatic tail ultimately confirmed as benign schwannoma by histopathology and S-100/SOX10 positivity, illustrates the typical diagnostic challenge and favorable prognosis of this tumor. The main clinical difficulty is preoperative differentiation from other common pancreatic neoplasms. This challenge was evident in our patient, whose contrast-enhanced CT and MRI showed a well-defined encapsulated solid mass with progressive mild enhancement, which was highly suggestive of SPT but lacked pathognomonic features[13].

SPT and schwannoma may both present as well-encapsulated solid or cystic-solid masses in middle-aged women, but SPTs tend to occur in younger females and often show intratumoral hemorrhage or cystic degeneration on imaging. Immunohistochemically, SPTs are positive for nuclear β-catenin and CD10, while schwannomas strongly express S-100 and SOX10. PNETs are typically hypervascular with intense arterial enhancement, unlike the hypovascular or gradually enhancing pattern seen in our case. Mucinous cystic neoplasms are mostly cystic with internal septa and sometimes peripheral calcifications, making them unlikely in this solid lesion[14]. Gastrointestinal stromal tumors and other mesenchymal tumors are positive for CD117, DOG1, or SMA, which were all negative here. This overlap confirms the limitations of imaging and the necessity of histopathological confirmation.

Endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) with immunohistochemistry can facilitate preoperative diagnosis of schwannoma by identifying spindle cells and S-100 positivity[15]. EUS-FNA was not performed in this case because of the high preoperative suspicion of resectable SPT and the decision for upfront surgery. This represents a clinical limitation: Preoperative pathological confirmation may help select parenchyma-sparing surgery and reduce morbidity.

Our experience highlights the rarity and diagnostic challenges of pancreatic schwannoma. Recent studies support EUS-FNA for preoperative diagnosis, which may enable more conservative management in selected patients[16]. Complete surgical resection remains the curative treatment for benign lesions, with an excellent long-term prognosis, as seen in our patient’s 12-month disease-free follow-up. This study has limitations: It is a single case report with relatively short follow-up. Malignant transformation of pancreatic schwannoma is extremely rare but has been reported, warranting long-term surveillance.

CONCLUSION

Pancreatic schwannoma is an exceptionally rare mesenchymal tumor that presents a significant preoperative diagnostic challenge because of its nonspecific clinical and radiological features. In this case, a 58-year-old female presented with an incidentally discovered, well-encapsulated mass in the pancreatic tail. While advanced imaging modalities such as CT and MRI are crucial for characterizing the lesion's benign features and its relationship with surrounding structures, they cannot be used to definitively distinguish it from other pancreatic neoplasms. The definitive diagnosis was ultimately established by postoperative histopathological and immunohistochemical analysis, which confirmed the classic features of a schwannoma, including strong positivity for S-100 and SOX10. This case underscores that complete surgical resection is the treatment of choice and offers an excellent long-term prognosis. Therefore, the presence of a pancreatic schwannoma should be considered in the differential diagnosis of any well-circumscribed, solid, or cystic-solid pancreatic lesion. A multidisciplinary approach, culminating in surgical excision and pathological confirmation, remains the cornerstone of effective management for this rare entity.

ACKNOWLEDGEMENTS

The authors sincerely thank the patient for her consent and cooperation. We are also grateful to the clinical and nursing teams for their dedicated patient care and support during the treatment and follow-up period.