|Ahead of print publication
Preoperative diagnosis of pancreatic schwannoma – Myth or reality
Vaibhav Kumar Varshney1, Taruna Yadav2, Poonam Elhence3, Binit Sureka2
1 Department of Surgical Gastroenterology, All India Institute of Medical Sciences, Jodhpur, Rajasthan, India
2 Department of Diagnostic and Interventional Radiology, All India Institute of Medical Sciences, Jodhpur, Rajasthan, India
3 Department of Pathology, All India Institute of Medical Sciences, Jodhpur, Rajasthan, India
|Date of Submission||02-Nov-2018|
|Date of Decision||15-Feb-2019|
|Date of Acceptance||15-May-2019|
|Date of Web Publication||30-Jan-2020|
Vaibhav Kumar Varshney,
Department of Surgical Gastroenterology, All India Institute of Medical Sciences, Basni Industrial Area, Phase-II, Jodhpur - 342 005, Rajasthan
Source of Support: None, Conflict of Interest: None
Pancreatic schwannoma is a rare, well-encapsulated tumor of the pancreas. Preoperative diagnosis of this tumor is uncommon due to marked degenerative change, its rarity, and overlapping clinical and imaging features with other pancreatic neoplasms. Here, we report two cases of pancreatic schwannoma, suspected preoperatively based on their multimodal imaging features, so that enucleation was possible. Extensive pancreatic surgeries can be avoided if imaging can provide clues about the benign nature of the pancreatic masses preoperatively.
Keywords: Enucleation, imaging, laparotomy, pancreas, schwannoma
| > Introduction|| |
Schwannomas are neoplasms originating from the Schwann cells of the peripheral nervous system. Pancreatic schwannomas (PSNs) are often misdiagnosed on imaging as other tumors such as solid pseudopapillary neoplasms and cystic neuroendocrine tumors, thus are usually diagnosed on histopathology postoperatively. The surgical approach for benign and malignant PSNs is variable ranging from enucleation to radical surgery.,,
According to the literature, imaging appearance of PSNs is highly variable. The imaging appearance of these tumors depends on the secondary changes such as hemorrhage, cystic changes, and calcifications. However, in recent years, imaging has played an important role in the preoperative diagnosis avoiding radical resection.,,,, Here, we describe two cases of PSNs which were diagnosed preoperatively based on their imaging features, which in turn led to the successful enucleation of the masses.
| > Case Reports|| |
A 42-year-old male patient presented with complaints of upper abdominal pain for 2 months, which was not associated with vomiting, fever, or yellowish discoloration of the eyes. He did not have any history of anorexia or weight loss or any other significant past medical or surgical history. Systemic and per-abdominal examination was within normal limits. Laboratory investigations revealed normal liver and pancreatic function tests.
Ultrasound (US) abdomen demonstrated a well-defined hypoechoic solid lesion in the neck of pancreas with no significant vascularity on color Doppler [Figure 1]a. Contrast-enhanced computed tomography (CECT) of the abdomen with pancreatic protocol reported a well-defined hypodense solid mass lesion (3.5 cm × 3.4 cm) in the pancreatic neck, posterior to splenoportal confluence. In pancreatic phase, mild enhancement was seen with progressively increasing enhancement in venous phase. No calcification or necrosis or vascular invasion or locoregional lymphadenopathy was seen [Figure 1]b and [Figure 1]c.
|Figure 1: (a) Ultrasound with color Doppler showed a hypoechoic solid mass behind the neck of pancreas with no significant vascularity; computed tomography images axial view, arterial phase (b) showed a hypoenhancing mass in pancreatic neck with mildly increased enhancement in venous phase (c); axial magnetic resonance imaging images: (d) Well-circumscribed heterogeneously hyperintense lesion on T2-weighted imaging, (e) Hypointense to pancreatic parenchyma on T1-weighted imaging, (f) diffusion-weighted imaging at b-700 show no diffusion restriction|
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On magnetic resonance imaging (MRI) of the abdomen, mass was heterogeneously hyperintense on T2-weighted imaging (T2WI) and hypointense on T1-weighted imaging (T1WI) with no diffusion restriction. Common bile duct or main pancreatic duct was not dilated [Figure 1]d, [Figure 1]e, [Figure 1]f. Based on these imaging features, diagnosis of benign pancreatic mass lesion possibly neurogenic tumor was made.
In view of benign nature of lesion, enucleation of the mass was done with meticulous dissection [Figure 2]a, [Figure 2]b, [Figure 2]c. On cut sections, grayish-white tumor with whorled appearance and foci of hemorrhage was seen. On histopathology, an encapsulated biphasic tumor was seen with hypocellular and hypercellular areas consisting of Antoni A and Antoni B areas. The tumor cells were ovoid to elongated with hyperchromatic nuclei and moderate amounts of ill-defined cytoplasm. Many Verocay bodies were seen. On Immunohistochemistry (IHC), cells were immune-reactive for S100 protein, confirming the diagnosis of pancreatic schwannoma [Figure 3]a, [Figure 3]b, [Figure 3]c. The patient did well in the postoperative period, with no recurrence of symptoms at a follow-up of 1½ year.
|Figure 2: Case 1: (a) Intraoperative image showing bulging tumor from posterior surface of pancreas, (b) Superior mesenteric vessels exposed after enucleation (marked with arrow); (c) resected specimen; Case 2: (d) Intraoperative image after kocherization showing tumor after division of pancreatic capsule and tissue, (e) bulged out tumor tissue from pancreas, (f) resected specimen|
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|Figure 3: (a) Verocay bodies with many hyalinized vessels, (H and E, ×10), (b) degenerative atypia in retroperitoneal location, (H and E, ×40); (c) intense S100 protein positivity, (IHC, ×10)|
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A 62-year-old female presented with complaints of intermittent episodes of vomiting for 2 months with a history of anorexia and weight loss was present. No history of abdominal pain, altered bladder and bowel habits, or gastrointestinal bleed was present. Her systemic and per-abdominal examination was within normal limits.
US abdomen revealed a well-defined hypoechoic solid lesion in the retroperitoneum adjacent to the pancreas [Figure 4]a. CECT abdomen with pancreatic protocol revealed a well-defined smoothly marginated, hypodense oval mass lesion along the lower part of the neck of pancreas (6 cm × 3.7 cm). Mass was present anterior to the aorta, posterior to the splenoportal confluence which was draping along its margins. Mass was also causing mediolateral splaying of superior mesenteric artery (SMA) and superior mesenteric vein (SMV), with no luminal compromise or invasion. It showed subtle mild arterial enhancement with mild increase in enhancement on venous phase without any calcification, necrosis, or lymphadenopathy [Figure 4]b, [Figure 4]c, [Figure 4]d.
|Figure 4: (a) Ultrasound abdomen demonstrating a well-marginated predominantly hypoechoic mass in the retroperitoneum; computed tomography abdomen (b) arterial phase-hypoenhancing mass in the neck of pancreas (c) increasing enhancement in venous phase; (d) coronal maximum intensity projection image shows splaying of splenoportal confluence and superior mesenteric artery by the mass|
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On MRI-abdomen, mass was heterogeneously hyperintense on T2WI showing peripheral hyperintense, central hypointense areas giving a “target“-like appearance, best seen on coronal T2WI. It was hypointense on T1WI with no diffusion restriction. Pancreatobiliary ducts were not dilated. Postcontrast administration, mass did not show significant enhancement, however, showed progressive enhancement on subsequent phases with few small nonenhancing central and peripheral areas [Figure 5]a-d]. Based on the size, absence of vascular invasion, mild progressive heterogeneous enhancement, and target appearance on MRI, diagnosis of benign pancreatic tumor possibly schwannoma was made.
|Figure 5: (a) Axial T2-weighted imaging – heterogeneously hyperintense mass in the neck of pancreas; (b) hypointense on T1-weighted imaging; (c) diffusion-weighted imaging, b-700 show no significant diffusion restriction; (d) coronal T2-weighted image showing “Target sign” with peripheral hyperintense and central hypointense areas|
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Intraoperatively, an encapsulated fleshy mass was present in the neck of pancreas abutting SMV and SMA. SMA was splayed over the mass. Enucleation of pancreatic mass was done [Figure 2]d, [Figure 2]e, [Figure 2]f. Grossly, the mass was globular, pale white, soft in consistency with glistening to mucoid cut surface with foci of hemorrhages. Microscopically, an encapsulated tumor was seen composed of fascicles and sheets of slender spindle-shaped cells with mildly pleomorphic, elongated to buckled nuclei, inconspicuous nucleoli, and ill-defined cytoplasm. Antoni A and Antoni B areas with many Verocay bodies were seen. Numerous hyalinized thick-walled vessels, edema, myxoid change, foci of hemorrhage, and sheets of foamy histiocytes were noted. Tumor cells showed intense immunopositivity for S100 protein consistent with schwannoma with extensive degenerative changes. The patient recovered well after surgery and was asymptomatic at a follow-up of 1 year.
| > Discussion|| |
Schwannomas are the tumors of Schwann cells of peripheral nerve sheaths and first reported by Verocay in 1910. Most common sites for these tumors are the flexor aspects of the extremities followed by the head-and-neck area and major nerve trunks.,, PSNs are uncommon variant of this neoplasm and originate from autonomic fibers which travel along the pancreas with the vagus nerve, and are most commonly located in the pancreatic head. According to the English literature, <70 cases of PSNs have been described till now.
PSNs usually encountered in adults with variable age range and no gender predilection. Usually, patients with PSNs presents with nonspecific abdominal complaints. PSNs are usually benign and malignant transformations have been described mostly in cases of von Recklinghausen's disease.,,,
The preoperative diagnosis of PSN is difficult due to its rarity, nonspecific symptoms, and imaging appearance. Degenerative changes such as hemorrhage, calcification, hyalinization, and cystic changes lead to variable imaging features and gross appearance of the tumor. Appearance of solid and cystic areas in these tumors depends on the proportion of Antoni A and B areas. Due to the cystic appearance, these tumors may mimic other cystic pancreatic lesions, such as cystic neoplasms, pseudocysts, cystadenocarcinomas, lymphangiomas, and neuroendocrine tumors. This heterogeneous variable appearance leads to high rate of preoperative misdiagnosis.,
Abdominal US of PSN appears as well-defined, hypoechoic lesions as compared to adjacent pancreatic parenchyma. Antoni A areas are highly cellular and vascular, so these tumors appear as well-defined, heterogeneous, hypodense, solid-enhancing masses, while Antoni B areas have low cellularity, loose myxoid stroma, and less vascular, so these tumors appear as homogeneous cystic masses showing less or no enhancement on CECT. The low-attenuation areas and/or cystic changes indicate the Antoni B component or the degenerative cystic changes occurring in the schwannoma.,, Further, characteristics on imaging such as small size, well-defined encapsulated and no infiltration in adjacent structures favor benign nature of lesion.,,, Similar features were encountered in our cases, which lead to inclination toward benign PSN.
On MRI, schwannomas show homogeneously hypointense signal on T1WI and appear hyperintense on T2WI. However, they may also appear heterogeneously hyperintense due to the variable amount of both Antoni A and Antoni B areas in the tumors. “Target sign” in MRI on T2WI can be useful for preoperative diagnosis of benign pancreatic lesion, as was seen in our second case., The relation of the lesion with pancreatic duct is also important before contemplating enucleation. In both of our cases, we ascertained this on MRCP which showed adequate distance of the lesion from main pancreatic duct.
The management of PSN is guided by location and locoregional involvement. Simple enucleation is the ideal treatment of choice for benign schwannomas. In tumors with malignant features, to achieve R0 resection pancreatoduodenectomy or distal pancreatectomy with/without splenectomy may be required. Intraoperative frozen sections may be helpful to establish the diagnosis of a benign over malignant schwannoma, helps to avoid extensive surgical resection and associated morbidity., In both cases, we achieved R0 resection with enucleation due to positive findings of benign PSN.
Definitive diagnosis is obtained by histopathology with immunohistochemical properties. Grossly, PSN is well-defined, encapsulated, homogeneous, yellow-tan mass with secondary degenerative changes. Microscopically, tumor is composed of hypercellular component (Antoni A areas) and a hypocellular component (Antoni B areas). Antoni B areas often show degenerative changes which are due to vascular thrombosis and subsequent necrosis. Benign schwannomas normally have low mitotic figures (<5/10 HPF). On IHC, PSN stain positively for S100, vimentin, and CD-56.,
Malignant transformation as well as recurrence are very rare, and it has been reported only in instances where incomplete resection was performed.,, Hence, the regular follow-up is required. To conclude, on imaging predominantly exophytic pancreatic lesion showing progressive enhancement without any evidence of vascular invasion or lymphadenopathy and target sign on T2-weighted MRI should prompt toward the differential diagnosis of PSN. Hence, confident diagnosis of PSN preoperatively can prevent radical excision.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
I would like to thank Dr. Bharti Varshney (Senior Resident, Department of Pathology, AIIMS, Jodhpur) for editing the manuscript.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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