Pancreatic schwannoma as a rare cause of epigastric abdominal pain

A previously healthy 55-year-old woman presented with 1-year epigastric abdominal pain. She refers losing 3 kg in the last months. Physical examination revealed a firm tender mass on the epigastrium-right hypochondrium. Laboratory findings revealed tumour markers within range except slightly abnormal CEA (CEA: 5.3 ng/ml; CA 125: 25.90 UI/ml; CA 15-3: 11.50 UI/ml; CA 19-9: 32 UI/ml).

Ultrasound (Figure 1) revealed a well-defined solid hypoechoic mass with cystic-appearing areas located at the pancreas head.

Contrast-enhanced abdominal CT scan (Figures 2, 3 and 4) showed a well-defined 6 cm oval solid lesion in contact with the pancreatic head and uncinate process. The lesion showed central low-attenuation cystic necrotic areas, isolated microcalcifications and mild peripheral enhancement.

MRI (Figures 5, 6, 7 and 8) demonstrated an encapsulated mass with low T1 signal. On T2 weighted images, there were areas of inhomogeneous increased signal intensity (solid-cystic nature). The solid component showed restricted diffusion on the high b-value diffusion-weighted images and ADC map. Contrast-enhanced T1 weighted images demonstrated progressive peripheral enhancement of the solid component.

Background

Pancreatic schwannomas are a rare nonepithelial neoplasm of the pancreas. They are benign peripheral nerve sheath tumours originated from Schwann cells. Schwannomas are usually found in the head and neck, trunk and extremities. Pancreatic schwannomas constitute 1% of all schwannomas and there are approximately 70 cases reported in the literature. The head and body of the pancreas are the most commonly affected locations. Malignant transformation is possible, but rare [1,2].

The pathologic features will define the imaging findings. Histologically, two areas can be differentiated: Antoni A and Antoni B (Figures 9 and 10). Antoni A areas are hypercellular zones of spindle cells. Antoni B areas are hypocellular, often with degenerative alterations such as cyst development. Appearance of cystic and solid areas will depend on Antoni A and Antoni B areas proportion [1,3].

Clinical Perspective

Pancreatic schwannomas typically occur in adults, with no gender preponderance. The clinical presentation is usually non-specific abdominal pain, although other symptoms such as gastrointestinal bleeding, weight loss, back pain and vomiting have been reported. The laboratory findings, including tumour markers, are usually normal [4]. They are slow growing and when large, it can lead to degeneration and cystic formation, increasing the proportion of Antoni B areas over Antoni A areas [1].

Imaging Perspective

The preoperative diagnosis is difficult due to their non-specific appearance.

As mentioned before, the pathologic features will define the imaging findings. Antoni A predominant schwannomas are solid lesions with heterogeneous enhancement. Antoni B predominant schwannomas are cystic masses, that may be multiseptated. The enhancement or the cystic component will vary according to Antoni A – Antoni B areas proportion.

US features are a well-circumscribed hypoechoic lesion that may contain anechoic cystic areas.

The most common finding on CT is an encapsulated hypoattenuating mass.

MR features include low T1 signal intensity and inhomogeneous increased T2 signal intensity. There is limited evidence regarding the role of DWI/ADC in pancreatic schwannoma diagnosis, however, the largest published series demonstrated restricted diffusion as showed in this case [5].

There is limited knowledge about the behaviour of pancreatic schwannoma on FDG-PET. Although they are benign, a hypermetabolic appearance has been reported [6].

The final diagnosis is usually made after histopathological tissue examination (biopsy or resected specimen). The use of ultrasound-guided fine needle aspiration remains controversial due to the high incidence of false-negative findings [2].

In our case, the diagnosis was made after cephalic duodenopancreatectomy, and the histopathologic findings can be seen in Figures 9 and 10.

Outcome

The usual management is simple enucleation, which would be curative in most patients. Imaging surveillance is another appropriate option, especially in cases with low growth rates [7].

Take Home Message / Teaching Points

Pancreatic schwannoma is a very rare benign entity with a non-specific imaging appearance. Understanding the histopathologic features will help recall the imaging features. It must be included in the differential diagnosis for a well-defined solid-cystic pancreatic lesion.

All patient data have been completely anonymised throughout the entire manuscript and related files.