Duodenal gastrointestinal stromal tumour imitating as pancreatic head tumour

Abstract

Duodenal gastrointestinal stromal tumours (D-GISTs) are a rare disease. It may arise commonly from the second or third part of the duodenum and can be erroneously diagnosed as a pancreatic head tumour due to proximity and morphology on imaging studies. We present a case of a 60-year-old woman who presented with abdominal pain and was diagnosed as a case of pancreatic neuroendocrine tumour on radiologic imaging and granulomatous lesion on aspiration cytology. A ~5×3 cm mass was noted in the pancreatic head on laparotomy, and pancreatoduodenectomy was performed. Histopathology reported an exophytic GIST arising from the second part of the duodenum. Hence, D-GIST can invade the pancreas and mimic pancreatic head tumours; therefore, these tumours should be kept in the differential diagnosis of an atypical pancreatic head mass.

Background

Gastrointestinal stromal tumours (GISTs) are uncommon mesenchymal tumours of the gastrointestinal tract. It may arise from the duodenum, but the incidence is less than 5% among all GISTs.¹ Such stromal tumours usually have an extraluminal extension and exophytic growth from the medial wall of the second part of the duodenum and may grow into the head of the pancreas and mimic a pancreatic tumour. Endoscopic ultrasound (EUS) assessment with fine-needle aspiration cytology has been reported to help in establishing the diagnosis but has low sensitivity and specificity.² Hence, it may mislead the preoperative diagnosis frequently, and an upfront surgical intervention may be the only way out.

We present a classic case of whodunit where the patient was diagnosed as having pancreatic pathology on both imaging and EUS-FNA but came out as duodenal GIST (D-GIST) at the end, along with a review of literature of similar such cases.

Case presentation

We encountered a 60-year-old woman who presented with pain in the upper abdomen for the last 4 months, which was dull aching, and gradually progressive. She also noticed anorexia and undocumented weight loss over the past month. However, there was no history of vomiting, haematemesis, jaundice, awareness of lump or altered bowel habits. Abdominal examination and biochemical investigations were within normal limits.

Investigations

She was evaluated with an ultrasound abdomen which showed dilated common bile duct (CBD) with intrahepatic biliary radical dilatation due to a mass in the pancreatic head region. Contrast-enhanced CT (CECT) of the abdomen showed a well-defined mass lesion (~5×4.2 cm) in the pancreatic head. The mass showed peripheral enhancement in the pancreatic phase, progressively increasing in the venous phase with few areas of central necrosis and foci of peripheral calcification. The lesion was causing a mass effect on the distal CBD with upstream dilatation, and a provisional diagnosis of pancreatic neuroendocrine tumour (PNET) was evoked (figure 1A–C). Subsequently, CE-MRI was done, which corroborated the findings of PNET as on CECT. Consequently, serum chromogranin A level was performed (157 ng/mL), which was mildly raised.

Figure 1.

Radiology images: (A) axial, (B) coronal images of contrast-enhanced CT in pancreatic phase show a heterogeneously enhancing mass (black arrows) with foci of calcifications and central non-enhancing areas. (C) 3D MRCP image shows dilated common bile duct (white arrow). The pancreatic duct is normal in calibre. 3D, three dimensional; MRCP, magnetic resonance cholangiopancreatography.

EUS revealed a heterogeneous mass in the head of the pancreas with increased vascularity and multiple specks of calcification. EUS-guided aspiration cytology from the lesion showed singly scattered and clusters of spindle-shaped cells resembling non-necrotising epithelioid cell granulomas, which adds the diagnostic dilemma (figure 2A, B).

Figure 2.

Fine-needle aspiration cytology: (A) H&E, ×10 and (B) H&E, ×40 showing spindle-shaped cells with epithelioid morphology (arrow).

Differential diagnosis

A provisional diagnosis of PNET with differential diagnosis of pancreatic tuberculosis, sarcoidosis or perivascular epithelioid cell tumour (PEComa) was kept, and the patient was planned for surgery.

Treatment

Intraoperatively, a hard cystic mass was found in the head of the pancreas, and pylorus resecting pancreatoduodenectomy (PD) was performed with pancreatico-jejunostomy by modified Heidelberg’s technique (figure 3A, B). Her postoperative course was smooth and allowed orally on the second postoperative day (POD) and subsequently discharged on the seventh POD.

Figure 3.

Pancreatoduodenectomy specimen images: (A) anterior and (B) posterior view of resected pancreatoduodenectomy specimen where tumour site marked with arrow and circle; (C) cut section of the specimen showing tumour involving the head of the pancreas with solid grey white areas; (D) bulky and projecting ampulla into the second part of the duodenum due to the tumour.

Outcome and follow-up

Cut section of the gross specimen revealed a firm growth involving the second part of duodenum close to the ampulla of Vater and occupying the head of the pancreas with solid grey white areas (figure 3C, D). Histopathology showed a circumscribed spindle cell tumour arising from the submucosa of the duodenum. Nests of tumour cells were separated by fibrocollagenous septa, which were infiltrated by lymphocytes and plasma cells admixed with neutrophils and eosinophils. Along with it, areas of necrosis and giant cell reaction were also noted. The tumour was abutting the pancreas and CBD; however, no definite invasion was noted in the pancreatic parenchyma (figure 4A–C). All surgical resection margins were free of the tumour with no lymphovascular or perineural invasion.

Figure 4.

Histopathology: (A) H&E, ×4 shows a tumour in the duodenal submucosal area (arrow); (B) H&E, ×4 shows pancreatic acini (indicated by the blue arrow) and tumour (red arrow); (C) H&E, ×40 spindle cell tumour arranged in fascicles; (D) Tumour cells showing diffuse immunoreactivity for DOG-1. dog-1, discovered on GIST-1.

On immunohistochemistry, spindle cells revealed strong immunoreactivity for ‘discovered on GIST-1’ marker, faint reactivity for (cluster of differentiation) CD34, and were non-reactive for S-100P with Ki-67 index of 1% (figure 4D). Hence, the final diagnosis was spindle cell type D-GIST with a mitotic rate of 2/50 high power fields. Given the large size of the tumour (>5 cm) and intermediate risk, adjuvant imatinib therapy (400 mg once a day) was started, and she is doing well at 12 months of follow-up.

Discussion

GISTs are common mesenchymal tumours and are encountered predominantly in the stomach (60%–70%), small intestine (25%–35%) and colorectum (10%).³ Only 1%–5% of GISTs occur in the duodenum, with the most common location being its second part.⁴ D-GIST with purely medial extra-luminal extension, especially from the second or third portion of the duodenum, may be difficult to diagnose pre-operatively. It may mimic non-functioning P-NET, islet cell tumour, retroperitoneal mass and PEComa, which is reported in the literature, akin to our case. On reviewing the literature, we could find only 11 such cases where D-GIST masquerades as pancreatic head mass (table 1), and the surgeon must be aware of such a unique conundrum.^5–15

Table 1.

Various cases of duodenal GIST masqueraded as pancreatic head mass

No	Authors	Age/gender	Symptoms	Preoperative CT findings	Preoperative diagnosis	Surgery performed
1	Futo et al5	79/M	Tarry stool and transient loss of consciousness	5 cm tumour in the pancreatic uncus, which was well-defined and enhanced from arterial to venous phase	Pancreatic NET	Pylorus-preserving PD
2	Dhakal et al6	58/F	Postprandial vomiting, loss of weight and appetite	Homogeneous soft-tissue tumour mass at the uncinate process of the pancreas	Pancreatic mass	A wedge resection with cholecystectomy
3	Vasile et al7	59/F	Abdominal pain, melena and faintness	Tumour mass ~6 cm in the head of the pancreas, which was hypodense, hypocaptive with ill-defined borders	Duodenal GIST	Partial resection of DII and total resection of DI, antrum, distal CBD and enucleation of the mass from the pancreatic head with RYHJ and GJ
4	Bormann et al8	64/F	Pain in the right upper abdomen	Heterogeneous mass of 5×3 cm in the pancreas with both enhancing and non-enhancing areas	Pancreatic mass	PD
5	Slavik et al9	49/F	Chronic abdominal pain	2.8 cm well-delineated and circumscribed pancreas head mass lesion	Non-functioning pancreas NET	PD
6	Mouaqit et al10	37/F	Recurrent pain right upper abdomen associated with sweating and nausea	Tumour of 7×5 cm with an area of central necrosis and intense contrast enhancement (arterial phase) in the pancreas head	NET or adenocarcinoma of the pancreas	PD
7	Singh et al11	30/M	Awareness of lump in the right upper abdomen with upper abdominal pain	Well defined mass ~15×10 cm with heterogeneous density extending from pancreas to pelvic brim; Enhancing peripheral component and non-enhancing (necrotic) central component	Pancreatic mass	PD
8	Frampton et al12	37/F	Recurrent right upper abdominal pain associated with sweating and nausea	~2 cm hypervascular lesion lying between the head of the pancreas and the second part of the duodenum	NET or a solid pseudopapillary tumour of the pancreas	Pancreatic head resection with duodenal segmentectomy
9	Ohtake et al13	60/F	Asymptomatic; discovered on screening ultrasound	A hypervascular tumour ~14 mm in the pancreas head	Pancreas NET	Tumour resection with a duodenal wedge resection
10	Kwon et al14	49/M	Incidentally detected in follow-up	Tumour in the uncinate portion of the pancreas ~2.3 cm in diameter; well-demarcated and strongly enhanced	Non-functioning islet cell tumour	Segmental resection of the duodenum and duodeno-jejunostomy
11	Uchida et al15	53/F	Asymptomatic	Well demarcated tumour in the pancreatic head region ~3.0 cm in size; enhancement in the arterial phase, which lasted until the delayed phase	Non-functioning islet cell tumour	Pylorus preserving PD

CBD, common bile duct; DI and DII, 1st and 2nd part of duodenum; F, female; GIST, gastrointestinal stromal tumour; GJ, Gastrojejunostomy; M, male; NET, neuroendocrine tumour; PD, pancreatoduodenectomy; RYHJ, Roux-en-Y hepaticojejunostomy.

The common symptomatology of all such differentials makes a preoperative diagnosis difficult. The typical presentation of D-GIST is recurrent pain in the epigastrium followed by a history of gastrointestinal bleeding due to the highly vascular duodenal submucosa. The other presentation may be palpable mass, features of gastric outlet obstruction, or infrequently diagnosed on routine screening. On the other hand, P-NETs are infrequent with 1%–2% incidence among all pancreatic neoplasms, and more than one-third of cases are non-functional. Hence, the presentation of the disease usually does not provide a convincing clue towards aetiology. The mean tumour size of D-GIST reported across literature was 6 cm (range 1.5–31 cm), similar to the presented case.^{4 16}

P-NETs and D-GISTs show intense arterial enhancement on CT scan; hence, diagnosing based only on imaging may be challenging. In 10%–20% of cases, D-GISTs have been misdiagnosed as pancreatic head mass.^{16 17} Therefore, it is suggested that D-GIST should be kept as a differential in patients with sizeable pancreatic head mass without jaundice.

Usually, the EUS is helpful in confirming the origin of D-GIST, which is either from the second (muscularis mucosae) or fourth (muscularis propria) layer of the duodenum. However, in larger and predominantly extraluminal tumours, this may not be possible due to its compression effect, as happened in our case. Further, EUS-FNA has been reported to be effective in diagnosing such lesions with a lower risk of complications. However, to differentiate D-GIST from the pancreatic tumour, there are concerns about the post-procedure bleeding as these lesions are vascular. Further, the sensitivity of EUS-FNA cytology is better for the gastric GISTs than the duodenal origin, as the reported yield is suboptimal in nearly two-thirds of cases.² In our case, pancreatic tuberculosis/sarcoidosis were kept as differentials as tumour stromal cells were misinterpreted as epithelioid granulomas. The limitation in our case was that we could not perform EUS-guided biopsy or prepare a cell block of the aspirated material on which immunohistochemistry could have been applied and might have helped reach a diagnosis preoperatively.

The optimal surgical procedure for D-GISTs, even with a preoperative diagnosis, is not distinct due to the complex anatomy of the pancreaticoduodenal region. The wide local excision or segmental duodenectomy has been reported to be oncologically and technically safe, but PD is warranted in cases where tumour size is large, involving second or third part of the duodenum, close to the ampulla of Vater or other vital structures and in cases with a diagnostic dilemma as in our case. It is reported that more than two-thirds cases of D-GISTs underwent PD due to diagnostic uncertainty and the large size of the tumour.^{5 11 16}

GIST of the small intestine is more aggressive and has more chances of recurrence than its gastric counterpart. Gold et al have developed a nomogram based on tumour site, size, mitotic rate to assess recurrence-free survival and patient selection for adjuvant therapy.¹⁸ In context to our case with tumour size >5 cm and mitotic rate ≤5 per 50 high power field, the risk of metastasis is noted in nearly one-fourth of the patient.³ Hence, imatinib therapy for 3 years is beneficial to prevent future recurrence.

In conclusion, GIST located in the second part of the duodenum is seldom diagnosed correctly in the preoperative phase, especially with a lesion in the pancreatic head or mesenteric side of the duodenum. Whenever feasible, the attempt to establish a preoperative diagnosis should be made with EUS-guided biopsy. PD is a safe and viable option with low morbidity for such lesions.

Learning points.

• Duodenal gastrointestinal stromal tumours (D-GIST) commonly arises from the second or third part of the duodenum and may masquerade as pancreatic head mass.

• Preoperative contrast-enhanced CT (CECT) abdomen and endoscopic-guided aspiration cytology can also miss the origin of the tumour.

• D-GIST may be considered a differential when the CECT abdomen shows a sizeable pancreaticoduodenal lesion with central necrosis and heterogeneous enhancement.

• Pancreatoduodenectomy is the commonly performed surgical procedure for D-GIST.

• Adjuvant imatinib therapy is prescribed in high-risk cases to prevent a recurrence.

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